Accident at TEPCo’s Fukushima-Daiichi NPP- LL for Operator/Industry -Akira OMOTO, University of Tokyo & AEC

1

 Part I
Part IIKey vulnerabilities
Lessons learned for Operator/Industry

2

Key vulnerabilities (1)1. Protection against natural hazard and resultant CCF “SBO+
Isolation from UHS”
(Tsunami)
 Original Tsunami design basis upgraded in 2002
 Using JSCE (Japan Society of Civil Engineers) guideline Deterministic approach considering 4 elements (Historical data,
Seismo-techtonics, Near-coast active faults, Very far earthquake) Probabilistic Tsunami Hazard analysis
 Evolution in late 2000’s, but not considered as matured
 Methodology guide from JSCE (2009) using logic tree to represent
epistemic uncertainties
 Superposition of waves from multiple earthquakes with time delays(SBO) For extended time period Power center, battery: mostly
located in lower level of Tb/B
and submerged in seawater Only one EDG(1F6 air-cooled EDG) survived
33.11 earthquake

Statement by the Headquarter for Earthquake Research, 11March2011
The Committee evaluated earthquake motion and tsunami for the individual region off-shore…..but occurrence of the earthquake that is linked to all of these regions is “out of hypothesis”.
[SOURCE] http://www.jishin.go.jp/main/index-e.html The 2011 off the Pacific Coast of Tohoku Earthquake

Government Report to the IAEA, June2011 : Initiation from B, then propagated westwards toarea A, and further to the North and South. The Headquarter had alerted 99% probability ofoccurrence within 30 years for the A region with a magnitude of M7.5, but had not correctly
estimated the size of the source area (400km x 200km) nor the magnitude (M9) nor the amountof slip[SOURCE] Gov. Report to the IAEA, June20114

3.11 Earthquake
At the Basement of Reactor Building

Nr.

1Fuku1
1Fuku2
1Fuku3
1Fuku4
1Fuku5
1Fuku6

MWe

460
784
784
784
784
1100

3.11 Observed (max. gal)

Design (Ss) (max. gal)

N-S

E-W

Vertical

N-S

E-W

Vertical

460
348
322
281
311
298

447
550
507
319
548
444

258
302
231
200
256
244

487
441
449
447
452
445

489
438
441
445
452
448

412
420
429
422
427
415

Note 1: Damage by the earthquake:
Not fully inspected but maybe not significant damage to safety systems,
considering the KK earthquake (2007) where no damage to safety functions
even though the observed acceleration exceeded design basis by factor 2-3.
However, all the 6 offsite power lines to 1F were lost due to failure of breaker,
and collapse of transmission line tower
One of the offsite power lines remained intact @2F
In KK earthquake (2007), 3 out of the 4 offsite power lines remained intact.)
Note 2: Reactor Scram by the earthquake
Set points by acceleration at R/B basement: Horizontal=135 gal, Vertical=100 gal
5Key vulnerabilities (2)14.46
15.38-41

Earthquake, Loss of offsite power, Start of EDG, IC/RCICTsunami followed by Loss of AC/DC, Isolation from UHS

Given this situation, operation to avoid core damage
Short term Reactor water makeup by AC-independent IC/RCIC/HPCI
Require workable/effective SAM
Then, while trying to restore AC/DC power and Heat Sink
 Depressurize Reactor Coolant System by Safety/Relief Valves
 Activate Low Pressure injection systems
 Containment vent to avoid over-pressure failure
Failure of RCIC/HPCI on the 3rd and 4th day
Delayed venting, de-pressurization of RCS and LP injection
Core degradation
Hydrogen explosion

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Existing BWR’s capability for extended SBO
20

100

TAF

BAF

5

50

Loss of water inventory
equivalent to Decay Heat

RCIC FlowFP Flow004050Time (h)

60

70

80

Containment Pressure (kPa[gage])
0
200
400
600
800

30

Flow Rate (kg/s)

15
10

Fuel uncovered
time period is short.
(less than 1 hour)

10

20

30

Depressurization

40
50
Time (h)

60

70

80

300

Venting
2Pd

250
200

Wetwell Temperature

150

427kPa[gage]

DrywellTemperature

Pd

100

Drywell Pressure

50

Wetwell Pressure

0
0

10

20

30

40
50
Time (h)

60

70

80

7

Containment Temperature (℃)

10
8
6
4
2

Rx Pressure
20

150

853kPa[gage ]0

RPV Pressure (MPa[gage])

Depressurization

10

RPV water level

1000

Battery to support operation of RCIC or essential
valves has 8-10 hours capability. RCIC kept running
for almost 3 days (1F2)0200

Depressurization

0

RPV Water Level (m)Operation
0-24hrs into the accident:Core water makeup by stored energy (RCIC)24 hrs: Depressurize RCS and LP injection(SAM)32 hrs: Heat dissipation to the alternative heatsink by Containment scrubbing venting (SAM)Devastation by Tsunami

Inundation height
14-15mAssumed Tsunami
height 5.7m

Tb/B

Tb/B

R/B

R/B

Hx/B

[SOURCE]
http://www.tepco.co.jp/cc/press/betu11_j/images/110618l.pdf and
TEPCO May 23 report8Limited available resources under harsh environment
Loss of communication tool (PHS) and plant safetyparameters (SPDS)
1) Use of limited available resources Fire Engines
 Flashlights/Cables/Tools
 Batteries taken from cars
 Mobile small Generators
 Mobile Engine-driven Air Compressors
 Mobile pumps/motors
2) Usage limited by scattered debris/tanks
3) Field works under devastation & damage byhydrogen explosions and aftershocks

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TMI and Fukushima core uncover: estimation
TMI
Day 1

Day 2

Fukushima00
Tb trip, Loss of FDW
00 Earthquake LOOP, EDGs start,
03 secSRV stuck open
IC/RCIC operation
3 min
HPI stop
1 hr Tsunami Blackout &loss of UHS
100 minCoolant circulation stop
174 minB pump start (fuel collapse)
113-174 min Core uncover
200 min
HPI restart
(1F1)
(1F2)
(1F3)
224 minSlumping to RPV bottom
4-15*
hrs
*Estimated time from start of core uncover
to start of successful injection

Day 3

Day 4
[SOURCE] Based on Gov. report to the IAEA and TEPCO May 23 report40 -43*hrs

75 -77*hrs
10Key vulnerabilities (3)Hydrogen leak path 1 : Excessive leakage by over-pressure at CV flange/airlocks
Hydrogen leak Path 2: Vent line SGTSR/B HVAC
(vent line merge with adjacent units)
Unit 1

Unit 3

SFP zone
Unit 2

Unit 4

1F2 blowout panel opened by
1F3 blast, which released H2

SFP zone

FP escape path to the environment by R/B hydrogen explosion
11Offsite : EPZ and predicted first year dose
More than80,000 evacuees

Zone II

Zone III

30km

20km

Zone I

30km radius

20km radius
EPZ
Zone I (20km); “evacuation”
Zone II (North-west): “Planned evacuation“
Zone III (20-30km); “prepared for evacuation”

Predicted annual dose (by 2012 Aug 11)
Assuming no decay, no weathering[SOURCE] http://radioactivity.mext.go.jp/ja/1750/
12
2011/08/1750_081914.pdf

12Part I Key vulnerabilities Part II Lessons learned for Operator/Industry

13Lessons Learned
 Government report to the IAEA (September) : update 28 Lessons in
5 specific areas (Prevention of SA, SAM, Emergency response, Safety
infrastructure, culture) and implementation status
http://www.meti.go.jp/earthquake/nuclear/backdrop/20110911.html

Key points are;
1. Design considerations against natural hazards
2. Design considerations against SBO and Isolation from UHS
3. Completeness/effectiveness of SAM
4. Emergency Management
5. Safety regulation and safety culture
6. Multiple unit installation
7. SFP design
8. International aspects
 This presentation goes a bit further through personal deliberationand to specifics by focusing on LL to Industry/Utility
 Need further in-depth study on culture & history necessary to avoid
accidents by other causes
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Lessons LearnedA) Safety regulation and safety culture
Safety regulation and safety culture in nuclear community
Regulation:
Responsibilities not in a single regulatory bodyRegulatory standards, Independence, competence (Government report to IAEA)
Decision by Cabinet (2011Aug15) on reorganization• Transfer of NISA, NSC, and other authorities (security,transportation safety) to MoE (Environment) except for SG• Statement by AEC (2011Aug30) on safety-first, public trust,technical competence etc.
Regulation/Utility: Focus on QA/Compliance rather than risks (after 2002)
Utility
Use of risk information using PSA by Owner/operator to address
vulnerabilities of its asset
Understanding of safety by every employees
Continuous improvement : [Ex] of SAM through drill and informationfrom outside considering “Accident can happen here”
“Sensitivity “to safety-related issues/information(Many understood the meaning of B5b in hindsight)
15 Attitude towards “uncertainties”

Safety Culture
Three-level model of Safety Culture
Artefacts-Visible Signs(greeting rituals, dress, housekeeping – visible)

Artifacts

Espoused Values(values that are adopted and supported bya person or organization based on
strategies/ goals)

Basic Assumptions

Espoused Values
visibleinvisible(Such as “human nature good or evil”)

Assumptions“Social Fabric”[SOURCE] Edgar Schein, former professor at the
MIT Sloan School of Management, expert on organizational culture16

According to experts: ASSUMPTIONS (BELIEFS) MATTER(Not describing Fukushima case)“The plant is robust, it has safety margin.”

ACCIDENT[SOURCE] Charles Packer, Cherrystone Management

17Lessons LearnedB) Workable/effective SAM
1. SAMG not robust enough to cover possible plant damage conditions
 Considera) integration of three Gs (internal event, external event andsecurity-related event, andb) implementation of recovery actions in harsh radiation environment
2. Provisions of Onsite or National/Regional Nuclear Crisis
Management Center for storage of mobile equipments & drill
under coordination by WANO?
(Supporting provision)
3. Accident instrumentation[Ex] What is the Water Level in drywell?
4. Prevention of hydrogen detonation/deflagration outside of the CV
5. Simulation of plant behaviour (Real-time or faster-than-real time)
as a decision aid and knowledge basis (ERSS)
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What SAM (Severe Accident Management) was in place?
(OECD/NEA)
In the aftermath of Chernobyl, OECD/NEA organizeda series of meetings by SESAM (Senior Expert for
Severe Accident Management)“Severe Accident Management”: published in 1992
“Implementing Severe Accident Management in
Nuclear Power Plants”, published in 1996
(Japan) NSC recommendation (1992)
 SAM study followed by SAMG and modifications (hardened vent,injection to RPV and RPV-pedestal region etc)
 Submittal of Utility report to NISA, followed by evaluation by NISA
 Later improvements such as onsite Fire Engines, UG water tanks andnew ERC with seismic isolation (KK experience 2007)
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What SAM (Severe Accident Management) was in place?
Stuck

Sever Accident Management
Alternative
Power source

SGTS

Alternative Core
injection/CV spray

Other Unitx

EDG

Filtered Water
Storage Tank
FP system“Hardened”
scrubbing
Vent

Pedestal injectionxx

Sea Water Pump

RHR Pump

Sea
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Onsite ERC by TEPCO: seismic isolation structure21

Lessons LearnedC) Emergency management
 Loss of communication tool and plant information (SPDS) at
NPP Dissemination of information
 Damage to social infrastructure by earthquake hampered
dissemination of information to local government and residents Lack of Information sharing- with local residents on dispersion of FP (SPEEDI) and risk of radiation- with neighboring countries on release of slightly-contaminated water

“Data but not information”
Who is in charge?
Ambiguity in delineation of responsibility
Recognized role by Joint (Government and TEPCO) ERC and local
resources center 20—30km away from NPP
 Offsite center: function was lost by loss of electricity and radiation
 Effective channeling of emergency supports
Systematize domestic/foreign helping hands for logistics/experts
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Lessons LearnedD) Design
Gedankenexperiment
What safety design could have saved Fukushima?
1. Protection against natural hazard
 Adding safety margin to the results of probabilistic Tsunami
hazard analysis
 Location of essential safe systems considering Tsunami/Flood
2. Plant capability against SBO and isolation from UHS
 Highly reliable assurance of 3 cooling functions (Core, CV, SFP)
including enabling systems (power/air/water source) such as
backup air supply to SRV
 Passive systems
3. SAMG Mobile equipments in onsite/offsite emergency center Robust SAMG workable under internal events,
external events and security-related events and drill
4. Enhanced system for aversion of “land contamination”
 Dependable scrubbing vent 2ndary containment filtration/H2 management system
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Supplementary IAEA request for information
National nuclear power plant’s response andassessment (ex. safety test results)
Role of operators at the plant under extreme conditions
On-site and off-site emergency responders under
extreme conditions
Current and future cooperation with the IAEA,
Cooperation with other international organizations,countries

24National nuclear power plant’s response and assessmentNISA Emergency Safety Measures Directive to each NPP from NISA: March 30th, April 9th, April 15th
 Utility’s responses and evaluation completed : May 6th
Short term Ensure emergency power supply and train SAM improvements (such as hydrogen, mobile sea water pumps)
Medium-to-Long term Countermeasure against anticipated Tsunami height (Example) KK to install 15-meter-tall wall by 2013

Stress test
 Announced by the Minister (METI) (July 6th) and the Cabinet (July11th) as an additional tool to verify safety of existing NPPs
 Phase I: plants ready for restart (assessment of safety margin) Phase II: All plants (integrated safety assessment) to determine
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continued operation or notEmergency Response

Government
Nuclear Disaster Management Hq. headed by PM
Off-Site Center

AdviceNuclear Safety
Commission

・NISA’s Staffs
・Local Government Staffs
・experts
Instruction

Instruction/
Technical advice

Instruction

 Law “Special Countermeasure against Nuclear Disaster”a) On Notification, off site center is set upb) On Declaration of Emergency, PM is in charge
 In reality, off-Site Center was not functional and relocatedNuclear facility

Local government (control evacuation, announcement)
Police (security, patrol in disaster area)
Fire office (fire-fighting, life saving)Self-defense force (transport support etc)
Support

Simplified scheme based on White paper on Nuclear Safety 2003 ( the Japanese Nuclear Safety Commit ion)26
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Never, Ever Again
anywhere in the world27
http://www.asahi.com/photonews/gallery/fukushimagenpatsu/