Fukushima-Daiichi NPP Accident

Koji OKAMOTOThe University of Tokyo
okamoto@n.t.u-tokyo.ac.jp

IAEA Safety Fundamentals (SF-1)
The fundamental safety objective isto protect people and the environment
from harmful effects of ionizing radiation.
Principle 1: Responsibility for safety
Principle 2: Role of government
Principle 3: Leadership and management for safety
Principle 4: Justification of facilities and activities
Principle 5: Optimization of protection
Principle 6: Limitation of risks to individuals
Principle 7: Protection of present and future generationsPrinciple 8: Prevention of accidents
Principle 9: Emergency preparedness and response
Principle 10: Protective actions to reduce existing or
unregulated radiation risks
http://www-pub.iaea.org/MTCD/publications/PDF/Pub1273_web.pdf

IAEA Safety of Nuclear Power Plant (NS-R-1)
Defense-in-Depth Concept

Defense-in-Depth Concept
1. Prevent deviations fromnormal operation
2. Prevent from escalating toaccident
3. Prevent core damage orsignificant off site release
4. Mitigate the consequenceof accident
5. Mitigate radiologicalconsequence

5 layer of DiD

Emergency response

Sever Accident

Design Basis Accident

Anticipated Transient
Accident

Design, Operation,
Maintenance,…

IAEA Safety of Nuclear Power Plant (NS-R-1)

1. Prevent deviations fromnormal operation
2. Prevent from escalating toaccident
3. Prevent core damage orsignificant off site release
4. Mitigate the consequenceof accident
5. Mitigate radiologicalconsequenceeventEarthquake&NPP

M9.0
3/11 14:46

１号機
２号機
３号機
４号機
５号機
６号機

Higashidori 1,100MW, 2005
Onagawa #1 524MW, 1984
#2 825MW, 1995
#3 825MW, 2002
Fukushima #1 460MW, 1971
Daiichi#2 784MW, 1974
#3 784MW, 1976
#4 784MW, 1978
#5 784MW, 1978
#6 1,100MW, 1979

1,100MW, 1978

Fukushima #1 1,100MW, 1982
Daini
#2 1,100MW, 1984
#3 1,100MW, 1985
#4 1,100MW, 1987
Tokai-Daini

Google map

南北
NSEW
東西
UD
上下

Extract from NISA HP

Ratio of Measured Maximum Acceleration
to Seismic Design Acceleration (Ss)on Base mat

１号機
２号機
３号機
４号機

1.4
1.2
1.0
0.8
0.6
0.40.2

東海第二0.0

1号機
2号機
3号機

Important Components have no damage
Seismic Design worked well, under current knowledge#1 #2 #3 #1 #2 #3 #4 #5 #6 #1 #2 #3 #4
Higashi Onagawa FukushimaFukushima- Tokai（方向不明）
女川福島第一
福島第二
DoriDaiichi
DainiDaini（記録が途中まで）

東通

Seismic Design on Fukushima Daiichi• Seismic Response Analysis– Almost elastic response for Buildings– Simulation shows no damages on safety related
Systems– Walk down for unit #5 found no damages onimportant components• Plant Parameter Evaluation before Tsunami– Parameter shows no leakages on primaryboundaries.
– Simulation correctly explain the responses ofcooling systems without any damages.
NISA meeting (Dec. 9, 2011)
Plant has no significant damage by Earthquake

Offsite Power lost

Offsite Power lost
Offsite Power lost
Offsite Power lost
Offsite Power lost
Offsite Power lost
Offsite Power lost

DiD2non-emerg. M/C Fire

Status of NPPs after Earthquake
Operation
DiD1
Onagawa #1 Full-power Shut-down#2 Start-up
Shut-down#3 Full-power Shut-down
Fukushima #1 Full-power Shut-down
Daiichi #2 Full-power Shut-down#3 Full-power Shut-down#4 Outage#5 Outage#6 Outage
Fukushima #1 Full-power Shut-downDaini#2 Full-power Shut-down#3 Full-power Shut-down#4 Full-power Shut-down
Full-power Shut-down
Tokai-DainiOnagawa after Earthquake

Tsunami heightTsunami

想定Estimatedtsunami
敷地高LandheightRun upwww.tohoku-epco.co.jp/news/atom/1183294_1065.html

Non-emergent M/C for Unit #1 had a fire

No damage for Class-S System Structure & Component (SSC)
A few damages for Class-B & C SSC

m16
14121086420

Higashidori Onagawa #1-4 #5-6 Fukushima Tokai-Daini（2.6m >）
Fukushima DainiDaiichi
Design against Tsunami was failed, causing Accidents

Status of NPPs after Tsunami

1D/G×DiD3 DiD4(AM)DiD5(Emergency)
Onagawa #1#2 2D/G×#3
Fukushima #1
SBO, LUHS Core Damage, Hydr. Exp.
Daiichi #2
SBO, LUHS Core Damage#3
SBO, LUHS Core Damage, Hydr. Exp.
#4
SBO, LUHS
Hydr. Exp.
#5
SBO, LUHS#6
LUHS
Fukushima #1
LUHS
Daini
#2
LUHS
#3
#4
LUHS
Tokai-Daini

Tokai-Dainiwww.meti.go.jp/press/2011/04/20110407003/20110407003.pdf<Protect Wall(7.0m)(Sealing was not enough)Sea water leakage
through cable pit

Emergency pump (S) Main Cooling Emergency pump (N)PumpTsunami(6.3m)

Fukushima-DainiSea water pump  damaged (except #3)
D/G  unit #1,#2 damaged
http://www.meti.go.jp/press/2011/04/20110413006/20110413006.pdf

Est. +5.2m
Height +12m
Tsunami+6.5～7m
South #1 +14m

○ ×Power, Cooling

○×○
1/3
6/7

○
××
×
1/3

#1

○
×

○
×*
×*
×*
○
○
2/3
4/5

#2

○
1/2

○
×*
○
○
○
○
2/3
7/7

#3

○
×○
×*
×*
○
○
○
2/3
4/5

#4

Status of Fukushima Daini after Tsunami
Offsite PowerEmergency D/G
A/C: Air-cooled*: cooling pump flooding

M/C (Emergency)
M/C (non-Emrg.）
P/C (Emergency）
P/C (non-Emrg.）
DC battery
Seawater Pump

Sea
water

Fukushima-Daini #1

Pump

Heat exchanger

LUHS Declared(Mar. 11, 18:33)

Pump

Motor
Power Panel×
×
×

Sea
water

Fukushima-Daini #1

S/C temp.  increase

S/CControl Rod

Fuel

R/V

C/V

Loss of Ultimate Heat Sink

Valve

Just after tsunami(Mar. 11, 15:34)

RCICTurbine
pump

Cooled by RCIC
(Mar. 11, 15:36)

C/V
R/V

Heat exchanger

Pump

Motor
Power Panel×
××(Mar. 12, 06:20)
Auxiliary Water Injection

MUWC,MUWP,..

waterPump(Mar. 12, 00:00)
ter MUWC
wa

Loss of Ultimate Heat Sink

Valve

Fuel

S/C

Control Rod

Accident Management

RaptureDisk

Ready for Vent
(Mar. 12, 18:30)

Depressurization(Mar. 12, 03:50)

S/C

Control Rod

Fuel

R/V

C/V

Loss of Ultimate Heat Sink

tsunami

RCIC

3/13

3/15

3/19

Cold shutdown
3/17

S/C Press. (kPa)

3/17

Sea
water

Fukushima-Daini #1

Pump

Heat exchanger(Mar. 14, 01:24)

Pump

replace

Motor
Power Panel×Power Car
P/C

Fukushima-Daini #1
Recovery fromLoss of Ultimate Heat Sink

Japanese government Report for IAEA (Sept. 2011)

3/19

S/C Temp. (C)RHR restart

3/15

Depressurization

Reactor Pressure [MPa]Valve

Cold Shut-down(Mar. 14, 17:00)

80
3/11
300

3/13

S/C cooling lost

Aux. water

Vent ready

0140

0
3/11

Summary for Loss of Ultimate Heat Sink
Accident Management at Fukushima-Daini NPP
is a good practice to learn lots of things.
1. LUHS has relatively large time margin
if AC power is available.
2. Complete SBO should be prevented in any
conditions.
3. To reduce the recovery term, backup
components should be prepared onsite/offsite.
4. Seawater pump should be installed inwaterproof building.
5. Air-cooling System might be considered for
improving the reliability of heat sink,especially, S/C and Spent Fuel Pool.

C/V
R/V
Steam
Fuel rod

water

Fire extinguisher

water

Alternative water injection:
cooling fuel decay heat

Vent: prevent C/V overpressure failure(To mitigate SA, all resources should be applied.)

Accident Management

Vent

steam

condense

C/V
R/V

Vent trial for Unit #1
Mar. 11, 15:37 Tsunami
Mar. 12, 00:06
Prepare for Vent
Mar. 12, 05:46 ~ 14:53
Water Injection byfire extinguisher car(Total 80ton)
Mar. 12, 15:35
Hydrogen Explosion
Mar. 12, 19:04
Sea water injection
http://www.tepco.co.jp/cc/press/betu11_j/images/110618l.pdf

ventFire car

Mar. 120:06 Prepare for Vent (by Station mgr.)
9:15 MO-V210 25% Open
9:30 AO-V90 Cannot approach
10:17 At operation room, V90 Open
14:00 Compressor operation(AO-V72)
14:30 Vent Success（D/W 0.750.58MPa）
http://www.tepco.co.jp/cc/press/betu11_j/images/110618l.pdf
15:35 Hydrogen ExplosionFukuichi Live Camera System

Steam were seen for the Vent from 14:30
at 15:35, Hydrogen Explosion at Unit #1
http://www.youtube.com/watch?v=y5FtdES8of0

Fuel rod

Steam

R/VC/VwaterFire carwaterfor reducing the radioactive risk

Filtered Vent Systemfor Valve operation and Instrument(small amount of electricity)

Backup DC battery

Summary of Accident Management (Vent)

Vent
FilteredVentSystemsteam

condense
Even when the core damaged,
radioactive materials could be filtered.

One of the most important lessons isPreventing C/V rupture
Preventing Radioactive material exhaustFukushima Daiichi NPP#1 C/V 7bar + Vent + H2 Explosion ~1day#2 C/V 7bar + No Vent + C/V rapture ~3.5day~3day#3 C/V 6bar + Vent + H2 Explosion
Prevent over-pressure C/V rupture + Exhaust of RI and H2
 Filtered Containment Venting System (FCVS)

MOV

Stuck

Prevent over-temperature C/V rupture + H2 leakage
 Special Emergency Heat Removal System (SEHR)
JSME visit Leibstadt NPP, Swiss, on Nov.11,2011

FCVS (Filtered Containment Venting System)

MOV

NormalCloseRupture Disk(~3bar)

NormalOpen

DF > 1000 aerosol> 100 I2

Backfitted on 1992 for DiD4 (mitigation of Sever Accident)

Steam
Fuel rod

NaOH

Solubility pH10
Solubility pH7 ~50

Prevent C/V overpressure failure
Capture radioactive materials
Feed and Bleed under Long SBO & LUHS

rupture disk

FCVS (Filtered Containment Venting System)

entrance

JSME visit Leibstadt NPP, Swiss, on Nov.11,2011

SEHR (Special Emergency Heat Removal System)

D/G

underground
wells

Heat
Exchanger

Backfitted on late ‘70s for DiD3 (additional C/V cooling)
and DiD4 (mitigation of Sever Accident)

Steam
Fuel rod

Suppression Pool

D/GTwo D/G for SEHR

Defense-in-Depth and regulation

1. Prevent deviations fromnormal operation
Deterministic
Approach

Regulation
Law

Accident
Management

Deterministic＋Probabilistic
Approach

New Regulation

Future2. Prevent from escalating toaccident

Self-evaluation
by utilities
New Law

Present

4. Mitigate the consequenceof sever accident
Emergency
Law

Regulation system hardly takes new knowledge

3. Prevent core damage orsignificant off site release

5. Mitigate radiologicalconsequence•••••••

Japanese NRC written in DPJ manifesto had not been
discussed more than 2 years after DPJ took government
Nuclear Facility Installation Guideline is never revised almost
50 years.
Seismic Design Guideline had been revised on 2006,
more than 10 years after the Kobe Earthquake on 1995.
In the safety analysis, very old code are still used, because
new code needs huge efforts for both utilities and regulators.
Risk-informed Regulation is still under discussion for morethan 10 years.
Safety target was still midterm report around 10 years.
Regulation for Sever Accident is also under discussion for
more than 10 years.

KAIZEN is most important to sustain the safety.

Lessons Learned from the Accident• People and the environment should be protectedfrom risk of radiation• Nuclear Safety should be based on the Defense-inDepth Concept– Accident Management should be re-checked with serious
viewpoints– Complete station blackout should be prevented in any
conditions– Alternate AC and DC system should be prepared– To recover Loss of ultimate heat sink, backup components
should be prepared– Air-cooled System should be considered for cooling diversity– Filtered Vent might be useful to protect environment• Kaizen from the experience should be most importantto keep the nuclear safety