A SUMMARY OF CDBI FINDINGS
IN SERVICE TESTING OWNERS GROUP
December 2010
Clearwater, Florida
2
Introduction
• Component Design Bases Inspections (CDBIs) are conducted by
the NRC to review risk significant components and ensure that
these components are capable of performing their intended
safety functions.
• Inservice Testing (IST) is performed to assess operational
readiness and detect and act upon indications of degradation to
ensure that components are capable of performing their
intended safety functions.
▫ Although the objectives are similar, they are not identical.
• CDBI reports and findings indicate that there is an increasing
emphasis on testing and test margins to ensure that design bases
are adequately demonstrated to the satisfaction of the inspector.
▫ Increasingly, the capacity to meet design requirements has been
linked to inservice test (IST) programs.
▫ This expectation is heightened when a design basis test has not
been developed.
3
IST 101
• IST is intended to assess the operational readiness of
components that may be required to place the plant in
safe shutdown, maintain safe shutdown or mitigate the
consequences of a design basis accident.
▫ Assessment is accomplished by testing the component
when known to be operating acceptably at a point that
may be readily duplicated during subsequent tests.
▫ Reference values are established at this test point and
subsequent tests are then performed at this reference
point with the intent of:
1.
2.
Assessing continued operational readiness.
Detecting and taking actions in response to degrading
component conditions.
4
IST 101
• IST acceptance limits are determined by imposing a
specific band around the original reference values.
The multipliers used to derive these bands vary
dependent on both the component and the design of
the component.
• Limiting values for many IST components may also
be found in the UFSAR or Technical Specifications.
These limits are usually expressed in terms of
hydraulic performance for pumps and limiting
stroke time values for power operated valves.
▫ UFSAR or Technical Specification limits take
precedence over ASME Code derived limits.
5
Regulatory
• In December of 1997, the NRC issued Information
Notice (IN) 97-090 to alert licensees to potential
problems associated with safety-related pump
surveillance testing
• IN 97-090 cited Appendix B, Criterion XI, "Test Control”
10 CFR Part 50 and stated that licensees have
concentrated on inservice testing (IST) requirements
without ensuring that design requirements were met.
• IN 97-090 also stated that there are two applicable
primary requirements for safety-related pump testing:
1.
2.
To ensure that Criterion XI is met in that each safetyrelated pump achieves its minimum design-required
performance.
To ensure that each safety-related pump meets the
requirements of the ASME OM Code.
6
Regulatory
• Criterion XI of Appendix B to 10 CFR Part 50 requires
that a test program be established with written test
procedures that incorporate the requirements and
acceptance limits contained in applicable design
documents.
• Although licensees have established IST acceptance
criteria that meet the requirements specified in the
ASME Code, the criteria at some plants allowed safetyrelated pumps to degrade below the performance
assumed in the accident analyses.
7
Regulatory
• IN 97-090 summary:
▫ IST is intended to monitor degradation of
components; however, does not require that pumps be
tested at design-basis conditions.
▫ ASME tests may be used to verify compliance with the
ASME Code and the pump design requirements
contained in plant design-basis documentation such as
the FSAR.
▫ If the minimum design performance as specified in the
plant design documentation is more stringent than the
ASME Code acceptance criteria, then the test
acceptance criteria must be adjusted to the more
conservative requirements.
▫ Original plant design-basis calculations, or revisions to
these calculations must be properly integrated into
surveillance test procedure acceptance criteria.
8
NRC Inspection Guidance
• The NRC Inspection Manual, Attachment 71111.21
contains prescriptive guidance for the conduct of a
Component Design Bases Inspection.
• This manual defines design margin as the margin in the
design calculations related to the performance of the
component.
▫ For example, the analytical margin for a pump includes
flow and head required for the pump to perform its
function compared to the calculated capacity of the
equipment.
• The Inspection Manual also requires that the inspector
determine whether the design basis is met by the
installed and tested configuration.
▫ How this requirement is met is somewhat subjective.
Without clear guidance, CDBI related conflicts are likely as
evidenced by industry OE.
9
IN 2008-02, IST Specific
• In March of 2008, the NRC issued IN 2008-02,
Findings Identified During Component Design
Bases Inspections - Testing.
 Failure to account for EDG under frequency in pump
test acceptance criteria.
 Failure to appropriately account for instrument
uncertainties.
 Failure to ensure adequate test equipment.
 Failure to account for valve pressure locking effects.
 Failure to verify the minimum containment cooling
coil fouling factor assumed in analyses.
 Failure to consider the effects of service water
strainer plugging on flow rate.
10
The Dilemma
• The ASME OM Code does not discuss design basis
capability, but does refer to operational readiness.
Typically, the IST program is used in conjunction with
other programs to confirm operability.
• Without question, the design basis must be protected;
however, the details related to what constitutes an
adequate design basis test program, what elements must
be considered or where this program should reside are
confusing to many.
• IST limits should be established in a manner that
envelopes design limits.
▫ For example, IST limits must consider instrument accuracy
when establishing limiting values.
11
The Dilemma
• This example is just one of many that illustrates the
conflict that may exist and the basis for the differing
expectations between the regulating authority and the
IST Engineer.
• Examples of questions provided on the following slides
indicate an increasing need for ISTOG to become
involved and provide assistance to IST Engineers. To do
this, guidance may be needed or clarifications to existing
requirements developed to provide a uniform set of
rules.
▫ Currently, guidance is being provided in the form of
Operating Experience.
• It is important to maintain perspective - Design Basis
testing need not be established in IST Procedures.
12
Industry OE - Example #1
Concern
Instrument uncertainty is not
accounted for in development of
IST acceptance criteria.
Considerations
1. Instrument accuracy is
addressed by ASME; however,
uncertainty is not.
2. What is the overall impact when
additional penalties associated
with instrument drift, M&TE
equipment, temperature
changes, orifice plate tolerance,
etc. are factored into the total
error for a parameter using the
square root of the sum of the
individual errors squared
(SRSS) methodology?
3. Minimize the effects by
performing post test calibration
checks of test instruments.
13
Industry OE - Example #2
Concern
Instrument uncertainty is
unaccounted for in shaft speed
for variable speed pumps.
Examples:
1. Steam driven turbine pumps.
2. Variable speed motor driven
pumps.
Considerations
1. Account for instrument
accuracy for variable speed
pumps.
14
Industry OE - Example #3
Concern
Check valve acceptance criteria
lack adequate basis and does not
ensure design requirements are
met.
Examples:
1. Differential pressure does
not ensure that idle pumps
are not rotating.
2. Differential pressure does
not consider additional
stress on the pump shaft
when a start signal is
received.
Considerations
1. Assess check valve reverse flow
acceptance criteria and tighten
limiting values, if possible.
2. Supplement the closure test by
including an additional
requirement to verify idle
pumps are not rotating.
 For example:
The check valve acceptance
criteria is met when
measured differential
pressure is > 80 psid AND
the idle pump is observed
and is not rotating.
3. Develop calculations to bound
the limiting values.
15
Industry OE - Example #4
Concern
The effects of limit switch
settings used in determining the
open and closed positions of
valves is not factored into IST
acceptance limits.
Considerations
1. Reduce the limiting value to
account for limit switch error.
 MSIVs closure may provide
one of the more limiting
challenges.
2. Is this concern only relevant
when addressing closure?
3. Does this concern vary
dependent on the valve design?
4. Can ISTOG develop a product to
address this concern?
5. Input from AOV, MOV
Engineers would be helpful.
16
Industry OE - Example #5
Concern
The effects of EDG frequency
droop on pump and valve
performance. Most Technical
Specifications permit frequency
variations as low as 58.8 hz.
Examples:
1. Motor stall for MOVs.
2. Lower EDG frequency
translates to slower pump
speed.
Pump speed is directly
proportional to flow rate and
pump head squared.
Considerations
1. Incorporate the impact of the
lowest allowable EDG frequency
into pump and power operated
valve calculations.
2. Minimize the impact by revising
Technical Specifications to
impose a tighter band.
 Some plants have
incorporated a new limit of +
0.5hz.
▫ The upper limit restriction
is in response to recent
findings associated with
EDG over frequency
concerns.
17
Industry OE - Example #6
Concern
The station did not have a process in
place to evaluate or prevent
unacceptable preconditioning of IST
components.
1. The NRC utilizes Inspection
Procedure, Part 9900 to evaluate
a stations ability to prevent
unacceptable preconditioning.
2. The Inspection Procedure is more
detailed than public information
provided in the form of two
previous Information Notices.
▫
INs 96-024 and 97-016
addressed preconditioning, but
did not address the subject in
detail and in present terms.
Considerations
1. A procedure can easily be developed to
mirror the NRC Inspection
Procedures.
 ISTOG has already developed a
Position Paper.
2. There is a valid concern related to the
differing views offered by the original
INs and the subsequent inspection
procedure.
3. Also, many are unsure of the
requirement to adhere or commit to an
NRC Inspection Procedure,
particularly one that differs from
previous guidance and was not
formally introduced.
4. This is a work management concern
that has inappropriately burdened IST.
5. PM models for valves that are tested at
cold shutdown can be revised to obtain
an as-found stroke prior to
maintenance.
18
Industry OE - Example #7
Concern
Surveillance testing drained
water from piping for a safety
related system with no
provisions to ensure the system
was refilled. Air was found in
the system after the inspectors
questioned the condition.
Considerations
1. NRC GL 2008-01, Managing
Gas accumulation in
Emergency Core Cooling,
Decay Heat Removal, and
Containment Spray Systems
2.Review procedures that drain
systems or portions of
systems.
 Most vulnerable when
performing check valve
closure tests.
19
Industry OE - Example #8
Concern
• The licensee inappropriately
took credit for postmaintenance valve testing as
inservice testing. This was not
a valid inservice test because it
was not representative of
baseline valve performance.
Considerations
1. Once again, this is a
Preconditioning topic.
20
Industry OE - Example #9
Concern
• The licensee failed to
demonstrate how instrument
uncertainties were correctly
translated into technical
specification values or
acceptance criteria of
surveillance tests.
• HPCI and RCIC pump
performance test acceptance
criteria did not bound the
applicable design values.
Licensee verified pump
operability based on actual
performance test results.
Considerations
1. Include instrument error or
provide adequate test
margin.
 Be extremely careful with low
margin components.
21
Industry OE - Example #10
Concern
• The licensee failed to ensure
that the turbine driven
emergency feedwater (EFW)
pump steam admission valve
inservice tests had stroke time
acceptance criteria that
incorporated design basis
requirements. The licensee
restored the valve to its design
basis stroke time range.
Considerations
1. Include instrument error or
provide adequate test
margin.
2.A firm understanding of
design basis requirements is
necessary.
▫ For older plants, making
this determination may be
challenging.
22
Industry OE - Example #11
Concern
• The licensee had not verified
the adequacy of design for the
turbine driven AFW pump.
Specifically, the pump
hydraulic analysis was nonconservative, but was used to
verify adequacy of surveillance
test acceptance criteria for
pump minimum discharge
pressure.
Considerations
1. Include instrument error or
provide adequate test
margin.
2.Post test calibration checks of
M&TE.
3.Ensure that variance around
the reference band is
included in these
determinations.
▫ It may be necessary to
restrict the allowable
variance.
 This will also result in
more consistent test
results.
23
SUMMARY
• Systems and components are designed and
operated, as described in the current licensing
basis and incorporate design margins, to ensure
that some loss of quality does not lead to
immediate failure.
• Current licensing basis includes commitments to
specific codes and standards, design criteria, and
some regulations that also dictate margins.
• Conservatism is typically incorporated into test
criteria to ensure that a partial loss of quality
does not immediately impact component
operability.
24
SUMMARY
• The problem for the IST Engineer and station
personnel is that 10 CFR Part 50, Appendix B,
Criterion XI requirements applicable to Test
Control is subjective.
• A better understanding is required for station
personnel to meet governing expectations.
▫ For this to occur, the expectations must be clear
and concise.
▫ The Station may then determine the appropriate
manner to meet these expectations.