3- Nuclear Risk - A-Yamaguchi

8/10/2019 3- Nuclear Risk - A-Yamaguchi

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FrameworkforEnsuringNuclearSafety:

BeingPreparedforNuclearRisk

AkiraYamaguchi

DepartmentofEnergyandEnvironment

Osaka

University,

Osaka,

Japan

1

PresentedatCSD&M,1214December,2012


2/21

Summaryof

Fukushima

Dai

ichi Accident

RadiationExposureofFukushimaResidents (for4monthsaftertheaccident) 99

out

of

25,520

exceed

10mSv

(public),

maximum

25.1mSv

48outof147exceed10mSv(workersinnuclearfacilities)

Confusioninevacuation,foodandwatercontrol

Contamination

of

land

is

significant

Ifemergencypreparednessworks,theyshouldhavebeenmitigated

Exposurelimitation

in

emergency

situation

Radioactivitycontrolinfoodanddrinks

Mitigationmeasureofsignificantradioactiverelease

2


3/21

TheTsunamiCausedStationBlackout(SBO)and

Lossof

Ultimate

Heat

Sink

3

Unit1 Unit2 Unit 3 Unit4 Unit5 Unit6

Offsitepower X(0/6/7) X(0/6/7) X(0/6/7) X(0/6/7) X(0/6/7) X(0/6/7)

EmergencyDG X X X

(X) (X)

X (X) X (X) (X) O

(X)

Metal clad(6.9kV) X X X X X (X)

X X X X X O

X X (X)

Power center

(480V)

X O X X O

X O X O X O

X X O

DCbattery X X O X O O

X X O X O O

Ultimate heatsink X X X X X X


4/21

Crossroadin

Fukushima

Dai

ichi Accident

EarthquakePracticallynodamageonsafetyfunctions at14:46,March11

TsunamiLossofmultifunctions(notonlysafetybutlogistics)at15:42

Stationblackout(SBO)

Lossofultimateheatsink(LUHS)

Lossofinstrumentationandcontrol

Lossofcommunicationandinformation(lighting,computer,mobilephone,

paging)

Lossofoffsiteexternalassistance

Fearonaftershockandanothertsunami

HydrogenExplosiononUnit1at15:36,March12

Lossofaccidentmanagement

Lossofaccessibility

Lossofhabitability

Fearonthenextexplosion

4


5/21

Recoveryfrom

Disaster

Thestaffalwaysconsideredpriority;toselectthebestaction

on

the

worst

unit Knowledgebasemanagement

Mobileequipment

Carbatteries

Informationishelpfulforgooddecisionmaking

HelicopterflightconfirmedwaterinthespentfuelpoolonMarch16

Externalsupportstarted(SelfDefenseForce,Fire

ManagementAgency,

etc)

Corecoolingusingfireengines

Spentfuelpoolcooling usingconcretepumpvehicles

5


6/21

LessonsLearned

Always,wecanmanage

Flexibility,knowledge

and

imagination

Agreementwithsocietybeforepreparation

Justificationof

nuclear

technology

Riskisuncertainty

6

Scrutinyofwhatwentwellandworseandpreparation

ofallpossibilitiesofSevereAccidentManagement


7/21

HowtoEnsureSafety

RiskModel

in

Mathematical

Form

Toensuresafety,suppresstherisktolowlevel ReduceFrequency

MitigateConsequence

ItworksonlyIfweknowthefrequencypreciselyandwecontroltheconsequence

7

Risk Frequency Consequence


8/21

FrequencyandConsequence;

WhichIs

More

Important?

8

Frequency

Consequence

Large Risk

Small Risk

LowConsequence

Low

Frequency

Lackofknowledge

andrecognition

Large risk means large uncertainty


9/21

LowFrequency:

What

Does

It

Mean?

9

F

requency

Consequence

Large Risk

Small Risk

LowConsequence

LowFrequency

Low frequency means less information (ignorance)

Lowlevelof

knowledge/

recognitionLikeliness


10/21

Approach

to

Ensure

Safety

Limit

the

Risk

Riskisnotfrequencytimesconsequence

Riskcomes

from

uncertainty

which

we

cannot

be

free

from

Wemustbepreparedforuncertaintyandovercomeignorance

Approachtoprepareforuncertaintyandtolimit

the

risk

is

: Defense

in

Depth Whatcausestherisk?

Sourcetermorradioactivematerial:fissionproductcausestherisk

Whosustains

the

risk?

Publichealthandsafetyandenvironmentsustaintherisk

10


11/21

WhatIsHazard? WhoShouldbe

Protected?

IdentifyHazardSource

Radioactivematerials

DefineSafetyObjective

Health

and

property

of

public

and

environment KeepHazardandPublicSeparate

11

Hazardous

Material

Publichealth

andproperty,

environmentManagement


12/21

3rd

Defense:Objective

Is

the

Goal

Toprotectpublicismostimportant

Emergencyresponse

is

scenarioless Scenarioisunpredictable

1st defensedependsonscenario

Flexibilityandknowledgebaseactionworks Managementsystem

Drilland

education

Safetyculture

12


13/21

2nd

DefenseIs

Flexible

and

Broad

13

Hazard

(Fission

Product)

Healthand

safety,and

propertyof

public

1st Defence

Prevention

3rd Defence

Emergency

preparedness

NoSevereAccident RespondtoEmergency

Barrier/Distance/Time

2nd Defence

Mitigation

ContainFissionProduct

Management

Purposeofthe2nd defenseisambiguous

Boundariesare

overlapped


14/21

AbsolutelyUnlikely

Is

Impossible

BlackSwan/WhiteRaven

14

BlackSwan (N.Taleb,2007) WhiteRavens(Hempel's Ravens)


15/21

Four

Categories

of

Undesirable

Event

15

Recognition

UnknownknownUnknownunknownKnowled

ge

KnownknownKnownunknown

TwoBeyond

Design

Basis

Type:

Unlikely

Event

and

Rare

Event

Unlikely

RareUnknown


16/21

Precursoris

Messenger

of

Safety

WhiteSnake(Iwakuni City,Yamaguchi,Japan)

Appearanceof

unknowns

is

messenger

of

safety

16


17/21

KnownUnknown

Becomes

Reality

17

EarthquakeandtsunamiintheIndian

OceanoffSumatra:Kalpakkam NPP

Flooding:LeBlayais NPP,France

FortCalhounNPP:Missouri

RiverFloodingin2011,USA


18/21

IdentificationandPreparationfor

Unknowns

KnownKnownisalreadyconsidered

Design

basis UnknownUnknownbecomesKnowns

PRAfindoutsequences(UnknownKnown) BWRcontainmentvesselfailure(SBOscenario):hardenedvent

Unexpectedevent

becomes

reality

(Known

Unknown)

SmallLOCAandhumanerror(TMI)

SBO+LUHS(FukushimaDaiichi)bytsunami

Unknownknown

is

investigated

in

detail

(stress

test)

Knownunknownisprotected(provisions)

18


19/21

Role

of

Stress

Test,

PRA

and

Provisions

19

PRA Stresstest

DesignBasisUrgent Provisions

Knownunknown

Recognitionlevel

Knownknown

UnknownknownUnknown

unknown

Knowle

dgelevel Beyondrecognition

BeyondknowledgeResidualRisk

The1st Defense

The2nd Defens

How

to

Deal

with

the

Residual?

The3rd Defense


20/21

Do

We

Accept

Residual

Risk?

20

Justitia

Justificationistheactionofdeclaringor

makingrighteousinthesightofGod

(OxfordDictionaryofEnglish)

Bereadytoacceptriskunderjustification

Butcontinue

to

reduce

/optimize

risk

IAEAFundamentalSafetyPrinciples

Facilitiesandactivitiesthatgiverisetoradiationrisksmustyield

anoverallbenefit.


21/21

Conclusions Goodmanagementandknowledgeleadustotheright

wayatcrossroads

Preparationfor

Uncertainty

(Unpostulated scenario)

DefenseinDepth

UnlikelyEventandRareEvent

BeingPrepared

for

Three

Types

of

Unknowns

Stresstestcoversrareevent:Unknownknown

Appropriatebackfitpreparesfor:Knownunknown

PRAdealwithunlikelyevent:UnknownUnknown

Thereexist

clue

to

survival

anywhere;

Try

to

find

it

alwaysandcontinually

21

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3- Nuclear Risk - A-Yamaguchi