Review of Pressurized Water Reactor
Pressurizer Heater Operating Experience
by
Daniel B. Denis
An Engineering Project Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
in Partial Fulfillment of the
Requirements for the Degree of
Master of Engineering
Major Subject: Engineering Science
Approved:
Ernesto Gutierrez-Miravete, Project Adviser
Rensselaer Polytechnic Institute
Hartford, CT
December, 2014
©2014
i
Table of Contents
List of Tables ..................................................................................................................................... 3
List of Figures .................................................................................................................................... 4
Acronyms ........................................................................................................................................... 5
Keywords ........................................................................................................................................... 6
Acknowledgements ............................................................................................................................ 7
Abstract.............................................................................................................................................. 8
1.0
2.0
3.0
4.0
Pressurizer Heater Introduction ................................................................................................. 1
1.1
Pressurizer Heater Operation ........................................................................................... 1
1.2
Pressurizer Heater Design ................................................................................................ 2
Pressurizer Heater Degradation ................................................................................................ 4
2.1
Sheath Degradation .......................................................................................................... 4
2.2
Sizewell B Incident............................................................................................................ 4
2.3
Industry Response ............................................................................................................ 6
Stress Corrosion Cracking .......................................................... Error! Bookmark not defined.
3.1
Reactor Coolant System Chemistry .................................................................................. 7
3.2
Combustion Engineering Alloy 600 Pressurizer Heater Sleeves ....................................... 9
Pressurizer Heater Operating Experience ............................................................................... 11
4.1
Pressurizer Heater Sheath Degradation ......................................................................... 11
4.2
Alloy 600 Events in Pressurizer Heaters ......................................................................... 16
5.0
Summary and Conclusion ....................................................................................................... 21
6.0
References .............................................................................................................................. 22
Appendix A : INPO Events Database .............................................................................................. 23
A.1 Pressurizer Heater Operating Experience (1970-1985)................................................... 23
A.2 Pressurizer Heater Operating Experience (1986-1990)................................................... 30
A.3 Pressurizer Heater Operating Experience (1991-1995)................................................... 52
6.2
Pressurizer Heater Operating Experience (1996-2000)................................................... 71
6.3
Pressurizer Heater Operating Experience (2000-2005)................................................... 77
6.4
Pressurizer Heater Operating Experience (2006-2010)................................................... 90
Pressurizer Heater Operating Experience (2011-2014) ......................................................... 100
ii
List of Tables
Table 1: Primary Chemistry Limits for RCS [4] ...................................................................................... 8
Table 2: Plants with Alloy 600 Pressurizer Sleeves and Year of Pressurizer Replacement ................. 10
iii
List of Figures
Figure 1: Schematic of Westinghouse Pressurizer [8] ........................................................................... 2
Figure 2: Typical Heater Cross-section [2] ......................................................................................... 2
Figure 3: Cross-section of Pressurizer Heater Used in Nuclear Applications ......................................... 3
Figure 4: Pressurizer with Inserted Heaters [2]...................................................................................... 3
Figure 5: Leak Site at Sizewell B [8] ...................................................................................................... 5
Figure 6: Failed Heater Elements from Sizewell B [8]............................................................................ 6
Figure 7: Axial Cracks in a Plant Heater [8] ........................................................................................... 6
Figure 8: Gordon Curve of Incidents of SCC of Austenitic Stainless Steel in High Temperature Water
by Oxygen and Chloride Concentration .................................................................................................. 8
Figure 9: Nickel-base Alloys in Combustion Engineering Pressurizers [3] .............................................. 9
iv
Acronyms
B&W
DMW
EPRI
IGSCC
LTOP
MNSA
MgO
Mg(OH)2
ppb
ppm
PWR
RCS
SCC
TGSCC
Babcock & Wilcox
Dissimilar Metal Weld
Electric Power Research Institute
Intergranular Stress Corrosion Cracking
Low Temperature Overpressure Protection
Mechanical Nozzle Seal Assembly
Magnesium Oxide
Magnesium Hydroxide
parts per billion
parts per million
Pressurized Water Reactor
Reactor Coolant System
Stress Corrosion Cracking
Transgranular Stress Corrosion Cracking
v
Keywords
Heater
Heater Well Inserts
Pressurizer
Pressurizer Heater
Pzr
Reactor Coolant System
Sheaths
Sleeves
Stress Corrosion Cracking
vi
Acknowledgements
I would like to thank Westinghouse Electric Company, Bob Lisowyj, Frank Gift, Dave Taylor, and
Damian Testa for their support. Westinghouse has contributed with its emphasis of my education and
on pressurizer heater events and future developments. Bob has provided frequent career advice and
has provided review of this document and other pressurizer heater projects in their entirety. Frank has
provided support for the RPI Master’s Program and has focused on the path of my technical and career
development. Dave and Damian (as the cognizant pressurizer heater engineer and manager,
respectively) have assisted with the gathering of pressurizer heater references and have reviewed
various pressurizer heater documentation.
I would like to thank Len, Lainey, and Jeffrey Denis for their unwavering support and for their
relentless insistence that this project work should be completed.
Finally, thanks are due to Ernesto Gutierrez-Miravete, for his unwavering support over the
school semesters and for his review and comments on this Master’s Project.
vii
Abstract
Pressurizer heaters have been utilized in Pressurized Water Reactors since original installation
to ensure that the primary reactor coolant system stay in liquid form without boiling. Because of the
function and relatively harsh environment of the heaters, they are prone to failure and redundancy is a
requirement. Pressurizer heaters have functioned throughout the plant lifetimes, but the Sizewell B
pressurizer heater incident brought additional attention to the potential for primary pressure boundary
leakage.
There is much documented operating experience related to pressurizer heaters, but because
many past events did not result in immediate primary coolant leakage, effects of sheath failures were
not necessarily evaluated. This assessment evaluated prior pressurizer heater operating history to
determine if any previous events had the potential for sheath damage that could eventually lead to
heater degradation. Each event was analyzed for contributing and latent factors in the event, and then
summarized for review. The events each had an assessment of potential for sheath degradation.
(Events related to Alloy 600 failure were also given importance.) Potential for heater degradation is not
an issue for only international plants but is a concern for domestic plants as well. There are a number
of non-functional heaters domestically that may have the potential for sheath degradation.
viii
1.0
1.1
Pressurizer Heater Introduction
Pressurizer Heater Operation
Pressurized water reactors (PWRs) maintain the coolant in liquid form, without boiling to
create a two phase system. Because of the temperature of the coolant (up to 650°F), it must be
maintained at a high pressure (2250 psia). Pressurizer heaters are vessel components used at
PWRs that function to maintain the pressure of the primary loop. The pressure maintenance
assures that the liquid coolant will be maintained as a single phase, without steam presence.
Within the pressurizer, this pressure is maintained by use of a steam bubble, whose relative
size regulates the system pressure. The steam bubble is expanded by adding heat from
pressurizer heaters, and the steam bubble is reduced by adding cold water from “spray valves”
at the top of the pressurizer.
The immersion heaters used to provide heat to the pressurizer contain electrical heating
elements, surrounded by an insulation material of magnesium oxide (MgO) and then protected
from the primary coolant by a stainless steel sheath. These heaters are inserted into the bottom
shell of the pressurizer through heater well inserts (HWIs) or sleeves. Heaters are typically
made of Type 316 stainless steel.
Austenitic materials are limited by the ASME Boiler & Pressure Vessel Code to a
temperature of 800°F to limit the possibility of time-dependent degradation such as creep [1].
However, because of the nature of the immersion heaters to heat the pressurizer, the Code of
Federal Regulations [7] has an exception to allow operation of pressurizer heaters to allow the
component to reach temperatures not exceeding 900°F. The pressurizer heaters become one
of the highest temperature components in the reactor coolant system (RCS), with the exception
of nuclear fuel and fuel cladding.
1
Figure 1: Schematic of Westinghouse Pressurizer [8]
1.2
Pressurizer Heater Design
The pressurizer heater sheaths are frequently made of stainless steel (typically Type
316) that is swaged down around the heater elements (resistance heaters). Because of the
cold work induced by the swaging process, tensile residual stress exists at the outer diameter of
the sheath material. A magnesium oxide is used because of its dielectric properties and ability
to be backed inside the sheath material.
Figure 2: Typical Heater Cross-section [2]
2
Figure 2 and Figure 3 show the cross-sectional arrangement for heaters produced for
pressurizer heaters. Figure 4 shows the insertion of the heaters in the bottom of the pressurizer
for operation.
Figure 3: Cross-section of Pressurizer Heater Used in Nuclear Applications
Figure 4: Pressurizer with Inserted Heaters [2]
3
2.0
Pressurizer Heater Degradation
2.1
Sheath Degradation
Because of the cold working process, accumulated residual stress, the high temperature
of the heater, and the environment of primary water in the pressurizer, stainless steel
pressurizer heater sheaths are potentially susceptible to SCC, which can initiate and propagate
in the stainless steel material. The construction of the heater makes this degradation especially
problematic, as water ingress through the sheath can wet the MgO insulation. MgO is
hygroscopic, absorbing water to change from MgO to magnesium hydroxide (Mg(OH) 2),
accompanied by a volume change that can exacerbate sheath cracks and rupture the sleeve of
the heater.
Accompanying the water ingress, the electrical system of the heater will generally cease
to function, shutting down the heater and reducing the overall plant pressurizer heater margin.
There may be some amount of incubation time between crack initiation and eventual rupture.
Material failures can eventually lead to pressure boundary leakage, as a path is established
between the primary coolant in the pressurizer and the outer low alloy steel shell of the
pressurizer.
An additional issue with ruptured and swollen heaters is that removal is non-trivial. The
expanded heaters exceed the prior dimensional tolerances, and the Mg(OH)2 insulation is
difficult to drill out of the heater. Electrical issues in heaters are a common occurrence and are
not necessarily indicative of any material concerns outside of the heating element.
2.2
Sizewell B Incident
On March 16, 2010 the Sizewell B high radiation alarms were triggered in the
containment building. The reactor coolant system was leaking at a rate of 4.5 L/min, which
triggered the high radiation alarms [8]. The leak was from one of the seventy-eight pressurizer
heater wells. The leak was marginally above the Technical Specifications limit that required
under safety protocol to shut down the reactor, which was safely shutdown March 17, 2010. An
axial crack (approximately 13mm) was located on the heater well insert of a pressurizer heater
[14].
The Sizewell B pressurizer has two horizontal support plates for the heaters. Between
2000 and 2010, a total of ten heaters became non-functional. Although the electrical nonfunctionality was observed, a potential root cause could have been sheath degradation. The
4
failure mechanism for sheath degradation was reported as stress corrosion cracking in the
stainless steel sheath material. As the crack propagated, the heater sheath was breached,
allowing water to make contact with the magnesium oxide (MgO) insulation of the heater, which
undergoes a reaction to transform to magnesium hydroxide (MgOH2). Figure 5 shows the leak
site, and Figure 6 shows the degraded heaters with insulation emerging from the sheath.
Figure 5: Leak Site at Sizewell B [8]
Three heaters were found with significant mechanical damage in addition to the heater
associated with the leak. These heaters (and thirteen heaters that were electrically nonfunctional) were removed from the pressurizer. The electrically non-functional heaters had
ceased function over thirteen previous years, beginning in 1997. The heater of concern was
electrically non-functional and then suffered sheath failure within an eighteen month cycle.
Seventeen total heaters were removed.
5
Figure 6: Failed Heater Elements from Sizewell B [8]
2.3
Industry Response
Currently, the industry recommends that non-functional heaters be removed from
service at the “next convenient opportunity”, which is considered to be the next refueling
outage. There is currently no technique to definitively demonstrate that a non-functional
heater has only been damaged electrically. Many plants respond different to the occurrence
of a non-functional heater, and there is currently no standard plan in the industry for
addressing such issues. Figure 7 shows an axial crack in a heater from an operating plant.
Figure 7: Axial Cracks in a Plant Heater [8]
6
3.0
Material Degradation of Pressurizer Heaters
Stress corrosion cracking (SCC) is a material degradation mechanism potentially
associated with austenitic stainless steels. Components in PWRs can be susceptible to SCC
when three conditions are met:
1. Susceptible material or material condition
2. Aggressive environment
3. Tensile operating stress
Elimination of any of these conditions will preclude the occurrence of SCC. Austenitic stainless
steel is susceptible to both intergranular stress corrosion cracking (IGSCC) and transgranular
stress corrosion cracking (TGSCC) under the appropriate conditions.
Austenitic stainless steel has a nominal (weight) composition of 18 chromium and 8
nickel. The chromium provides corrosion protection and the nickel stabilizes the austenite.
IGSCC generally occurs in austenitic stainless steels that have undergone sensitization by
experiencing the temperature range of 800°F-1,500°F [6]. During sensitization, the chromium
that is present in the material precipitates out of solution at grain boundaries as chromium
carbides, which locally depletes the chromium from the zone adjacent to the grain boundaries.
This process reduces the resistance to corrosion in an area around the boundary, allowing
initiation of a crack that will propagate between the grains and along the grain boundaries in
IGSCC. Low carbon grades (e.g., 304L, 316L, etc, with limits on carbon content of 0.035%) can
often preclude sensitization, as less carbon is available to form the chromium carbides along the
grain boundary.
IGSCC can also occur with materials that are subject to cold work. The cold work
increases the strength of the material but also increases the susceptibility of the material to
SCC. Stagnant flow locations, where oxygen and chlorides can accumulate, can provide an
area of increased susceptibility for TGSCC to initiate and propagate across the grain
boundaries.
(Note: For the purposes of this report, primary water stress corrosion cracking (PWSCC)
is considered to be associated with iron-nickel base alloys such as Alloy 600 and its associated
weld metals Alloy 82 and Alloy 182.)
3.1
Reactor Coolant System Chemistry
The bulk chemistry conditions for the primary reactor coolant system are defined by
guidelines provided by EPRI [1]. The limits are set for reactivity control, pH balance, and to limit
7
the deleterious effects from foreign contaminants for corrosion, neutron moderation, departure
from nucleate boiling, and worker dose rate control. The main contributors to SCC are dissolved
oxygen and chlorides that can accumulate in stagnant low-flow areas of the system, as shown
by Figure 8.
Figure 8: Gordon Curve of Incidents of SCC of Austenitic Stainless Steel in High Temperature
Water by Oxygen and Chloride Concentration
The limits in Table 1 are imposed to reduce potential corrosion, degradation, and
material interaction, while maintaining appropriate limits for fuel moderation, criticality
management, and fuel reliability.
Table 1: Primary Chemistry Limits for RCS [4]
Control Parameter
Chloride, ppb
Flouride, ppb
Sulfate, ppb
Lithium, ppm
Hydrogen, cc
(STP)/kg H2O
Dissolved Oxygen,
ppb
Action Level 1
Plant-specific
Plant-specific
Plant-specific
Plant-specific
<25
>50
>5
8
Action Level 2
>150
>150
>150
N/A
<15
Action Level 3
>1,500
>1,500
>1,500
N/A
<5>
>100
>1000
3.2
Combustion Engineering Alloy 600 Pressurizer Heater Sleeves
Original fabrication of many pressurizers for the Combustion Engineering domestic fleet
used Alloy 600 nickel-base material for pressurizer heater sheaths. Alloy 600 is an iron/nickelbase material that is generally susceptible to primary water stress corrosion cracking (PWSCC)
in primary coolant. As a general best practice to replace pressure boundary Alloy 600, many
pressurizers were replaced. For the units that also had Alloy 600 sheath material heaters, new
heaters with stainless steel sheath material were introduced. Table 2 lists the CE designed
plants with the status of their pressurizer replacement.
Figure 9: Nickel-base Alloys in Combustion Engineering Pressurizers [3]
At time of release of CE NPSD 555 (Task 585) of the Combustion Engineering Owners
Group, a survey was conducted to obtain information regarding pressurizer heater operating
experience. Of low watt density pressurizer heaters with Inconel Alloy 600 sheaths made by one
manufacturer (Manufacturer A), the plants Palisades, Fort Calhoun, St. Lucie Unit 1, and
Millstone Unit 2 returned survey results. Of the 432 heater population of these plants, six
heaters were reported to be electrically non-functional. (No sheath assessment has been
specifically performed as these Alloy 600 heaters were subsequently replaced. The electrical
non-functionality may have been indicative of sheath degradation.)
9
Table 2: Plants with Alloy 600 Pressurizer Sleeves and Year of Pressurizer Replacement
Plant
Replaced
Fort Calhoun Station
Yes (Fall 2006)
Maine Yankee*
No
Calvert Cliffs Unit 1
No
Calvert Cliffs Unit 2
No
St. Lucie Unit 1
Yes (Fall 2005)
St. Lucie Unit 2
Yes
Millstone Unit 2
Yes (Fall 2006)
San Onofre Unit 1*
No
San Onofre Unit 2*
No
San Onofre Unit 3*
No
*Unit currently decommissioned or without plan for restart
Ninety-six Alloy 600 sheath heaters were constructed by one manufacturer
(Manufacturer B)and supplied to Arkansas Nuclear One Unit 2. Twenty-three of these heaters
were non-functional when energized in Air. Two additional non-functional heaters were since
reported. (No sheath assessment has been specifically performed as these Alloy 600 heaters
were subsequently replaced. The electrical non-functionality may have been indicative of
sheath degradation.)
Twenty-nine Alloy 600 sheath heaters that were constructed by one manufacturer
(Manufacturer C) were delivered as replacements for Arkansas Nuclear One Unit 2 to replace
twenty-three non-functional heaters that were replaced in 1982 (ans two replacement heaters
were electrically non-functional in 1985). In April of 1987 a leaking heater sleeve was verified at
the X1 position. The X1 and T4 heaters have ruptured sheaths and heater AA1 was electrically
non-functional. Locations X1 and T4 were subsequently plugged. The remaining twenty-one
heaters from Manufacturer C were removed and replaced with six spare heaters and fifteen
sleeve plugs.
From May 1985 until February 1990, no issues with high watt density pressurizer
heaters with alloy 600 sheaths were reported. High watt density pressurizer heaters with Type
316 stainless steel sheaths. No issues from December 1987 through February 1990 were
reported for Palo Verde Unit 3. Non-functional heaters were reported for Waterford Unit 3 (9
heaters) and St. Lucie Unit 2 (1 heater). San Onofre Unit 3 and Palo Verde Unit 2 both
experienced pressurizer heater sheath degradation.
10
4.0
Pressurizer Heater Operating Experience
Because the Sizewell B incident was extremely severe relative to the leak rate and the
unplanned outage duration, 2010 re-emphasized the importance of maintaining the integrity of
the pressurizer heater sheath. There are many issues in operating experience that have been
documented relative to the pressurizer heater, but the emphasis on sheath degradation was not
at the same level when many of these instances occurred.
This project reviews nuclear industry operating experience from a variety of sources to
determine the potential for latent sheath degradation in incidents that have occurred during plant
operation during over 45 years of plant operation. Because the Babcock & Wilcox design
(B&W) have a different design arrangement of heaters, the events have been noted but the
sheath degradation is not applicable.
A complete list of entries is covered in Appendix A. Entries highlighted in red have relation
to the potential for sheath degradation (stainless steel), while the blue highlighted entries have
relation to Alloy 600 PWSCC material degradation.
4.1
Pressurizer Heater Sheath Degradation
On April 22, 1987, at Arkansas Nuclear One Unit 2, a degraded sheath was confirmed
leading to a leak rate of 60 drops per minute. Stress corrosion cracking of the heater sheath
was determined, allowing water to react with magnesium oxide insulation which expanded on
hydration and ruptured the “X1” and “T4” heater sleeves. The “X1” heater was damaged
severely enough to produce an external leak through the welded sleeve fitting. The “X1” and
“T4” heaters were removed and plugs were installed (RAC 2-87-050) [ICES Report #52488]
Sheath Degradation Assessment: This issue was determined to have been caused from
degradation of a heater sheath.
On September 26, 1989, at Calvert Cliffs Unit 1, weepage-type leakage was detected in
20 pressurizer heaters by visual examination at Calvert Cliffs Unit 2. The root cause was
IGSCC (PWSCC) of the Alloy 600 heater sleeves. The heaters were inspected at Unit 1 and 12
heaters were removed, and no leakage was detected from Unit 1. [ICES Report #296493]
Sheath Degradation Assessment: The sleeves and potentially sheaths of the pressurizer
heaters had material damage.
On April 3, 1991, at Beaver Valley Unit 1, the “C” pressurizer heater bank did not have
full capacity. Heater 45 and heater 69 had a short circuit that caused the breakers to trip, which
was considered normal heater wear. The in-place heaters were temporarily retired in place.
They are to be replaced at a future date. [ICES Report #107402]
Sheath Degradation Assessment: The heater become non-functional due to a heater
electrical issue which could be associated with sheath degradation.
11
On June 21, 1992, at Three Mile Island Unit 1, a pressurizer heater was non-functional
and confirmed with resistance and meggar checks. The rest of the group that was functional
was returned to service. [ICES Report #126009]
Sheath Degradation Assessment: Although this is a B&W plant and the assessment is not
applicable, the heater potential suffered from some sheath degradation that could have caused
the heater non-functionality.
On September 22, 1992, at Three Mile Island Unit 1, heaters 32, 33, and 39 were found
to be open circuits. This was not an issue because of the large number of redundant heaters.
Leads were lifted to remove the heaters from service. [ICES Report #129294]
Sheath Degradation Assessment: Because this is a B&W plant, this assessment is not
applicable. The non-functional heaters may have the potential for associated sheath material
degradation that could have caused the non-functionality.
On July 6, 1994, at Calvert Cliffs Unit 1, pressurizer heater insulation during the April
1994 outage was discovered at location CC-1, indicating failed heater cladding. All heaters had
been replaced with new 13.3 kW heater manufactured by Watlow. The magnesium oxide
insulation had swollen and the heater had been lodged in place and impossible to remove. The
heater internals were later drilled out and the location plugged. Previous industry expectation
was that the pressurizer heaters with a failed cladding would not swell that quickly. It was
believed that the heater sheath breach was made during installation and was not a
manufacturing defect. [ICES Report #146877]
Sheath Degradation Assessment: The magnesium oxide swelling was associated with water
ingress and a pressurizer heater sheath breach.
On January 23, 1999, at Prairie Island Unit 1, 5 heaters were reported as non-functional.
One heater failed prior to 1986, one in 1991, one in 1992, one in 1995, and one in 1997. The
non-functional heaters were disconnected. No further resolution was provided in the report.
[ICES Report #177791]
Sheath Degradation Assessment: The non-functional heaters may have associated sheath
degradation. No clear root cause was determined as the reason for the heater non-functionality.
On July 6, 1999, at South Texas Unit 1, the primary circuit breaker for circuit #4 for
pressurizer heater group 1A was found in the tripped condition. The breaker was reset and
remained closed after the heater was energized. The breaker was replaced, but tests still had
to be made on the heater condition. [ICES Report #180901]
Sheath Degradation Assessment: The heater might have an issue with grounding since
additional testing has to be performed, so sheath degradation is possible.
On July 30, 2000, at ANO Unit 2, boric acid crystals were bound under the pressurizer
on the electrical cables of heaters B2 and D2. Ten additional heater sleeves exhibited similar
evidence of leakage, but to a smaller extent. Eight of the sleeves (A2, B2, B4, C3, D2, D3, D45,
and AA3) had heaters installed while four of the sleeves (AA4, B1, B3, and G2) had dummy
heaters. Nine of the twelve sleeves were located in the first row around the surge nozzle. The
cause of the sleeve ruptures was PWSCC of Alloy 600 material, and sheath swelling,
presumably from sheath degradation, was also noted. Information is documented in CEOG
Report CEN-393-P. [ICES Report #187535]
Sheath Degradation Assessment: The swollen sheath is an indicator of sheath degradation.
12
On October 4, 2000, at Palo Verde Unit 2, at the beginning of U2R9, evidence of heater
sleeve leakage was detected (at location A06) and documented in ISI report #00-342. A sleeve
plug at location B18 (another previously plugged heater location) was removed and the remnant
was examined by eddy current testing. The axial cracks had been confirmed in 1991. Heater
sheath swelling problems were also noted in Unit 2 A06 and B18. The sleeve was inspected
and repaired. [ICES Report #188724]
Sheath Degradation Assessment: The swollen sheath is an indicator of sheath degradation.
On August 27, 2002, at Kewaunee Unit 1, pressurizer heater backup group 1E heaters
had an open phase that was detected. The heater was powered from C/B 1-562. No specific
resolution was mentioned in the report. [ICES Report #199827]
Sheath Degradation Assessment: A root cause for the open phase was not provided. A
degraded sheath could manifest as an open phase in the heater.
On October 2, 2003, at Palo Verde Unit 3, the A train pressurizer heater bank circuit
breaker tripped open. The heater (B-09) had a 20 year life but was considered non-functional.
The heater was considered “consumable”. Train A was restored by wiring in a heater from a
non-class heater bank. [ICES Report #206680]
Sheath Degradation Assessment: Because the heater was considered non-functional and
remains in service, sheath degradation is a possibility. The heater may have had only electrical
issues or may have associated sheath failure.
On April 7, 2004, at Diablo Canyon Unit 1, degradation was identified on the termination
from the electrical cable to the heater element due to overheating damage. A significant
amount of chlorides were detected. The wires with corrosion were replaced and repaired. [ICES
Report #209708]
Sheath Degradation Assessment: The element wires connect to the heater, so sheath
degradation is unlikely. The presence of significant chlorides negatively impacts corrosion to
the heater.
On August 25, 2004, at Palo Verde Unit 2, pressurizer heating element 2MRCEA10
ceased to function, so it was electrically isolated. This brought the total number of isolated
heater elements to four. The heating margin is appropriate with up to seven isolated elements.
During U2R11, approximately 50% of the heaters were replaced. The unit will replace all of the
pressurizer heater elements. The elements in Unit 3 are being replaced during U3R11 with a
new heater (Framatone style). The Unit 1 elements will be replaced during U1R12. [ICES
Report #211809]
Sheath Degradation Assessment: The non-functional heater may be associated with sheath
degradation.
On February 16, 2005, at Palo Verde Unit 3, heater 3MRCEB02 because non-functional
and was the third pressurizer heater failure since installing Framatone/Thermocoax heaters. All
three phases were grounded. The previous heater events were December 24, 2004 for bank #1
and January 5, 2005 for bank #2. All 36 Framatone/Thermocoax heaters were later replaced.
[ICES Report #214396]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible. These heaters were removed from service.
On March 28, 2005, at Palo Verde Unit 2, pressurizer heater bank B tripped on a ground
fault and 2MRCEB10 pressurizer heater was non-functional. A jumper was used to install a
13
spare heater into the failed heater’s position. The B10 heater is a Watlow heater. 2MRCEA12
was installed electrically. During U2R11 all heater sleeving was removed and all heaters were
removed. 25 new General Electric heaters were installed and 9 heaters from Unit 2 were
recycled. The recycled heaters had the following non-functionalities B11 (December 30, 2003),
A10 (September, 16 2004), and B10 (March 28, 2005). These heaters were removed and plugs
were installed. [ICES Report #215123]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible. These heaters were removed from service.
On May 26, 2005, at Waterford Unit 3, Framatome/Thermocoax heaters installed in the
pressurizer ceased to function during refuel 13. Upon energizing, two heaters experienced
partial ejection of the epoxy in the receptacle area, six were non-functional due to grounding,
and several others experienced partial melting of the silicon type sealant material at the bottom
of the receptacle. The device had been modified by the manufacturer to enhance reliability and
make fabrication easier. The ability of the heater to remove heat from a sensitive electrical area
was reduced. Twenty-three heaters were replaced with spare and reusable Watlow heaters.
[ICES Report #216255]
Sheath Degradation Assessment: Because of early issues upon activation, sheath
degradation is unlikely, and the heaters in question are not in service. Still, non-functionality of
heaters is an indicator of potential sheath degradation.
On March 22, 2006, at Palo Verde Unit 1, pressurizer heater 1MRCEA05 became nonfunctional. This issue is described by Report #222893. [ICES Report #220408]
On April 4, 2006, at San Onofre Unit 3, degradation was found in the heaters
manufactured by Framatome ANP/Thermocoax, after 15 months of operation. Three heaters
had been known prior to be non-functional. Many of the Generation I Framatome heaters had
been removed and replaced prior to restart from the mid-cycle outage with Framatome
Generation II heaters. [ICES Report #220623]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible.
On April 25, 2006, at Braidwood Unit 1, leakage was found from IGSCC of the stainless
steel pressurizer heater sleeve number 52, through a locally sensitized section of Type 316
stainless steel base material. The failed sleeve portion was removed, plugged, and sealed. All
78 sleeves and couplings were visually inspected, and number 52 was confirmed to be the only
leakage source. [ICES Report #220951]
Sheath Degradation Assessment: Sheath degradation is unlikely due to the degradation
being IGSCC of only the heater sleeve material. Still, this is a significant material degradation
event. Events during which sleeve rupture occurs may have associated sheath degradation. In
this incident, however, the heater was still operable, reducing the likelihood of present sheath
degradation.
On June 25, 2006, at Catawba Unit 1, the pressurizer heater group 1C was not
operating properly due to an open fuse in the silicon controlled rectifier caused by moisture
intrusion. The fuse was replaced. Heaters 34, 63, and 63 were isolated and then bank C was
energized. It is unclear from the report whether the three heaters in question remained nonfunctional. [ICES Report #221896]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible.
14
On September 18, 2006, at Palo Verde Unit 1, a pressurizer heater became nonfunction. Nine Watlow heaters are installed in Unit 2 and twelve Watlow heaters are installed in
Unit 3. This issue is described by report #222893. [ICES Report #222906]
On September 18, 2006, at Palo Verde Unit 1, heater element 1MRCEA14 became nonfunctional. During U1R12, all 36 pressurizer heaters were replaced with new heaters fabricated
by Watlow. Several heaters became non-functional in less than 6 months. The heaters were
electrically isolated. The MRCEA05 heater was analyzed and came back with IGSCC results
on the outside surface. Five failed heaters were sent to Westinghouse for analysis. Nonfunctional heaters were as follows: 1MRCEA05 (March 22, 2006), 1MREAB18 (June 27, 2006),
1MRCEB09 (July 31, 2006), 1MRCEA14 (July 31, 2006), B/U Bank-1 BRKR-1 Non-Class
(September 18, 2006), B/U Bank-1 BRKR-1 Non-Class (September 18, 2006), B/U Bank-1
BRKR-1 Non-Class (September 18, 2006). The Unit 1 heaters (thirty-five of thirty-six) were
replaced with heaters manufactured by Doosan (except location B18). Location B18 was
unable to be removed and the heater was plugged. [ICES Report #222893]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible.
On September 9, 2007, at Millstone Unit 2, a number of backup pressurizer heaters
became non-functional. Five heaters were found to be non-functional and an additional two
heaters were later documented as being non-functional. Hard grounds were identified on
several breakers. A number of heaters are planned for replacement. [ICES Report #228372]
Sheath Degradation Assessment: The heater became non-functional, so sheath degradation
is possible.
On October 22, 2007, at Palo Verde Unit 1, heating element 1MRCEA11 became nonfunctional. A-11 is a non-class heater back-up #7. No further specific mention of resolution was
provided in the report. [ICES Report #229142]
Sheath Degradation Assessment: The heater became non-functional, so sheath degradation
is possible.
On October 16, 2008, at Millstone Unit 3, control bank pressurizer heater had blown a
fuse and the breakers on one heater string (three elements) had opened. A heater element was
found missing potting compound and one connection tab. In total, five of seventy-eight control
and back-up heaters have been removed from service due to heater element failure (heater
non-functionality). [ICES Report #234466]
Sheath Degradation Assessment: The heater became non-functional, so sheath degradation
is possible.
On May 9, 2010, at Fort Calhoun Unit 1, inspections to determine the integrity of heater
26 indicated a cracked sheath. The ground on the heater was found May 9, 2010. Visual
inspection of heater 26 in November 2011 did not identify the cracking. A crack was observed
on May 19, 2012. The heater sheath was removed and replaced. [ICES Report #293138]
Sheath Degradation Assessment: The heater sheath was confirmed to be degraded.
On January 4, 2011, at Millstone Unit 2, a heater element was suspected to be a repeat
failure. This issue is documented in Report #246910. [ICES Report #246919]
On January 4, 2011, at Millstone Unit 2, heater element P2C11 became non-functional
(Framatome heater). Pressurizer heater element B13 shorted to ground in January 2009. The
heater was replaced during 2R19 with a heater of the same design but with improved
15
manufacturing processes. [ICES Report #246910]
Sheath Degradation Assessment: Since the heater became non-functional, sheath
degradation is possible.
On May 25, 2011, at St. Lucie Unit 2, pressurizer heaters became non-functional due to
heater element issues subsequent to replacement. The non-functional heaters were B1 (April 6,
2011), C3 (April 13, 2011), D3 (April 27, 2011), C1 (May 25, 2011), and B2 (June 13, 2011).
The Unit 1 heaters are of “significantly different” design. The corrective action is to ensure
compliance from manufacturer for additional testing. [ICES Report #249343]
Sheath Degradation Assessment: Since the heaters became non-functional, there is
potential for sheath degradation.
On June 13, 2011, at St. Lucie Unit 2, five of thirty pressurizer heaters were electrically
non-function after replacement. The issues occurred within three months of being placed in
service. Forensic processes were ongoing. [ICES Report #249634]
Sheath Degradation Assessment: The heater became non-functional, so sheath degradation
is possible.
On May 23, 2012, at Fort Calhoun Unit 1, a pressurizer heater was found damaged.
The issue is described in Report #293138. [ICES Report #254068]
On March 3, 2014, at Millstone Unit 2, the group 1 proportional heater power level was
lower than the Tech Spec requirement during a capacity test. A heater element had failed in
January and remained out of service. The controlled element was calibrated and a backup
heater element was connected in place of the non-functional proportional element. [ICES
Report #310253]
Sheath Degradation Assessment: A non-functional heater may be associated with potential
sheath degradation.
4.2
Alloy 600 Events in Pressurizer Heaters
On March 21, 1994, at Calvert Cliffs Unit 1, boron deposits were discovered on the Unit
1 pressurizer heater sleeve B-3 indicating leakage from an Alloy 600 component of the reactor
coolant system pressure boundary. Deposits were also noted on sleeve FF-1. The Unit 1
sleeves were examined, and sleeve FF-1 was plugged with an Alloy 600 plug. SER 31-87
“Pressurizer Vessel Corrosion Due To Pressurizer Heater Rupture” from November 10, 1987 is
of note. [ICES Report #144384]
Sheath Degradation Assessment: The sleeve was a result of PWSCC of the Alloy 600
sleeve. No apparent sheath degradation was noted in the report.
On July 22, 1995, at San Onofre Unit 3, minimal weepage was detected from a pressurizer level
instrument nozzle due to PWSCC of Alloy 600 material. No further resolution is provided in the
report. [ICES Report #154360]
Sheath Degradation Assessment: The pressurizer instrument nozzles are separate from the
heater, so sheath degradation is unlikely. Still, this issue is related to material degradation of
Alloy 600.
On April 14, 1998, at Calvert Cliffs Unit 1, heater sleeve B-1 had boric acid
16
accumulations due to PWSCC of Alloy 600 material. Visual and ultrasonic inspections were
made of the heater sleeves. The sleeve was removed and the penetration was replaced. [ICES
Report #172389]
Sheath Degradation Assessment: The sleeve is separate from the heater, but sheath
degradation could be possible with a degraded sheath. This is PWSCC of Alloy 600 material.
On April 17, 1998, at Calvert Cliffs Unit 1, a pressurizer heater sleeve was found cracked
during inspection. The crack was a pre-existing crack that was nickel plated in 1994. The
sleeve was removed and the penetration was plugged. This sleeve was Alloy 600 material that
cracked due to PWSCC [ICES Report #172440]
Sheath Degradation Assessment: The sleeve is separate from the heater, but sheath
degradation could be possible with a degraded sheath. This is PWSCC of Alloy 600 material.
On July 25, 1998, at Calvert Cliffs Unit 2, a pressurizer instrument nozzle failed because
of an Alloy 600 issue. The leading nozzle was repaired and the other nozzles were visually
inspected. All data were collected, and the unit was returned to power. The Alloy 600 nozzles
were replaced with Alloy 690 material but were still welded with Alloy 600-type weld metal.
[ICES Report #174468]
Sheath Degradation Assessment: The instrument nozzle is separate from the heater, so
sheath degradation is unlikely. This is PWSCC of Alloy 600 material.
On July 25, 1998, at Calvert Cliffs Unit 2, a pressurizer instrument nozzle failed because
of an Alloy 600 issue. The leading nozzle was repaired and the other nozzles were visually
inspected. All data were collected, and the unit was returned to power. [ICES Report #174476]
Sheath Degradation Assessment: The instrument nozzle is separate from the heater, so
sheath degradation is unlikely. This is PWSCC of Alloy 600 material.
On October 4, 2000, at Palo Verde Unit 2, boric acid indications were found for a heater
sleeve, due to PWSCC of Alloy 600 material. The sleeve was repaired. [ICES Report
#188723]
Sheath Degradation Assessment: The pressurizer heater sleeve is separate from the heater,
so sheath degradation is unlikely. This is PWSCC of Alloy 600 material. The same incident
was later associated with sheath swelling.
On October 17, 2000, at Waterford Unit 3, leaking MNSA clamps let to primary pressure
boundary leakage in the pressurizer heater sleeve due to Alloy 600 material PWSCC. The
MNSA was not installed correctly by the vendor. [ICES Report #188992]
Sheath Degradation Assessment: The pressurizer heater sleeve is separate from the heater,
so sheath degradation is unlikely. This is PWSCC of Alloy 600 material.
On October 22, 2000, at Fort Calhoun Unit 1, the water space temperature element on
the pressurizer suffered from PWSCC of Alloy 600 material that was found from a small steam
leak from thermowell TE-108. A successful partial weld repair was performed on TE-108, and
preventive maintenance of TE-107 was employing using a Mechanical Nozzle Seal Assembly
(MNSA). [ICES Report #189090]
Sheath Degradation Assessment: The instrument nozzle is separate from the heater, so
sheath degradation is unlikely. This is PWSCC of Alloy 600 material.
17
On February 19, 2002, at Millstone Unit 2, leakage was present at two heater
penetration locations (A1 and C4) on drawing 25203-32007 due to PWSCC of Alloy 600
material. MNSA clamps were installed on each leaking nozzle. [ICES Report #196610]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On April 30, 2002, at ANO Unit 2, leakage was found on the pressurizer heater sleeve
nozzles C2, E2, F4, G1, and E1. Two locations (at J3 and N3) were difficult to inspect due to
insulation present. MNSA 2 was installed on each of the five leaking sleeves. The issue was
caused by Alloy 600 PWSCC. [ICES Report #197886]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On March 29, 2003, at Palo Verde Unit 3, an RCS leak was found relating to a
pressurizer heater sleeve. This issue is described in Report #203600. [ICES Report #203600]
On March 29, 2003, at Palo Verde Unit 3, leakage was found on pressurizer heater
sleeves A-1 and A-15. This issue is described in Report #203600. [ICES Report #203610]
On March 29, 2003, at Palo Verde Unit 3, boric acid residue was found around
pressurizer penetration A01. Heater sleeve A15 was initially suspected of leaking but was later
verified to not have visual evidence of leakage. The degradation was due to axially oriented
PWSCC of Alloy 600 material. The heater sleeve was repaired using a MNSA. [ICES Report
#203600]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On October 11, 2003, at Millstone Unit 2, heater penetration C3 was identified as having
wet boric acid leakage. Another location identified as F4 on drawing 25203-20527 Sheet 15
was found to be suspected of additional leakage. MNSA clamps were installed to prevent
leakage. New pressurizer (without Alloy 600) installation is planned for fall 2006. [ICES Report
#206835]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On October 15, 2003, at Palo Verde Unit 2, circumferential cracks were found in
pressurizer heater sleeves. The issue is described by Report #206889. [ICES Report #206900]
On October 15, 2003, at Palo Verde Unit 2, six pressurizer heater sleeves had
circumferential flaw indications and six additional sleeves had axial flaw indications from
PWSCC of Alloy 600 material. The Alloy 600 material was replaced with Alloy 690 material
(more resistant to PWSCC). Replacement is also planned for Unit 1 and Unit 2. [ICES Report
#206889]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On October 24, 2003, at Waterford Unit 3, two pressurizer heater sleeves (locations C-1
and C-3) were leaking because of PWSCC of Alloy 600 material. The sleeves were repaired
with MNSA 2 clamps. [ICES Report #207068]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
18
On October 26, 2003, at Waterford Unit 3, two top pressurizer nozzles were found
leaking due to Alloy 600 PWSCC. These nozzles were repaired by a welding replacement.
[ICES Report #207098]
Sheath Degradation Assessment: The instrument nozzles are separate from the heater, so
sheath degradation is unlikely. The instrument nozzle degradation is due to Alloy 600 PWSCC.
On November 2, 2003, at Millstone Unit 2, two additional pressurizer heater sleeve
leakages were found (four total since spring 2002 2R14) due to PWSCC of Alloy 600 material.
The cracks were axial in orientation. The leakage rate was low at less than 0.1 gallons per
minute. MNSA clamps were installed to prevent further leakage. [ICES Report #207197]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On November 4, 2003, at Three Mile Island Unit 1, a leak was identified in the
pressurizer heater bundle diaphragm plate due to PWSCC of Alloy 600 material. The issue was
resolved by grinding the plate and applying a seal weld. On November 23, 2003, during post
maintenance testing, additional leakage was observed. The assembly was replaced with a new
heater bundle assembly. Subsequently, the plate was replaced with a stainless steel Type 304
plate. [ICES Report #207234]
Sheath Degradation Assessment: As this is a B&W design the sheath degradation
assessment is not applicable. The material degradation was due to PWSCC of Alloy 600.
On February 29, 2004, at Palo Verde Unit 3, pressurizer heater sleeve A03 was found to
be leaking. The issue is described by Report #209042. [ICES Report #209045]
On February 29, 2004, at Palo Verde Unit 3, the penetration sleeve for pressurizer
heater 3MRCEA03 failed due to PWSCC of Alloy 600 material. Boric acid residue had been
found, so the sleeve was repaired with a MNSA. Sleeve replacement was planned for fall of
2004. The sleeve was later replaced with Alloy 690 using a half nozzle repair. Issues were
found with sleeves A1, A3, and A15. [ICES Report #209042]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On October 17, 2004, at San Onofre Unit 3, two pressurizer heaters (and sleeves) were
to be replaced because of PWSCC axial and circumferential indications. No leakage was
detected. A proactive decision was made to replace all pressurizer heater sleeves with an Alloy
690 half-nozzle repair. Two leaks were later discovered from repair weld pads during parallel
refueling. [ICES Report #212622]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On March 9, 2005, at ANO Unit 2, heater sleeve leakage was found. This issue is
described by Report #214924. [ICES Report #214781]
On March 12, 2005, at ANO Unit 2, heater sleeve leakage was found. This issue is
described by Report #214924. [ICES Report #214843]
On March 16, 2005, at ANO Unit 2, leakage was identified from pressurizer heater
penetrations during 2R17 due to PWSCC of Alloy 600 material. Ten total penetrations had
leakage (P1, V1, P2, J2, U3, G3, H4, C4, and X3). The MNSA 2 is the planned repair method.
19
Penetration X1 contains a plug and will be repaired using a mid-wall nozzle repair. [ICES
Report #214924]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On April 10, 2005, at Millstone Unit 2, one heater sleeve showed minor leakage at
penetration B-2 due to PWSCC of Alloy 600 material. One axial indication was found. The
sleeve was repaired using a MNSA. A pressurizer replacement was planned for the next
outage (2R17). [ICES Report #215391]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On April 19, 2005, at Waterford Unit 3, boric acid was discovered near pressurizer
heater sleeves C-4 and D-2 due to PWSCC of Alloy 600 material. Two axially oriented flaws
were identified for C-4 but no indications were found for D-2. D-2 was determined to not have
an RCS leak. The leaking penetration was repaired using an Alloy 690 half-sleeve replacement,
as part of planned preventive maintenance for all Alloy 600 pressurizer sleeves. Guidance is
given in NRC bulletin 2004-01. [ICES Report #215602]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from
the heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600
PWSCC.
On February 25, 2008, at Calvert Cliffs Unit 1, a leak was found on pressurizer heater
sleeve after finding residual dry boron residue. Ultrasonic examination confirmed the absence
of a circumferential flaw. The cause of this event was PWSCC of Alloy 600 material. The
sleeve was repaired by installation of a mechanical clamp. [ICES Report #231015]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On February 17, 2011, at Calvert Cliffs Unit 2, visual inspections identified a through wall
leak in the RCS pressure boundary at a weld join for pressurizer heater location N-3. The weld
metal used to replace the Alloy 600 base metal in 1990 was Alloy 82, similar to Alloy 600 (but in
weld metal form). The cracking was from PWSCC of Alloy 600-type material. The affected
heater and sleeve were removed and plugged. [ICES Report #247617]
Sheath Degradation Assessment: As this is an issue with the heater sleeve, sheath
degradation is unlikely. This issue involves PWSCC of Alloy 600-type material.
20
5.0
Summary and Conclusion
Evident in the operating history for pressurizer heaters are instances of events with
heater sheath degradation that are potential contributors to pressure boundary leakage. The
event reports do not contain all of the information associated with the utility’s disposition and
mitigation of potential events, nor does it extrapolate the consequences of various response
options available to the plants.
Most of the issues associated with the pressurizer heaters relate to electrical issues
within the control, power, and monitoring systems, without relation to the material degradation of
the heater sheaths. These electrical issues are manageable and can frequently be remedied with
replacement of electrical equipment, unlike sheath degradation that requires advanced refueling
outage preparation and execution to repair or replace components.
Although a small fraction of the operating experience, sheath degradation is one of the
more highly consequential failures that can occur to the pressurizer heaters. The heating
functionality of each individual heater is highly redundant, with backup banks and excess heating
margin available should a heater become non-functional or unresponsive to control. For sheath
degradation, one breach can force a plant to shutdown for extended periods of time, a
tremendous economic impact to the operating utility and a negative response from the public
perception of plant reliability and safety. The review shows that the issue present at Sizewell B is
a potential concern for the currently operating PWR fleet in the United States, and lessons
learned from the degradation at Sizewell should be used in maintaining the integrity of pressurizer
heaters.
The industry has been addressing these issues for both currently operating, and newly
under construction plants, to improve the pressurizer heater design to ensure reliable use for
continuing operation. Utilities should continue to review operating experience as it emerges to
track current industry issues and prepare for organizational and operational vulnerabilities.
It is the responsibility for all proponents and opponents of nuclear power to be aware of
the issues affecting operation, reliability, and safety, to continue to improve the utilization of the
technology. The power generation industry will continue to encounter issues in the future, and
engineers must address these issues to promote public safety and welfare.
21
6.0
References
1. ASME Boiler & Pressure Vessel Code, Section III, Division 1 – Subsection NB, Class 1
Components, “Rules for Construction of Nuclear Facility Components,” 2013 Edition.
2. Watlow Catalog <http://www.watlow.com/downloads/en/catalogs/heaters.pdf> Accessed
October 4, 2014.
3. IAEA Nuclear Energy Series, No. NP-T-3.2, “Heavy Component Replacement in Nuclear
Power Plants: Experience and Guidelines,” October 2008.
4. Pressurized Water Reactor Primary Water Chemistry Guidelines: Volume 1, Revision 6.
EPRI, Palo Alto, CA: 2007. 1014986.
5. Materials Reliability Program: PWR Internals Material Aging Degradation Mechanism
Screening and Threshold Values (MRP-175). EPRI, Palo Alto, CA: 2005. 1012081.
6. United States Nuclear Regulatory Agency Regulatory Guide, Regulatory Guide 1.44,
Rev. 1, “Control of the Processing and Use of Stainless Steel,” March 2011.
7. Code of Federal Regulations, 10 CFR 50.55(a), “Codes and Standards”, 77 FR 3074,
January 23, 2012.
8. Westinghouse Report, WCAP-17801, Rev. 0, “Feasibility Assessment for Characterizing
Non-functional Pressurizer Heaters,” February 10, 2014.
9. Materials Reliability Program: Stress Corrosion Cracking of Stainless Steel Components
in Primary Water Circuit Environments of Pressurized Water Reactors (MRP-236).
EPRI, Palo Alto, CA: 2007 1015540.
10. Combustion Engineering Owners Group Document, CE NPSD-555 CEOG Task 585,
“Pressurizer Heater Performance in C-E Plants,” February 1990.
11. United States Nuclear Regulatory Commission Information Notice, IN 2006-04, “Design
Deficiency in Pressurizer Heaters for Pressurized-water Reactors,” Februrary 13, 2006.
12. Framatome ANP Report, ADAMs Accession Number ML052140277, “10 CFR Part 21
Notification of Existence of a Defect,” July 28, 2005.
13. Exelon Report, TMI-12-154 (ADAMs Accession Number ML12298A035), “Licensee
Event Report (LER) No. 2012-003-00 “Pressurizer Heater Bundle Leak””, October 22,
2012.
14. INPO Level 3 Event Report 12-10, “Primary Coolant Leak Caused by Swelling and
Mechanical Failure of Pressurizer Heaters” January 31, 2012. Referenced by [13].
15. Database on Industry Events <http://www.inpo.org/inpo/OESearch.asp> Accessed
October 4, 2014.
22
Appendix A: INPO Events Database
Events were documented through October 2014. Entries highlighted in red have relation
to the potential for sheath degradation (stainless steel), while the blue highlighted entries have
relation to Alloy 600 PWSCC material degradation.
A.1
Pressurizer Heater Operating Experience (1970-1985)
On October 22, 1974, at Prairie Island Unit 1, the pressurizer heater supply breaker would
not close. The breaker was repaired and put into service. [ICES Report #343]
Sheath Degradation Assessment: Because the breaker is separate from the heater, sheath
degradation is unlikely.
On October 15, 1975, at San Onofre Unit 1, an SCR failed for current phase B of
pressurizer heater group “A”. The SCR was subsequently replaced. [ICES Report #1158]
Sheath Degradation Assessment: Because the SCR is separate from the heater, sheath
degradation is unlikely.
On April 15, 1979, at Connecticut Yankee Unit 1, an indicator light for the auto-shutoff for
the pressurizer heater failed. The light source was replaced. [ICES Report #4867]
Sheath Degradation Assessment: Because the light source is separate from the heater,
sheath degradation is unlikely.
On September 11, 1981, at Connecticut Yankee Unit 1, pressurizer group “E” would not
energize at plant startup. A dirty contact on a breaker prevented operation. The contacts were
subsequently cleaned with contact spray. [ICES Report #7746]
Sheath Degradation Assessment: Because the breaker contacts are separate from the
heater, sheath degradation is unlikely.
On February, 22, 1982, at Kewaunee Unit 1, a low megger reading (insulation resistance)
was found on Group 1D during preventative maintenance. The connections were “dirty” and
were therefore cleaned and tightened. No information about a subsequent reading was given.
[ICES Report #8467]
Sheath Degradation Assessment: Low insulation resistance has been thought to be
associated with a short between the sheath and the heater elements, potentially from water
ingress due to sheath degradation. Because no subsequent reading was given in the report, it
is assumed that the low megger reading might be an indication of potential sheath degradation.
On September 21, 1982, at David-Besse Unit 1, breaker BE106 opened causing
MCCE12A to de-energized. Readings and test current showed that a heater in the bank was
open. The breaker was repaired. [ICES Report #9592]
Sheath Degradation Assessment: Because the breaker is separate from the heater, sheath
degradation is unlikely.
23
On March 26, 1983, at Farley Unit 2, the pressurizer heater group breaker did not auto
close, resulting in a high pressurizer level deviation. The operator attempted to close the
breaker remotely and with local hand switches without success. The micro switch was adjusted
and the breaker tested satisfactory and was returned to service.
Sheath Degradation Assessment: Because the switch and breaker are separate from the
heater, sheath degradation is unlikely.
On August 18, 1983, at Three Mile Island Unit 1, for the pressurizer “A” group, a failed light
lit on the controller for group 3. Heater number 23 of group 3 was found to have its threaded
connection melted and separated from the bundle. The remained of group 3 was returned to
service at the time of failure. In the 1990 outage all connectors for heaters were eliminated and
replaced with a silver soldered connect between the cable and heater element and the potted in
a ceramic material. [ICES Report #12137]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable.
On September 29, 1983, at Zion Unit 1, pressurizer heater backup group “C” breaker 1373B would not trip on signal. The defective amptector on breaker 137-3B was replaced. [ICES
Report #12585]
Sheath Degradation Assessment: Because the amptector is separate from the heater,
sheath degradation is unlikely.
On November 11, 1983, at Beaver Valley Unit 1, the pressurizer heater group A” bell
alarm was working intermittently. Because the bell assembly was dirty, the bell was cleaned
and lubed. [ICES Report #12957]
Sheath Degradation Assessment: Because the bell assembly is separate from the heater,
sheath degradation is unlikely.
On January 24, 1984, at North Anna Unit 2, the air flow switch on the pressurizer heater
controller failed, preventing control heater bank 3 from energizing. The loose wire was
retightened and tested. Heaters then energized and operated in a satisfactory manner, returned
to service. [ICES Report #14281]
Sheath Degradation Assessment: Because the air flow switch is separate from the heater,
sheath degradation is unlikely.
On February 11, 1984, at San Onofre Unit 2, the pressurizer heater circuit breaker would
not close or reset. The cause was a failed pressurizer heater element, with a repair scheduled
for a future outage. Electronic characterization and diagnostic testing found an open element
with an unknown cause. [ICES Report #14707]
Sheath Degradation Assessment: The failed heater element due to an unknown cause would
demonstrate a potential for sheath degradation that could have allowed for water ingress that
subsequently caused failure of the heater element. Also, because the heater was not
immediately replaced, there could be potential for a degraded sheath to remain installed. An
installed degraded heater could leak to issues with pressure boundary leakage.
24
On April 18, 1984, at St. Lucie Unit 1, the pressurizer backup heater circuit breaker would
not open or close due to sticking or binding of the trip unit. The breaker was replaced. [ICES
Report #16345]
Sheath Degradation Assessment: Because the circuit breaker is separate from the heater,
sheath degradation is unlikely.
On May 24, 1984, at Connecticut Yankee Unit 1, the group “A” pressurizer heater circuit
breaker would not control as required. Dirt on the X-relay caused binding movement which
failed to operate the close coil. The X-relay was replaced and the breaker cleaned. The
generic problem with the breaker design was identified at a later date. [ICES Report #17255]
Sheath Degradation Assessment: Because the circuit breaker and X-relay separate from the
heater, sheath degradation is unlikely.
On June 5, 1984, at Summer Unit 1, the pressurizer heater power panel back-up group 2
tripped after installation. The breaker was replaced and operated satisfactorily. [ICES Report
#17522]
Sheath Degradation Assessment: Because the power panel is separate from the heater,
sheath degradation is unlikely.
On July 7, 1984, Kewaunee Unit 1, the feeder breaker for a pressurizer heater kept
tripping. The fuse was subsequently replaced. [ICES Report #18367]
Sheath Degradation Assessment: Because the fuses are separate from the heater, sheath
degradation is unlikely.
On August 3, 1984, at North Anna Unit 1, pressurizer heater fuses were blown, due to high
temperature and resistance fatigue. The fuses were replaced and tested for operability and
made ready for service. [ICES Report #18972]
Sheath Degradation Assessment: Because the fuses are separate from the heater, sheath
degradation is unlikely.
On August 3, 1984, at North Anna Unit 2, an electrical connector failed due to a high
temperature and resistance fatigue. The connector was replaced and tested for operability and
was ready for service. [ICES Report #18974]
Sheath Degradation Assessment: It is unclear from the report where specifically the
connector was in relation to the heater. Although this incident does not seem to be associated
with sheath degradation, a localized elevated temperature for a heater (relative to nearby
heaters) would be a cause for concern in screening for susceptibility to SCC, as higher
temperatures are at greater risk for SCC relative to lower temperatures.
On August 14, 1984, at Surry Unit 2, the circuit breaker for pressurizer heater AB tripped
and would only reset for short duration. Fatigue of the breaker was determined to cause the
failure. The breaker was subsequently replaced. [ICES Report #19204]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
25
On August 23, 1984, at North Anna Unit 2, a pressurizer heater electrical connector failed,
due to high temperature and resistance fatigue. A new connector was installed and tested for
operability. The circuit was tested and made ready for service. [ICES Report #19434]
Sheath Degradation Assessment: It is unclear from the report where specifically the
connector was in relation to the heater. Although this incident does not seem to be associated
with sheath degradation, a localized elevated temperature for a heater (relative to nearby
heaters) would be a cause for concern in screening for susceptibility to SCC, as higher
temperatures are at greater risk for SCC relative to lower temperatures.
On September 5, 1984, at St. Lucie Unit 2, a pressurizer heater breaker BRK-40304
tripped and would not reset. The trip unit was found to be defective and replaced. The breaker
was installed, tested, and returned to service. [ICES Report #19746]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 16, 1984, at Farley Unit 2, a pressurizer heater breaker closing spring
would not charge. A charging motor model was shorted and was subsequently replaced to
return the breaker to service. [ICES Report #20000]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 21, 1984, at Connecticut Yankee Unit 1, the pressurizer heater control
would not calibrate. The resistors within the converter were replaced. [ICES Report #20112]
Sheath Degradation Assessment: The converter is separate from the heater, so sheath
degradation is unlikely.
On November 13, 1984, at St. Lucie Unit 2, a pressurizer heater breaker BRK-40304
would not close and was mechanically bound. The closing mechanism was out of adjustment,
was subsequently adjusted, tested, and found to operate satisfactorily. [ICES Report #21603]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On December 7, 1984, at Arkansas Nuclear One (ANO) Unit 2, a blown fuse and silicon
controlled rectifier (SCR) were found to be defective, possibly worn. The fuse, SCR, and diode
were replaced. [ICES Report #22349]
Sheath Degradation Assessment: Because the fuse, SCR, and diode are separate from the
heater, no sheath degradation is expected.
On March 1, 1985, at Arkansas Nuclear One (ANO) Unit 1, proportional heater T1 was
non-functional due to a failed heater element. The defective element was drawing excessive
current, which blew fuses in the heater control circuitry. The root cause was “normal, expected
wear”. The element was replaced. [ICES Report #24929]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable.
On March 5, 1985, at Farley Unit 2, a pressurizer heater group would not energize due to
26
a supply breaker not properly closing. An open conductor was found and replaced to return the
breaker to service. [ICES Report #25031]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On April 6, 1985, at Arkansas Nuclear One (ANO) Unit 1, pressurizer heater T1 became
non-functional due to heater element number six in bank #28 and element eleven in bank #30.
The plant is of a B&W design. The root cause determined that the heater failure was due to
“normal, expected wear”. [ICES Report #26058]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable.
On April 25, 1985, at Waterford Unit 3, a heater was accidentally removed from service
when a loaded breaker was accidentally removed from maintenance, lowering the capacity of a
pressurizer heater bank from 150 kW to 100 kW, violating technical specifications. Work
authorizations were made to correct the issue. [ICES Report #277286]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On June 20, 1985, at San Onofre Unit 1, defects were found in the pressurizer heater
group “C” backup breaker during preventive maintenance. Latch adjustement and lubrication
were made to clear up the issue. Over-torqueing of bolts by the vendor was an issue for the
breaker. [ICES Report #28593]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On June 26, 1985, at San Onofre Unit 3, some bus bars were overheating, causing failure.
Clips were replaced and lugs tightened (crimped). In addition some lugs and stabs were
replaced to bring the item to proper service. [ICES Report #28785]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On June 26, 1985, at San Onofre Unit 2, a low-power system for pressurizer heaters
failed. Some lugs and stabs were replaced to correct the issue and return to satisfactory
operation. [ICES Report #28796]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On July 8, 1985, at Beaver Valley Unit 1, pressurizer heater back up group B supply
breaker was found out of specifications during maintenance. The power sensor (defective due
to wear) was replaced with a rebuilt sensor. [ICES Report #29146]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On August 16, 1985, at St. Lucie Unit 2, circuit breaker 40302 would not close as indicated
in the control room. A defective overload device was replaced, tested, and found to be
27
satisfactory. [ICES Report #30418]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On September 11, 1985, at McGuire Unit 1, pressurizer heater group 1B was inoperable
while diesel generator 1A was inoperable. McGuire has four banks of heaters (A, B, C, and D).
A breaker for group 1B was tripped, rendering the bank inoperable and placed the Unit in Action
Statement C of the technical specifications (3.8.1.1). The diesel generator was returned to
operable to remedy the situation. No further mention of the heaters was made in the report,
with the assumption that they were later brought back to service from the breaker trip. [ICES
Report #278472]
Sheath Degradation Assessment: The circuit breaker and the diesel generator are separate
from the heater, so sheath degradation is unlikely.
On September 25, 1985, at Indian Point Unit 3, a circuit breaker from heater backup group
number 31 was unable to be closed from the control room. Maintenance personnel adjusted the
breaker for proper operation. [ICES Report #31710, #31619]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On October 15, 1985, at San Onofre Unit 1, pressurizer heater group “A” control breaker
tripped and would not reset. A piece of the latching mechanism had broken off. Service was
returned to the bank by use of a spare breaker. The breaker was later repaired with
replacement parts. [ICES Report #32404]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On October 29, 1985, at Byron Unit 1, a pressurizer heater breaker stab and conductors
overheated (Breaker 1RY03ED-B3) due to an improperly undersized stab. The breaker
continued to operate. The existing breakers were replace with a proper model to address the
issue. [ICES Report #32962, #32960]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On November 6th, 1985, at Summer Unit 1, during routine preventive maintenance on the
pressurizer heater backup circuit breaker, after replacement of a broken cotter pin, the breaker
would not operate. This was during an outage. The charging motor brushes were replaced, the
breaker was cycled, and tested satisfactorily. [ICES Report #33301]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On November 14, 1985 at Beaver Valley Unit 1, a circuit breaker to the pressurizer backup
heater (Group E ACB) was not functioning properly. The handle on the breaker was replaced
and the closing assembly was adjusted until proper operation was attained. [ICES Report
#33592]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
28
degradation is unlikely.
29
A.2
Pressurizer Heater Operating Experience (1986-1990)
On January 23, 1986, at McGuire Unit 1, pressurizer heater control panel 1A was
suspected of having a blown fuse because of a low current flow. The blown fuse was found and
replaced. [ICES Report #36096]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 26, 1986, at McGuire Unit 1, a pressurizer heater bank alarmed the control
room of a loss of the #1 heater bank in Group A because the Y-Phase fuse to the heater was
blown and a loose wire connection existed for the heater group. The fuse was replaced and the
loose connection was tightened. [ICES Report #36182]
Sheath Degradation Assessment: The fuse and loose wire connection are separate from the
heater, so sheath degradation is unlikely.
On January 28, 1986, at Palo Verde Unit 1, a fire watch could not make the rounds to
rooms appropriately for various reasons. The areas affected included the unit pressurizer
heater transformer room and the Unit 2 pressurizer heater transformer room. [ICES Report
#279650]
Sheath Degradation Assessment: The transformer rooms are separate from the heater, so
sheath degradation is unlikely.
On January 28, 1986, at Sequoyah Unit 1 (and Sequoyah Unit 2), a fire watch was
unable to complete his route because of various reasons. The areas included the unit 1
pressurizer heater transformer room and the unit 2 pressurizer heater transformer room. [ICES
Report #279652]
Sheath Degradation Assessment: The transformer rooms are separate from the heater, so
sheath degradation is unlikely.
On February 18, 1986, at Kewaunee Unit 1, a broken tab was found on the circuit
breaker switch for pressurizer heater group 1C because of an end to life due to age. The circuit
breaker was replaced. [ICES Report #36954]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 3, 1986, at D.C Cook Unit 2, the safety pins in the fire door 316 protecting the
pressurizer heater transformer room were in place with no personnel in the area, making the fire
door inoperable. The issue was corrected in procedures. [ICES Report #279934]
Sheath Degradation Assessment: The pressurizer heater transformer fire door is separate
from the heater, so sheath degradation is unlikely.
On April 7, 1986, at Surry Unit 1, the pressurizer heater circuit breaker 1B12 had tripped.
After resetting it continued to trip because of a short in the breaker. The breaker was replaced.
[ICES Report #38994]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
30
On April 7, 1986, at Arkansas Nuclear One Unit 2, a 480 V breaker supplying power for
pressurizer heater bank #6 was removed from service and was found to be inoperable due to a
broken right phase contact assembly. The two secondary disconnects, operator mechanism,
base and contact molding, and contact assembly were replaced. The breaker tested
satisfactorily and was returned to service. [ICES Report #38967]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 10, 1986, at Byron Unit 1, during pressurizer heater surveillance, the variable
heaters failed to register any current flow because the pressure control card in the variable
heater circuit went bad. Therefore, the failed card was replaced and the bad card was shelved
for repair. [ICES Report #39118]
Sheath Degradation Assessment: The pressure control card is separate from the heater, so
sheath degradation is unlikely.
On May 6, 1986, at Farley Unit 2, the group “A” pressurizer heater breaker would not
close because the breaker trip shaft was out of adjustment. The trip shaft was adjusted, verified
for proper operation, and returned to service. [ICES Report #40118]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 22, 1986, at San Onofre Unit 1, maintenance was requested to investigate the
cause of pressurizer heater group “A” control breaker tripping free. The breaker would trip free
on automatic closure, but would close on manual signal. Amptector mounting bolts were too
long, impeding the latching mechanism. Previous modifications may have contributed to issues.
The amptector mounting bolts were replaced with new bolts, the breaker was tested and
returned to service. [ICES Report 40721]
Sheath Degradation Assessment: The amptector mounting bolts are separate from the
heater, so sheath degradation is unlikely.
On June 2, 1986, at Arkansas Nuclear One Unit 1, the control room received a
pressurizer heater ground fault alarm for proportional heater bank II, group #14. The heater
bank short was possibly caused by heat and moisture, but the root cause is uncertain. The
grounded heater was removed from service (disconnected). [ICES Report #41089]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable.
On June 7, 1986, at St. Lucie Unit 1, a routine observation indicated that pressurizer
heater #2 on the 1B bank was not working. Circuit breaker 40302 was tripped and would not
reset due to mechanical binding of the linkage. Adjustment and realignment of the breaker
linkage was made. The breaker was tested and operated satisfactorily. [ICES Report #41306]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On June 16, 1986, at Callaway Unit 1, while measuring and recording the phase
31
currents of pressurizer heater banks number 5, number 6, and number 27, phase “B” of the
feeder breaker gave no reading. The breaker was found to be open on the “B” phase. A new
breaker was installed, and heater megger readings were acceptable. [ICES Report #41522]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On June 26, 1986, at San Onofre Unit 2, infrared inspection of the pressurizer heater
distribution panel was performed to investigate possible overheating of the bus bars. The
investigation found bad connections on bucket to bus bars, causing “extreme” overheating. The
clips were replaced and the lugs were tightened (crimped). Some lugs and stabs were
replaced, verification of power to the panel was performed and the item was satisfactorily
returned to service. [ICES Report #42075]
Sheath Degradation Assessment: The distribution panel is separate from the heater, so
sheath degradation is unlikely.
On August 12, 1986, at McGuire Unit 2, the plant tripped when an individual accidentally
“bumped” the main supply breaker. Included in the incident was pressurizer heater group B
tripped. The circuit was reset and a protective cover was put in place to avoid the a similar
incident in the future. [ICES Report #281319]
Sheath Degradation Assessment: The main supply breaker is separate from the heater, so
sheath degradation is unlikely.
On August 13, 1986, at San Onofre Unit 1, the pressurizer heater group “C” backup
breaker would not close on signal from control room because the investigation found a piece of
broken arc chute was jammed between the control relay contacts, keeping the relay from
closing. The arc chute piece was removed and a new piece was installed, tested, and returned
to service. [ICES Report # 43724
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 25, 1986, at St. Lucie Unit 2, the control panel for pressurizer heater
bank circuit breaker 40303 would trip a few minutes after energizing because a relay was
defective due to fatigue. A new relay was installed, and the breaker was tested and returned to
service. [ICES Report #45208]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On October 1, 1986, at Arkansas Nuclear One Unit 2, there was no power to the 1
pressurizer heater bank because the circuit breaker was cycling (but there was no output from
the controller) due to the silicon controlled rectifier being out of calibration, and three fuses were
blown. The fuses were replaced and the SCR was calibrated. [ICES Report #45404]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 6, 1986, at San Onofre Unit 1, the pressurizer heater group “A” control
breaker was unable to be closed electrically after the breaker was reracked due to a broken
32
latching mechanism. The latching lever was replaced, the breaker was tested and returned to
service. [ICES Report #46681]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 6, 1986, at Sequoyah Unit 2, pressurizer heater circuit breaker (off 2A-A
shutdown board) would not open from main control room handswitch when the breaker was
closed because possibly the relay coil burned up due to normal wear. The relay was replaced,
the fuses and fuses holders were cleaned, and the breaker was returned to service. [ICES
Report #46683]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 16, 1986, at San Onofre Unit 1, the breaker for pressurizer heater group
“A” could not be opened because the auxiliary switch linkage had come loose preventing the
breaker from opening. The linkage was reset and the breaker was returned to service. [ICES
Report #46975]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 17, 1986, at Sequoyah Unit 1, pressurizer heater backup group 1B-B was
operating erratically because the main toggle pin for mechanical mechanism pivoting broke due
to frequent operation of the breaker. The main toggle pin was replaced and the breaker was
returned to service. [ICES Report #47012]
Sheath Degradation Assessment: The toggle pin is separate from the heater, so sheath
degradation is unlikely.
On November 21, 1986, at Racho Seco Unit 1, pressurizer heaters in the bundle were
damaged because the pressurizer level monitoring system was incorrectly reading the water
level in the pressurizer, which caused the heaters to energize inappropriately. [ICES Report
#282106]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable
On November 29, 1986, at Sequoyah Unit 2, pressurizer heater 2A would not open, after
closing, until manually tripped because the mechanical pivot arm that actuated the auxiliary
contacts was loose. The pivot arm was tightened to actuate the auxiliary contacts. [ICES
Report #47482]
Sheath Degradation Assessment: The pivot arm is separate from the heater, so sheath
degradation is unlikely.
On November 29, 1986, at Arkansas Nuclear One Unit 1, pressurizer heater number 3 in
the lower heater bundle had termination problems. The element had a loose terminal and a
broken ceramic insulator. The damaged termination could not be repaired. The heater element
was disconnected. [ICES Record #47487]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
33
applicable.
On December 8, 1986, at San Onofre Unit 1, there were breaker trips on pressurizer
heater group “A” control because the “first toggle leve” had a broken piece. The broken piece
was replaced and the breaker was adjusted, tested, and returned to service. [ICES Report
#47783]
Sheath Degradation Assessment: The toggle lever is separate from the heater, so sheath
degradation is unlikely.
On January 15, 1987, at Three Mile Island Unit 1, an open circuit was found on element
34 of group 5 heaters. The connector on element number 34 in the middle of the bundle was
faulty. It was potentially due to high temperature but not confirmed because all connectors
experience the same temperature. During the 1990 refueling outage, all heater connectors
were removed and replaced with a silver soldered connection between the cable and the heater
element that was then potted in a ceramic material. [ICES Report #48967]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable.
On January 21, 1987, at Farley Unit 2, the breaker for pressurizer heater group “A”
(breaker “EA-11”) would not automatically charge when racked in. The auxiliary contact and the
motor cut off switch were dirty because of expected wear and aging. The contacts and cut off
switch were cleaned and proper breaker operation was verified. [ICES Report #49177]
Sheath Degradation Assessment: The auxiliary contact and motor cut off switch were
separate from the heater, so sheath degradation is unlikely.
On February 1, 1987, at Arkansas Nuclear One Unit 2, the pressurizer heater controllers
would not synchronize because a rectifier on the “B” phase of the 1 controller was shorted, so
the rectifier was replaced and the controllers were synchronized. [ICES Report #49546]
Sheath Degradation Assessment: The rectifier is separate from the heater, so sheath
degradation is unlikely.
On February 9, 1987, at Sequoyah Unit 2, the 2C pressurizer heater breaker failed the
physical inspection portion of surveillance because the trip coil had burned up due to normal
wear. The trip coil was replaced and all circuits in the breaker were checked for shorts or
grounds. The limit switch was cleaned and the breaker was returned to service. [ICES Report
#49781]
Sheath Degradation Assessment: The trip coil and the limit switch are separate from the
heater, so sheath degradation is unlikely.
On February 15, 1987, at McGuire Unit 1, pressurizer heater bank “B” failed its quarterly
capacity test. Three fuses were found to be blown in the group “B” circuits. The fuses were
replaced and the heaters passed the capacity test. [ICES Report #49978]
Sheath Degradation Assessment: The fuses are separate from the heater, so sheath
degradation is unlikely.
On March 31, 1987, at McGuire Unit 1, pressurizer heater bank “B” went out of service
34
when rainwater got into the breaker panel and blew fuses. The panel was dried and the fuses
were replaced. [ICES Report #51654]
Sheath Degradation Assessment: The breaker panel and fuses are separate from the heater,
so sheath degradation is unlikely.
On April 15, 1987, at San Onofre Unit 3, the pressurizer heater backup bank feeder
breaker tripped. The breaker was replaced with an appropriately rated breaker and returned to
service. [ICES Report #52243]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 18, 1987, at Sequoyah Unit 2, the pressurizer heater control group 2D breaker
arcing contact was cracked due to normal wear. The contact was replaced and the contact
bolts were torqued. The breaker was closed three times to ensure proper seating. [ICES Report
#52347]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 19, 1987, at Sequoyah Unit 2, the pressurizer heater control group 2D closing
time was too fast. The bridge pivot pressure was out of adjustment, so the pressure was
adjusted to obtain acceptable opening and closing times, and the item was returned to service.
[ICES Report #52360]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 20, 1987, at Sequoyah Unit 1, the breaker for pressurizer heater control group
1D was closing too fast, due to normal wear. The opening and closing time was adjusted to
meet surveillance criteria, and the item was returned to service. [ICES Report #52382]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 22, 1987, at Arkansas Nuclear One Unit 2, a degraded sheath was confirmed
leading to a leak rate of 60 drops per minute. Stress corrosion cracking of the heater sheath
was determined, allowing water to react with magnesium oxide insulation which expanded on
hydration and ruptured the “X1” and “T4” heater sleeves. The “X1” heater was damaged
severely enough to produce an external leak through the welded sleeve fitting. The “X1” and
“T4” heaters were removed and plugs were installed (RAC 2-87-050) [ICES Report #52488]
Sheath Degradation Assessment: This issue was determined to have been caused from
degradation of a heater sheath.
On May 31, 1987, at Diablo Canyon Unit 1, pressurizer heater group 1-3 circuit breakers
5 and 5R and 1 and 1R were found tripped open. The failure was attributed to an open heater.
The circuit breakers were left open and the failed (non-functional) heater will be determined
during the next unit shutdown, or heater maintenance. [ICES Report #54038]
Sheath Degradation Assessment: This heater may have become non-functional due to
35
sheath degradation, as no root cause was determined. The future plan for mitigating any issue
has only vague details with regard to specific resolution.
On June 23, 1987, at Vogtle Unit 1 pressurizer heater bank “D” did not automatically
energize when pressure dropped to the low pressurizer pressure setpoint. An operational check
of bank “D” was performed by repeatedly automatically energizing the bank. During subsequent
trips the bank properly energized. The reactor tripped from a main turbine trip from a main
generator trip. [ICES Report #283756]
Sheath Degradation Assessment: The main turbine and main generator are separate from
the heater, so sheath degradation is unlikely.
On July 6, 1987, at Arkansas Nuclear One Unit 2, a primary reactor coolant system
pressure boundary leak was discovered at the pressurizer heater weld. The leakage was
approximately three drops per minute and was documented on RAC 2-87-095. There was a
personnel error in the welding process that led to a lack of fusion between the weld filler
material and the base metal. Five heaters were cut out and plugs were removed and replaced
by new plugs per a plant design change package. [ICES Report #55367]
Sheath Degradation Assessment: The weld in question was not specifically mentioned.
Leakage can be associated with sheath degradation, so the removal of the heaters mitigates the
potential issue associated with heater insulation swelling and causing primary leakage.
On July 8, 1987, at Diablo Canyon Unit 2, pressurizer heater group 24 was found to
have a ground. The failure was attributed to loose pigtail connections on the charging motor
and a ground sensor relay. The motor and relay were replaced, and the breaker was returned
to service. [ICES Report #55435]
Sheath Degradation Assessment: The motor and relay are separate from the heater, so
sheath degradation is unlikely.
On August 19, 1987, at San Onofre Unit 3, the pressurizer heater backup heater circuit
breaker tripped. The breaker and the lugs were damaged beyond repair and caused by
previous maintenance. The breaker was replaced with a new one. The bus leads to the
breaker were repaired and returned to service. [ICES Report #56789]
Sheath Degradation Assessment: The breaker and lugs are separate from the heater, so
sheath degradation is unlikely.
On September 20, 1987, at North Anna Unit 1, a pressurizer heater was found
grounded. The cause of failure was unknown and “normal aging” was suspected. The heater
was repaired and successfully returned to service. [ICES Report #57963]
Sheath Degradation Assessment: The specifics were not provided in the report about how
the heater was repaired and whether it was replaced or modified. A non-functional heater may
convey the potential for a degraded heater sheath. Although repair removed from the heater
may not be associated with sheath degradation, the specifics for this incident were not clearly
delineated.
On October 9, 1987, at Byron Unit 1, the 10 amp supply fuse blew when the control
switch for the pressurizer heater backup group “B” contactor control was closed. The contactor
36
coils were found burned so that the breaker would not work. All of the coils and blown fuses
were replaced. The circuit tested satisfactory. [ICES Report #58642]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On October 9, 1987, at St. Lucie Unit 1, the feeder breaker for pressurizer heater
transformer 1A3 would not close when operated from the control room. The fuses were
cleaned, and the breaker was successfully tested and returned to service. [ICES Report
#58670]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 5, 1987, at Indian Point Unit 3, the breaker for pressurizer heater number
33 would not remain in the closed position. A loose wire from the shunt trip coil was found. The
loose wire was reattached, retested, and put pressurizer heater group number 33 back in
service.
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 26, 1987, at St. Lucie Unit 2, long term trip screws were out of
adjustment, tripping the pressurizer heater circuit breakers at a thermal temperature of 40
degrees. The overloads were changed out and the air gap on the long term trip paddle was
adjusted. [ICES Report #60490]
Sheath Degradation Assessment: The trip screws are separate from the heater, so sheath
degradation is unlikely.
On December 17, 1987, at Palo Verde Unit 3, following a trip, a relay/contact (94/CNTR)
assembly did not operate properly which resulted in the Class 1E pressurizer heaters continuing
to remain energized below the low level trip setpoint. The relay/contact assembly was replaced
and the heaters were verified to be operating properly. [ICES Report #285167]
Sheath Degradation Assessment: Although initial sheath damage is unlikely, continued
potential operation at greater than design temperatures would be a contributor to increased
susceptibility to stress corrosion cracking and associated sheath degradation.
On December 17, 1987, at Palo Verde Unit 3, a pressurizer heater did not energize as
required due to a malfunction following a reactor trip. The report is incomplete. The root cause
was associated with a deviation in positioning of two control element assembly subgroups.
[ICES Report #295171]
Sheath Degradation Assessment: Although the details are unclear, the control element
assembly subgroups and electronic controls for the heater are separate from the heater, so
sheath degradation is unlikely.
On December 22, 1987, at Sequoyah Unit 2, an abnormality indicated that pressurizer
heater backup group “2A-A” would not trip electrically. The spring that kicks the closing lever
back was adjusted and the arc chute assembly was replaced. The breaker was verified to be
37
operating properly. [ICES Report #61433]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 12, 1988, at Diablo Canyon Unit 2, the pressurizer heater group 4 circuit
breaker failed to close upon demand from the control room. The cause was unknown but the
breaker bench tested satisfactorily, the auxiliary contact stabs were cleaned and the breaker
was returned to service. [ICES Report #62134]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January, 16, 1988, at North Anna Unit 1, the number 4 pressurizer heater breaker
would not close on demand from the control room. The close button on the breaker was
sticking shut. The contacts were cleaned and lubricated, and the breaker tested satisfactorily.
[ICES Report #62283]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 21, 1988, at Davis-Besse Unit 1, pressurizer heater bank 2 would not
energize from the control room manually. Manual operation from the auxiliary shutdown panel
was attempted but also unsuccessful. A faulty relay in a circuit breaker was discovered. In
addition, blown fuses were found on the primary and secondary sides of the control transformer.
The defective relay was replaced and the circuit was tested, found operable, and returned to
service. [ICES Report #62467]
On February 28, 1988, at Zion Unit 1, the pressurizer backup heater circuit breaker for
bank “C” heaters would not open with the control switch in the off position. The breaker would
not open even with attempts locally. Electricians cleaned, overhauled, and lubricated the
backup heater’s circuit breaker. [ICES Report #63928]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 7, 1988, at Trojan Unit 1, an operator noticed pressurizer heater breaker B1029 was tripped while performing rounds and again noticed it on March 9, 1988. The failure
was due to the breaking heating up as a result of high resistance, and tripping on thermal
overload. Although the cause of the high resistance was unknown, the breaker was replaced
and returned to service. [ICES Report #64253]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 11, 1988, at Davis-Besse Unit 1, pressurizer heater Bank #2 would not
energize from the control room. A fuse was blown on the primary side of the control
transformer. The cause was unknown, and the pressurizer heater system was scheduled to be
further revamped during the refueling outage. [ICES Report #64417]
Sheath Degradation Assessment: An unknown issue preventing the energizing of a heater
may be associated with sheath degradation that caused short circuits within the heater system.
38
Some heaters may have common circuitry that can cause multiple issues. The non-resolution
of the root cause of the non-functional heaters may point to the potential for a degraded sheath.
On March 12, 1988, at St. Lucie Unit 2, a circuit breaker to backup bank “B2” kept
tripping. A dirty connection was noted and subsequently cleaned with “Scotch Brite”. The
breaker was reassembled and returned to service. [ICES Report #64495]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 28, 1988, at St. Lucie Unit 1, Pressurizer Heater backup bank “B-6” would not
close. Hot spots were found on the breaker and line starter connections, and the contacts were
dirty and pitted. The contacts were cleaned and the breaker test satisfactorily. [ICES Report
#65102]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 22, 1988, at San Onofre Unit 2, the pressurizer heater circuit breaker was found
that the “C” phase had no current flow. The breaker had an open circuit in the “C” phase, so it
was replaced, tested, and returned to service. [ICES Report #66104]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 27, 1988, at St. Lucie Unit 1, pressurizer heater bank “B6” supply breaker would
not reset. The stab was disassembled, repaired, cleaned, reinstalled, test, and returned to
service. [ICES Report #66300]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 13, 1988, at Farley Unit 1, when closure of the supply breaker for pressurizer
heater backup group “B” was attempted, the breaker would not close. Failure was attributed to
a previous repair. The contacts were placed in the normal closed position, verified, and
returned to service. [ICES Report #66920]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 1, 1988, at San Onofre Unit 3, the pressurizer heater controller feeder breaker
had a faulty secondary disconnect. The disconnected piece part was replaced and was
returned to service. [ICES Report #68505]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 8, 1988, at Trojan Unit 1, an operator found group “B” pressurizer heater
breaker tripped while performing rounds. The breaker would trip at 100% and 90% of its rated
100 ampere limit, so the breaker was replaced and returned to service. [ICES Report #68712]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
39
On July 15, 1988, at Oconee Unit 2, the vacuum supply breaker for pressurizer heater
group “2J” was found tripeed after heater bank #4 neither responded in automatic nor manual
mode of operation. The breaker was reset and tested. [ICES Report #68896]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable.
On July 18,1988, at St. Lucie Unit 1, during preventive maintenance inspection,
pressurizer heater breaker PP-130-CKT-4 would not reset. The cause of the failure was
unknown, but a new breaker was installed, tested, and returned to service. [ICES Report
#68999]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 18, 1988, at Diablo Canyon Unit 2, in hot shutdown a pressurizer heater
isolation circuit breaker repeatedly cycled while the heater control switch was in the off position.
The closing coil was out of alignment and sticking, causing the mechanism to “bound up”. The
breaker was replaced with a spare that tested satisfactorily. [ICES Report #68984]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 24, 1988, at Diablo Canyon Unit 2, the breaker for pressurizer heater group
number 4 was tripped on overcurrent during cold shutdown when placing the group in service.
The main contacts of the breaker were damaged and the breaker was therefore replaced. [ICES
Report #69174]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 29, 1988, at Wolf Creek Unit 1, the control room received a “pressurizer high
level deviation heater on” alarm and a “pressurizer heater group lock-out” alarm. Portions of the
control system failed low, and therefore the NCB-1 card was replaced.
Sheath Degradation Assessment: The NCB-1 card is separate from the heater, so sheath
degradation is unlikely.
On September 25, 1988, at Oconee Unit 3, a computation module failed that controlled
the pressurizer heaters. Operators bypassed the interlock to allow operation of the heaters and
the static multiplier was removed from service. A “like” replacement module was modified per
instrument procedure and installed in the cabinet. The multiplier was tested for proper operation
successfully. [ICES Report #71357]
Sheath Degradation Assessment: The multiplier module is separate from the heater, so
sheath degradation is unlikely.
On October 14, 1988, at Beaver Valley Unit 1, the pressurizer heater backup group “E”
power supply circuit breaker tripped during the overcurrent test. The power sensor was
defective, so it was replaced with a new model that tested satisfactorily. [ICES Report #72087]
Sheath Degradation Assessment: The power sensor is separate from the heater, so sheath
40
degradation is unlikely.
On October 16, 1988, at San Onofre Unit 1, a breaker for pressurizer heater group “C”
backup heater circuit breaker was found that the left movable pole was binding. The breaker
was disassembled and the main contact assembly was replaced. The arc contact gap was
adjusted and the breaker was reassembled. The breaker was functionally tested and returned
to service. [ICES Report #72145]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On October 20, 1988, at Three Mile Island, a blown fuse was found related to failed
pressurizer heater elements. Insulation installed in 1986 caused heat accelerated degradation
of these connectors, which then caused insulation between the conductors to fail, allowing a
short. The blown fuses were replaced and in 1990, all of the cable to heater connectors were
replaced with a silver soldered connection which was then potted in a ceramic material. The
insulation for the bundle flange was also permanently removed. [ICES Report #72321]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable.
On November 20, 1988, at Arkansas Nuclear One Unit 1, the pressurizer heater
automatic/manual transfer relay failed to integrate up when placed in the “automatic” start
position during a surveillance test. The root cause of the failure was insulation breakdown
within the relay coil from a worn out relay card that allowed overload. The defective relay was
removed and replaced and proper operation was performed. [ICES Report #73528]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable.
On November 22, 1988, at San Onofre Unit 2, the pressurizer hater circuit breaker was
found tripped. The breaker had shorted out and upon reset it tripped accompanied by a loud
pop and arcing that propagated through the enclosure door seal. The shorted light socket and
burnt lugs were replaced, and the breaker tested as satisfactory. [ICES Report #73603]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On December 8, 1988, at Arkansas Nuclear One Unit 1, there was a ground on one of
the circuit breakers to a pressurizer heater group, and the breaker would not remain energized.
The grounded cable’s leads were lifted so that the other heaters in the group would be
operational. [ICES Report #74192]
Sheath Degradation Assessment: As this plant is of B&W design, this assessment is not
applicable. However, an unknown root cause may be associated with an issue with sheath
integrity.
On January 19, 1989, at St. Lucie Unit 1, backup bank pressurizer heater circuit breaker
40603 tripped when the heater was energized because of poor alignment between the stabs
and the vertical bus. New stabs were installed and adjusted to align with the bus bar. The item
was returned to service. [ICES Report #75624]
41
Sheath Degradation Assessment: The stabs and vertical bus are separate from the heater,
so sheath degradation is unlikely.
On January 24, 1989, at Palisades Unit 1, circuit breaker 52-1608 for the pressurizer
heater backup group tripped. The linkage screws were tightened and the linkage plate was
replaced. The breaker was reinstalled, the heaters were determined to be operable and
returned to service. [ICES Report #75831]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On January 27, 1989, at Waterford Unit 3, the pressurizer h eater capacity was not
sufficient to maintain pressure due to a spray control value that would not close.[ICES Report
#75944]
Sheath Degradation Assessment: As this was a spray valve issue, sheath degradation is
unlikely.
On January 28, 1989, at Three Mile Island Unit 1, two blown fuses were found on the
group 4 controller, and further investigation found heaters on breaker 7 were grounded. The 7
breaker heaters were isolated at the main terminal box and other heaters for group 4 were
returned to service. The fuses were replaced and tested satisfactorily. [ICES Report #75982]
Sheath Degradation Assessment: As this is a B&W unit, this assessment is not applicable.
On February 26, 1989, at Three Mile Island Unit 1, pressurizer heater group 4 alarm was
received. Heaters in the lower bundle 4, heaters 10, 11, and 12 were grounded. Heat
accelerated degradation of the cable to heater connectors was an issue due to more efficient
insulation that was installed during the 1986 refueling outage. The grounded heaters were
isolated and group 4 was returned to service. During the 1990 refueling outage the cable to
heater connected were replaced. [ICES Report #77254]
Sheath Degradation Assessment: As this is a B&W unit, this assessment is not applicable.
On March 1, 1989, at Three Mile Island Unit 1, an alarm was received on pressurizer
heater controller group RCGCU0005 because two fuses were found blown in the control panel.
Heater number 2 grounded at the pressurizer, thought to be from wear and aging. Heater 2 was
isolated at the main terminal box and other heaters were returned to service. [ICES Report
#77351]
Sheath Degradation Assessment: As this is a B&W unit, this assessment is not applicable.
On March 21, 1989, at Calvert Cliffs Unit 2, when pressurizer heater 21A was turned on
the amperage fluctuated because the channel was degraded but still worked. The gate trigger
circuit was worn out and defective. The gate trigger unit was replaced and the heater circuit was
put into service. [ICES Report #78171]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On March 21, 1989, at Calvert Cliffs Unit 2, pressurizer heater 22A failed to work
because there was a broken wire in the control circuit. The wire was replaced and the heater
42
circuit was put in service. [ICES Report #78170]
Sheath Degradation Assessment: The control circuit is separate from the heater, so sheath
degradation is unlikely.
On March 27, 1989, at Sequoyah Unit 1, the breaker to pressurizer heater backup group
1B would not close, so the breaker was replaced with an identical spare and the heaters were
brought back to service. [ICES Report #78448]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 12, 1989, at Farley Unit 2, pressurizer heater backup group 2B supply breaker
spring would not charge because the breaker motor cut off switch was dirty and would not mate
up. The switch contacts were cleaned and the item was brought back to service. [ICES Report
#79112]
Sheath Degradation Assessment: The breaker motor is separate from the heater, so sheath
degradation is unlikely.
On April 23, 1989, at Farley Unit 1, pressurizer heater group “B” supply breaker did not
have any position “light” indication because the breaker fuse block terminals had some loose
connections due to wear. The connections were tightened and the item was returned to service.
[ICES Report #79565]
Sheath Degradation Assessment: The fuse block terminals are separate from the heater, so
sheath degradation is unlikely.
On April 26, 1989, at Three Mile Island Unit 1, the pressurizer heater group 3 ground
alarm was received in the control room. Heaters 1, 2, and 3 in the upper bundle1, group 13,
and heaters 7, 8, and 9 in upper bundle 3, group 13, and heaters 13, 14, and 15 in upper bundle
5, group 12 were grounded. The root cause determined that the more efficient insulation
installed in 1986 caused heat accelerated degradation of the cable to heater connectors at the
pressurizer heater bundle flange. The grounded heaters were isolated and the remaining
heaters in group 3 were brought back to service. In 1990 during the outage, all of the cable to
heater connectors were replaced. [ICES Report #79746]
Sheath Degradation Assessment: As this is a B&W unit, this assessment is not applicable.
On May 2, 1989, at Three Mile Island Unit 1, the pressurizer heater group failure light
was lit on the control panel. Heater 10, 11, and 12, in the upper bundle 4 group 12 were
grounded. Heat accelerated degradation of the cable to heater connectors was present due to
a more efficient insulation that was installed on the pressurizer in 1986. The bad heaters were
isolated and during the 1990 outage all of the connectors at the heater bundle flange were
replaced. [ICES Report #79967]
Sheath Degradation Assessment: As this is a B&W unit, this assessment is not applicable.
On May 5, 1989, at Calvert Cliffs Unit 2, pressurizer heater leakage was discovered
(References SER 31-87, CE Infobulletin 87-04 and CE Infobulletin 88-06). [ICES Report
#296397]
Sheath Degradation Assessment: The sleeves experienced material damage, and it is
43
unknown whether sheath degradation was associated with the sleeve damage.
On May 5, 1989, at Calvert Cliffs Unit 2, boric acid buildup was discovered at the partial
penetration well in the pressurizer heater sleeve. The electrical insulation was removed for
further investigation. Unit 1 was also shut down to investigated. [ICES Report #296281]
Sheath Degradation Assessment: The sleeves experienced material damage, and it is
unknown whether sheath degradation was associated with the sleeve damage.
On May 5, 1989, at Calvert Cliffs Unit 2, the outage was extended to make repairs to the
pressurizer due to coolant leakage during the outage. The sleeves were removed, new sleeves
were welded in, and the vessel was put in service. [ICES Report #80132]
Sheath Degradation Assessment: The sleeves experienced material damage, and it is
unknown whether sheath degradation was associated with the sleeve damage.
On May 15, 1989, at Salem Unit 1, and operator smelt electrical “burning” from one of
the pressurizer heater bus transformers, 1E6D/460V, because the transformer had some
insulation breakdown causing the smell. The transformer was replaced with the same model
and the heater bus was returned to service. [ICES Report #80579]
Sheath Degradation Assessment: The transformer for the heater bus is separate from the
heater, so sheath degradation is unlikely.
On May 15, 1989, at Farley Unit 2, the main control board indication for the pressurizer
heater group 2D breaker was out because the secondary stabs for control power were dirty.
The stabs were cleaned and the breaker was returned to service. [ICES Report #80582]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 23, 1989, at St. Lucie Unit 2, pressurizer heater circuit breaker 40304 kept
tripping because of high ambient temperature in the breaker cubicle. A fan was installed int eh
breaker cubicle to reduce the ambient temperature. The breaker operated satisfactorily. [ICES
Report #80908]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 30, 1989, at Indian Point Unit 2, pressurizer heater breaker 52/PBU2 kept
tripping because a trip lever was bent. The trip lever was repaired and retested successfully.
[ICES Report #81157]
Sheath Degradation Assessment: The trip lever is separate from the heater, so sheath
degradation is unlikely.
On June 9, 1989, at Three Mile Island Unit 1, an alarm was received on pressurizer
heater controller group RCGU0002. Two fuses were blown and heaters 22 and 23 in bank 8
and heaters 25, 26, and 27 in bank 9 were burnt open or grounded. Blown fuses were replaced
and the defective heaters were isolated. [ICES Report #81579]
Sheath Degradation Assessment: As this is a B&W Unit, the assessment is not applicable.
However, the non-functional heaters are due to either an electrical issue or a material
44
degradation issue.
On June 20, 1989, at Calvert Cliffs Unit 1 (and Unit), both units were shut down for
pressurizer heater repair. A breaker would not open on signal and the vendor was contacted to
resolve the issue. [ICES Report #296435]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On June 22, 1989, at Seabrook Unit 1, the pressurizer heater tripped because of a
reactor coolant pump trip during a natural circulation test. No pressurizer-related issues were
corrected [ICES Report #288846]
Sheath Degradation Assessment: The reactor coolant pump is separate from the heater, so
sheath degradation is unlikely.
On July 9, 1989, at Three Mile Island Unit 1, an alarm was received on pressurizer
heater controller group RCGU0003. Three heaters were found grounded in the group. Heat
accelerated degradation of a heater cable was determined to be the root cause. All of the
cables were replaced during the 1990 outage. [ICES Report #82714]
Sheath Degradation Assessment: The cables are separate from the heater, so sheath
degradation is unlikely.
On July 10, 1989, at Harris Unit 1, the group “A” pressurizer heater back-up power panel
supply breaker had failed to open on demand. The breaker was replaced with an identical unit,
tested, and placed into service. [ICES Report #82782]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 13, 1989, at Sequoyah Unit 2, pressurizer heater control group “2D” was
continuously energized but one train of pressurizer heaters was degraded because a power
control was not functioning properly. The control and a diode were replaced to return the item
to service. [ICES Report #82869]
Sheath Degradation Assessment: The power control and diode are separate from the heater,
so sheath degradation is unlikely.
On July 24, 1989, at Three Mile Island Unit 1, the metering control transformer for heater
controller RCGU0001 had elevated temperatures. The gate trigger unit was replaced and the
transformer was returned to service. [ICES Report #83194]
Sheath Degradation Assessment: The gate trigger unit for the heater controller is separate
from the heater, so sheath degradation is unlikely.
On July 31, 1989, at St. Lucie Unit 2, backup bank pressurizer heater circuit breaker
40604 tripped when the heater was energized. New stabs were installed and adjusted so that
they would align with the bus bar. [ICES Report #83455]
Sheath Degradation Assessment: The stabs and bus bar are separate from the heater, so
sheath degradation is unlikely.
45
On August 2, 1989, at St. Lucie Unit 2, pressurizer heater backup bank circuit breaker
40303 tripped and would not reset. New stabs were installed and adjusted. [ICES Report
#83523]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On August 15, 1989, at Calvert Cliffs Unit 1, investigations of pressurizer heaters was
continued. All 120 pressurizer heater sleeves are planned for replacement at Unit 2. Twelve
Unit 1 sleeves contained no cracks. [ICES Report #296431]
Sheath Degradation Assessment: Unit 1 had no cracks, so no clear degradation is apparent.
On September 23, 1989, at Oconee Unit 1, a fault was found in the seal weld on the
upper pressurizer heater bundle. The fault was ground out and weld repairs were made. The
system was returned to service. [ICES Report #85354]
Sheath Degradation Assessment: The seal weld issue was related to a fabrication error, so
sheath degradation is unlikely.
On September 26, 1989, at Calvert Cliffs Unit 1, weepage-type leakage was detected in
20 pressurizer heaters by visual examination at Calvert Cliffs Unit 2. The root cause was
IGSCC (PWSCC) of the Alloy 600 heater sleeves. The heaters were inspected at Unit 1 and 12
heaters were removed, and no leakage was detected from Unit 1. [ICES Report #296493]
Sheath Degradation Assessment: The sleeves and potentially sheaths of the pressurizer
heaters had material damage.
On September 26, 1989, at Callaway Unit 1, a supply breaker spuriously tripped. The
breaker linkage was worn, so the breaker was replaced and returned to service. [ICES Report
#85465]
Sheath Degradation Assessment: The breaker linkage for the supply breaker is separate
from the heater, so sheath degradation is unlikely.
On September 27, 1989, at Three Mile Island Unit 1, the pressurizer heater controller
group RCGCU0006 triggered an alarm because of an issue with the gate trigger unit. The unit
was replaced and the controller group tested successfully. [ICES Report #85559]
Sheath Degradation Assessment: The controller is separate from the heater, so sheath
degradation is unlikely.
On November 1, 1989, at San Onofre Unit 2, the pressurizer heater circuit breaker failed
the thermal trip test. The breaker was replaced and returned to service. [ICES Report #87073]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 7, 1989, at Diablo Canyon Unit 1, the 480 volt circuit breaker for
pressurizer heater 1-2 would not trip because of a nonfunctioning latch assembly. The latch
assembly was replaced and tested. [ICES Report #87284]
Sheath Degradation Assessment: The latch assembly is separate from the heater, so sheath
degradation is unlikely.
46
On November 27, 1989, at Kewaunee Unit 1, pressurizer heater group E would not
energize. The circuit breaker (14304) for group E heaters was open and discharged. The Yrelay was replaced and tested successfully. [ICES Report #88059]
Sheath Degradation Assessment: The Y-relay for the breaker is separate from the heater, so
sheath degradation is unlikely.
On December 7, 1989, at San Onofre Unit 1, the pressurizer heater (Group A) control
circuit breaker failed to operate. The circuit breaker was replaced. The operating mechanism
internal spring had come loose from its notch in the shaft and was replaced. [ICES Report
#88510]
Sheath Degradation Assessment: The breaker operating mechanism is separate from the
heater, so sheath degradation is unlikely.
On January 26, 1990, at Crystal River Unit 3, pressurizer heater group 1 would not
operate due to a failed gate triggering unit in the controller. A spare gate triggering unit was
installed and the controller was returned to service. [ICES Report #90207]
Sheath Degradation Assessment: The controller is separate from the heater, so sheath
degradation is unlikely.
On January 30, 1990, at Surry Unit 1, the pressurizer heater backup circuit was in the
tripped position due to internal grounding. The circuit breaker was replaced. [ICES Report
#90368]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 8, 1990, at Crystal River Unit 3, the pressurizer heater group 2 controller
had failed. A spare gate triggering unit was installed and group 2 was returned to service.
[ICES Report #90707]
Sheath Degradation Assessment: The controller is separate from the heater, so sheath
degradation is unlikely.
On February 28, 1990, at St. Lucie Unit 1, pressurizer heater breaker PP-130-CKT-5
would not close because of a lack of lubrication on the hinge pin. The breaker was removed and
the hinge pin was lubricated. [ICES Report #91407]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 28, 1990, at St. Lucie Unit 1, the pressurizer heater circuit breaker PP-127CKT-4 would not close because of a lack of lubrication on the breaker hinge pin. The breaker
was removed and the hinge pin was lubricated. The breaker was returned to service. [ICES
Report #91406]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 19, 1990, at Cook Unit 1, backup heater numbers 43, 73, and 74 supply
breaker tripped on closure. The breaker was replaced and returned to service. [ICES Report
#92213]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
47
degradation is unlikely.
On March 21, 1990, at Wolf Creek Unit 1, pressurizer heater breaker PG2108 tripped, so
the failed breaker was replaced with a like for like breaker and returned to service. [ICES Report
#92346]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 11, 1990, at Surry Unit 1, the pressurizer heater control summator was drifting,
so the summator was adjusted back into tolerance. [ICES Report #93280]
Sheath Degradation Assessment: The summator is separate from the heater, so sheath
degradation is unlikely.
On April 22, 1990, at Diablo Canyon Unit 2, the 480 volt pressurizer heater 2-4 was
found with a burnt trip coil, so the trip coil was replaced and returned to service. [ICES Report
#93759]
Sheath Degradation Assessment: The trip coil is separate from the heater, so sheath
degradation is unlikely.
On April 25, 1990, at St. Lucie Unit 2, pressurizer heater circuit breaker 40304 tripped.
The overload trip unit was replaced and returned to service. [ICES Report #93933]
Sheath Degradation Assessment: The trip unit is separate from the heater, so sheath
degradation is unlikely.
On May 18, 1990, at Millstone Unit 3, backup group “A” pressurizer heater tripped from
service while operating. The defective isolator was replaced with a new one. [ICES Report
#94904]
Sheath Degradation Assessment: The breaker isolator is separate from the heater, so sheath
degradation is unlikely.
On May 23, 1990, at Surry Unit 2, the alarm for group “C” pressurizer heaters would not
clear. The circuit breaker was cleaned and the component was returned to service. [ICES
Report #95101]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 27, 1990, at Turkey Point Unit 3, backup pressurizer heater group “3A” breaker
30107 tripped and would not shut. The brush assembly was replaced and returned to service.
[ICES Report #95239]
Sheath Degradation Assessment: The brush assembly is separate from the heater, so
sheath degradation is unlikely.
On June 8, 1990, at Palisades Unit 1, circuit breaker 152-305 tripped but then tripped
again on reclosure. Two transformers were replaced during the outage. [ICES Report #95694]
Sheath Degradation Assessment: The transformer is separate from the heater, so sheath
degradation is unlikely.
48
On June 9, 1990, at Palisades Unit 1, a breaker that fed the pressurizer heater
transformer tripped. A temporary measure was installed to restore power to the pressurizer
heaters. [ICES Report #296872]
Sheath Degradation Assessment: The transformer is separate from the heater, so sheath
degradation is unlikely.
On June 9, 1990, at South Texas Unit 1, pressurizer heater group iD citcuit breaker
failed to close on demand. The bent racking linkage was straightened. The breaker was tested
and returned to service. [ICES Report #95751]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On June 25, 1990, at Calvert Cliffs Unit 1, circuit breaker 52-1218 for the motor control
center would not close. The shutters were lubricated and the breaker was appropriately closed.
[ICES Report #96340]
Sheath Degradation Assessment: The shutter is separate from the heater, so sheath
degradation is unlikely.
On June 27, 1990, at Indian Point Unit 3, a breaker trouble light from pressurizer heater
group 32 circuit breaker 52/PBU2 had tripped from overload. No corrective action was made.
[ICES Report #96419]
Sheath Degradation Assessment: Because the heater subsequently operated appropriately,
sheath degradation is unlikely.
On July 3, 1990, at Fort Calhoun Unit 1, the breaker for pressurizer heater bank 4
groups 10, 11, and 12 had tripped. The breaker and overheated cable were replaced. [ICES
Report #96678]
Sheath Degradation Assessment: The shunt coil and latch coil are separate from the heater,
so sheath degradation is unlikely.
On July 4, 1990, at Millstone Unit 3, the pressurizer heater group “D” was unable to be
de-energized. The trip shunt coil and magnetic latch coil were replaced. [ICES Report #96693]
Sheath Degradation Assessment: The shunt coil and latch coil are separate from the heater,
so sheath degradation is unlikely.
On July 16, 1990, at Harris Unit 1, the breaker for the pressurizer heater “B-1B” tripped
twice in a three hour period. The breaker (that had weakened due to age) was replaced with a
new one and the item was returned to service. [ICES Report #97108]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On August 6, 1990, at St. Lucie Unit 1, the service feeder breaker for the pressurizer
heater back-up bank B2 kept tripping open. A new trip overload device was installed, tested,
and returned to service. [ICES Report #97714]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
49
On August 23, 1990, at Comanche Peak Unit 1, the pressurizer back heater group a
power supply breaker failed to close on demand due to failure of the breaker close coil. The
breaker was replaced. [ICES Report #98336]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On August 23, 1990, at North Anna Unit 2, pressurizer hater breakers were tripping
because the ceramics and terminal lugs on heaters 28, 29, 51, and 66 were missing and/or
cracked and burned into. The ceramics and terminal lugs were replaced and the component
was tested and returned to service. [ICES Report #98352]
Sheath Degradation Assessment: The lugs and ceramics are separate from the heater
sheath, so sheath degradation is unlikely.
On September 7, 1990, at Sequoyah Unit 1, pressurizer heater bank “1D” breaker for
heater elements 47, 49, and 51 tripped. The breaker was replaced and returned to service after
testing. [ICES Report #98844]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On September 27, 1990, at Sequoyah Unit 2, the fire watch was unable survey an area
that contained the Unit 2 pressurizer heater transformer. [ICES Report #291142]
Sheath Degradation Assessment: This incident is unrelated to pressurizer heater operation.
On October 3, 1990, at Cook Unit 2, pressurizer heater groups A3 and C1 tripped.
Operators were able to realign the equipment to desired status. [ICES Report #99891]
Sheath Degradation Assessment: Because the heaters were able to be returned to
operation, sheath degradation is unlikely.
On November 5, 1990, at Sequoyah Unit 2, the pressurizer heater backup group “2B-B”
breaker tripped for no apparent cause. The breaker was tested and returned to service. [ICES
Report #101365]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On November 6, 1990, at South Texas Unit 1, the backup group 1B circuit breaker
dripped during heater operation and the backup 1B train was degraded due to the momentary
loss of the set of heaters in the group because the “A” phase was loose due to a loose screw.
The screw was tightened and the breaker was satisfactorily tested. [ICES Report #101395]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On December 2, 1990, at Diablo Canyon Unit 1, a 480 volt circuit breaker for pressurizer
heater group 1-3 would not rack in and it exhibited excessive resistance. The failure was
caused by a rough grounding shoe because the silver surface was off in several places and the
copper showing through was worn and rough. Lubrication was applied to the breaker which
50
brought it back to operating status. The grounding shoe will be replaced during the next
refueling outage. [ICES Report #102400]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On December 28, 1990, at Indian Point Unit 2, while performing pressurizer heater
control maintenance during normal power operation, the output controller fluctuated when the
chassis was disturbed slightly. The controller was replaced and returned to service. [ICES
Report #103390]
Sheath Degradation Assessment: The output controller is separate from the heater, so
sheath degradation is unlikely.
51
A.3
Pressurizer Heater Operating Experience (1991-1995)
On February 17, 1991, at St. Lucie Unit 1, the control received no output from the “1B”
pressurizer heater controller because there was an open circuit on control rectifiers CR1, CR2,
and CR3. Blown fuses were also discovered. The control rectifiers and blown fuses were
replaced. [ICES Report #105493]
Sheath Degradation Assessment: The control rectifiers and blown fuses are separate from
the heater, so sheath degradation is unlikely.
On March 3, 1991, at Palisades Unit 1, the 480 volt pressurizer backup controller heater
circuit breaker 52-1506 did not open (deenergize) when placed in the off position because the
contactor was sticking from breaker parts becoming stressed by heat. The coild and contact
internals were replaced and reinstalled. [ICES Report #106012]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 19, 1991, at South Texas Unit 1, pressurizer heater control group “1C”
breaker tripped because there was a loose connection. The connection was inspected and
tightened. [ICES Report #106712]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 1, 1991, at Oconee Unit 3, the time delay relay for the “3C” pressurizer heater
control circuit faled to actuate and prevented the group 3G, 3I, and 3J heaters from operating.
The relay had failed due to a moisture leak. The relay was replaced and the component
operated appropriately. The leak that caused the moisture was repaired. [ICES Report
#107309]
Sheath Degradation Assessment: The relay is separate from the heater, so sheath
degradation is unlikely.
On April 3, 1991, at Beaver Valley Unit 1, the “C” pressurizer heater bank did not have
full capacity. Heater 45 and heater 69 had a short circuit that caused the breakers to trip, which
was considered normal heater wear. The in-place heaters were temporarily retired in place.
They are to be replaced at a future date. [ICES Report #107402]
Sheath Degradation Assessment: The heater become non-functional due to a heater
electrical issue which could be associated with sheath degradation.
On April 8, 1991, at Trojan 1, the group “B” pressurizer heater bank supply breaker B1022 would not work because arcing had welded a control relay closed. The control relay was
removed and replaced and the breaker tested successfully. [ICES Report #107641]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 6, 1991, at North Anna Unit 2, the pressurizer heat ouput had decrased by the
kilowatt equivalent of three pressurizer heaters because of heat buildup in the fuse cabinet. The
failed fuses were replaced and the component was returned to service. [ICES Report #108931]
Sheath Degradation Assessment: The fuses are separate from the heater, so sheath
52
degradation is unlikely.
On May 11, 1991, at Farley Unit 1, pressurizer heater backup group 10 supply breaker
was tripping because the long time delay was set on “0.8” and hsoul have been set on “0.9”,
associated with setpoint drift. The long time delay was reset to “0.9” and returned the
component to service. [ICES Report #109159]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 24, 1991, at Sequoyah Unit 1, the backup heaters were cycling on and off
because a fuse had blown, a semiconductor rectifier had shorted, and a firing board was
defective. The fuse, board, and semiconductor rectifier were replaced. [ICES Report #109746]
Sheath Degradation Assessment: The fuse, board, and semiconductor rectifier are separate
from the heater, so sheath degradation is unlikely.
On May 31, 1991, at Ginna Unit 1, the “C” amp meter on the pressurizer heater control
board was indicating “0” amperes because of a failed silicon rectifier and blown fuses. No
information is presented about the issue resolution. [ICES Report #109985]
Sheath Degradation Assessment: The rectifier and fuses are separate from the heater, so
sheath degradation is unlikely.
On June 3, 1991, at Harris Unit 1, the “B” pressurizer heater group failed to turn off when
the reset point was reached because the high pressure controller relay failed to energize due to
a piece of cable tie that had lodged in the relay. The cable tie was removed and the operability
of the heater was verified [ICES Report #110075]
Sheath Degradation Assessment: The controller relay is separate from the heater, so sheath
degradation is unlikely.
On June 20, 1991, at Beaver Valley Unit 1, circuit breaker 480VUS-1-9P12 would not
close because the reset arm was out of adjustment. The breaker was adjusted and the reset
arm was tested successfully. [ICES Report #110651]
Sheath Degradation Assessment: The reset arm is separate from the heater, so sheath
degradation is unlikely.
On July 15, 1991, at Fort Calhoun Unit 1, when the circuit breaker for the pressurizer
heater controller was opened, high temperature alarms were received because of a faulty circuit
card within the safety parameters display panel. The card was replaced with a new one.[ICES
Report #111474]
Sheath Degradation Assessment: The card is separate from the heater, so sheath
degradation is unlikely.
On July 24, 1991, at Connecticut Yankee Unit 1, the circuit breaker for pressurizer
heater group “A” was in the tripped position because the element cables were old and the
insulation was brittle. The cables were therefore spliced and insulated. A recommendation was
made that the cables should be replaced in the future. [ICES Report #111723]
Sheath Degradation Assessment: The cables are separate from the heater, so sheath
degradation is unlikely.
53
On August 10, 1991, at Diablo Canyon Unit 1, a pressurizer heater was deenergized as
a result of ventilation isolation due to personnel error. No pressurizer corrective action was
necessary. [ICES Report #292411]
Sheath Degradation Assessment: The issue was with a system unrelated to the pressurizer,
so sheath degradation is unlikely.
On August 13, 1991, at Cook Unit 2, a breaker for the pressurizer heater system had be
wired incorrectly due to a phase being reversed. The breaker was required in accordance with
design documents. [ICES Report #112342]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On August 19, 1991, at Oconee Unit 3, pressurizer heater bank 1 group “3A” and heater
bank 2 group “3K” were not operating because the controller overheated due to a cooling fan’s
burned out resistor. A burned out fuse was replaced and the controller will be replaced with a
spare controller. [ICES Report #112540]
Sheath Degradation Assessment: The controller is separate from the heater, so sheath
degradation is unlikely.
On September 5, 1991, at North Anna Unit 2, five fuses which provide secondary
protection for the pressurizer heater electrical containment penetrations failed to meet the
criteria of a resistance test. The fuses were replaced and the system was brought back to
operation. [ICES Report #292494]
Sheath Degradation Assessment: The fuses separate from the heater, so sheath
degradation is unlikely.
On October 6, 1991, at Catawba Unit 1, there was a low ampere output from the
controller for pressurizer heater group “C” that prevented the heaters from maintaining
temperature. This was due to normal aging of a silicon rectifier within the controller. The silicon
rectifier was replaced. [ICES Report #114388]
Sheath Degradation Assessment: The silicon rectifier is separate from the heater, so sheath
degradation is unlikely.
On October 10, 1991, at Diablo Canyon Unit 2, circuit breaker for pressurizer heater
group 2 would not close from the control room. This was caused by a broken racking gear. The
breaker was replaced and returned to service. [ICES Report #114546]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 17, 1991, at Cook Unit 2, pressurizer heater group GRC1 was
sporadically turning off with the control switch in the closed position because of a faulty
disconnect on the circuit breaker 21PHC2. This was due to the primary male to female
disconnects becoming distorted. The disconnect was replaced and the breaker was returned to
service. [ICES Report #116236]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
54
degradation is unlikely.
On November 19, 1991, at San Onofre Unit 1, pressurizer heater group “B” control
breaker 52-1215 would not close because of normal wear and aging of the components due to
cyclic operation. The failed breaker was removed and replaced, and the item was returned to
service. [ICES Report #116343]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 26, 1991, St. Lucie Unit 1, pressurizer heater backup bank 2A3 circuit
breaker 40304 tripped open and would not reset because the thermal djustement setting was
out of adjustment. The setting was reset to a higher setting and the breaker was planned to be
replaced during the next outage. [ICES Report #117719]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 17, 1992, at Indian Point Unit 3, pressurizer heater breaker 52/PBU2 would
not close due to an out of adjustment overcurrent trip switch actuator. The actuator was
adjusted.[ICES Report #118522]
Sheath Degradation Assessment: The actuator is separate from the heater, so sheath
degradation is unlikely.
On January 24, 1992, at Trojan 1, a pressurizer heater tripped because the phase C
contacts were not operating correctly due to improper closing. The failed breaker was replaced
and tested. [ICES Report #118882]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 14, 1992, at Ginna Unit 1, a pressurizer proportional heater had a
downgraded silicon control rectifier and blown fuses for the three phases. The fuses were
replaced but the rectifier remained in service. [ICES Report #119694]
Sheath Degradation Assessment: The fuses and rectifier are separate from the heater, so
sheath degradation is unlikely.
On February 18, 1992, at Ginna Unit 1, a pressurizer proportional heater had a
downgraded silicon control rectifier and blown fuses for the three phases. The rectifier and the
fuses were replaced. [ICES Report #119837]
Sheath Degradation Assessment: The fuses and rectifier are separate from the heater, so
sheath degradation is unlikely.
On March 3, 1992, at San Onofre Unit 3, a circuit breaker for a pressurizer heater failed
to trip on overcurrent. The breaker could not be repaired, so it was replaced and brought back
to service. [ICES Report #120582]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
55
On March 9, 1992, at McGuire Unit 2, pressurizer heater panel 2B tripped three times in
a forty-eight hour period because of a new cable that was installed. No specific resolution ws
provided in the report. [ICES Report #120888]
Sheath Degradation Assessment: The heater panel is separate from the heater, so sheath
degradation is unlikely.
On March 12, 1992, at Comanche Peak Unit 1, the DS-416 breaker in the pressurizer
heater cabinet was damaged. No specific resolution of the issue was described in the report.
[ICES Report #121024]
Sheath Degradation Assessment: The volt breaker is separate from the heater, so sheath
degradation is unlikely.
On April 7, 1992, at Indian Point Unit 3, pressurizer heater backup group 31 supply
circuit breaker exceeded the administrative criteria. The out of calibration amtector was
adjusted to within limits. [ICES Report #122428]
Sheath Degradation Assessment: The volt breaker amtector is separate from the heater, so
sheath degradation is unlikely.
On April 16, 1992, at Sequoyah Unit 2, the ground fault relay for pressurizer heater
group 2D failed surveillance testing due to the non-functionality of a relay. The relay was
replaced and returned to service. [ICES Report #122987]
Sheath Degradation Assessment: The relay is separate from the heater, so sheath
degradation is unlikely.
On May 13, 1992, at St. Lucie Unit 2, circuit breaker 40302 (bus backup heater bank B1) would not trip on demand possibly due to failure from aging. A new breaker was installed
and tested.[ICES Report #124420]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 31, 1992, at South Texas Unit 1, pressurizer heater group 1D primary CKTBRK
tripped open while the heater group was energized because of a stripped screw threads that
resulted in a loose connection. The terminal bar was replaced and the CKTBRK was tested
satisfactorily. [ICES Report #125195]
Sheath Degradation Assessment: The terminal bar is separate from the heater, so sheath
degradation is unlikely.
On June 19, 1992, at Ginna Unit 1, one of three control phases for the pressurizer
heater proportional heater had blowne fuses due to a failed silicon control rectifier. The rectifier
was replaced during the 1992 outage. [ICES Report #125950]
Sheath Degradation Assessment: The rectifier is separate from the heater, so sheath
degradation is unlikely.
On June 21, 1992, at Three Mile Island Unit 1, a pressurizer heater was non-functional
and confirmed with resistance and meggar checks. The rest of the group that was functional
was returned to service. [ICES Report #126009]
56
Sheath Degradation Assessment: Although this is a B&W plant and the assessment is not
applicable, the heater potential suffered from some sheath degradation that could have caused
the heater non-functionality.
On July 2, 1992, at Sequoyah Unit 1, pressurizer heater group 1D would not maintain
pressure in the pressurizer because of train of heater control was degraded because a bridge
amplifier failed. The capacitors, relay, and firing board were replaced. [ICES Report #126469]
Sheath Degradation Assessment: The capacitor, relay, and firing board of the bridge
amplifier are separate from the heater, so sheath degradation is unlikely.
On July 5, 1992, at Byron Unit 2, pressurizer heater group A circuit breaker was tripping
because of a loose connection of the line to lead wire. The line to lead wire was replaced and
relanded. [ICES Report #126533]
Sheath Degradation Assessment: The line to lead wire is separate from the heater, so
sheath degradation is unlikely.
On July 5, 1992, at Byron Unit 2, the pressurizer heater circuit breaker in cubicle B1
would not stay reset because of a loose connection on the B phase wire. The wire was repaired
by tightening. [ICES Report #126532]
Sheath Degradation Assessment: The wire in the breaker is separate from the heater, so
sheath degradation is unlikely.
On July 6, 1992, at Ginna Unit 1, the pressurizer proportional heaters was going on and
off. The breaker had tripped because capacitor C3 had blown. Capacitors C1 through C6,
resistors R3, R4, R13 through 18, and fuses F1 through F8 were replaced. [ICES Report
#126573]
Sheath Degradation Assessment: The capacitors, resistors, and fuses are separate from the
heater, so sheath degradation is unlikely.
On July 22, 1992, at Calvert Cliffs Unit 1, the closing springs for breaker 52-1127 for
pressurizer heater motor control center 109 would not close. Misalignment of the forward pivot
pin may have been the cause. The pin was centered and the breaker closed appropriately.
[ICES Report #127160]
Sheath Degradation Assessment: The pin and breaker are separate from the heater, so
sheath degradation is unlikely.
On August 3, 1992, at Calvert Cliffs Unit 2, the circuit breaker for the 22 pressurizer
proportional heater had tripped. The breaker trip was caused by a failure of the pressurizer
heater controller (reported separately). A broken wire was reterminated to the limit switch.
[ICES Report #127558]
Sheath Degradation Assessment: The controller and broken wire are separate from the
heater, so sheath degradation is unlikely.
On September 13, 1992, at St. Lucie Unit 1, pressurizer proportional heater bank P1
was only putting out 20% of its rated capacity due to a pressurizer heater control that had two
57
blown fuses, possibly due to aging. The two new fuses were obtained and installed, with
returned normal operation. [ICES Report #128926]
Sheath Degradation Assessment: The fuses and controller are separate from the heater, so
sheath degradation is unlikely.
On September 22, 1992, at Three Mile Island Unit 1, heaters 32, 33, and 39 were found
to be open circuits. This was not an issue because of the large number of redundant heaters.
Leads were lifted to remove the heaters from service. [ICES Report #129294]
Sheath Degradation Assessment: Because this is a B&W plant, this assessment is not
applicable. The non-functional heaters may have the potential for associated sheath material
degradation that could have caused the non-functionality.
On September 26, 1992, at Farley Unit 1, pressurizer heater backup group B did not
give a local or remote indication for the supply breaker and the breaker could not be opened.
The shunt trip coil was replaced and correct alignment was verified. [ICES Report #129500]
Sheath Degradation Assessment: The breaker and shunt trip coil are separate from the
heater, so sheath degradation is unlikely.
On October 18, 1992, at Diablo Canyon Unit 1, pressurizer heater group 1-1 would not
trip consistently. The solid state trip device and the magnetic latch device were replaced. The
breaker was tested and returned to service. [ICES Report #130443]
Sheath Degradation Assessment: The breaker and magnetic latch device are separate from
the heater, so sheath degradation is unlikely.
On October 21, 1992, at Sequoyah Unit 1, pressurizer heater bank 1D breaker for heater
elements 47, 49, and 51 tripped, removing one-sixth of the bank heating capacity because a lug
had galled threads. The breaker was replaced and proper torqueing of the lugs was verified.
[ICES Report #130590]
Sheath Degradation Assessment: The breaker and lugs are separate from the heater, so
sheath degradation is unlikely.
On November 16, 1992, at Beaver Valley Unit 1, pressurizer heaters powered from class
1E 480 volt busses 8N and 9P were not appropriately analyzed for loading considerations.
Appropriate administrative guidance was provided to increase the overcurrent trip setting. [ICES
Report #131499]
Sheath Degradation Assessment: The volt busses are separate from the heater, so sheath
degradation is unlikely.
On November 18, 1992, at Waterford Unit 3, a pressurizer heater control circuit failed in
service after 50 cycles due to a circuit board failure in the control system. No resolution was
included in the report. [ICES Report #131564]
Sheath Degradation Assessment: The circuit board is separate from the heater, so sheath
degradation is unlikely.
58
On November 25, 1992, at Indian Point Unit 3, it was discovered that in certain
scenarios, the insulation and conductors for the three phases of the pressurizer heater circuit
could have potentially deteriorated in the containment penetration, providing a path from
containment atmosphere to the outside environment. No information was given in the report on
resolution. [ICES Report #131781]
Sheath Degradation Assessment: The insulation and cables are separate from the heater, so
sheath degradation is unlikely.
On December 1, 1992, at Zion Unit 2, pressurizer heater group 2A breaker had a broken
trip latch assembly that could prevent tripping of the breaker. The trip latch assembly was
replaced and the breaker was returned to service. [ICES Report #131960]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 3, 1992, at Arkansas Nuclear One Unit 1, heater bank number 2 was
repeatedly tripping because of a grounded pressurizer heater element. The circuit breaker was
replaced all cable connection were tightened after connected a spare pressurizer heater. [ICES
Report #132029]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 22, 1992, at San Onofre Unit 2, pressurizer heater 2E624 failed because
of a circuit breaker failure. The breaker was removed and replaced. [ICES Report #132611]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 30, 1992, at Crystal River Unit 3, pressurizer heater groups 1 and 7
through 9 were unavailable because the pressurizer level transmitters RC-1-LT1 and RC-LT3
were down. The transmitter was replaced, calibrated, and functioned properly. [ICES Report
#132741]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 19, 1993, at Ginna Unit 1, a bus 14 alarm that feeds the pressurizer heater
control cabinet occurred because of blown fuses and a blown silicon controlled rectifier. The
heater control group wiring was meggered during the outage and found to be acceptable. No
other resolution was mentioned in the report. [ICES Report #133304]
On January 26, 1993, at Byron Unit 2, pressurizer heater group A circuit breaker had
tripped open, potentially from a burnt contactor coil. The contactor coil was replaced and the
breaker operated properly. [ICES Report #133485]
Sheath Degradation Assessment: The contactor coil is separate from the heater, so sheath
degradation is unlikely.
On January 28, 1993, at Salem Unit 2, the pressurizer heater number 22 circuit breaker
failed during reactor trip, but other backup heaters were utilized. No resolution was mentioned
in the report. [ICES Report #133569]
59
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 2, 1993, at Cook Unit 2, technical specification action was not met due to
personnel error after blocking open a fire door to the pressurizer heater transformer room.
[ICES Report #133732]
Sheath Degradation Assessment: The pressurizer heater transformer room is separate from
the heater, so sheath degradation is unlikely.
On February 11, 1993, at Turkey Point Unit 3, a heater controller for heater phase A
wattmeter was not functioning properly due to a silicon controlled rectifier gate trigger unit. The
gate trigger unit was replaced and calibrated. [ICES Report #133997]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On February 27, 1993, at Byron Unit 1, the pressurizer heater group B breaker actuation
time was outside allowable ranges due to aging of the breaker from wear. The breaker was
replaced and retested. [ICES Report #134362]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 28, 1993, at Byron Unit 1, pressurizer heater backup group a primary
breaker failed to close on demand due to aging of the breaker from wear. The breaker was
replaced and tested to verify operation. [ICES Report #134382]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 2, 1993, at St. Lucie Unit 2, leakage was identified from pressurizer
instrument nozzles. The cracked nozzles were replaced with a more resistant material. [ICES
Report #134430]
Sheath Degradation Assessment: The instrument nozzles are separate from the heater, so
sheath degradation is unlikely. This issue does have relation to material degradation in general.
On March 3, 1993, at St. Lucie Unit 2, pressurizer heater instrument nozzles cracked
due to Alloy 600 cracking. The event is detailed in INPO Significant Event Report 2-90
“Pressurizer Heater Sleeve Cracking” and NRC Information Notice 90-10 “Primary Water Stress
Corrosion Cracking (PWSCC) of Inconel 600”. [ICES Report #134474]
Sheath Degradation Assessment: The instrument nozzles are separate from the heater, so
sheath degradation is unlikely. This issue does have relation to material degradation in general.
On April 23, 1993, at Ginna Unit 1, the gate triggering unit for the silicon controlled
rectifiers for the backup pressurizer proportional heaters failed due to normal wear and aging.
The gate triggering unit was replaced and the heaters tested satisfactorily. [ICES Report
#136228]
Sheath Degradation Assessment: The gate triggering unit is separate from the heater, so
sheath degradation is unlikely.
60
On May 13, 1993, at Arkansas Nuclear One Unit 2, the pressurizer heater supply
brakers did not charge because of a failed charging motor because of normal wear of the motor.
The breaker spring motor was replaced and the breaker was returned to service. [ICES Report
#136811]
Sheath Degradation Assessment: The spring motor is separate from the heater, so sheath
degradation is unlikely.
On June 17, 1993, at McGuire Unit 2, the pressurizer heater group 2D tripped because
of an open coil on the circuit breaker trip relay. The relay coil was replaced and the breaker was
returned to service. [ICES Report #137639]
Sheath Degradation Assessment: The relay coil is separate from the heater, so sheath
degradation is unlikely.
On June 26, 1993, at Comanche Peak Unit 1, the pressurizer group C switchboard was
issuing a burnt smell and smoke, possibly due to a controller issue. Two silicon controlled
rectifiers and three diodes were replaced, and the controller was repaired. [ICES Report
#137827]
Sheath Degradation Assessment: The rectifiers, diodes, and controllers are separate from
the heater, so sheath degradation is unlikely.
On July 3, 1993, at Sequoyah Unit 2, the pressurizer heater control group 2D silicon
control rectifier output was erratic and fuses had blown. The rectifier and the fuses were
replaced. [ICES Report #137975]
Sheath Degradation Assessment: The rectifier and fuses are separate from the heater, so
sheath degradation is unlikely.
On July 15, 1993, at Crystal River Unit 3, pressurizer heater group 1 silicon controlled
rectifier failed due to an issue with the gate triggering unit, so the gate triggering unit was
replaced. [ICES Report #138209]
Sheath Degradation Assessment: The gate triggering unit is separate from the heater, so
sheath degradation is unlikely.
On August 7, 1993, at Braidwood Unit 2, a burnt smell came from the the pressurizer
heater group A contactor. The transformer, contactor coils, and fuses were replaced. [ICES
Report #138713]
Sheath Degradation Assessment: The transformer, contactor coils, and separate from the
heater, so sheath degradation is unlikely.
On August 13, 1993, at Indian Point Unit 2, the breaker for pressurizer heater backup
group number 23 would not close due to a shunt trip assembly. The assembly may have
become misaligned. The shunt trip assembly was replaced with a new one and returned to
service. [ICES Report #138869]
Sheath Degradation Assessment: The shunt trip assembly is separate from the heater, so
sheath degradation is unlikely.
On August 26, 1993, at Crystal River Unit 3, pressurizer heater group 2 silicon controlled
61
rectifier bank had failed due to a defective gate triggering unit for the group. A new gate
triggering unit was installed and controller operation was verified. [ICES Report #139156]
Sheath Degradation Assessment: The gate triggering unit is separate from the heater, so
sheath degradation is unlikely.
On September 12, 1993, at Byron Unit 1, group A pressurizer backup heater primary
contactor was in the on position and the feed breaker was closed in with no current indicated on
the ampmeter because of a loose connection of the contactor. The contactor connection was
tightened and tested to verify operability. [ICES Report #139557]
Sheath Degradation Assessment: The contactor is separate from the heater, so sheath
degradation is unlikely.
On September 20, 1993, at Connecticut Yankee Unit 1, pressurizer backup heater
breaker for group A heaters failed to shut on demand because the X-relay failed, which
prevented energizing the breaker shutting coil. The breaker was replaced and returned to
service. [ICES Report #139770]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 25, 1993, at Farley Unit 2, no indication for pressurizer heater group 2A
was observed because a trip coil in breaker EA11 had shorted, causing a loss of power. The
trip coil was replaced and returned to service. [ICES Report #139939]
Sheath Degradation Assessment: The trip coil is separate from the heater, so sheath
degradation is unlikely.
On October 5, 1993, at Diablo Canyon Unit 1, the backup circuit breaker for pressurizer
heater group 13 failed to close because the closing mechanism had bound due to dried
lubricant and dirt on the magnetic latch paddle. The circuit breaker was cleaned, tested, and
returned to service. [ICES Report #140240]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On October 7, 1993, at Harris Unit 1, the pressurizer heater overload alarm was
triggered, resulting in loss of power to the backup heater group 1D. The magnetic latching
mechanism was reset from tripped position and the breaker was cycled to verify operation.
[ICES Report #140343]
Sheath Degradation Assessment: The magnetic latching mechanism is separate from the
heater, so sheath degradation is unlikely.
On October 7, 1993, at Three Mile Island Unit 1, a pressurizer heater element was found
to have an open B phase when the breaker was closed. The circuit breaker was replaced and
tested satisfactorily. [ICES Report #140351]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On October 13, 1993, at Crystal River Unit 3, the pressurizer heater group 5 silicon
62
controlled rectifier failure alarm was triggered. A fuse was additionally found blown. The gate
triggering unit also had failed. The fuse and gate trigger unit were replaced. [ICES Report
#140523]
Sheath Degradation Assessment: The fuse and gate trigger unit are separate from the
heater, so sheath degradation is unlikely.
On October 13, 1993, at South Texas Unit 1, pressurizer heater group B backup breaker
failed to trip when the overcurrent trip unit (amptector) fired. The amptector was replaced.
[ICES Report #140549]
Sheath Degradation Assessment: The amptector is separate from the heater, so sheath
degradation is unlikely.
On October 31, 1993, at Oconee Unit 1, the supply breaker for pressurizer heater
groups C, F, and I had tripped because the breaker short circuited due to high moisture in the
breaker. The breaker was replaced. [ICES Report #141074]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 6, 1993, at Crystal River Unit 3, the pressurizer heater group 4 silicon
controlled rectifier bank had failed. One fuse was found blown and replaced. The break was
also replaced. [ICES Report #142034]
Sheath Degradation Assessment: The breaker and fuse are separate from the heater, so
sheath degradation is unlikely.
On December 17, 1993, at St. Lucie Unit 1, the pressurizer heater control PIC-1100X
failed, possibly due to aging. A new controller was installed and put into service. [ICES Report
#142259]
Sheath Degradation Assessment: The heater controller is separate from the heater, so
sheath degradation is unlikely.
On December 27, 1993, at San Onofre Unit 3, pressurizer heater controls that were
connected to heater bank 3E122 had an alarm due to a defective solid state trip device. The
defective device was replaced and the breaker was returned to service. [ICES Report #142462]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 4, 1994, at Palo Verde Unit 1, pressurizer heater power control unit 100A
failed due to normal aging and fatigue. Fuses F3 and F5 to the silicon controlled rectifier power
control unit were found to be open. The bad fuses were replaced and the heater circuitry was
checked. The item was returned to operation. [ICES Report #142595]
Sheath Degradation Assessment: The fuses are separate from the heater, so sheath
degradation is unlikely.
On January 13, 1994, at South Texas Unit 1, pressurizer heater group 1A breaker failed
to close on demand when operations personnel attempted to place the heaters in service due to
a breaker toggle handle that could not be reset due to normal fatigue. The breaker was
63
replaced and placed in service. [ICES Report #142836]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 24, 1994, at Calvert Cliffs Unit 2, the proportional heater controller 2NB420
for pressurizer heater 21 was not sending the correct control signal due to a shorted diode and
a blown fuse. The diode and fuse were replaced in the controller, and the controller and heaters
were returned to operation. [ICES Report #143115]
Sheath Degradation Assessment: The fuses and diode are separate from the heater, so
sheath degradation is unlikely.
On February 13, 1994, at South Texas Unit 2, a 480 volt circuit breaker for pressurizer
heater group A backup heaters had a malfunctioning spring charging motor brush rigging and
brushes. The spring charging motor was replaced. [ICES Report #143548]
Sheath Degradation Assessment: The spring charging motor is separate from the heater, so
sheath degradation is unlikely.
On February 28, 1994, at Oconee Unit 3, a circuit breaker for group 3C had a blown
control fuse due to a voltage surge, preventing contacts from picking up and providing power. A
new fuse was installed and the heater operated properly. [ICES Report #143880]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On March 3, 1994, at Crystal River Unit 3, a power supply was unavailable for a
pressurizer heater that would have resulted in a violation. The item was not identified until June
13, 1000, when a similar violation was recognized and questioned. [ICES Report #143950]
Sheath Degradation Assessment: The power supply is separate from the heater, so sheath
degradation is unlikely.
On March 12, 1994, at Summer Unit 1, the circuit breaker for pressurizer heater control
group panel APN4106 would not properly make up when the breaker was racked up due to age
and normal cyclic fatigue. The plug was replaced during the outage and the breaker performed
satisfactorily. [ICES Report #144178]
Sheath Degradation Assessment: The breaker plug is separate from the heater, so sheath
degradation is unlikely.
On March 15, 1994, at Oconee Unit 3, a loose or defective electrical connection caused
low current reading on heaters during surveillance testing for heater group B. The breaker was
replaced and megger tested.[ICES Report #144247]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 16, 1994, at St. Lucie Unit 2, boric acid on the exterior of the pressurizer
steam space C instrument nozzle was noted. This was due to a fabrication issue using shielded
metal arc welding. No further resolution is noted in the report. [ICES Report #144265]
Sheath Degradation Assessment: The instrument nozzles are separate from the heater, so
sheath degradation is unlikely. Still, this is a material-related degradation mechanism.
64
On March 21, 1994, at Calvert Cliffs Unit 1, boron deposits were discovered on the Unit
1 pressurizer heater sleeve B-3 indicating leakage from an Alloy 600 component of the reactor
coolant system pressure boundary. Deposits were also noted on sleeve FF-1. The Unit 1
sleeves were examined, and sleeve FF-1 was plugged with an Alloy 600 plug. SER 31-87
“Pressurizer Vessel Corrosion Due To Pressurizer Heater Rupture” from November 10, 1987 is
of note. [ICES Report #144384]
Sheath Degradation Assessment: The sleeve was a result of PWSCC of the Alloy 600
sleeve. No apparent sheath degradation was noted in the report.
On March 30, 1994, at Braidwood Unit 1, pressurizer heater control group C circuit was
grounded, attributed to human error. A lead had been landed on a wrong terminal in panel
1PA25J. The lead was landed on the correct terminal. [ICES Report #144632]
Sheath Degradation Assessment: The panel in the auxiliary relay cabinet is separate from
the heater, so sheath degradation is unlikely.
On April 20, 1994, at Calvert Cliffs Unit 1, an increased sulfate content was noted after
nickel plating work was performed on pressurizer heater sleeves earlier in the outage. The
issue was resolved while in cold standby. [ICES Report #145209]
Sheath Degradation Assessment: The issue was related to chemistry concentration controls,
so sheath degradation is unlikely.
On May 31, 1994, at Davis-Besse Unit 1, the circuit breaker for non-essential pressurizer
heater tripped after about 18 hours of operation because of the stabs causing a high resistance
electrice joint from annealing. The breaker stabs were replaced with new stabs of correct iron
content. [ICES Report #146182]
Sheath Degradation Assessment: The stabs are separate from the heater, so sheath
degradation is unlikely.
On June 16, 1994, at Diablo Canyon Unit 1, the pressurizer heater group 12 alternate
feed circuit breaker would not close by remote operation because of binding from old dried up
grease. The circuit breaker was cleaned, relubricated, and tested. [ICES Report #146526]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On June 21, 1994, at Oconee Unit 1, the pressurizer heater controller for bank number 1
would not respond to the system control signal because of circuit integrity from an unanticipated
high electrical current. The controller was replaced and the voltage, current, and indicating
lamp were checked with satisfactory results. [ICES Report #146630]
Sheath Degradation Assessment: The controller is separate from the heater, so sheath
degradation is unlikely.
On July 6, 1994, at Calvert Cliffs Unit 1, pressurizer heater insulation during the April
1994 outage was discovered at location CC-1, indicating failed heater cladding. All heaters had
been replaced with new 13.3 kW heater manufactured by Watlow. The magnesium oxide
insulation had swollen and the heater had been lodged in place and impossible to remove. The
heater internals were later drilled out and the location plugged. Previous industry expectation
65
was that the pressurizer heaters with a failed cladding would not swell that quickly. It was
believed that the heater sheath breach was made during installation and was not a
manufacturing defect. [ICES Report #146877]
Sheath Degradation Assessment: The magnesium oxide swelling was associated with water
ingress and a pressurizer heater sheath breach.
On August 5, 1994, at Diablo Canyon Unit 1, a 480 volt circuit breaker for pressurizer
heater group 1-1 would not reclose from the control room, potentially from cell interlock switches
that would not make up. The breaker was inspected and the cell interlock switches were
adjusted and aligned. The breaker was then returned to service. [ICES Report #147460]
Sheath Degradation Assessment: The breaker and cell interlock switches are separate from
the heater, so sheath degradation is unlikely.
On September 22, 1994, at Wolf Creek Unit 1, circuit breaker 52PG2102 for backup
pressurizer heater group A heaters 23, 49, and 50 found that the breaker failed the trip current
test on phase C. The breaker was replaced, tested, and returned to operation. [ICES Report
#148347]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 30, 1994, at Wolf Creek Unit 1, for backup pressurizer heater group A
number 17, 18, and 42 failed the thermo trip test and failed to open at 300% of its current rating
in the prescribed time due to circuit breaker 52PG2111 from normal wear and aging. [ICES
Report #148536]
Sheath Degradation Assessment: The circuit breaker is separate from the heater, so sheath
degradation is unlikely.
On October 7, 1994, at Three Mile Island Unit 1, only two of the three phases in
pressurizer heater group 5 were operational due to an issue with the gate trigger unit providing
pulses of insufficient amplitude to the control unit for one of the phases to energize. A defective
capacitor and resistor were later found in this trigger unit. The gate trigger unit was replaced,
aligned, and verified for proper operation. [ICES Report #148721]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On October 8, 1994, at Comanche Peak Unit 2, spoke was reporting coming from the
pressurizer heater controller 2-01 due to two failed electrolytic capacitors in the silicon controller
rectifier gate trigger units. The two capacitors in the silicon controlled rectifier gate trigger unit
were replaced and the unit was tested. [ICES Report #148752]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On October 18, 1994, at Salem Unit 2, the circuit breaker for heater backup group 1
failed due to a faulty overcurrent trip device. The trip device was replaced with an identical
spare part and returned to service. [ICES Report #149005]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
66
degradation is unlikely.
On December 18, 1994, at St. Lucie Unit 2, the transformer for the B1 pressurizer
backup heaters had a trouble alarm because of a failed circuit breaker possibly due to normal
aging. A spare breaker was installed. [ICES Report #150199]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
67
On February 7, 1995, at Davis-Besse Unit 1, a circuit breaker for a pressurizer heater
tripped open during spray activities due to a high electrical resistance joint on the breaker stabs.
The stabs were replaced with new stabs of correct iron content. [ICES Report #151103]
Sheath Degradation Assessment: The breaker stabs are separate from the heater, so sheath
degradation is unlikely.
On February 14, 1995, at Calvert Cliffs Unit 1, the backup pressurizer heaters would not
energize because of the failure of 1BKR52-10902, the breaker for a backup pressurizer heater
group. A train of three heaters was lost. The cause was blackened and pitted breaker contacts.
The contacts were cleaned and the breaker was returned to service. Later, the contacts were
replaced with new ones and returned to service. [ICES Report #151274]
Sheath Degradation Assessment: The breaker contacts are separate from the heater, so
sheath degradation is unlikely.
On March 7, 1995, at Callaway Unit 1, the breaker for heaters number 39, 69, and 70
failed to meet its trip setpoint. A new breaker was installed and returned to service. [ICES
Report #151732]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 10, 1995, at Summer Unit 1, the ground alarm for the pressurizer heater
power panel control group was received by operations due to insulation being pierced by a
mounting screw. The insulation was repaired. [ICES Report #151824]
Sheath Degradation Assessment: The insulation is separate from the heater, so sheath
degradation is unlikely.
On March 27, 1995, at North Anna Unit 1, the pressurizer heatup and cooldown
temperatures exceeded tech spec limits. The event is not considered significant. [ICES Report
#152180]
Sheath Degradation Assessment: Overall temperature was not out of specification for long
time to promote SCC, so sheath degradation is unlikely.
On April 8, 1995, at Fort Calhoun Unit 1, the circuit breaker for pressurizer heater bank 4
group 12 spuriously tripped. No known failure was identified. The breaker was replaced and
returned to service. [ICES Report #152501]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 3, 1995, at Robinson Unit 2, the pressurizer heater control summator was out of
calibration tolerances due to age/cyclic fatigue and was considered to be from normal
usage/wear. The old summator was replaced and tested satisfactorily. [ICES Report #153052]
Sheath Degradation Assessment: The summator is separate from the heater, so sheath
degradation is unlikely.
On June 8, 1995, at Ginna Unit 1, phase C of the pressurizer proportional heaters were
draing low amperage due to blown fuses and failed silicone controlled rectifiers. The fuses and
68
rectifiers were replaced and the controller was brought back to service. [ICES Report #153662]
Sheath Degradation Assessment: The fuses and rectifiers are separate from the heater, so
sheath degradation is unlikely.
On June 13, 1995, at Calvert Cliffs Unit 1, pressurizer heater 12 proportional controller
would not allow activation of the heater due to controller failure from normal aging of the internal
components. Three diodes, three silicone controlled rectifiers, and two fuses were replaced.
The item was returned to service. [ICES Report #153741]
Sheath Degradation Assessment: The diodes, rectifiers, and fuses are separate from the
heater, so sheath degradation is unlikely.
On July 22, 1995, at San Onofre Unit 3, minimal weepage was detected from a
pressurizer level instrument nozzle due to PWSCC of Alloy 600 material. No further resolution
is provided in the report. [ICES Report #154360]
Sheath Degradation Assessment: The pressurizer instrument nozzles are separate from the
heater, so sheath degradation is unlikely. Still, this issue is related to material degradation of
Alloy 600.
On August 6, 1995, at Palisades Unit 1, there was no current draw for pressurizer heater
group one because of an issue with the silicon controlled rectifier of group one circuit breaker
52-1501. Further testing found a defective gate trigger unit. [ICES Report #154579]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On August 8, 1995, at St. Lucie Unit 1, pressurizer heater circuit breaker 20403 failed to
close on demand, resulting in a loss of 3 of 6 backup heaters and 1 of 2 proportional heaters for
the pressurizer due to setpoint drift. The floor tripper was properly adjusted, and breaker 20403
was returned to service. [ICES Report #154616]
Sheath Degradation Assessment: The floor tripper is separate from the heater, so sheath
degradation is unlikely.
On August 25, 1995, at St. Lucie Unit 1, pressurizer heater breaker 20403 failed to close
on demand due to a latch check switch that was out of adjustment. The switch was tested and
the breaker was returned to service. [ICES Report #154873]
Sheath Degradation Assessment: The latch check switch spring is separate from the heater,
so sheath degradation is unlikely.
On August 8, 1995, at Oconee Unit 1, the pressurizer heater group D main 3 phase
contact bar was found broken during inspection due to wear from aging. The spring was
replaced and returned to service. [ICES Report #154965]
Sheath Degradation Assessment: The spring is separate from the heater, so sheath
degradation is unlikely.
On September 12, 1995, at Indian Point Unit 2, a power decrease resulted from the
inflow of excess dissolved boron from the pressurizer due to operation of the backup pressurizer
heaters. No additional resolution was necessary. [ICES Report #155216]
69
Sheath Degradation Assessment: Because there were no issues with the pressurizer
heaters, sheath degradation is unlikely.
On September 13, 1995, at Cook Unit 1, the fire detection system for the Unit 2
pressurizer heater transformer room was inoperable. No further resolution was provided in the
report. [ICES Report #155220]
Sheath Degradation Assessment: The fire detection system is separate from the heater, so
sheath degradation is unlikely.
On October 11, 1995, at Three Mile Island Unit 1, a fuse for the silicon controlled rectifier
for the pressurizer heater was found. It was replaced and operation was verified. [ICES Report
#155842]
Sheath Degradation Assessment: The fuse for the silicon controlled rectifier is separate from
the heater, so sheath degradation is unlikely.
On November 2, 1995, at Calvert Cliffs Unit 2, the 22 pressurizer proportional heater
bank had low amperage because of a failed gate trigger unit. The gate trigger unit was replaced
and tested. [ICES Report #156342]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On November 2, 1995, at South Texas Unit 2, pressurizer hater 2D turned off because a
supply breaker would not reclose due to the charging motor being in the off position. The switch
was placed in the on position and the limit switches were replaced. [ICES Report #156344]
Sheath Degradation Assessment: The charging motor and limit switches are separate from
the heater, so sheath degradation is unlikely.
On December 12, 1995, at Arkansas Nuclear One Unit 2, the breaker for the pressurizer
heater backup system failed to perform its intended function because of a defect in the spring
material. A broken spring was replaced and the breaker was returned to service. [ICES Report
#157094]
Sheath Degradation Assessment: The breaker spring is separate from the heater, so sheath
degradation is unlikely.
70
6.2
Pressurizer Heater Operating Experience (1996-2000)
On January 9, 1996, at Braidwood Unit 2, backup pressurizer heater group A was found
to be deenergized. A blown control power fuse, damage to two coils, and a burnt smell in the
panel for the backup group A due to an overheating panel. The blown control fuses and the
contactor coils were replaced. The charging mechanism arm was also cleaned. [ICES Report
#157503]
Sheath Degradation Assessment: The control power fuses and the contactor coils are
separate from the heater, so sheath degradation is unlikely.
On February 7, 1996, at Kewaunee Unit 1, pressurizer heater control group 1C 1-21, 147, and 1-48 circuit breaker (MCC33A-A1) tripped, while pressurizer group C was in operation.
Because of a bad contact on a phase, the breaker was replaced and returned to service. [ICES
Report #157971]
On May 1, 1996, at Diablo Canyon Unit 2, a 480 volt circuit breaker for pressurizer
heater group 3 (breaker 52PH23-5) failed with high amps on phase C. The breaker was
replaced and returned to service. [ICES Report #159615]
On June 10, 1996, at Millstone Unit 3, electrical separation noncompliance was found in
systems associated with Train A and B pressurizer backup heaters. The event is considered
not significant. [ICES Report #160251]
Sheath Degradation Assessment: The heater cables are separate from the heater, so sheath
degradation is unlikely.
On September 12, 1996, at Salem Unit 1, cables supplying power to the backup
pressurizer heaters were not adequately separated, which was caused when a design analysis
did not address cables in a modification. No specific resolution was provided. [ICES Report
#161342]
Sheath Degradation Assessment: The heater cables are separate from the heater, so sheath
degradation is unlikely.
On October 15, 1996, at Farley Unit 1, pressurizer heater group 2E did not power up due
to breaker EN07 charging continuously. The charging mechanism was sticking, so the breaker
was cleaned and lubricated. [ICES Report #161850]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On October 18, 1996, at Maine Yankee Unit 1, both proportional heater banks had
suffered blown heater output fuses. The fuses were replaced to correct the problem and future
replacement of heater controller should correct future problems.[ICES Report #161904]
Sheath Degradation Assessment: The heater breaker and controllers are separate from the
heater, so sheath degradation is unlikely.
On October 24, 1996, at Diablo Canyon Unit 2, the 480 volt breaker 52-23e-05 failed to
fully close and energize the heaters. The breaker closed manually but not automatically, due to
71
mechanical binding between the close release latch and shunt trip coil bracket. The breaker
was replaced and returned to service. [ICES Report #162004]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 19, 1997, at Surry Unit 1, the reactor was tripped due to loss of a
proportional heater group due to a control unit circuit card failure. The circuit card was replaced
and recalibrated. [ICES Report #163824]
Sheath Degradation Assessment: The circuit card is separate from the heater, so sheath
degradation is unlikely.
On March 18, 1997, at Ginna Unit 1, an increased voltage on Bus 16 caused the
pressurizer heaters to put out more heat. [ICES Report #164373]
Sheath Degradation Assessment: This was a singular high voltage event, so sheath
degradation is unlikely.
On March 24, 1997, at Diablo Canyon Unit 1, a latch/lock/interlock for pressurizer heater
PHPG2 failed due to an out of adjustment close latch release rod. The device was repaired.
[ICES Report #164519]
Sheath Degradation Assessment: The latch release rod is separate from the heater, so
sheath degradation is unlikely.
On May 23, 1997, at Byron Unit 1, the 480 volt breaker failed for pressurizer heater
group B due to main contact coil failure. No further information on resolution was
provided.[ICES Report #165800]
Sheath Degradation Assessment: The main contact coils are separate from the heater, so
sheath degradation is unlikely.
On July 12, 1997 at Braidwood Unit 1, pressurizer heater group B had a replacement
coil in the distribution panel fail. The coil was subsequently replaced. [ICES Report #166802]
Sheath Degradation Assessment: The coil is separate from the heater, so sheath
degradation is unlikely.
On July 20, 1997, at Oconee Unit 2, a fuse in the circuit breaker that supports
pressurizer heater 2RC_HE0002 failed. The heater was declared inoperable. [ICES Report
#166952]
Sheath Degradation Assessment: As this unit is of the B&W design, the sheath degradation
assessment is not applicable.
On July 27, 1997, at Byron Unit 1, the B pressurizer heater group contactor coil
overheated and ignited due to two coils that overheated, causing a short in the wire. The
control cables, the rectifier, and both coils were replaced. [ICES Report #167097]
Sheath Degradation Assessment: The control cables, rectifier, and coils are separate from
the heater, so sheath degradation is unlikely.
On September 3, 1997, at Byron Unit 1, the A group pressurizer heater contactor
72
1PM05J failed. The backup heater group B was energized to recover pressure. No additional
information regarding resolution was given in the report. [ICES Report #167780]
Sheath Degradation Assessment: The heater contactors are separate from the heater, so
sheath degradation is unlikely.
On April 7, 1998, at North Anna Unit 2, fuses were found blown on the C phase. The
proportional controller was repaired, including replacement of six fuses, one capacitor, and the
gating controller. [ICES Report #172226]
Sheath Degradation Assessment: The fuses, capacitor, and gating controller are separate
from the heater, so sheath degradation is unlikely.
On April 14, 1998, at Calvert Cliffs Unit 1, heater sleeve B-1 had boric acid
accumulations due to PWSCC of Alloy 600 material. Visual and ultrasonic inspections were
made of the heater sleeves. The sleeve was removed and the penetration was replaced. [ICES
Report #172389]
Sheath Degradation Assessment: The sleeve is separate from the heater, but sheath
degradation could be possible with a degraded sheath. This is PWSCC of Alloy 600 material.
On April 17, 1998, at Calvert Cliffs Unit 1, a pressurizer heater sleeve was found cracked
during inspection. The crack was a pre-existing crack that was nickel plated in 1994. The
sleeve was removed and the penetration was plugged. This sleeve was Alloy 600 material that
cracked due to PWSCC [ICES Report #172440]
Sheath Degradation Assessment: The sleeve is separate from the heater, but sheath
degradation could be possible with a degraded sheath. This is PWSCC of Alloy 600 material.
On May 8, 1998, at Harris Unit 1, nine 480 volt circuit breakers were not testing during a
60 month interval, which is a preventive maintenance requirement. The breaker operability was
not affected. [ICES Report #172937]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 25, 1998, at Calvert Cliffs Unit 2, a pressurizer instrument nozzle failed because
of an Alloy 600 issue. The leading nozzle was repaired and the other nozzles were visually
inspected. All data were collected, and the unit was returned to power. The Alloy 600 nozzles
were replaced with Alloy 690 material but were still welded with Alloy 600-type weld metal.
[ICES Report #174468]
Sheath Degradation Assessment: The instrument nozzle is separate from the heater, so
sheath degradation is unlikely. This is PWSCC of Alloy 600 material.
On July 25, 1998, at Calvert Cliffs Unit 2, a pressurizer instrument nozzle failed because
of an Alloy 600 issue. The leading nozzle was repaired and the other nozzles were visually
inspected. All data were collected, and the unit was returned to power. [ICES Report #174476]
Sheath Degradation Assessment: The instrument nozzle is separate from the heater, so
sheath degradation is unlikely. This is PWSCC of Alloy 600 material.
On August 5, 1998, at Oconee Unit 3, a pressurizer heater bank was inoperable. Heater
73
element MB37 had a ground. The element was replaced with element LB21. [ICES Report
#174638]
Sheath Degradation Assessment: As this is a B&W plant, the sheath assessment is not
applicable.
On September 8, 1998, at Summer Unit 1, the group 2 pressurizer heater breaker
(XSW1DB 05) tripped without apparent cause. The pressurizer heaters were megged [sic] and
bridged without abnormal readings. The breaker was determined to work appropriately for the
plant operation without safety issue. [ICES Report #175229]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 15, 1999, at Robinson Unit 2, pressurizer heater molded case breaker
(backup GP-A-2) would not manually open to clear a ground on the 480 volt system due to the
poles on A phase of the breaker were welded shut as a result of a high energy fault. No further
resolution in the report is provided. [ICES Report #177424]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 18, 1999, at South Texas Unit 1, primary breaker #4 on heater group 1A
was in the tripped condition due to loose connections. The connections were tightened and
thermography was performed on components. [ICES Report #177691]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 23, 1999, at Prairie Island Unit 1, 5 heaters were reported as non-functional.
One heater failed prior to 1986, one in 1991, one in 1992, one in 1995, and one in 1997. The
non-functional heaters were disconnected. No further resolution was provided in the report.
[ICES Report #177791]
Sheath Degradation Assessment: The non-functional heaters may have associated sheath
degradation. No clear root cause was determined as the reason for the heater non-functionality.
On January 24, 1999, at Oconee Unit 2, a heater in bank 2B had a ground in it with only
six of nine elements available. Element LB9 was bad, element LB33 was open and 30K Ohms
to ground. The drawings would be revised to show the deleted heater element. [ICES Report
#177810]
Sheath Degradation Assessment: As this is a B&W design plant, the sheath assessment is
not applicable. The heater element was damaged and inoperable.
On January 25, 1999, at North Anna Unit 2, breaker #5 for the pressurizer heater
tripped. The corrective action was to reclose the breaker and monitor it for spurious opening.
The breaker was upgraded and not problems occurred since that upgrade. No further corrective
actions were deemed necessary. [ICES Report #177832]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 16, 1999, at Summer Unit 1, the group 2 pressurizer heater breaker
(XSW1DB 05) tripped without apparent cause. The pressurizer heaters were megged [sic] and
bridged without abnormal readings. The breaker was determined to work appropriately for the
plant operation without safety issue. [ICES Report #178208]
74
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 16, 1999, at South Texas Unit 2, the cell switch for 480 volt pressurizer heater
group 2B failed during the performance of a cell switch check. The cell switch was replaced and
the item was returned to service. [ICES Report #178761]
Sheath Degradation Assessment: The cell switch is separate from the heater, so sheath
degradation is unlikely.
On March 18, 1999, at Diablo Canyon Unit 2, pressurizer heater group 2-2 feeder
breaker did not close properly due to the potential for mechanical binding in the mechanism.
The breaker was cycled twice locally and then operated appropriately. [ICES Report #178821]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 28, 1999, at McGuire Unit 2, pressurizers de-energized during Channel 3
testing (problem similar to the one documented in PIP 2-M98-3367). The channel testing was
suspended and the test process revised to use a hand-held multimeter rather than long jumper
cables. [ICES Report #179690]
Sheath Degradation Assessment: The heater channels are separate from the heater, so
sheath degradation is unlikely.
On May 10, 1999, at Millstone Unit 3, breaker testing guidance was not following such
that ten breakers had not been tested since 1991. The breakers were subsequently tested and
operated satisfactorily. [ICES Report #179930]
Sheath Degradation Assessment: As this issue is related to administrative controls, sheath
degradation is unlikely.
On May 11, 1999, at Summer Unit 1, the group 2 pressurizer heater breaker (XSW1DB
05) tripped without apparent cause. The pressurizer heaters were megged [sic] and bridged
without abnormal readings. The breaker was determined to work appropriately for the plant
operation without safety issue. [ICES Report #179965]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 12, 1999, at Oconee Unit 1, low temperature overpressure protection (LTOP)
protocols were not met for operator response time from first pressure alarm. The methods for
mitigating LTOP were not compromised. [ICES Report #179971]
Sheath Degradation Assessment: As this issue related to administrative controls, sheath
degradation is unlikely.
On May 26, 1999, at Catawba Unit 1, pressurizer heater group 1A lost emergency
supply power capability. The breaker ETBBKGTA01 was fully engaged to address the issue.
[ICES Report #180248]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 6, 1999, at South Texas Unit 1, the primary circuit breaker for circuit #4 for
pressurizer heater group 1A was found in the tripped condition. The breaker was reset and
remained closed after the heater was energized. The breaker was replaced, but tests still had
75
to be made on the heater condition. [ICES Report #180901]
Sheath Degradation Assessment: The heater might have an issue with grounding since
additional testing has to be performed, so sheath degradation is possible.
On October 20, 1999, at Oconee Unit 3, all 9 of the unit 3 SSF pressurizer heater
elements were deenergized due to the actuation of ground fault protection circuitry. The ground
fault of the bank 2, group B pressurizer heaters was caused by failure of one of three heater
elements on the circuit with breaker LB8. A “Run to Failure” analysis was performed. [ICES
Report #182776]
Sheath Degradation Assessment: As this is a B&W plant, the sheath assessment is not
applicable.
76
6.3
Pressurizer Heater Operating Experience (2000-2005)
On January 13, 2000, at Vogtle Unit 2, pressurizer heater breaker 2NBPB203-1 failed to
reset during performance of surveillance. The failed breaker was replaced.[ICES Report
#184191]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 19, 2000, at Seabrook Unit 1, breakers were not tested appropriately per
tech specs. The issue occurred during outage 5 (1997). [ICES Report #184293]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
unlikely.
On January 29, 2000, at North Anna Unit 2, breaker #4 in cabinet 2-EP-CB-10D (“H”
train backup pressurizer heater) was found tripped open. The breaker was reset, as no cause
of the trip was found. [ICES Report #184466]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 1, 2000, at South Texas Unit 2, a circuit breaker would not trip open when the
handswitch was moved to off. The cell switch was troubleshooted and the breaker was
reracked successfully. [ICES Report #185570]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 8, 2000, at Palo Verde Unit 3, a breaker was found tripping below the required
level. The breaker was replaced and determined to be failed from normal aging. [ICES Report
#185734]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 1, 2000, at Crystal River Unit 3, two breakers (RCDP-3 breaker 7 and RCDP-1
breaker 7) tripped and therefore failed to supply the pressurizer heaters with power.
Requirements for pressurizer heater trains are located in NUREG 737. The breakers were
replaced with new breakers. [ICES Report #186132]
Sheath Degradation Assessment: The breakers are separate from the heater, so sheath
degradation is unlikely.
On June 23, 2000, at Wolf Creek Unit 1, for breakers that failed a test on the first phase,
subsequent phases were not tested, as appropriate. All phases should be tested.[ICES Report
#187000]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
unlikely.
On July 30, 2000, at ANO Unit 2, pressurizer heater sleeve leakage was noted. This is
discussed in Report #187535. [ICES Report #187536]
On July 30, 2000, at ANO Unit 2, boric acid crystals were bound under the pressurizer
on the electrical cables of heaters B2 and D2. Ten additional heater sleeves exhibited similar
evidence of leakage, but to a smaller extent. Eight of the sleeves (A2, B2, B4, C3, D2, D3, D45,
and AA3) had heaters installed while four of the sleeves (AA4, B1, B3, and G2) had dummy
77
heaters. Nine of the twelve sleeves were located in the first row around the surge nozzle. The
cause of the sleeve ruptures was PWSCC of Alloy 600 material, and sheath swelling,
presumably from sheath degradation, was also noted. Information is documented in CEOG
Report CEN-393-P. [ICES Report #187535]
Sheath Degradation Assessment: The swollen sheath is an indicator of sheath degradation.
On September 10, 2000, at Calvert Cliffs Unit 1, the 11 proportional heater group was
not firing due to a gate trigger unit that had burn marks on one of the terminal boards because
of a loosened nut and bolt in the internals. The gate trigger unit was replaced and returned to
service. [ICES Report #188233]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On September 30, 2000, at North Anna Unit 2, pressurizer heater breaker 2-EP-CB-10B
#5 was noted to be in the tripped position. The breaker was checked, no errors were found, and
the breaker was successfully reclosed. [ICES Report #188651]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On October 4, 2000, at Palo Verde Unit 2, boric acid indications were found for a heater
sleeve, due to PWSCC of Alloy 600 material. The sleeve was repaired. [ICES Report
#188723]
Sheath Degradation Assessment: The pressurizer heater sleeve is separate from the heater,
so sheath degradation is unlikely. This is PWSCC of Alloy 600 material. The same incident
was later associated with sheath swelling.
On October 4, 2000, at Palo Verde Unit 2, at the beginning of U2R9, evidence of heater
sleeve leakage was detected (at location A06) and documented in ISI report #00-342. A sleeve
plug at location B18 (another previously plugged heater location) was removed and the remnant
was examined by eddy current testing. The axial cracks had been confirmed in 1991. Heater
sheath swelling problems were also noted in Unit 2 A06 and B18. The sleeve was inspected
and repaired. [ICES Report #188724]
Sheath Degradation Assessment: The swollen sheath is an indicator of sheath degradation.
On October 17, 2000, at North Anna Unit 2, breakers 1, 4, and 5 on 2-EP-CB-10A
tripped due to loose connections. The items were tightened, returned to service, and no further
issues emerged. [ICES Report #188997]
Sheath Degradation Assessment: The breakers are separate from the heater, so sheath
degradation is unlikely.
On October 17, 2000, at North Anna Unit 2, pressurizer heater groups 1 and 4 tripped
due to loose connections in the breakers. The breakers were retightened and operated
properly. [ICES Report #188990]
Sheath Degradation Assessment: The breakers are separate from the heater, so sheath
degradation is unlikely.
On October 17, 2000, at Waterford Unit 3, leaking MNSA clamps let to primary pressure
boundary leakage in the pressurizer heater sleeve due to Alloy 600 material PWSCC. The
MNSA was not installed correctly by the vendor. [ICES Report #188992]
Sheath Degradation Assessment: The pressurizer heater sleeve is separate from the heater,
so sheath degradation is unlikely. This is PWSCC of Alloy 600 material.
78
On October 19, 2000, at South Texas Unit 2, breakers 4 and 5 for pressurizer heater 2A
tripped during a load check due to loose connections. The connections were identified and
tightened. The B Phase bus bar was also replaced to ensure reliability. [ICES Report #189032]
Sheath Degradation Assessment: The connections and bus bar are separate from the
heater, so sheath degradation is unlikely.
On October 22, 2000, at Fort Calhoun Unit 1, the water space temperature element on
the pressurizer suffered from PWSCC of Alloy 600 material that was found from a small steam
leak from thermowell TE-108. A successful partial weld repair was performed on TE-108, and
preventive maintenance of TE-107 was employing using a Mechanical Nozzle Seal Assembly
(MNSA). [ICES Report #189090]
Sheath Degradation Assessment: The instrument nozzle is separate from the heater, so
sheath degradation is unlikely. This is PWSCC of Alloy 600 material.
On November 11, 2000, at Calvert Cliffs Unit 1, pressurizer heater motor control center
109PH feeder breaker failed due to the breaker’s push-to-close mechanisms that were out of
adjustment. The levering and push-to-close mechanisms were adjusted and the breaker was
returned to service. [ICES Report #189504]
Sheath Degradation Assessment: The levering and push-to-close mechanisms are separate
from the heater, so sheath degradation is unlikely.
On December 16, 2000, at Catawba Unit 1, pressurizer heater 1A did not energize on
May 5, 1993. A “control relay” was replaced but a time relay module also needed replacement
and was replaced with an upgraded model. [ICES Report #190008]
Sheath Degradation Assessment: The breaker and time relay module are separate from the
heater, so sheath degradation is unlikely.
On January 4, 2001, at ANO Unit 1, an amperage reading was improper for pressurizer
heater bank #1. The silicon controlled rectifier control board was replaced and adjusted,
resulting in balance current and voltage readings. [ICES Report #190236]
Sheath Degradation Assessment: The silicon controlled rectifier control board is separate
from the heater, so sheath degradation is unlikely.
On January 13, 2001, at Oconee Unit 1, pressurizer heater bank #1 experienced
problems so banks #2 and #3 were manually energized. Three of the nine elements in bank #1
did not operate due to a breaker fault. No specific resolution was mentioned in the report. [ICES
Report #190377]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On March 23, 2001, at Millstone Unit 2, a gate trigger unit failed due to aged and
degraded capacitors, so the gate trigger unit was replaced with a refurbished spare. The
replacement frequency was changed from 10 years to every 5 years. [ICES Report #191440]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On March 27, 2001, at Fort Calhoun Unit 1, relay 63X/PIC-103 for the pressurizer
backup heaters burned out after 29 years of service. A similar failure occurred in 1991. The
relay was worked under work order 82643. [ICES Report #191510]
Sheath Degradation Assessment: The relay is separate from the heater, so sheath
79
degradation is unlikely.
On May 6, 2001, at Byron Unit 1, a contactor coil failed due to age-related thermal
degradation of the insulation caused by high operating temperature. This is the same failure
mechanism as a failure in 1997. Specific resolution was not further mentioned in the report.
[ICES Report #192218]
Sheath Degradation Assessment: The contactor coil is separate from the heater, so sheath
degradation is unlikely.
On May 7, 2001, at Oconee Unit 3, pressurizer heater bank 2 was not cycling to
maintain RCS pressure due to heater element LB25 being shorted. Other items had element
failure but not functional failure. Specific resolution was not mentioned in the report. [ICES
Report #192239]
Sheath Degradation Assessment: As this is a B&W design, the sheath assessment is not
applicable.
On June 6, 2001, at Oconee Unit 2, the bank 1 pressurizer heaters had not been
operating properly. This related to an issue with total heater capacity. [ICES Report #192726]
Sheath Degradation Assessment: As this is a B&W design, the sheath assessment is not
applicable.
On July 4, 2001, at Oconee Unit 1, a ground fault was found for pressurizer heater
connected to MCC 1XI, compartment 3A and compartment 1A. The breakers were reclosed.
[ICES Report #193155]
Sheath Degradation Assessment: As this is a B&W design, the sheath assessment is not
applicable.
On October 11, 2001, at Catawba Unit 2, pressurizer heater group 2B (2NCEHPZRB)
would not energize. Operations used troubleshooting to verify proper operation. [ICES Report
#194633]
Sheath Degradation Assessment: As the heater is fully functional, sheath degradation is
unlikely.
On December 15, 2001, at Vogtle Unit 1, breaker 1NB10-05 tripped while the heater was
in service, resulting in a loss of power to 1NB10. Root cause was not determined, but the
breakers were replaced. [ICES Report #195657]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 16, 2002, at Summer Unit 1, a pressurizer heater group fuse was blown for
backup group 1. A faulty heater was ruled out due to meggering. The fuse was blown due to
high temperature from a gap between the blade and jaw from a manufacturing defect. The 100ampere disconnects were again completely replaced and the power supply fuses are checked
once per shift. [ICES Report #196079]
Sheath Degradation Assessment: The fuse is separate from the heater, so sheath
degradation is unlikely.
On February 19, 2002, at Millstone Unit 2, leakage was present at two heater
penetration locations (A1 and C4). The leakage rate was 10-12 milliliters per minute. The issue
is described in Report #196610. [ICES Report #196618]
80
On February 19, 2002, at Millstone Unit 2, leakage was present at two heater
penetration locations (A1 and C4) on drawing 25203-32007 due to PWSCC of Alloy 600
material. MNSA clamps were installed on each leaking nozzle. [ICES Report #196610]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On March 7, 2002, at Oconee Unit 1, not enough heater capacity would be available per
procedure during certain standby shutdown facility events. This issue is described in Report
#196899. [ICES Report #196907]
On March 7, 2002, at Oconee Unit 3, not enough heater capacity would be available per
procedure during certain standby shutdown facility events. This issue is described in Report
#196899. [ICES Report #196909]
On March 7, 2002, at Oconee Unit 2, not enough heater capacity would be available per
procedure during certain standby shutdown facility events. This issue is described in Report
#196899. [ICES Report #196908]
On March 7, 2002, at Oconee Unit 1, not enough heater capacity would be available per
procedure during certain standby shutdown facility events. The ambient heat loss from the
pressurizer was greater than anticipated. The procedure was revised accordingly. [ICES
Report #196899]
Sheath Degradation Assessment: As this issue is related to administrative controls, sheath
degradation is unlikely.
On April 15, 2002, at ANO Unit 2, pressurizer heater sleeves were found to be leaking.
The issue is covered in Report #197902 and #197886. [ICES Report #197614]
On April 30, 2002, at ANO Unit 2, a sixth pressurizer heater sleeve nozzle was found to
be leaking (see Report #197886) and was repaired with a MNSA 2. The issue was related to
PWSCC of Alloy 600 material. [ICES Report #197902]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On April 30, 2002, at ANO Unit 2, leakage was found on the pressurizer heater sleeve
nozzles C2, E2, F4, G1, and E1. Two locations (at J3 and N3) were difficult to inspect due to
insulation present. MNSA 2 was installed on each of the five leaking sleeves. The issue was
caused by Alloy 600 PWSCC. [ICES Report #197886]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On May 27, 2002, at Summer Unit 1, pressurizer heater backup group 2 breaker tripped
while energized. This issue is discussed in Report #198405. [ICES Report #198385]
On May 28, 2002, at Summer Unit 1, the pressurizer heater backup group 2 breaker
tripped while energized. The breaker was replaced and the heaters themselves were
determined to not be the root cause of the issue. The trip of XSW1DB 05 was left as an open
item. [ICES Report #198405]
Sheath Degradation Assessment: As the heater itself was not a potential cause of the trip,
sheath degradation is unlikely.
81
On August 27, 2002, at Kewaunee Unit 1, pressurizer heater backup group 1E heaters
had an open phase that was detected. The heater was powered from C/B 1-562. No specific
resolution was mentioned in the report. [ICES Report #199827]
Sheath Degradation Assessment: A root cause for the open phase was not provided. A
degraded sheath could manifest as an open phase in the heater.
On January 11, 2003, at Indian Point Unit 3, the 31 pressurizer backup heater was found
tripped, due to an unknown reason. The transformer was rebuilt and returned to service. [ICES
Report #202082]
Sheath Degradation Assessment: The transformer is separate from the heater, so sheath
degradation is unlikely.
On March 1, 2003, at South Texas Unit 1, pressurizer heater group 1B failed to energize
when required (using the automatic function). The root cause of the issue is not known but was
suspected to be a result of operator control. [ICES Report #202988]
Sheath Degradation Assessment: The heaters operated appropriately, so sheath
degradation is unlikely.
On March 4, 2003, at South Texas Unit 2, a racking assembly that supports pressurizer
heater 7R112EHT101D (in heater backup group D) failed due to a racking lever out of
adjustment. The racking lever was adjusted to the required position and the breaker functioned
appropriately. [ICES Report #203047]
Sheath Degradation Assessment: The lockout reset relay is separate from the heater, so
sheath degradation is unlikely.
On March 29, 2003, at Palo Verde Unit 3, an RCS leak was found relating to a
pressurizer heater sleeve. This issue is described in Report #203600. [ICES Report #203600]
On March 29, 2003, at Palo Verde Unit 3, leakage was found on pressurizer heater
sleeves A-1 and A-15. This issue is described in Report #203600. [ICES Report #203610]
On March 29, 2003, at Palo Verde Unit 3, boric acid residue was found around
pressurizer penetration A01. Heater sleeve A15 was initially suspected of leaking but was later
verified to not have visual evidence of leakage. The degradation was due to axially oriented
PWSCC of Alloy 600 material. The heater sleeve was repaired using a MNSA. [ICES Report
#203600]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On April 8, 2003, at Kewaunee Unit 1, a lockout reset relay associated with pressurizer
heater group A failed. The locket reset relay was repaired. [ICES Report #203828]
Sheath Degradation Assessment: The lockout reset relay is separate from the heater, so
sheath degradation is unlikely.
On August 7, 2003, at Kewaunee Unit 1, pressurizer heater group 1B had a low current
alarm and the breaker 1-574 was found tripped, deenergizing heaters 1-40 and 1-70. Only 12
energized heaters remained in heater group 1B. The breaker was replaced and the heaters
returned to service. [ICES Report #205707]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
82
On August 11, 2003, at Calvert Cliffs Unit 2, the gate trigger unit for 21 proportional
heaters failed as a result of filer capacitor C209 not being solidly connected to the circuit board.
The gate trigger units were replaced and the heaters were put back into service. [ICES Report
#205742]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 2, 2003, at Catawba Unit 1, the 1D pressurizer heater was cycling on and
off. This issue is discussed in Report #206724. [ICES Report #206130]
On October 2, 2003, at Palo Verde Unit 3, the A train pressurizer heater bank circuit
breaker tripped open. The heater (B-09) had a 20 year life but was considered non-functional.
The heater was considered “consumable”. Train A was restored by wiring in a heater from a
non-class heater bank. [ICES Report #206680]
Sheath Degradation Assessment: Because the heater was considered non-functional and
remains in service, sheath degradation is a possibility. The heater may have had only electrical
issues or may have associated sheath failure.
On October 5, 2003, at Catawba Unit 1, for pressurizer heater group 1D, the optical
isolator was not properly designed for the circuit, so the pressurizer was inoperable. The issue
was resolved by adding an interposing relay to energize the main contactor M coil. [ICES Report
#206724]
Sheath Degradation Assessment: The optical isolator is separate from the heater, so sheath
degradation is unlikely.
On October 11, 2003, at Millstone Unit 2, heater penetration C3 was identified as having
wet boric acid leakage. Another location identified as F4 on drawing 25203-20527 Sheet 15
was found to be suspected of additional leakage. MNSA clamps were installed to prevent
leakage. New pressurizer (without Alloy 600) installation is planned for fall 2006. [ICES Report
#206835]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On October 15, 2003, at Palo Verde Unit 2, circumferential cracks were found in
pressurizer heater sleeves. The issue is described by Report #206889. [ICES Report #206900]
On October 15, 2003, at Palo Verde Unit 2, six pressurizer heater sleeves had
circumferential flaw indications and six additional sleeves had axial flaw indications from
PWSCC of Alloy 600 material. The Alloy 600 material was replaced with Alloy 690 material
(more resistant to PWSCC). Replacement is also planned for Unit 1 and Unit 2. [ICES Report
#206889]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On October 21, 2003, at South Texas Unit 1, pressurizer heater backup group 1D did
not energize due to a breaker closure failure caused by a weak torsion spring in the Y-Relay
assembly of the feeder breaker. The weak torsion spring was replaced. [ICES Report
#207013]
Sheath Degradation Assessment: The torsion spring is separate from the heater, so sheath
degradation is unlikely.
83
On October 24, 2003, at Waterford Unit 3, two pressurizer heater sleeves (locations C-1
and C-3) were leaking because of PWSCC of Alloy 600 material. The sleeves were repaired
with MNSA 2 clamps. [ICES Report #207068]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On October 26, 2003, at Waterford Unit 3, two top pressurizer nozzles were found
leaking due to Alloy 600 PWSCC. These nozzles were repaired by a welding replacement.
[ICES Report #207098]
Sheath Degradation Assessment: The instrument nozzles are separate from the heater, so
sheath degradation is unlikely. The instrument nozzle degradation is due to Alloy 600 PWSCC.
On November 2, 2003, at Millstone Unit 2, two additional pressurizer heater sleeve
leakages were found (four total since spring 2002 2R14) due to PWSCC of Alloy 600 material.
The cracks were axial in orientation. The leakage rate was low at less than 0.1 gallons per
minute. MNSA clamps were installed to prevent further leakage. [ICES Report #207197]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On November 4, 2003, at Three Mile Island Unit 1, a leak was identified in the
pressurizer heater bundle diaphragm plate due to PWSCC of Alloy 600 material. The issue was
resolved by grinding the plate and applying a seal weld. On November 23, 2003, during post
maintenance testing, additional leakage was observed. The assembly was replaced with a new
heater bundle assembly. Subsequently, the plate was replaced with a stainless steel Type 304
plate. [ICES Report #207234]
Sheath Degradation Assessment: As this is a B&W design the sheath degradation
assessment is not applicable. The material degradation was due to PWSCC of Alloy 600.
On November 7, 2003, at Catawba Unit 1, breaker BKSMXGF05C for the 1D pressurizer
heaters was cycling causing an indicating light to flicker. The problem was corrected by adding
an interposing relay to the control circuit. [ICES Report #207291]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 4, 2004, at Kewaunee Unit 1, circuit breaker for pressurizer heater backup
group 1E would not close due to a bad spring release coil and a worn B phase clevis from
normal wear. The piece part was replaced, and the breaker was returned to service. [ICES
Report #208659]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 10, 2004, at Calvert Cliffs Unit 1, a power supply breaker would not close
due to tacky grease that caused the operating mechanism drive link roller not to seat. The roller
was cleaned and lubricated. The breaker was returned to service. [ICES Report #208749]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 29, 2004, at Palo Verde Unit 3, pressurizer heater sleeve A03 was found to
be leaking. The issue is described by Report #209042. [ICES Report #209045]
On February 29, 2004, at Palo Verde Unit 3, the penetration sleeve for pressurizer
84
heater 3MRCEA03 failed due to PWSCC of Alloy 600 material. Boric acid residue had been
found, so the sleeve was repaired with a MNSA. Sleeve replacement was planned for fall of
2004. The sleeve was later replaced with Alloy 690 using a half nozzle repair. Issues were
found with sleeves A1, A3, and A15. [ICES Report #209042]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On March 8, 2004, at Oconee Unit 2, control of bank 2 group C pressurizer heaters was
removed without providing enough pressurizer heaters to effectively maintain or restore RCS
pressure. This was caused by time pressure for making multiple minor modifications. [ICES
Report #209186]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
unlikely.
On April 7, 2004, at Diablo Canyon Unit 1, degradation was identified on the termination
from the electrical cable to the heater element due to overheating damage. A significant
amount of chlorides were detected. The wires with corrosion were replaced and repaired. [ICES
Report #209708]
Sheath Degradation Assessment: The element wires connect to the heater, so sheath
degradation is unlikely. The presence of significant chlorides negatively impacts corrosion to
the heater.
On May 11, 2004, at Braidwood Unit 2, the 2C pressurizer heater was declared
inoperable due to issues with the control board panel 2RY03EC. The piece part was replaced.
[ICES Report #210293]
Sheath Degradation Assessment: The control board panel is separate from the heater, so
sheath degradation is unlikely.
On August 25, 2004, at Palo Verde Unit 2, pressurizer heating element 2MRCEA10
ceased to function, so it was electrically isolated. This brought the total number of isolated
heater elements to four. The heating margin is appropriate with up to seven isolated elements.
During U2R11, approximately 50% of the heaters were replaced. The unit will replace all of the
pressurizer heater elements. The elements in Unit 3 are being replaced during U3R11 with a
new heater (Framatone style). The Unit 1 elements will be replaced during U1R12. [ICES
Report #211809]
Sheath Degradation Assessment: The non-functional heater may be associated with sheath
degradation.
On September 25, 2004, at Braidwood Unit 2, pressurizer heater groups A and D were
inoperable. This issue is described by Report #212232. [ICES Report #212252]
On September 25, 2004, at Braidwood Unit 2, pressurizer heater groups A and D were
inoperable due to issues with control board panels 2RY03EA and 2RY03ED. The settings on
the panels were readjusted. [ICES Report #212232]
Sheath Degradation Assessment: The control board panels are separate from the heater, so
sheath degradation is unlikely.
On September 29, 2004, at ANO Unit 2, two alternating current circuit breakers were
found in a tripped condition, rendering one of two proportional heater banks inoperable. This
issue is described by Report #212335. [ICES Report #212304]
85
On September 30, 2004, at ANO Unit 2, the number 2 proportional heater bank failed to
produce the required output because breakers 2PP6-1 and 2PP6-3 were in a tripped condition
because breaker to bus contactor screws were overtorqued leading to localized heating and
spurious trips. The devices were repaired. [ICES Report #212335]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On October 17, 2004, at San Onofre Unit 3, two pressurizer heaters (and sleeves) were
to be replaced because of PWSCC axial and circumferential indications. No leakage was
detected. A proactive decision was made to replace all pressurizer heater sleeves with an Alloy
690 half-nozzle repair. Two leaks were later discovered from repair weld pads during parallel
refueling. [ICES Report #212622]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On November 20, 2004, at North Anna Unit 2, breaker 2-EP-BKR-10E-1-CKTBRK
(supply breaker for Unit 2 pressurizer heaters 3, 4, and 25) was found tripped for spurious
reasons. The breaker was replaced. Twelve breakers had been replaced to date and Unit 2
had decided to have a new set of more reliable breakers installed. [ICES Report #213135]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 29, 2004, at North Anna Unit 2, pressurizer heater group 4 breaker failed
to close. This issue is described by Report #213647. [ICES Report #213650]
On December 29, 2004, at North Anna Unit 2, the 480 volt feeder breaker for the group
4 pressurizer heaters failed to close due to a defective moveable contact assembly. A spare
breaker was put in service to supply power to the group 4 pressurizer heaters. [ICES Report
#213647]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
86
On January 11, 2005, at Vogtle Unit 1, pressurizer backup heater group A breaker
tripped and would not reclose. The breaker was subsequently replaced. [ICES Report
#213825]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 11, 2005, at Summer Unit 1, a pressurizer heater breaker tripped due to a
type of semiconductor used on the solid state relay card. The triac was turned to correct the
issue, but another breaker tripped for this reason in 2006. A time delay to eliminate signal noise
was added in spring 2008. [ICES Report #213819]
Sheath Degradation Assessment: The feeder breaker and solid state relay card are separate
from the heater, so sheath degradation is unlikely.
On February 16, 2005, at Palo Verde Unit 3, heater 3MRCEB02 because non-functional
and was the third pressurizer heater failure since installing Framatone/Thermocoax heaters. All
three phases were grounded. The previous heater events were December 24, 2004 for bank #1
and January 5, 2005 for bank #2. All 36 Framatone/Thermocoax heaters were later replaced.
[ICES Report #214396]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible. These heaters were removed from service.
On February 17, 2005, at Palisades Unit 1, there was an issue with the diesel generator.
This issue is described by Report #217935. [ICES Report #214421]
On February 17, 2005, at Palisades Unit 1, the pressurizer heater breaker 152-211 had
a discrepancy in response to a load shed signal due to an issue with the diesel generator. The
bus was re-energized and the pressurizer heaters from bus 1D were put back into service.
[ICES Report #217935]
Sheath Degradation Assessment: The breaker and diesel generator are separate from the
heater, so sheath degradation is unlikely.
On March 9, 2005, at ANO Unit 2, heater sleeve leakage was found. This issue is
described by Report #214924. [ICES Report #214781]
On March 12, 2005, at ANO Unit 2, heater sleeve leakage was found. This issue is
described by Report #214924. [ICES Report #214843]
On March 16, 2005, at ANO Unit 2, leakage was identified from pressurizer heater
penetrations during 2R17 due to PWSCC of Alloy 600 material. Ten total penetrations had
leakage (P1, V1, P2, J2, U3, G3, H4, C4, and X3). The MNSA 2 is the planned repair method.
Penetration X1 contains a plug and will be repaired using a mid-wall nozzle repair. [ICES
Report #214924]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On March 28, 2005, at Palo Verde Unit 2, pressurizer heater bank B tripped on a ground
fault and 2MRCEB10 pressurizer heater was non-functional. A jumper was used to install a
spare heater into the failed heater’s position. The B10 heater is a Watlow heater. 2MRCEA12
was installed electrically. During U2R11 all heater sleeving was removed and all heaters were
removed. 25 new General Electric heaters were installed and 9 heaters from Unit 2 were
recycled. The recycled heaters had the following non-functionalities B11 (December 30, 2003),
87
A10 (September, 16 2004), and B10 (March 28, 2005). These heaters were removed and plugs
were installed. [ICES Report #215123]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible. These heaters were removed from service.
On April 10, 2005, at Millstone Unit 2, one heater sleeve showed minor leakage at
penetration B-2 due to PWSCC of Alloy 600 material. One axial indication was found. The
sleeve was repaired using a MNSA. A pressurizer replacement was planned for the next
outage (2R17). [ICES Report #215391]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On April 19, 2005, at Waterford Unit 3, boric acid was discovered near pressurizer
heater sleeves C-4 and D-2 due to PWSCC of Alloy 600 material. Two axially oriented flaws
were identified for C-4 but no indications were found for D-2. D-2 was determined to not have
an RCS leak. The leaking penetration was repaired using an Alloy 690 half-sleeve replacement,
as part of planned preventive maintenance for all Alloy 600 pressurizer sleeves. Guidance is
given in NRC bulletin 2004-01. [ICES Report #215602]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from
the heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600
PWSCC.
On May 26, 2005, at Waterford Unit 3, Framatome/Thermocoax heaters installed in the
pressurizer ceased to function during refuel 13. Upon energizing, two heaters experienced
partial ejection of the epoxy in the receptacle area, six were non-functional due to grounding,
and several others experienced partial melting of the silicon type sealant material at the bottom
of the receptacle. The device had been modified by the manufacturer to enhance reliability and
make fabrication easier. The ability of the heater to remove heat from a sensitive electrical area
was reduced. Twenty-three heaters were replaced with spare and reusable Watlow heaters.
[ICES Report #216255]
Sheath Degradation Assessment: Because of early issues upon activation, sheath
degradation is unlikely, and the heaters in question are not in service. Still, non-functionality of
heaters is an indicator of potential sheath degradation.
On August 25, 2005, at Summer Unit 1, a heater control signal failed to start a
pressurizer backup heater bank due to an issue with a controller driver card. The card was
replaced and the heaters subsequently functioned as expected. [ICES Report #217513]
Sheath Degradation Assessment: The controller driver card is separate from the heater, so
sheath degradation is unlikely.
On December 3, 2005, at San Onofre Unit 2, a feeder breaker failed to close on
demand. The issue is described by Report #218959. [ICES Report #218909]
On December 3, 2005, at San Onofre Unit 2, a breaker for bank 2E129 failed. The issue
is described by Report #218959. [ICES Report #218908]
On December 7, 2005, at San Onofre Unit 2, a supply breaker (2B0602) was inoperable
for pressurizer heater bank 2E129 due to the combined effects of misalignment and
interferences between the breaker and the cubicle. The breaker was modified to eliminate the
interference. [ICES Report #218959]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
88
degradation is unlikely.
89
6.4
Pressurizer Heater Operating Experience (2006-2010)
On January 12, 2006, at Byron Unit 2, molded circuit breakers failed the thermal trip test.
This issue is described by Report #219382. [ICES Report #219381]
On January 12, 2006, at Byron Unit 2, the molded case circuit breakers 2RY03EB-A4A
and 2RY03EB-A4B (for pressurizer heaters) both failed the thermal trip test. The devices were
replaced. [ICES Report #219382]
Sheath Degradation Assessment: The circuit breakers are separate from the heater, so
sheath degradation is unlikely.
On February 13, 2006, a notice was issued regarding design deficiencies in the
Framatome/Thermocoax design of pressurizer heaters. [ICES Report #219837]
On March 18, 2006, at Palo Verde Unit 1, 1EPGBL32E3 class B pressurizer heater
breaker failed to trip due to a failed shunt trip coil. The shunt trip coil and breaker maintenance
were performed. [ICES Report #220347]
Sheath Degradation Assessment: The shunt trip coil and breaker are separate from the
heater, so sheath degradation is unlikely.
On March 22, 2006, at Palo Verde Unit 1, pressurizer heater 1MRCEA05 became nonfunctional. This issue is described by Report #222893. [ICES Report #220408]
On March 25, 2006, at Crystal River Unit 3, pressurizer heater banks D and E were
energized. The level 4 alarm for RCDP-3, breaker 5 tripping was received. The device was
replaced. [ICES Report #220468]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 4, 2006, at San Onofre Unit 3, degradation was found in the heaters
manufactured by Framatome ANP/Thermocoax, after 15 months of operation. Three heaters
had been known prior to be non-functional. Many of the Generation I Framatome heaters had
been removed and replaced prior to restart from the mid-cycle outage with Framatome
Generation II heaters. [ICES Report #220623]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible.
On April 6, 2006, at ANO Unit 2, a drawing showed a protrusion of the tallest heater in
the pressurizer as 13 inches above the upper support plate when it should have been 17.4
inches above the support plate. The incorrect dimension adversely affects heater margin.
[ICES Report #220652]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
unlikely.
On April 19, 2006, at Braidwood Unit 1, boric acid accumulation was found on the
bottom of the pressurizer. This issue is described by Report #220951. [ICES Report #220860]
On April 25, 2006, at Braidwood Unit 1, leakage was found from IGSCC of the stainless
steel pressurizer heater sleeve number 52, through a locally sensitized section of Type 316
stainless steel base material. The failed sleeve portion was removed, plugged, and sealed. All
78 sleeves and couplings were visually inspected, and number 52 was confirmed to be the only
90
leakage source. [ICES Report #220951]
Sheath Degradation Assessment: Sheath degradation is unlikely due to the degradation
being IGSCC of only the heater sleeve material. Still, this is a significant material degradation
event. Events during which sleeve rupture occurs may have associated sheath degradation. In
this incident, however, the heater was still operable, reducing the likelihood of present sheath
degradation.
On May 21, 2006, at Catawba Unit 1, a fuse failed for pressurizer heater NCEHPZRB for
the 1B group. The piece part was replaced. [ICES Report #221383]
Sheath Degradation Assessment: The fuse is separate from the heater, so sheath
degradation is unlikely.
On May 30, 2006, at Diablo Canyon Unit 1, potential debris was noted on the pressurizer
heater cables. Tray covers were installed to protect the heater cable insulation from breaking
off during s loss of coolant accident. [ICES Report #221509]
Sheath Degradation Assessment: The cable insulation is separate from the heater, so sheath
degradation is unlikely.
On June 10, 2006, at ANO Unit 1, the three amperage meters for the proportional heater
bank 1 cabinet C117 had a disparity in readings due to a defective circuit. No specific resolution
of the issue was provided in the report. [ICES Report #221669]
Sheath Degradation Assessment: The amperage meters are separate from the heater, so
sheath degradation is unlikely.
On June 13, 2006, at Ginna Unit 1, the backup heater breaker tripped and failed to close
due to a shunt trip assembly failure to reset. A spare breaker was installed and setup for the
heater. [ICES Report #221708]
Sheath Degradation Assessment: The breaker and shunt trip assembly are separate from
the heater, so sheath degradation is unlikely.
On June 15, 2006, a document was issued, NSAL-06-8, with regard to circumferential
flaws in Combustion Engineering designed pressurizer heater sleeves. [ICES Report #221735]
On June 25, 2006, at Catawba Unit 1, the pressurizer heater group 1C was not
operating properly due to an open fuse in the silicon controlled rectifier caused by moisture
intrusion. The fuse was replaced. Heaters 34, 63, and 63 were isolated and then bank C was
energized. It is unclear from the report whether the three heaters in question remained nonfunctional. [ICES Report #221896]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible.
On July 17, 2006, INPO released an information notice (IN 2006-27) on circumferential
cracking in stainless steel pressurizer heater sleeves for PWRs. This issue is related to the
Braidwood Unit 1 pressurizer sleeve issue from spring 2006. [ICES Report #227617]
On September 18, 2006, at Palo Verde Unit 1, a pressurizer heater became nonfunction. Nine Watlow heaters are installed in Unit 2 and twelve Watlow heaters are installed in
Unit 3. This issue is described by report #222893. [ICES Report #222906]
On September 18, 2006, at Palo Verde Unit 1, heater element 1MRCEA14 became nonfunctional. During U1R12, all 36 pressurizer heaters were replaced with new heaters fabricated
91
by Watlow. Several heaters became non-functional in less than 6 months. The heaters were
electrically isolated. The MRCEA05 heater was analyzed and came back with IGSCC results
on the outside surface. Five failed heaters were sent to Westinghouse for analysis. Nonfunctional heaters were as follows: 1MRCEA05 (March 22, 2006), 1MREAB18 (June 27, 2006),
1MRCEB09 (July 31, 2006), 1MRCEA14 (July 31, 2006), B/U Bank-1 BRKR-1 Non-Class
(September 18, 2006), B/U Bank-1 BRKR-1 Non-Class (September 18, 2006), B/U Bank-1
BRKR-1 Non-Class (September 18, 2006). The Unit 1 heaters (thirty-five of thirty-six) were
replaced with heaters manufactured by Doosan (except location B18). Location B18 was
unable to be removed and the heater was plugged. [ICES Report #222893]
Sheath Degradation Assessment: The heaters became non-functional, so sheath
degradation is possible.
On October 18, 2006, at Braidwood Unit 2, the pressurizer vessel bottom and heater
sleeve inspection was delayed due to an unanticipated insulation configuration on October 16,
2006. This resulted in an unplanned increase in both work scope and radiation dose. [ICES
Report #223384]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
unlikely.
On November 15, 2006, at Summer Unit 1, breaker XSW1DB 05 for pressurizer heater
backup group #2 had a spurious trip. The issue is described by Report #213819. [ICES Report
#223870]
On February 19, 2007, at Palo Verde Unit 2, a non-class pressurizer heater did not
energize due to a maintenance induced failure (misaligned contact assembly). The misaligned
contact assembly was realigned and rested satisfactorily. [ICES Report #225182]
Sheath Degradation Assessment: The contact assembly is separate from the heater, so
sheath degradation is unlikely.
On March 21, 2007, at North Anna Unit 2, a white substance was found on the
pressurizer heaters that through isotopic chemical analysis was found to not be from RCS
leakage. The substance is thought to have been from the soldering process (potentially a white
brazing flux). Plans to clean up the deposits on the heater sleeves are being developed to
ensure that visual inspection for coolant leakage are effective. [ICES Report #225731]
Sheath Degradation Assessment: No heater issue was found, so sheath degradation is
unlikely.
On April 14, 2007, at Robinson Unit 2, a white substance was found on pressurizer
heaters. It was sent for analysis and confirmed to not be boric acid residue. It was determined
that the substance was potentially from old insulation. [ICES Report #226162]
Sheath Degradation Assessment: No heater issue was found, so sheath degradation is
unlikely.
On May 4, 2007, at Seabrook Unit 1, a circuit breaker tripped 20 minutes after
energizing. This issue is described by Report #226523. [ICES Report #226530]
On May 4, 2007, at Seabrook Unit 1, the circuit breaker 1EDUS23AM4 for heater control
group breaker tripped approximately 20 minutes after energizing. The breaker was replaced and
recalibrated. [ICES Report #226523]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
92
On May 5, 2007, at Callaway Unit 1, a breaker tripped for the pressurizer heaters,
possibly due to noise or spikes from the pressurizer level and pressure transmitter, resulting in a
false trip signal. The item was reracked and returned to service. [ICES Report #226555]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 9, 2007, at Millstone Unit 2, a number of backup pressurizer heaters
became non-functional. Five heaters were found to be non-functional and an additional two
heaters were later documented as being non-functional. Hard grounds were identified on
several breakers. A number of heaters are planned for replacement. [ICES Report #228372]
Sheath Degradation Assessment: The heater became non-functional, so sheath degradation
is possible.
On September 12, 2007, at Waterford Unit 3, the gate trigger unit for the controller of
pressurizer proportional heater bank #2 failed. The failed gate trigger unit was replaced. [ICES
Report #228436]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
On September 12, 2007, at Robinson Unit 2, the control switch for pressurizer heater
backup group B was taken from auto to on to energize the heaters, but the heaters did not
energize, due to a breaker failing to close on demand. The inertial latch of the breaker may
have prevented the breaker from closing. The breaker was replaced. [ICES Report #228425]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 18, 2007, at Byron Unit 1, breakers for the backup pressurizer heater
banks A, B, and D had to be replaced due to issues with temperature. This issue is described by
Report #229025. [ICES Report #228546]
On September 21, 2007, at Byron Unit 1, breakers for the backup pressurizer heater
banks A, B, and D had to be replaced due to issues with temperature. This issue is described by
Report #229025. [ICES Report #228600]
On October 1, 2007, a document, NSAL-07-8, was issued with regard to high density
power heaters and their temperature limits relative to 800ºF and 900ºF limits imposed. [ICES
Report #228753]
On October 2, 2007, at Cook Unit 1, a silicon controlled rectifier for the pressurizer
heater circuit breaker tripped open, preventing the backup heater circuits from being energized.
The failed relay was replaced. [ICES Report #228771]
Sheath Degradation Assessment: The relay is separate from the heater, so sheath
degradation is unlikely.
On October 3, 2007, at Byron Unit 1, breakers for the backup pressurizer heater banks
A, B, and D had to be replaced due to issues with temperature. This issue is described by
Report #229025. [ICES Report #228802]
On October 3, 2007, at Farley Unit 1, white residue was observed on two heater
penetrations. The heaters were removed and non-destructive examination confirmed that the
93
sleeve pressure boundary was free of defects. The residue did not appear to be evidence of a
current RCS leak. [ICES Report #228793]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely.
On October 4, 2007, at Byron Unit 1, breakers for the backup pressurizer heater banks
A, B, and D had to be replaced due to issues with temperature. This issue is described by
Report #229025. [ICES Report #228805]
On October 8, 2007, at Byron Unit 1, breakers for the backup pressurizer heater banks
A, B, and D had to be replaced due to issues with temperature. This issue is described by
Report #229025. [ICES Report #228886]
On October 8, 2007, at Byron Unit 1, breakers for the backup pressurizer heater banks
A, B, and D had to be replaced due to issues with temperature. This issue is described by
Report #229025. [ICES Report #228887]
On October 10, 2007, at Byron Unit 1, breakers for the backup pressurizer heater banks
A, B, and D had to be replaced due to issues with temperature. This issue is described by
Report #229025. [ICES Report #228930]
On October 15, 2007, at Byron Unit 1, breakers for the backup pressurizer heater banks
A, B, and D had to be replaced due to issues with temperature. This issue is described by
Report #229025. [ICES Report #229024]
On October 15, 2007, at Byron Unit 1, breakers for the backup pressurizer heater banks
A, B, and D had to be replaced due to issues with temperature. This issue is similar to Report
#219382 for Unit 2. Many of the breakers had to be replaced. [ICES Report #229025]
Sheath Degradation Assessment: The breakers are separate from the heater, so sheath
degradation is unlikely.
On October 22, 2007, at Palo Verde Unit 1, heating element 1MRCEA11 became nonfunctional. A-11 is a non-class heater back-up #7. No further specific mention of resolution was
provided in the report. [ICES Report #229142]
Sheath Degradation Assessment: The heater became non-functional, so sheath degradation
is possible.
On December 24, 2007, at Byron Unit 2, breakers were found in the trip position. This
issue is described in Report #230081. [ICES Report #230078]
On December 24, 2007, at Byron Unit 2, breakers were found in the trip position. This
issue is described in Report #230081. [ICES Report #230079]
On December 24, 2007, at Byron Unit 2, breakers were found in the trip position. This
issue is described in Report #230081. [ICES Report #230080]
On December 24, 2007, at Byron Unit 2, breakers 2RY03EA-B1A and 2RY03EA-B4B
were found in the trip position after the operated notice the spray valve position did not appear
to be correct with the Group A energized heaters. The breakers 2RY03EA-B1A, 2RY03EAB4B, 2RY03EA-B4A, and 2RY03EC-B3A had been replaced in refueling outage B2R13 (spring
2007) and had been in operation for approximately nine months. The root cause determined
94
that excessive heat damaged the breakers. The four breakers were replaced. [ICES Report
#230081]
Sheath Degradation Assessment: The breakers are separate from the heater, so sheath
degradation is unlikely.
On February 19, 2008, at Indian Point Unit 3, the backup heater group 33 was placed in
service for group 31. This issue is described in Report #230926. [ICES Report #230936]
On February 19, 2008, at Indian Point Unit 3, pressurizer heater group 31 was
inoperable due to failed transformer. The transformer was sent to the vendor for root cause
analysis and a replacement transformer was installed to [ICES Report #230926]
Sheath Degradation Assessment: The transformer is separate from the heater, so sheath
degradation is unlikely.
On February 25, 2008, at Calvert Cliffs Unit 1, a leak was found on pressurizer heater
sleeve after finding residual dry boron residue. Ultrasonic examination confirmed the absence
of a circumferential flaw. The cause of this event was PWSCC of Alloy 600 material. The
sleeve was repaired by installation of a mechanical clamp. [ICES Report #231015]
Sheath Degradation Assessment: The pressurizer heater sleeves are separate from the
heater, so sheath degradation is unlikely. The sleeve degradation is due to Alloy 600 PWSCC.
On March 4, 2008, at Byron Unit 2, breaker 2RY03EB-A3B (breaker for pressurizer
heater group B heaters 9, 10, and 32) was found in the trip position due to heat input. The
breaker was replaced. [ICES Report #231147]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 21, 2008, at Vogtle Unit 1, pressurizer heater group A was inoperable during a
capacity test, where one of two series breakers for the heaters in groups A and C were in the
open position due to a maintenance error. The breakers had been tested by an electrician who
did not place the breakers back into the normal configuration of “On”. The breakers were closed
to restore operation. [ICES Report #231975]
Sheath Degradation Assessment: The breakers are separate from the heater, so sheath
degradation is unlikely.
On May 17, 2008, at Byron Unit 2, breaker 2RY03EA-B2B (breaker for pressurizer
heater group A heaters 23, 49, and 50) was found in the trip position due to heat input. The
breaker was replaced. [ICES Report #232438]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 6, 2008, at Catawba Unit 2, a loss of power to the blackout bus (2FTA) was
experienced that caused pressurizer heater group 2A to be unavailable. Group 2A is not
normally energized during normal plant operations. There was an apparent ground condition on
the Y-phase of switchgear 2FTA. The fault was cleared during Hi-Pot Testing. No subsequent
resolution is provided in the report. [ICES Report #233086]
Sheath Degradation Assessment: The blackout bus is separate from the heater, so sheath
degradation is unlikely.
On July 21, 2008, at St. Lucie Unit 2, the B1 pressurizer heater bank circuit PP-226 was
tripped. The breaker was reset and cycled, and subsequently operated properly. [ICES Report
95
#233278]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 28, 2008, at Byron Unit 1, a breaker 1RY03ED-B2B was in the tripped position
during operator rounds due to heat input. The breaker was replaced. [ICES Report #233354]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 11, 2008, at Palisades Unit 1, breaker for the pressurizer heater backup
was found in the tripped position due to a broken aux contact. The aux contact was replaced,
and the breaker was reset. [ICES Report #233965]
Sheath Degradation Assessment: The breaker and aux contact are separate from the heater,
so sheath degradation is unlikely.
On October 7, 2008, at Byron Unit 2, pressurizer heater breaker 2RY03EA-B3B (breaker
for heater group A heaters 7, 8, and 30) was found in the trip position. The cause of the breaker
issue was the damage from high heat input. The device was replaced. [ICES Report #234320]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On October 16, 2008, at Millstone Unit 3, control bank pressurizer heater had blown a
fuse and the breakers on one heater string (three elements) had opened. A heater element was
found missing potting compound and one connection tab. In total, five of seventy-eight control
and back-up heaters have been removed from service due to heater element failure (heater
non-functionality). [ICES Report #234466]
Sheath Degradation Assessment: The heater became non-functional, so sheath degradation
is possible.
On November 4, 2008, at Callaway Unit 1, breaker PG2101 for the group A backup
pressurizer heaters tripped open unexpectedly due to a bad F switch, but another occurrence
was due to the breaker not being locked out. No further resolution is provided in the report.
[ICES Report #234798]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 7, 2008, at Palisades Unit 1, a pressurizer heater breaker (EB-15) had
tripped due to a fault in the x-phase of the breaker. The breaker was replaced. [ICES Report
#235199]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 12, 2008, at Robinson Unit 2, breaker 52/10C tripped due to a damaged
cubicle rail that prevented the positioning/trip lever that allowed the breaker to back out of the
connected position. The breaker was replaced with a refurbished breaker that had a tighter fit.
The cubicle rail will also be replaced. [ICES Report #235282]
Sheath Degradation Assessment: The breaker and cubicle rail are separate from the heater,
so sheath degradation is unlikely.
96
On January 28, 2009, at ANO Unit 1, a continuous improvement was made in heater
performance. Multiple elements (three) were connected to one breaker, so even though a failed
element would not affect the operation of the other two elements, triggering the breaker to open
would still cause an issue for the other elements. [ICES Report #235861]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
unlikely.
On February 27, 2009, at ANO Unit 1, a heating element and an electrical termination
(lug/connector) failed. The issue is described in Report #236836. [ICES Report #236315]
On March 13, 2009, at Calvert Cliffs Unit 2, a pressurizer heater controller (gate trigger
unit) circuit card failed. Two controllers were replaced and the heaters operated properly.
[ICES Report #236534]
Sheath Degradation Assessment: The controllers are separate from the heater, so sheath
degradation is unlikely.
On March 31, 2009, at ANO Unit 1, an issue was noted with proportional bank II heater
due to either a heater element failure, a connector failure, or a wiring failure. No specific further
resolution was provided in the report. [ICES Report #236836]
Sheath Degradation Assessment: As this is a B&W design, the sheath degradation
assessment is not applicable.
On April 28, 2009, at South Texas Unit 2, a card failed that prevented pressurizer
heaters 2B, 2D, and 2E from energizing from the control room. Both the NPL and NQC cards
were replaced. [ICES Report #237343]
Sheath Degradation Assessment: The NPL and NQC cards are separate from the heater, so
sheath degradation is unlikely.
On May 28, 2009, at Indian Point Unit 2, the train 21 pressurizer backup heater did not
function due to an inoperable breaker caused by a defective level defeat switch.
Troubleshooting was performed on the 52/PBUI breaker and repair was the breaker control
relay trip was performed.[ICES Report #237877]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On June 8, 2009, at Byron Unit 2, pressurizer heater breaker 2RY03EA-B3B (breaker for
heater Group A heaters 7, 8, and 30) was found in the tripped position due to a poor connection
between a field cable and lug on the phase C load side. The device was replaced. [ICES
Report #238010]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 1, 2009, at Palisades Unit 1, a new style pressurizer heater terminal block was
installed to improve equipment reliability.[ICES Report #299596]
Sheath Degradation Assessment: As there is no heater issue, sheath degradation is unlikely.
On July 10, 2009, at Seabrook Unit 1, a component failed due to failure of a stab
connection for the circuit breaker that supports pressurizer heater 1RCE10. The breaker was
tested in numerous cycles, was refurbished, and returned to service. [ICES Report #238443]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
97
On August 19, 2009, at Byron Unit 2, pressurizer heater breaker 2RY03EB-A3A (breaker
for pressurizer heater group B heaters 9, 10, and 32) was found in the tripped position. The
breaker was left in the closed position because no deficiencies were found. [ICES Report
#239003]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 5, 2009, at Byron Unit 2, pressurizer heater breaker 2RY03ED-B2A
(breaker for pressurizer heater group D heaters 28, 55, and 56) was found in a tripped position.
The rear cable lug was properly connected to the breaker stab and the breaker was reset. The
breaker had been previously replaced in April 2007. [ICES Report #239224]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On September 9, 2009, at Byron Unit 2, breakers 2RY03ED-A2B and 2RY03ED-A6A for
group D pressurizer heaters. The breakers potentially failed due to high heat input. The two
breakers were reset and closed successfully. For the A2B breaker, the rear cable lug was
properly connected to the breaker stab. [ICES Report #239277]
Sheath Degradation Assessment: The breakers are separate from the heater, so sheath
degradation is unlikely.
On November 6, 2009, at Byron Unit 2, pressurizer heater breakers were found in the
tripped position due to installation deficiencies leading to high resistance connections, which
resulted in tripping the breaker thermally. Connection screws were tightened when they were
found loose. [ICES Report #240269]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 31, 2009, at Robinson Unit 2, a fuse for pressurizer heater backup group
B. The fuse was replaced and the heaters operated properly. [ICES Report #240955]
Sheath Degradation Assessment: The fuse is separate from the heater, so sheath
degradation is unlikely.
On March 19, 2010, at Surry Unit 2, pressurizer heater group A failed to energize on
demand both automatically and manually using the heater breaker control switch. The breaker
had not been shut during a previous event. The device was tested and returned to service.
[ICES Report #242157]
Sheath Degradation Assessment: The breaker control switch is separate from the heater, so
sheath degradation is unlikely.
On March 29, 2010, at Robinson Unit 2, for pressurizer heater backup group B feeder
breaker 52/6B was closed locally due to blown control power fuses. The fuses were replaced
and breaker 52/6B was cycled. [ICES Report #242342]
Sheath Degradation Assessment: The breaker and fuse are separate from the heater, so
sheath degradation is unlikely.
On May 9, 2010, at Fort Calhoun Unit 1, inspections to determine the integrity of heater
26 indicated a cracked sheath. The ground on the heater was found May 9, 2010. Visual
inspection of heater 26 in November 2011 did not identify the cracking. A crack was observed
on May 19, 2012. The heater sheath was removed and replaced. [ICES Report #293138]
98
Sheath Degradation Assessment: The heater sheath was confirmed to be degraded.
On May 27, 2010, at St. Lucie Unit 1, pressurizer backup heater receptacle connections
failed. Six heaters were identified that were the result of the deterioration of the epoxy potting
within the heater receptacle connection assembly. The heaters were put in service in 2005 with
the replacement of the pressurizer and operated for three cycles (54 months). There was no
sheath degradation. [ICES Report #243477]
Sheath Degradation Assessment: Sheath degradation was ruled out for this issue.
On June 1, 2010, at Oconee Unit 2, a main breaker for pressurizer heater 2RC_HE0002
tripped potentially caused by moisture in the power cables in containment. Status monitoring
was described to prevent this issue in the future. [ICES Report #243553]
Sheath Degradation Assessment: The breaker and power cables are separate from the
heater, so sheath degradation is unlikely.
On June 19, 2010, at Catawba Unit 2, a pressurizer heater 2NCEHPZRA was inoperable
due to loss of the blackout bus. An action was initiated to perform a review of sensitive
protective relays and to identify additional safeguards that should be implemented. [ICES
Report #243856]
Sheath Degradation Assessment: The blackout bus is separate from the heater, so sheath
degradation is unlikely.
On July 22, 2010, at Palisades Unit 1, a 480V molded case breaker was found tripped
during a containment entry. The tripped breaker was found with internal degradation which
most likely caused the trip of the breaker. The specific corrective action is not listed in the
report. [ICES Report #244301]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On October 30, 2010, at North Anna Unit 1, during start up, 1-EP-BKR-14C1-2
pressurizer heater group #5 tripped due to a latent human performance error. The breaker
overloads were reset to correct setpoints and the breaker was reinstalled. [ICES Report
#245964]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 5, 2010, at Seabrook Unit 1, a circuit breaker that supports pressurizer
heater 1RCE10 failed, potentially due to loose connections. The component was tested and
returned to service. [ICES Report #246080]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On November 29, 2010, at Oconee Unit 3, a fuse for immersion heater 3RC_HE0002
(heater group D) failed. The piece part was replaced. [ICES Report #246470]
Sheath Degradation Assessment: The fuse is separate from the heater, so sheath
degradation is unlikely.
99
Pressurizer Heater Operating Experience (2011-2014)
On January 4, 2011, at Millstone Unit 2, a heater element was suspected to be a repeat
failure. This issue is documented in Report #246910. [ICES Report #246919]
On January 4, 2011, at Millstone Unit 2, heater element P2C11 became non-functional
(Framatome heater). Pressurizer heater element B13 shorted to ground in January 2009. The
heater was replaced during 2R19 with a heater of the same design but with improved
manufacturing processes. [ICES Report #246910]
Sheath Degradation Assessment: Since the heater became non-functional, sheath
degradation is possible.
On January 15, 2011, at Oconee Unit 1, a pressurizer heater in pressurizer heater bank
2 tripped. No further information on resolution was provided in the report. [ICES Report
#247095]
Sheath Degradation Assessment: As this is a B&W design, the sheath degradation
assessment is not applicable.
On February 14, 2011, at Calvert Cliffs Unit 2, boric acid residue was discovered on
pressurizer heater sleeve N-3. The issue is described by Report #247617. [ICES Report
#247539]
On February 17, 2011, at Calvert Cliffs Unit 2, visual inspections identified a through wall
leak in the RCS pressure boundary at a weld join for pressurizer heater location N-3. The weld
metal used to replace the Alloy 600 base metal in 1990 was Alloy 82, similar to Alloy 600 (but in
weld metal form). The cracking was from PWSCC of Alloy 600-type material. The affected
heater and sleeve were removed and plugged. [ICES Report #247617]
Sheath Degradation Assessment: As this is an issue with the heater sleeve, sheath
degradation is unlikely. This issue involves PWSCC of Alloy 600-type material.
On April 6, 2011, at St. Lucie Unit 2, the heater element B1 became non-functional. The
issue is described in Report #249343. [ICES Report #248461]
On April 13, 2011, at St. Lucie Unit 2, the heater element B1 became non-functional.
The issue is described in Report #249343. [ICES Report #248594]
On April 28, 2011, at Braidwood Unit 2, cables supporting pressurizer heaters were
identified to have localized heat damage on a portion of the field cables. Breaker stab
assemblies and field coils will be replaced. [ICES Report #248879]
Sheath Degradation Assessment: The breaker and field cables are separate from the heater,
so sheath degradation is unlikely.
On May 25, 2011, at St. Lucie Unit 2, pressurizer heaters became non-functional due to
heater element issues subsequent to replacement. The non-functional heaters were B1 (April 6,
2011), C3 (April 13, 2011), D3 (April 27, 2011), C1 (May 25, 2011), and B2 (June 13, 2011).
The Unit 1 heaters are of “significantly different” design. The corrective action is to ensure
compliance from manufacturer for additional testing. [ICES Report #249343]
Sheath Degradation Assessment: Since the heaters became non-functional, there is
potential for sheath degradation.
On June 1, 2011, at Oconee Unit 1, it was determined that actuation of the thermal
100
overloads in circuit breakers supporting pressurizer heaters could occur during certain events.
Further specific resolution is not provided in the report. [ICES Report #249454]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On June 6, 2011, at Point Beach Unit 2, a breaker (2B-04) for the pressurizer heaters
tripped prematurely, causing the loss of pressurizer heater operability. The device was
replaced. [ICES Report #249516]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On June 7, 2011, at Oconee Unit 1, pressurizer heater bank 2 failed to operate from the
auxiliary shutdown panel due to a primary fuse blown for the 1B pressurizer heater group
caused by a fault with the control power transformer. The device was replaced. [ICES Report
#249553]
Sheath Degradation Assessment: The fuse and control power transformer are separate from
the heater, so sheath degradation is unlikely.
On June 13, 2011, at St. Lucie Unit 2, five of thirty pressurizer heaters were electrically
non-function after replacement. The issues occurred within three months of being placed in
service. Forensic processes were ongoing. [ICES Report #249634]
Sheath Degradation Assessment: The heater became non-functional, so sheath degradation
is possible.
On June 24, 2011, at Oconee Unit 1, testing of breakers for pressurizer heaters revealed
that three of the four 70 amp breakers installed tripped prior to reaching the maximum test
temperature of 267ºF. The piece parts were replaced. [ICES Report #249806]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On June 30, 2011, at Kewaunee Unit 1, the circuit breaker for a switchgear for
pressurizer heater backup group 1D failed to open on demand using the control room control
switch due to a control power fuse in the breaker being open. No further resolution was given in
the report. [ICES Report #249893]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On July 8, 2011, at Oconee Unit 1, pressurizer panel boards inside containment could
potentially trip on high ambient temperature. Administrative actions were taken to rectify the
situation. [ICES Report #250009]
Sheath Degradation Assessment: As this was an administrative issue, sheath degradation is
unlikely.
On July 28, 2011, a Technical Bulletin, TB-11-08 was issued with regard to the Sizewell
B sheath degradation. [ICES Report #250253]
On August 6, 2011, at Palo Verde Unit 1, B train class 1E pressurizer backup heaters
failed to turn on. The control received an alarm that the breaker (for heater 1MRCEA05) had
tripped. A new breaker was tested and installed to replace the failed breaker. [ICES Report
#250375]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
101
degradation is unlikely.
On August 11, 2011, at Oconee Unit 1, the pressurizer heater system was not compliant
with requirements for a loss of offsite power event. An alternate configuration was made to be
compliant. [ICES Report #250439]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
unlikely.
On September 26, 2011, at Robinson Unit 2, pressurizer heater backup group B heaters
failed to energize following a reactor trip. The issue is described in Report #251451. [ICES
Report #251077]
On October 7, 2011, at Watts Bar Unit 1, pressurizer heater backup group 1B-B was
attempted to be put into service, but the breaker for this group failed to close due to the closing
latch monitoring switch that had failed from poor design. The micro switch was replaced. [ICES
Report #251255]
Sheath Degradation Assessment: The breaker and micro switch are separate from the
heater, so sheath degradation is unlikely.
On October 20, 2011, at Robinson Unit 2, pressurizer heater backup group B failed to
energize following a reactor trip and would not reset when operators attempted to energize
them. The root cause was determined to be a control relay that cycles an associated
switchgear breaker. The control circuitry and breakers are not designed for rapid operation.
The fuse was replaced. [ICES Report #251451]
Sheath Degradation Assessment: The breaker, fuse, and control relay are separate from the
heater, so sheath degradation is unlikely.
On October 29, 2011, at Fort Calhoun Unit 1, pressurizer backup heater bank #1 group
#2 tripped immediately when closed. The breaker was “hard” to close so it was considered that
breaker might not have been appropriately closed. The breaker was retested and returned to
service. [ICES Report #251606]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On February 28, 2012, at Calvert Cliffs Unit 1, the pressurizer heater sleeve temporary
plug for location G4 was identified as missing during a visual verification. The pressurizer was
dry and after removal of all sleeves, temporary plugs were put into place. The “short plug” was
replaced with a “long plug”. [ICES Report #253163]
Sheath Degradation Assessment: The temporary plug is separate from the heater, so sheath
degradation is unlikely.
On March 18, 2012, at Wolf Creek Unit 1, the group 1 pressurizer backup heater breaker
was found in a tripped position due to a short in the load side cables. The circuit breaker was
replaced. [ICES Report #300806]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On April 14, 2012, at Oconee Unit 3, the failure of a push button prevented actions to
turn off the bank 2 pressurizer heaters. Operators used an alternate control switch to turn the
heaters off. No further resolution of the issue was provided in the report. [ICES Report
#253770]
102
Sheath Degradation Assessment: The push button is separate from the heater, so sheath
degradation is unlikely.
On May 23, 2012, at Fort Calhoun Unit 1, a pressurizer heater was found damaged.
The issue is described in Report #293138. [ICES Report #254068]
On June 20, 2012, at Robinson Unit 2, pressurizer backup group B heaters did not
energize because the control power fuses had blown for the control power for the 52/6B
breaker. The fuses were replaced. [ICES Report #300320]
Sheath Degradation Assessment: The control power fuses are separate from the heater, so
sheath degradation is unlikely.
On June 28, 2012, at Oconee Unit 3, pressurizer heater group D was not energized due
to a broken bracket on a starter/contactor. The piece part was replaced. [ICES Report
#293478]
Sheath Degradation Assessment: The bracket and starter/contactor are separate from the
heater, so sheath degradation is unlikely.
On July 24, 2012, at Millstone Unit 2, two proportional heaters had low capacity due to a
heater controller being out of calibration from a failed trigger circuit board. The trigger circuit
board was replaced. [ICES Report #310658]
Sheath Degradation Assessment: The trigger circuit board is separate from the heater, so
sheath degradation is unlikely.
On August 22, 2012, at Three Mile Island Unit 1, the plant was shutdown to repair a
pressurizer heater diaphragm leak. The pressurizer heater bundle was replaced and the unit
was returned to power. The root cause was PWSCC of Alloy 600 material. [ICES Report
#300485]
Sheath Degradation Assessment: As this is a B&W plant, the sheath assessment is not
applicable.
On November 5, 2012, at Ginna Unit 1, an unapproved crimper was used on pressurizer
heater cables that required a specific type of crimper. Corrective maintenance was performed.
[ICES Report #302172]
Sheath Degradation Assessment: The cable is separate from the heater, so sheath
degradation is unlikely.
On December 14, 2012, at Palo Verde Unit 2, a design challenge was revealed in the
class backup heaters after review of the electrical elementary diagram. This issue is described
in Report #302722. [ICES Report #302721]
On December 14, 2012, at Palo Verde Unit 1, a design challenge was revealed in the
class backup heaters after review of the electrical elementary diagram. This issue is described
in Report #302722. [ICES Report #302412]
On December 14, 2012, at Palo Verde Unit 3, a design challenge was revealed in the
class backup heaters after review of the electrical elementary diagram. The train B pressurizer
heater control circuits did not provide the capability to isolate the remote shutdown system from
a postulated control room fire induced circuit faults. Plant modifications are planned. [ICES
Report #302722]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
103
unlikely.
On January 29, 2013, at Palo Verde Unit 1, a design challenge was revealed in the class
backup heaters after review of the electrical elementary diagram. This issue is described in
Report #302722. [ICES Report #302729]
On January 29, 2013, at Palo Verde Unit 3, a design challenge was revealed in the class
backup heaters after review of the electrical elementary diagram. This issue is described in
Report #302722. [ICES Report #302732]
On January 29, 2013, at Palo Verde Unit 1, a design challenge was revealed in the class
backup heaters after review of the electrical elementary diagram. This issue is described in
Report #302722. [ICES Report #302733]
On January 29, 2013, at Palo Verde Unit 3, a design challenge was revealed in the class
backup heaters after review of the electrical elementary diagram. This issue is described in
Report #302722. [ICES Report #302735]
On January 29, 2013, at Palo Verde Unit 2, a design challenge was revealed in the class
backup heaters after review of the electrical elementary diagram. This issue is described in
Report #302722. [ICES Report #302731]
On January 29, 2013, at Palo Verde Unit 2, a design challenge was revealed in the class
backup heaters after review of the electrical elementary diagram. This issue is described in
Report #302722. [ICES Report #302734]
On February 27, 2013, at Braidwood Unit 2, breaker 2411 for Bus 241 to Bus 243
tripped. Pressurizer heater groups A and D are supplied through Bus 241 for power, so the plant
had a Tech Spec issue. The breaker was removed and replaced. [ICES Report #305473]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 6, 2013, at South Texas Unit 1, pressurizer heater backup group A feeder
breaker E1A1 failed to open due to binding of the arcing contacts. The breaker was removed
and replaced. [ICES Report #306077]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On May 14, 2013, at Vogtle Unit 1, pressurizer heater backup group A failed to energize
due to contact oxidation in a breaker. The contacts on the breaker were cleaned, allowing the
breaker to properly close. [ICES Report #306695]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On August 10, 2013, at Wolf Creek Unit 1, a capacitor in a gate trigger unit failed,
reducing the pressurizer heater capacity. A design change package was developed to replace
the complete controller system cabinet due to the obsolescence of the previous system. The
defective gate trigger unit was removed and repaired. The decision was made to not reinstall
the repaired gate trigger unit. [ICES Report #307590]
Sheath Degradation Assessment: The gate trigger unit is separate from the heater, so
sheath degradation is unlikely.
104
On September 30, 2013, at Fort Calhoun Unit 1, the contactor in the pressurizer heater
backup bank tripped and overheating and smoking were observed. The root cause was from a
metal oxide varistor shorting. The bank of heaters was declared inoperable. The metal oxide
varistor was replaced. [ICES Report #308352]
Sheath Degradation Assessment: The metal oxide varistor is separate from the heater, so
sheath degradation is unlikely.
On December 11, 2013, at Wolf Creek Unit 1, a pressurizer heater circuit breaker failed
during testing. The breaker was replaced. [ICES Report #310957]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On December 16, 2013, at South Texas Unit 2, pressurizer heater backup group 2B
failed to energize when turned on due to a breaker issue with the charging motor. The spring
charging motor was replaced. [ICES Report #309109]
Sheath Degradation Assessment: The breaker is separate from the heater, so sheath
degradation is unlikely.
On January 30, 2014, at Millstone Unit 2, a Tech Spec issue occurred because a
pressurizer proportional heater group breaker tripped while the opposite train diesel generator
was out of service. Administrative procedures were revised. [ICES Report #309971]
Sheath Degradation Assessment: As this is an administrative issue, sheath degradation is
unlikely.
On March 3, 2014, at Millstone Unit 2, the group 1 proportional heater power level was
lower than the Tech Spec requirement during a capacity test. A heater element had failed in
January and remained out of service. The controlled element was calibrated and a backup
heater element was connected in place of the non-functional proportional element. [ICES
Report #310253]
Sheath Degradation Assessment: A non-functional heater may be associated with potential
sheath degradation.
On March 17, 2014, at Turkey Point Unit 3, pressurizer heater #11 was confirmed to
have been leaking primary coolant as revealed by dry boric acid and rust staining. The leak
location is at the partial penetration weld joining the heater sleeve to the pressurizer vessel. A
half nozzle repair of the heater #11 sleeve was performed. The RCS pressure boundary was
moved to the outside of the pressurizer around the heater #11 penetration. [ICES Report
#310917]
Sheath Degradation Assessment: The stainless steel heater sleeve is separate from the
heater, so sheath degradation is unlikely. Sleeve damage can be associated with sheath
damage, but this issue was localized to the partial penetration weld.
On March 22, 2014, at South Texas Unit 1, nearly half of the termination cover boots
along with some Raychem sleeves were found to be cracked or damaged, compromising the
insulator function. The root cause is that heat stress caused by gaps in the blanket insulation
covering the bottom of the pressurizer. The damaged cover boots and sleeves were replaced.
[ICES Report #311620]
Sheath Degradation Assessment: The cover boots and sleeves are separate from the heater,
so sheath degradation is unlikely.
105