IHTC-15 : The 15th International Heat Transfer Conference

Panel on “The Role of Thermal Science
for Nuclear Disaster Resilience”

Resilience Related Lessons Learned
from Fukushima Daiichi Accident
August 14, 2014, Kyoto, JAPAN
SUGIMOTO, Jun
Department of Nuclear Engineering
Graduate School of Engineering, Kyoto University
Kyoto, JAPAN1

What happened at Fukushimaon March 11, 2011?

- All operating reactors whenearthquake occurred wereautomatically shutdown- Emergency DGs have worked
properly until the Tsunami attacked

Grid line

1

1. Loss of external power
supply due to earthquake
Tsunami (Estimated about 15m)

Electric receiving devices
TurbineBuilding

3

Reactor
Building

2

power panel power panel
DC Power

Motor
Elevation
Approx.
10m

Seawater Level
Seawater Pump

2. Loss of DG function due to Tsunami+ Loss of DC power (except Unit 3),
3. Loss of function of sea water pump

Loss of all AC power (station blackout)
including ECCS function, DC power for
instrumentation & control systems and2
ultimate heat sink

Distribution of seismic intensity

3[http://www.nisa.meti.go.jp/english/press/2012/06/en20120615-1.html]

Loss of external power supply due to damage ofpower receiving devices, collapse of power
supply tower, caused by earthquake (14:46)

4

Emergency diesel generators, automatically
activated after the scrum, were terminated
due to water inundation by tsunami (15:37)

5Estimation of failures of reactor pressure vessel and containment vesselMar. 11Mar. 12Mar. 13

4:00Start of alternative cooling

14:4615:37

Insufficient
Cooling
2:45 Venting
RPV
Hydrogen exp.
failure14:00 15:36
CVTsunami leakage
No cooling

Unit 1:Operation
Earthquake

Mar. 15

Mar. 14

Sufficient cooling12:30 19:57
Unit 2:

Cooling by RCIC

Operation

Opening of blowout panel

11:36 12:35
Unit 3:Operation

RCIC

2:42

HPCI

Works
affected

21:00

9:25

RPVfailureCV
7:00
failureInsufficient cooling
Hydrogen exp.
RPVVenting
failureCVleakage

11:01

Unit 4:inspection

Hydrogen exp.
Backflow ofHydrogen[Ref] Government Investigation Committee, July 2012

6:00
6

Possible Hydrogen Leakage Routeand Hydrogen Explosion
Unit 1: 3/12 15:36

FlangeHatch,
airlock,
penetra-tions

Unit 3：3/14 11:01

Unit 4：3/15 6:00

7Estimated fission products released to EnvironmentOrganization

I-131

Cs-137NSC/JAEA (August, 2011) *130

11JAEA (March, 2012) *120

9NISA/JNES (June, 2011) **160

15NISA/JNES (February, 2012) **

150

8.2

TEPCO (June, 2012) *500

10(Ref）Chernobyl Accident*1760

85（1015Bq）* Estimated with environmental monitoring data and diffusion analysis(SPEEDI/DIANA etc)** Estimated with reactor accident progression analysis (MELCOR)

8Major technical causes of accident
occurrence and escalation
 Optimistic assumptions against externalevents (earthquake, tsunami) Insufficient measures against station
blackout (including loss of DC power)
 Insufficient severe accident management
measures (alternative cooling, CV venting) Insufficient measures against commoncause events at multiple units site
 Lack of appropriate severe accident
progression prediction tools
 Insufficient education and training forsevere accident situations
9

Investigation reports on Fukushima
accident issued in Japan:
 Independent Investigation Commission, Feb 2012

Chaired by Prof. Kitazawa
 Tokyo Electric Power Company, June 2012
Chaired by Vice-president Yamazaki National Diet Investigation Commission, July 2012
Chaired by Prof. Kurokawa
 Government Investigation Committee, July 2012
Chaired by Prof. Hatamura
 Atomic Energy Society of Japan, April 2014
Chaired by Prof. Tanaka
10General meaning of “Resilience”
・the ability of people or things to feel better
quickly after something unpleasant, such as
shock, injury, etc [Oxford]
・the ability to become strong, healthy, or
successful again after something bad happens[Webster]Four elements in “Resilience Engineering”
 Respond(Prof. Kitamura) Monitor
 Anticipate11

 Learn

Resilience related lessons learned from
Fukushima accident (1)Independent Investigation Commission, Feb 2012

Final Chapter “Lessons of the Fukushima Daiichi
Nuclear Power Station Accident and Quest forResilience”“There can be no resolution of the Fukushima crisis
until we study the causes of the accident and thehavoc it wreaked, learn the lessons of the steps
taken to respond to it, and forge a new national
consensus. Those have been the key objectives of
our investigation. Above all, we must strive toenhance Japan’s resilience: the resilience ofJapan’s government, its institutions and its people.”
12

Resilience related lessons learned from
Fukushima accident (2)Government Investigation Committee, July 2012

Chairperson’s Final Remarks“(5) Everything changes, respond flexibly tochanges”“…the only way to stop situations such as thisfrom happening is to consider that all matters willchange, pay scrupulous attention to observation,
show humility in being open to external ideas,
and continue to respond appropriately”

13Resilience related lessons learned from
Fukushima accident (3)Atomic Energy Society of Japan, April 2014

Recommendation 8.2.2“(2) Strengthen severe accident measures”“Since the event does not always proceed as
expected in severe accident condition, an ability
to respond flexibly to cope with the situationsuch as a management is necessary. In order toenhance this ability, improvement activities
should be continuously conducted throughtraining and practices.”14https://www.nsr.go.jp/english/e_news/data/13/0912.pdf

15

https://www.nsr.go.jp/english/e_news/data/13/0912.pdf

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Importance of “Resilience” forFuture Reactor Safety
1. Safety measures have been greatly improved
based on lessons learned from Fukushima
accident both in hardware and software(including management and training).
2. However unexpected event still may lead todisastrous situation as we encountered in TMI-2,Chernobyl and Fukushima accidents.
3. It is highly expected that the application ofresilience engineering can cope with unexpected
event that has extremely low probability but has
extremely high consequences.
17

Concluding Remarks
 Some investigation reports on Fukushima
accident in Japan emphasize the importance of“resilience” in lessons learned.
 Although the safety level has been greatly
enhanced based on these lessons, unexpected
event with extremely low probability may stilllead to disastrous situation. It is expected thatthe application of resilience engineering cancope with this situation.
 Keywords to characterize TMI and Chernobyl
accidents are internationally recognized as“human error” and “safety culture”, respectively.
That for Fukushima accident may be “resilience”,depending on the outcome of the present panel.
18Thank you for your attention!

19

Summary of Damage after Tsunami AttackUnit１

２

３４５６Operation
StatusFull-power operation

Under inspection

Off-site power

×××××

×

Emergency
diesel generator
A : Air-cooled××××A×××
×A×××〇A×

Emergency
power panel

×××××〇

Normal powerpanel

×××××

×

DC Powersource

××〇

×〇

〇

Sea-water
cooling pump

××××××20

Sea water pumps lost all functions

21

Isolation condenser (Unit 1)

22

Containment Venting System

23

Reacted Zr mass (mg/cm2)

Zircalloy-water reaction
250200150100500500

Baker –Just Equation

700

900

1100

1300

Reaction temperature (℃)

1500
24

Possible Hydrogen Flow Path from Unit 3 to Unit 4
Unit 4 R/B
Stack iscommonly used
between Units
3 and 4

Unit 3 R/B

Government’s Investigation Committee (July, 2012)25

3. Release of fission products
Analysis results by JNES with MELCOR code
JNES: Japan Nuclear Energy Safety Organization
MELCOR: Severe accident analysis code developed by USNRC
Environment
NodingdiagramDrywell
RPV

Wetwell

Reactorbuilding

http://www.jnes.go.jp/content/000119740.pdf
26

Estimation of FP release from atmospheric diffusion -Inverse estimation with SPEEDI codeConcept of inverse estimation
Calculated value

Assume 1 Bq/h release
Calculate air concentration
and absorbed dose rate atmeasured locations

Measured value

Air concentration andabsorbed dose rate

Release rate(Bq/h)= Measured/ Calculated
http://nsed.jaea.go.jp/ers/environment/envs/FukushimaWS/jaea1.pdf

27

https://www.nsr.go.jp/english/e_news/data/13/0912.pdf

28

Main works and steps for the decommissioning Fuel removal from Unit 4 spent fuel pool (SFP) has
been underway since Nov. 18, 2013. The work at Unit 4
will be accomplished around the end of 2014.
 Preparatory works for fuel removal from Unit 1-3 SFP
and fuel debris removal are ongoing.
 It is said that it will take 30 to 40 years for thecompletion of the final decommissioning.
29

Important HRD for Nuclear Safety in the Lightof Lessens Learned from Fukushima Accident(1)Top professional at the plant to cope with
unexpected event(2)Operators under top professional toproperly conduct necessary procedures

30

(1)Top professional at the plant to copewith unexpected event
 No manual exist to cope with unexpected event
 Need to understand what happens with limited
information
 Need to properly predict what will happen next
 Need to develop effective measures to prevent
disastrous situations
How to develop HR?

 Physics-based essentially in-depth knowledge
 Dispatch of personnel to research institutes
 Extensive team training without scenario
 Systematic training on leadership31

(2) Operators under top professional toproperly conduct necessary procedures No manual exist to cope with unexpected event
 Need to understand technical reasons of thedirections by the top professional
 Need to properly conduct necessary actions
 Need to precisely report the results to top
professional
How to develop HR?

 In-depth knowledge on plant behaviors
 Extensive team training without scenario
 Systematic training on communication
32