KIVI Symposium
The Hague, Netherlands
KIVI
Symposium
November 23, 2012
The Hague, Netherlands
November 23, 2012
Responses taken to fight the nuclear accident and to
mitigate the consequences
Hisashi NINOKATA
Professor, Politecnico di Milano
Department of Energy
CeSNEF-Nuclear Engineering Division
Nuclear Reactors Group
Professor Emeritus, Tokyo Institute of Technology
H. Ninokata - Nuclear Reactors Group
Focus on:
 The nuclear reactor core of units 1 – 3 of
Fukushima Daiichi NPS (1F1, 1F2, 1F3)
 The events in a first few days
H. Ninokata - Nuclear Reactors Group
KIVI Symposium
The Hague, Netherlands
November 23, 2012
Looking back at that time,
KIVI Symposium
The Hague, Netherlands
November 23, 2012
 Very little information available in a first few weeks with only
“circumferential evidences” --- ex. Radiation level in RB
 Heat balance calculations gave the idea
------------------------------------ With information disclosure under control, we (university
professors, in particular) were given a role to explain what
were going on at the 1F NPS, and at other NPS sites in Japan
− by all news media (TV, newspapers, radios, …)
− in particular on request by the public
− at symposiums, workshops, science cafes, lectures,
conferences, inside and outside Japan
H. Ninokata - Nuclear Reactors Group
Looking back at that time,
H. Ninokata - Nuclear Reactors Group
KIVI Symposium
The Hague, Netherlands
November 23, 2012
“No damage from the earthquake”
KIVI Symposium
The Hague, Netherlands
November 23, 2012
 The most likely assumption: the magnitude 9
earthquake did not damage reactor structure, pipes
and cooling systems, and the important safety
functions of all Fukushima Daiichi units of concern
were all maintained
 In fact, IAEA walkdown examination of the
Onagawa NPS, August 10, 2012, much closer to
the epi-center than Fukushima, has revealed the
nuclear power plant
Remarkably intact
H. Ninokata - Nuclear Reactors Group
Onagawa much closer to the epicenter
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November 23, 2012
130 km offshore from the NPS
H. Ninokata - Nuclear Reactors Group
Onagawa Plant
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November 23, 2012
H. Ninokata - Nuclear Reactors Group
Onagawa vs Fukushima
Ref. Isao Kato, Tohoku EPC, NUTHOS-9, Sept 12, 2012, Kaohsiung, Taiwan
H. Ninokata - Nuclear Reactors Group
KIVI Symposium
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November 23, 2012
Why at Fukushima Daiichi?
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November 23, 2012
 Onagawa Unit-1 PCV is Mark-I, Unit-2 to 3 are of improved Mark-I
and Fuk-2 four units are of Mark-II
The newer design, the better prepared for tsunami with new
knowledge on the tsunami history
 Fuk-1 units consist of BWR-3 and BWR-4 with Mark-I PCV
H. Ninokata - Nuclear Reactors Group
Why at Fukushima Daiichi?
KIVI Symposium
The Hague, Netherlands
November 23, 2012
 In particular the Unit-1 of Fuk-I (1F1) was constructed based on the
imported technology. After having digested the imported technology,
at least that was the way we thought, Japan has spent more efforts
in improvement and new development.
 Vulnerability of Fuk-I was pointed out against tsunami but has been
put aside, given its First of a Kind nature in Tepco, given that it was
constructed almost 40 years ago before many updates in regulations,
given that constructing new defense was extremely expensive.
The lessons would be useful for new nuclear countries who import
foreign technology for a starter.
H. Ninokata - Nuclear Reactors Group
On reflection
KIVI Symposium
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November 23, 2012
 Before the Fukushima Daiichi accident, we trusted the improved NPP
safety performance resulted in the health and safety of the public,
given any of the anticipated accident scenarios
 In Japan, more so with more strict operation and maintenance
requirements, with much more rigid and stronger anti-seismic
structure and design/construction
 After the Fukushima Daiichi, the need to prepare for the unexpected
and the unforeseen, including the beyond design basis, has become
a most important issue, but too belatedly
H. Ninokata - Nuclear Reactors Group
On reflection
KIVI Symposium
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November 23, 2012
 On reflection, it is evident that TEPCO and the broader nuclear
industries were not prepared for unexpected and highconsequence situations to respond
− to maintain critical safety functions; or
− to implement effective emergency response procedures and
accident management strategies
under the extremely severe conditions encountered at Fukushima
Daiichi. (INPO 11-005)
H. Ninokata - Nuclear Reactors Group
How severe was it?
KIVI Symposium
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November 23, 2012
 Beyond my description
 The following 7 slides are due to the courtesy of Dr.
Sakae Muto of TEPCO
H. Ninokata - Nuclear Reactors Group
Difficult to Access
On-site Testimony
 As the tremendous aftershocks occurred, with our full face masks still
on, we frantically headed off to the upper ground.
 While laying down cables at night, we were terrified that we might be
electrocuted due to the outside water puddles.
Wide crevices around there
Scattered debris & Fire hoses
Water injection by Fire Engine
Tank adrift on the road
14
Response in Dark Control Room
Shift Supervisor’s Testimony
 When the power source failed, I felt completely helpless.
 Heated discussions broke out among the operators regarding whether it
was important to remain in the control room or not.
Connected portable Batteries
15
Difficulty of Venting Containment(1)
Shift
Supervisor Testimony: As the work required high radiation
 “I asked for volunteers to manually open the vent valves. exposure,
I decided to not involve the young workers.
Young operators raised their hands as well; I was overwhelmed.”
Step1: SUCCESS
Exhaust
stack
Ruptured
MO
MO
210
at
0.549MPabs
0.549MPabsで破壊
D/W maximum
operating pressure:
D/W最高使用圧力
0.528MPaabs
0.528MPabs
Shift workers operation to
AO
manually open
AO
83 閉
Closed
valve
Venting
Solenoid
valve
AO
AO
1
Cylinder
Closed
ボンベ
AO
AO
90 閉
ベント実施圧力
pressure:
0.954MPabs
閉
Closed
IA
電磁弁
排気筒
Broke
disc
ラプチャーディスク
0.954MPaabs
RPV
D/W
ボンベ
Cylinder
IA
AO
MO
213
AO
AO
72 閉
Closed
電磁弁valve
Solenoid
Entry with self air set
16
Difficulty of Venting Containment(2)
Onsite Testimony
 When I climbed on top of the torus to reach for
the high positioned valve, the soles of my boots
quickly melted away.
Couldn't approach,
•High radiation
•High temperature
S/C vent
valve
(AO valve)
R/B B1F
Step2; Couldn’t approach…
(Hi Rad, Hi Temp.)
Step2’; Use mobile
compressor to remote
open.
17
Voices from Operators
 “In an attempt to check the status of Unit 4 D/G, I was trapped inside the security gate compartment. Soon the tsunami came and I was a few minutes before drowning, when my colleague smash opened the window and saved my life.”
 “In total darkness, I could hear the unearthly sound of SRV dumping steam into the torus. I stepped on the torus to open the S/C spray valve, and my rubber boot melted.”
 “The radiation level in the main control room was increasing 0.01 mSv (1 mrem) in every 3 seconds but I couldn’t leave—I felt this was the end of my life.”
 “I asked for volunteers to manually open the vent valves. Young operators raised their hands as well; I was overwhelmed.”
 “Unit 3 could explode anytime soon, but it was my turn to go to the main control room. I called my dad and asked him to take good care of my wife and kids should I die.”
18
Voices from Maintenance Staff
 “We saw our car crashed by the explosion of the Unit 3. If we had gotten on the car a few minutes earlier, all of us would have been dead.”
 We were replacing fire hoses when the explosion of Unit 3 occurred. We felt almost dying since many large rubbles were falling down to us. I urgently ran underneath a nearby fire engine. One of my colleagues got injuries in his leg and stomach.”
 “There were so many manholes opened by the tsunami. In order to lay cables, we had to proceed step by step carefully checking safety in the complete darkness.”
 “We were working in the Unit 3/4 control room when the explosion occurred. I was resigned to my fate. Dose rate was going up in the room after the explosion and we desperately tried to find places with lower dose rate.”  “After replacing an air cylinder for the PCV ventilation of Unit 3, I heard sound of steam and saw white mist around us. I got into a panic for a while.”
19
Sequence of Events after the Earthquake
The Great East Japan Earthquake around 14:46, Mar. 11th
Reactor SCRAM due to the Earthquake (Automatic Emergency Shutdown)
*1
Loss of Off-site Power, PCV Isolation, D/G Started-up
Operation after SCRAM as Intended
Operation after SCRAM as Intended
Tsunami struck Fukushima-Daiichi & Fukushima-Daini NPPs around 15:20~ , Mar. 11th
Units 1～3
Fukushima‐Daiichi
Unit 4
[Power] SBO w/o EDG LUHS
[Seawater system] Not available
H2O injection & heat transport to S/C via
HP system, e.g., RCIC/HPCI; DHR by IC
Units 5,6
[Power] D/G 6B start-up
[Seawater system] Not available
Power supply from Unit 6 to Unit 5
Water injection via LP system (Alternative) (Freshwater & Seawater)
Interrupted Injection and LUHS:
no route secured for heat removal
Cold Shutdown Condition (Dec. 16)
Fukushima‐Daiich 1~4
*1 D/G：Emergency Diesel Generator
Fukushima‐Daini
[Power] Off-site Power available
[Seawater system] Not available*2
Water injection via HP (Steamdriven) & LP systems
Water injection via LP system
Heat removal secured by temporary
power source & seawater pump
Heat removal secured by temporary
power source & motor replacement
etc.
Cold Shutdown (Mar. 20)
Cold Shutdown (Mar. 15)*3
Fukushima‐Daiichi 5,6
*2 RHR Seawater System
Fukushima‐Daini 1~4
*3 Fukushima-Daini Emergency State was Lifted on Dec.26tth
20
1F1
3/11
3/12
Earthquake/ tsunami
AM
IC on (A & B)
1503off man’lly
Rad level high in RBs
3am RPV failure ?
5am PCV failure?
Prep vent
1830 Open‐close
1F2
17~1800 TAF
2130 No access to IC
Core melt
(before mdngt)
3/13
PM
3/14
AM
PM
1430 Vent successfuil?
1536 H2 expl.
1502 RCIC on
w/o DC power
(>70 hours)
RCIC valves not compl closed?
11am try PCV venting (not success)
Car batteries for instrumen‐
tation and to open SRVs 1F3
(20 hours)
(14 hours)
1506 RCIC on
1136 RCIC off
RPV p falls down due to possible RPV failure – high peak p pulse: by MFCI ? Not likely but still under debate
1230 HPCI on
No coolant injection !
(21 hours)
0242 HPCI off
700 TAF then
Core metldown
started
841 PCV vent
(insufficient)
908 SRV open
925 sea water injection
Tsunami
SBO and LUHS
RCIC/HPCI
operation
W/o
UHS
Core melt,
RPV and PCV
failures
PM
AM/PM
S/C temp high (sat)
PCV pres high – rupture level set too high; difficult to vent and open SRV
PCV failure expcted due to excess temp
Highest rad level at the main gate
Alternate water injection line (CRD pump, SLC pump lines) and PCV vent lines damag’d
by H2 detonat.
1325 RCIC off
PCV p high
No makeup
until 1954
1730 TAF
1802 SRV op
1830 Whole core uncov.
No coolant injection !
Makeup was delayed until 1954
600 H2 expl? Near S/C or #4
Large scale release of rad‐
active materials
2000 a large portion of the core melt down to bottom head (est)
1100 H2 explosion
PCV venting was higher priority at TEPCO
1312 Sea water inject (for ~12 hrs: insufficient)
21
In Short,
Earthquake
S/C temp too high (no condensatn)
AM
3/15
KIVI Symposium
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November 23, 2012
• Loss Of Off-site Power (LOOP), MSIV closed = PCV isolation
• AC power from Emergency Diesel Generator (EDG)
• 1F1: Isolation Condenser (IC) automatic start
• 1F2, 1F3: Reactor Core Isolation Cooling (RCIC) - manual start for injection
• Primary Containment Vessel (PCV) Isolation RHR in service (RHR: Residual Heat
Removal)
• Decay heat removal as planned and on the way toward the cold shutdown mode
• Station black out (SBO), RHR inoperable resulting in Loss of Ultimate Heat Sink (LUHS)
• 1F2, 1F3 under LUHS conditions; 1F1 LUHS after IC termination and HPCI not operable
w/o aux cooling
• DC power lost except for 1F3
• 1F2 RCIC kept (its crippled) operation for 72 hours after tsunami w/o DC for valve control
(RCIC line isolation valves possibly partially stack open) but unstable
• 1F3 RCIC continued operation for ~20 hrs, followed by HPCI for 14 hrs
• Core heat-up and melt due to long duration of uncovery after RCIC/HPCI termination for
1F2 and 1F3
• Difficulties in RPV depressurization by Safety Relief Valve (SRV) opening w/o DC and
air pressure; first priority was on the PCV venting
• Resulting in the delay in alternate low pressure injection;
• By the time of Suppression Chamber (S/C) venting success, PCV failure due to high
temperature and pressure: LR (Large Release)
• By the time SRV relief valves opened, core damaged severely and H2 produced
The worst scenario --- PCV failure and radiological release.
H. Ninokata - Nuclear Reactors Group
Responses
to fight against the accident and to mitigate
the consequences
Unit 1 Isolation Condenser (IC) operation - 1
KIVI Symposium
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November 23, 2012
 The unit 1 had two ultimate heat sinks: sea water through RHR circuit and
air atmosphere through IC
 Two trains (A and B), four PCV isolation valves (see Fig. next slide)
 One train in use for the RPV pressure control before the tsunami by on-off
strategy
Train A
H. Ninokata - Nuclear Reactors Group
Train B
Heat sink
=atmosphere
Unit 1 Isolation Condenser (IC) operation - 2
Train A
Train B
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November 23, 2012
Heat sink
=atmosphere
 On tsunami attack, IC was off with the one outboard valve (DC driven)
closed; other valves were open but set to close with the loss of DC
power (PCV isolation)
 When tsunami came and caused the SBO, and soaked all the DC
batteries, all the valves were to close (fail to close); however,
 Actually the in-bound valves (AC-M driven) seemed to have remained
partially open due to the loss of AC power
H. Ninokata - Nuclear Reactors Group
Unit 1 Isolation Condenser (IC) operation - 3
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November 23, 2012
 At 6:27 pm, 3/11, with a dim revival of DC battery power, the
operators opened the outboard isolation valve, successful
 Then why the operators closed the valve again?
 Closed worrying about the damage to the IC if all water was lost out
of IC when the crew could not see the white steam coming out of
the IC (according to TEPCO) --- -- If they trusted the water level in the shell side of the IC (water tank)
and didnʼt stop the IC operation, the unit 1 core might have survived
without serious damage;
Note: even if the water tank is empty, no need to stop the IC operation
 After stopping the IC, the unit 1 was under the loss of ultimate heat
sink condition
H. Ninokata - Nuclear Reactors Group
Core Meltdown --- Unit 1
KIVI Symposium
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November 23, 2012
 Virtually nothing could be done for the Unit 1 with possible
misreading of RPV water level; and the control room indications
were unavailable; and no information fed and an optimism about the
IC status by the site ERC (Too much trust on the passive safety)
 In this respect, IC is not perfect passive
 Pointed out: Communication between control room and site ERC,
RPV water level reading, SAM drills/training … etc.
 Core meltdown after a few hours of IC termination (core uncover
started ~5pm, 3/11: fact much earlier than suspected)
 Radiation level was high already around 10PM in the RB
 Most of the fuels have melted and relocated to the bottom head,
some leaked through the CRD/instrumentation guide tubes into the
pedestal (CRD cavity room)
H. Ninokata - Nuclear Reactors Group
Core Meltdown --- Unit 1
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November 23, 2012
 3/11 21:30 IC valve was open (according to TEPCO)
 Access to IC had been difficult due to the high temperature and high
dose level
 PCV radiation level very high in the RB after midnight PCV venting
took longer time due to lack of ….
 3/12 14:30 Venting finally done
 3/12 15:36 H2 explosion is after the core melt
 TEPCO continues sea water injection from 3/12 19:04
PM office reportedly suggested (ordered?) to stop sea water
injection worrying recriticality event; TEPCO ignored the order
(but pretended to obey for 19:25-8:20)
However, as the day continues, Boron was added to address
criticality concerns.
H. Ninokata - Nuclear Reactors Group
GE BWR, Mark-I Nuclear Reactor
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November 23, 2012
H. Ninokata - Nuclear Reactors Group
After Tsunami SBO and LUHS [units 2 and 3]
Major components that do not require AC: RCIC/HPCI, SRV
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November 23, 2012
 Enthalpy build up in S/C

Boiling; no condensation
and no scrubbing
 PCV radiation level high
 PCV p and T high
 Need PCV venting
Temperatures
Pressure
Radiation
level
………..
HX
Sea
SBO
 LUHS
by tsunami
RHRS
RCIC/HPCI
 NO DHR
Source: Boling Water Reactor (BWR) Systems (Modified)
USNRC Technical Training Center
H. Ninokata - Nuclear Reactors Group
Core Meltdown --- Unit 2 (day 3/13-14)
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November 23, 2012
 High (and low!) pressure water injection by RCIC (w/o DC), enthalpy
build up in the suppression chamber (S/C) w/o heat removals
 At the site Emergency Response Center (ERC), PCV venting was a
first priority to dump the decay heat; then RPV depressurization by
SRV opening for coolant injection by alternate pumps --(reasonable)
 3/13 0810 Manually opened MO-valve of the PCV DW ventilation
line (25% open and stand-by)
 3/13 1100 To open the AO-valve of the S/C (WW) ventilation line,
the E-M valve was forced to open with the power from a mobile
generator in the control room; however, PCV pressure not high
enough to rupture the rupture disk on the S/C vent line
 3/14 1100 The H2 explosion (unit 3) damaged much of the S/C
vent line and fire engine injection line set ups
H. Ninokata - Nuclear Reactors Group
Core Meltdown --- Unit 2 (day 3/13-14)
KIVI Symposium
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November 23, 2012
 3/14 1325 RCIC off after 72 hours of staggering operation
PCV pressure high; no coolant make up until 19:54
 3/14 17:30 TAF
 An order of open SRV was issued by the PM office w/ an advise from
NSC
 Alternate water injection line was not yet ready when SRV opened
(3/14 18:02); and this SRV opening was suspected to accelerate the
core meltdown and result in very likely worse accident consequence
 3/15 Manually tried to open the DW vent line valve; a few minutes
later confirmed the valve closed; S/C vent not yet due to the low S/C
pressure
H. Ninokata - Nuclear Reactors Group
Core Meltdown and Release --- Unit 2
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November 23, 2012
 3/14 18:30 Whole core uncovery suspected
 Water injection delayed by ~2 hours (3/14 19:54)
 When injection was made, RPV pressure went high again due to
evaporation, disabling further injection
As the day continued, Boron was added to address criticality
concerns. Misunderstanding again on criticality
 Then failures of RPV are well suspected
 Followed by PCV failure due to high temperature (> 450 deg C) and
high pressure steam and gas mixture of high radioactivity, a large
scale radioactive materials release was well-suspected (3/15 ~ 8am)
H. Ninokata - Nuclear Reactors Group
Core Meltdown --- Unit 3
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 20 hours of RCIC operation, followed by the 14 hours of HPCI
operation;
 3/13 02:42 HPCI terminated; restarting efforts in vain
 Then, a long time duration of no coolant make up was
suspected – due to difficulties in opening ADS-SRVs
 PCV pressure high. During this period, safety valves opening
resulting in lowering the water level rapidly
 Efforts on venting and SRV opening were continued
 SRV did not open due to its mechanism w/o both air pressure
and DC power
 RPV back pressure high impedes the fire engine pump
injection
H. Ninokata - Nuclear Reactors Group
Core Meltdown --- Unit 3
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November 23, 2012
 3/13 ~8am Core exposure and meltdown afterward
 3/13 9:08am SRV opening – was said questionable because RPV
pressure rapid reduction before the reported SRV opening and after
strong pressure spike ~9am: due to MFCI (?) not likely but still
under discussion
 3/13 ~9:25am Borated fresh water injection (~ 1220)
 3/13 1300~ below TAF and not recovered

1312 Sea water injection --- could not recover TAF
 In spite of 12 hours of sea water injection efforts, ERC recognized
water level was kept below TAF

Circumferential evidence for RPV failures
 3/14 11am H2 detonation
H. Ninokata - Nuclear Reactors Group
1F1
3/11
3/12
Earthquake/
tsunami
AM
IC on (A & B)
1503off man’lly
Rad level
high in RBs
3am RPV
failure ?
5am PCV
failure?
Prep vent
1830 Open-close
1F2
17~1800
TAF
2130 No
access to IC
Core melt
(before mdngt)
3/13
PM
1F3
PM
AM
1536 H2 expl.
(>70 hours)
Alternate
water injection
line (CRD
pump, SLC
pump lines)
and PCV vent
lines damag’d
by H2 detonat.
11am try PCV
venting (not
success)
(20 hours)
(14 hours)
(21 hours)
1506 RCIC on
1136 RCIC
off
RPV p falls down
due to possible
RPV failure – high
peak p pulse: by
MFCI ? Not likely
but still under
36debate
1230 HPCI on
No coolant
injection !
PM
S/C temp high (sat)
PCV pres high –
rupture level set too
high; difficult to vent
and open SRV
PCV failure expcted
due to excess temp
1430 Vent
successfuil?
RCIC valves
not compl
closed?
Car batteries
for instrumentation and to
open SRVs
3/14
AM
1502 RCIC on
w/o DC power
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3/15
November 23, 2012
0242 HPCI off
700TAF then
Core metldown
started
841 PCV vent
(insufficient)
908 SRV open
925 sea water
injection
H. Ninokata - Nuclear Reactors Group
S/C temp
too high (no
condensatn)
1312 Sea
water inject
(for ~12 hrs:
insufficient)
No coolant
injection !
1100 H2
explosion
1325 RCIC
off
PCV p high
No makeup
until 1954
1730 TAF
1802 SRV op
1830 Whole
core uncov.
Makeup was
delayed until
1954
AM/PM
Highest rad
level at the
main gate
600 H2 expl?
Near S/C or #4
Large scale
release of radactive materials
2000 a large
portion of the
core melt down
to bottom head
(est)
PCV venting
was higher
priority at
TEPCO
Summary: LUHS Fukushima path to Core Melt - 2

KIVI Symposium
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November 23, 2012
After LUHS, PCV venting delay or failure with various reasons in dumping out the
accumulated energy from PCV was fatal, resulting in PCV damage

Subsequent delayed RPV depressurization with difficulties in opening relief
valves (SRV), w/o ADS, and alternate low pressure coolant injection difficult 
no coolant injection for long hours

Core exposure by continuous safety valves (SRV) opening and possible
depressurization due to possible leakage paths formation at RPV and other primary
boundaries (Unit 2 and 3)  Core melt

PCV failure -- Eventual lower PCV pressure -- due to most likely leakage path
formation in unit 2 (due to excess temperature, …)

Irony that the RPV depressurization was achieved by RPV failures and the PCV
venting due more likely to possible PCV failures that made the low pressure injection
possible and stabilized the degraded core with the atmosphere as ultimate heat
sink
H. Ninokata - Nuclear Reactors Group
1F1 core meltdown 3/11, 6-8pm
1F2 3/14~15, 1F3 ~ 3/13 in the morning
H. Ninokata - Nuclear Reactors Group
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November 23, 2012
Any success path to no core damage with LUHS?
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November 23, 2012
 Easy to say “if IC were not terminated”; “if RCIC and HPCI
were not stopped manually”, … , etc.
 These afterthoughts are not totally correct
 True that the reactor core seemed to have survived as long as
IC or RCIC/HPCI were operating but this does not mean that
the core could avoid core damage and melting w/o heat sinks
 F & B might be an answer as shown next but with many ifʼs.
H. Ninokata - Nuclear Reactors Group
Extremely slim success path w/o IC, RCIC/HPCI – under LUHS
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conditions -- F&B (SAM: Severe Accident Management)
November 23, 2012
I.
Depressurize RPV to 6~7 bars immediately after termination of IC, RICI
or HPCI forcing SRV (ADS) open to alternate pump capability --- with
DC + High Pres. Air or N2 required
II.
W/o delay, inject make-up water by alternate high power diesel pumps
or fire engine pumps
III.
Carry out PCV venting to release the enthalpy transported by the steam
out of the RPV into the atmosphere (heat sink) --- Filtered vent system
 Repeat these procedures; all these actions must be done smooth and
absolutely w/o delay when the level well above TAF
 Wait for RHRSW restoration
 If RHR is not restored for one week or so, it would be difficult to
keep the nuclear reactor core intact
H. Ninokata - Nuclear Reactors Group
Possible success path to save the cores
KIVI Symposium
The Hague, Netherlands
November 23, 2012
 Success possibility extremely slim
 Nevertheless, it seems to me that TEPCO was following the
path in principle
 Frequent strong aftershocks and tsunami warnings, tsunami
debris, no lighting in the darkness, w/o much information, …,
and reportedly some frequent intervenes hindered the
TEPCOʼs efforts at the site ERC and operation control room
activities from the very beginning of the accident
H. Ninokata - Nuclear Reactors Group
Natural and man-made hazards
KIVI Symposium
The Hague, Netherlands
November 23, 2012
 Extremely low frequency but large consequence Q event
 Why this tsunami risk was ignored?
− Very low frequency -- perception
− Underestimated the historical records
− Cost consciousness of TEPCO (non-nuclear sectors)
 Why resulted in the nuclear disaster?
1.
2.
3.
4.
(SBO=)LUHS; for BDBE, lack of diversity of ultimate heat sink
Lack of D-i-D 4th layer (mitigation of Q by Accident Management / Risk
Management after the breach of the 3rd layer)
Neglect of the TMI lessons, IAEA recommendation on regulatory system, …
…
 Due to
•
•
•
Overconfidence by regulatory body, utilities, nuclear professionals, .., in
DBE safety, high reliability in power grid system in Japan, …,
Complacency
4th Disaster
H. Ninokata - Nuclear Reactors Group
Information Control
KIVI Symposium
The Hague, Netherlands
November 23, 2012
 All these core meltdown facts were not disclosed
until May 15, 2011 by TEPCO Press Release
 TEPCO was well aware of the meltdown from the
beginning; so were NISA/JNES
 NISA/JNES did not or could not disclose the
information against their intention (my guess)
H. Ninokata - Nuclear Reactors Group
Post-Fukushima
KIVI Symposium
The Hague, Netherlands
November 23, 2012
 Immediately after the accident, installation of the
counter-measures against higher tsunami attack and
SBO, E/March 2011
 Roadmap to stabilization
 Many lessons learned and safety improvement;
hardware, and software, regulatory system
 Nuclear power plants are made much safer by putting
the lessons from Fukushima-Daiichi into practice
H. Ninokata - Nuclear Reactors Group
Post-Fukushima
KIVI Symposium
The Hague, Netherlands
November 23, 2012
 Still in the realm of the deterministic
 DEC and strengthened D-i-D 4th layer (software)
 Inevitable preparation for the unforeseen events and a
disaster that exceeds all worst-case scenarios;
Expect and prepare for the unexpected but how?
− Example: Tsunami disaster education for the children in
Kamaishi, a small coastal town (pop: ~ 40,000) in Iwate
Prefecture
H. Ninokata - Nuclear Reactors Group
KIVI Symposium
The Hague, Netherlands
KIVI Symposium
November 23, 2012
The Hague, Netherlands
November 23, 2012
END
Responses taken to fight the nuclear accident and to
mitigate the consequences
Hisashi NINOKATA
Professor, Politecnico di Milano
Department of Energy
CeSNEF-Nuclear Engineering Division
Nuclear Reactors Group
Professor Emeritus, Tokyo Institute of Technology
H. Ninokata - Nuclear Reactors Group