Fukushima Daiichi (1F)My Thought on Risk on D&D andSafety
Akio YamamotoProfessor, Graduate School of Engineering,
Nagoya University(a-yamamoto@energy.nagoya-u.ac.jp)
1

Risk at 1F“Do you think how many different risks at 1F?

https://www.tepco.co.jp/decommission/progress/

2

Risk to be considered for 1F
Because of varieties of risks to be considered for D&D,
comprehensive decision-making is needed by reflecting
associated risks below“Risk Informed Decision-Making”


1) Nuclear safety
2) Working Safety irrelevant to radioactivity
3) Increment cost increase needed for D&D
4) Prolonged work period due to D&D
5) Increased amount of waste due to D&D
6) Additional needs to sustain human resources
7) Societal risk like social reputation
8) Others

Which is most critical?

3Power Plant vs. 1F D&DPower Generation（General）
Objectives

Long term safe and stable generation)

Features

No large changes at facilities

Characterization offacilities

１F F&D (Unique, Custom-make)Y3

Early risk decrease exposed by accident
Continuous changes

Assuredness based on design (mostly designbased)

Large uncertainties （site and facilities dependent)High energy：rapid accident propagation

Low energy : slow accident propagation

Integral buildings, structures

Y0

Damaged building, structures

Y1

Solid containment (passive boundary)

Incomplete containment (active boundary)

Risk profile

Accident=low frequent but high impact

Normal operation / Assumed events = Frequency
occurrence and low impact

Safety management

Plan on design and system

Safety secured by design and operation jointly

Regulation / Code andstandard

Reactor Law：comprehensive rule andstandardSpecialized Nuclear Facility : rules adjustable

Features of work

Study in advance anticipating all the events

Trial and error, flexible

Y2

Y4

What is the major difference in terms of D&D?
4スライド 4
Y0

accident progression
Yamamoto, 2021-10-10T21:55:07.251

Y1

accident progression
Yamamoto, 2021-10-10T21:55:16.787

Y2

confinement
Yamamoto, 2021-10-10T21:55:25.679

Y3) を削除
Yamamoto, 2021-10-10T21:55:42.587

Y4

adaptive rules
Yamamoto, 2021-10-10T21:56:34.200

Management of Projects with large
Uncertainties
PDCA Cycle
PDCA：Plan, Do, Check, Action
 No Go-head without “Plan”?


DLTG Cycle

DLTG：Do, Look, Think, Grow

Lead & Learn

Lead: to go with or in front of a person or ananimal to show the way or to make them go in theright direction (Oxford Learner’s Dictionary)5Safety Philosophy under large Uncertainties:
Defense in Depth (DiD)
DiD:
Varieties of protective Measures combined as
Preparedness for Uncertainties aiming at theincreased trust Y0on whole Protection Measures
Combined Prevention of Occurrence, Detection,Mitigation
 Prepare different angles of protective Measures Y1
6

スライド 6Y0

reliability
Yamamoto, 2021-10-10T21:57:01.841

Y1protections with different natures
Yamamoto, 2021-10-10T21:57:46.126

DiD Example: CarPrevention of abnormal Occurrences

Ex. No ignition without setting shift lever to “P”

Mitigation of abnormal Event, Prevention ofProgress to Accidents
Ex. Brake support (Enhanced automatic brake at
hard stoppage) Antiskid brakePrevention of Human Damage
Seat belt
 Air bag

Mitigation of Human Damage
Emergency Ambulance7

Why DiD needed?
No needs at “the World withoutUncertainties”


DiD should be prepared for Uncertainties

No needs if all of Accident Sequence known
What are required for that?

Single preventive Measure cannot be “SilverBullet”

Single, all mighty measure (either preventive ormitigation) has definite weak point. Trust as awhole to be improved by combining varieties of*) a bullet cast from silver
is often one of the Measures
few weapons that are effective against a werewolf or witch. The term silver
protectivebullet is also a metaphor for a simple, seemingly magical, solution to a difficult problem: for example, penicillin circa 1930 wasa “silver bullet” that allowed doctors to treat and successfully cure many bacterial infections.
:（Wikipedia)

8DiD on Power Plant
Defense level

Objectives

Measures applied

Original Design

High quality of conservative
design andconstruction/operation

BeyondDesign BasisEmergency

Level 1Prevention of abnormal
operation and failures

Level 2Control of abnormal
Surveillance characteristics ofoperation and detection of control, limitation, protection
and other systems
failures

Level 3Control of the accident
under design basisLevel 4Control of the plant under
severe conditions toprevent accident
propagation andmitigation of SA impact
conditions

Accident management
including aux. Measures andprotection of containment

Level 5

Mitigation of the radiation
impact due to large scalerelease of radioactive
materials

Off-site emergency
preparedness

Plant conditions
Normal operation
AnticipatedOperational
Occurrence （AOO）

Engineered safety system and Design basis accident
accident procedures(single failure mode)

How DiD at 1F could be in place?

Multiple failure
accident（SevereAccident）［Design enlargedY0conditions ］

Refer AESJ-SC-TR005 (ANX):2013 ON Fundamental Philosophy of9Nuclear Safety, Vol.1 App. Philosophy of Defense in Depthスライド 9Y0extended
Yamamoto, 2021-10-10T21:59:58.525

Risk Management at D&D WorkTransition of nuclear safety risk, worker’s exposure risk,
occupational damage risk, environmental damage risk

Negative damage andfrequency to humanConditions of 1F and Project Risk

SeriousMediumLowTime10

Risk Management at D&D

Short-term and long-term Risk

Short-term Risk; Risk at certain unit of timeLong-term Risk; Integrated risk at certain time duration
Possible increase of short-term risk at site work of 1F due totime constraint
Allowable increase of short-term risk could be considered byusing the optimization concept used for radiation protection
in contrast to long-term risk decrease

11Risk Management at D&D
Long-term･Increase
Shortterm・Increase

Not allowed

Shortterm・No
changeShortterm・Decrease

Not allowed
Likely when avoiding
imminent risk. Low
possibility for D&D work
but justifiable only
avoidance of imminentrisk. Risk decreasemeasures requested
afterwards.

Long-term・No
changeNot allowed

Long-term・Decrease
Large long-term risk
decrease justifiable, whenassessing short-tem riskincrease carefully, in
consideration of the longterm risk decrease.
Measures to decrease shortterm risk as much as
possible is needed
Recommendable

No effect and notrecommendable interms of cost vs. benefit
Recommendable
Recommendable

1210 Years Look BackTime

EventTime of Emergency （2011～2013）2011.3.11

1F Accident occurred（Nuclear Emergency Response Headquarters）

2011.12.16

Step 2 ”Reactor Cold Shutdown” achieved addressed to termination of the accident / Mid-andLong Term (M&L) Roadmap (ver.1) (12.21)

2012.11.7

1F site categorized as Specialized Nuclear Facility（9.19 @NRA）

2013

Messed with varieties of troubles（station blackout caused by rat, leakage from undergroundstorage tank, leakage from contaminated water tankY0etc.)

2013.11.18

Start of spent fuel (SF) removal at unit 4（End of M&L Road Map)

Time of risk assessment and M&L plan（2014〜
2014.4.1

TEPCO’ s D&D Company / NDF’s decommissioning facilitation operation（2014.8.18)

2015.5.27

High density contaminated water treatment / Seaside impermeable wall completed (10.26) ) /Frozen soil wall
Y1completed (2018.3.7)

2017.9.26

Fuel debris retrieval policy determined (M&L Road Map ver.4) / First unit of fuel debris retrieval
and associated method (2019.12.27)

Time for establishing Quality Management System (2019〜
2019.4.15

Start of SF removal at unit 3（Quality issue focused)

Time for full-scale Project Management (2020〜2020.4.1

Restructuring of TEPCO D&D company (Project Management Organization・D&D Safety QualityOffice)13

スライド 13
Y0loss of powerYamamoto, 2021-10-10T22:03:40.094

Y1HighlyYamamoto, 2021-10-10T22:04:55.906

Change Management
Temporary→Enhanced Reliability→Permanent Not optimized→Locally→Partially→Overalloptimization
 “Safety Culture” for D&D?


IAEA GSR Part 2:” Leadership and management for safety isessential for the fostering and sustaining strong safety culture”
IAEA INSAG-4: “Safety culture is that assembly of characteristics andattitudes in organizations and individuals which establishes that, as
an overriding priority, nuclear plant safety issues receive theattention warranted by their significance”

Who do you think takes the leadership toimplement D&D in safe and rational manner?
14Change ManagementLearning from Jane Jacobs’ “Systems of Survival: A Dialogue on
the Moral Foundations of Commerce and Politics”
Moral foundations of Politics （ex. Aiming at Royalty,sustainability of order in the organization)


Avoid trade / Be brave / Compliance / Risk of rank / Be royal / Revenge /Betray for the purposes / Make full use of leisure / Show off / Be agenerous giver / Be exclusive / Be resolute / Accept destiny / Respect honorMoral foundation of Commerce（ex. Aiming at Sincerity, cooperative
relationship with others)

Exclude violence / Agree voluntarily / Be honest / Easy cooperation withothers or foreigners / Sense of Invention / Open to novelty / High efficiency/ Improved comfort and convenience / Disagree depending on thepurposes / Invest for production / Be diligent / Save money / Be optimistic

To distinguish two Moral Foundations and select intentionally
Never confuse, Risky mixture!
D&D work necessitates both moral foundation for commerceand politics

15

1F D&D, TomorrowWork with high difficulty like fuel debris
retrieval to come from now Needless to say off-site work is important,while to secure and sustain safety at on sitewould be further important More important with overall optimization
 Change mind : To pursue both moral
foundation of politics and commerce at one
time together16