mitigation coverage estimation of passive system s using ... · • after solving boolean equation...

NuclearPlantReliabilityandInformationLab

Mitigation coverage estimation of passive systems using causal reasoning analysis with Multi-level Flow Model

Rensselaer polytechnic institute In Seop Jeon, Junyung Kim, Robby Christian, Hyun Gook Kang

•  Multilevelflowmodeling(MFM)isaqualitativemodelingmethodologyforrepresentingcomplex

systemsatdifferentabstractionlevel.

•  Itrepresentsgoalsandfunctionsofindustrialprocessinvolvinginteractionsbetweenfunctionsofmaterialandenergy.

2

Multilevel flow modeling

SyntaxofMFMmethod

•  Functionalmodelingframeworkhashierarchicalmodelingcapabili

tytohandleacomplicatedengineeringsystem.

•  Sinceitisdifficulttohandleallthecomplexitiestogetheratadetaile

dlevel,thisabstractionmethodologyhasadvantagestosimplifycom

plexsystemssystematicallyatdifferentabstractionlevel.

3

MFM modeling for PWR •  SystemsconsideredinMFMmodel

•  Reactorcoolantsystem

•  Safetyinjectionsystem

•  High-pressureinjectionsystem

•  Low-pressureinjectionsystem

•  Main&Auxfeedwatersystem

•  Motor-drivensystem

•  Turbine-drivensystem

•  Circulatingwatersystem

•  Electricitysupplysystem

•  In-containmentrefuelingstoragetank MFMmodelofPWR

•  IntheMFMmodel,thecausalrelationsbetweenthecomponentsintheNPPcanbeexpressedinlinguistic

representation.

4

Causal inference analysis

CausalinferencepropagationinMFMmo

del

Heatgenerationfromfuellow

Decayheattransferratefromfueltove

ssellow

Highheataccumulationinwaterofves

sel

Lowheattransferratefromvesseltoh

ot-leg

Highheataccumulationinwaterofhot-

leg …

→Fuel(Energysource)

Vessel Hot-leg →

Unsatisfactoryofgoal(Decayheattransferratefrom

fueltovessel“LOW”)

EnergystructureofRCS

→HeatremovalthroughSIinjection

Heatremovalthroughsecondarycooling

Influencepropagation

MassstructureofRCS


Startingpoint


•  Allcauses(=abnormalstates)thatinduceunsatisfactorygoalofMFM(=maintaindecayheat

removal)aredefinedbycausalinferenceanalysis.

•  Conversionprocess:fromabnormalstatestofailureevents

•  OnlyabnormalstatescanbeobtainedastheresultsfromtheMFManalysis.

•  SomeabnormalstatesderivedfromtheMFMareonlyconvertedintofailure

events.

•  Aneliminationprocesshasbeenadditionallyproposedtodeterminethe

abnormalstatesthatcanbeappliedtotheconversionprocess.(=3stages)

5

Conversion & Elimination process

Abnormalstates

Converting→

Failureevents Lessamountofcoolantincoldleg Coldlegbreak LowmassflowratethroughMSSV MSSVstuckclose Highmassflowratetoatmosphere

throughADV � ADVstuckopen

•  Basedonresultsoffailuremodeandeffectanalysis,two

typesoffailureeventsareconsidered.

•  Abnormaloperationofcomponents

•  Breakofcomponents

Stage1

Stage2

Stage3

Anexampleofconversionprocess

•  Forredundancydesign,thetruthtablesareappliedtoMFMtodecide

whetherornottargetfunctionsareinabnormalconditionduetoafailureof

someadjacentfunctions.

•  ThesetablesaredevelopedbasedonsuccesscriteriaofsystemsandTH

analysisresults.

•  Booleanequationisutilizedtodevelopallcombinationsoffailureeventsthat

inducedecayheatremovalfailurebasedonMFMmodelandtruthtables.

6

Development of accident scenarios PUMP1fails

PUMP2isavailable

TANK

Leveloftankcanbemaintained

V FALSE TRUE

FALSE FALSE TRUE

TRUE TRUE TRUE

PUMP1

PUMP2

TANK

Combinationthatcauseslowleveloftankcanbedefined(Pump1failureandPump2failure)

Truthtable

SolvingBooleanequation scenario Combinationsoffailure

#1

#2

Truthtabledata

•  AftersolvingBooleanequationwithlogicdiagram,478failurecombinationsaredefinedaspossibleaccident

scenarioswhichcausedecayheatremovalfailure.

7

Development of accident scenarios

# Failure1 Failure2 Failure3 Failure4

1DVIvalvestuckopen

POSRVstuckopen - -

2DVIlinebreak

RCGVSstuckopen - -

3DVIlinebreak

U-tubebreak - - … …

476 SIPfailure MDPfailureMainfeedwaterisolationvalvestuckclose

Turbinebreakfor

TDP

477 SIPfailure MDPfailureMainfeedwaterpumpfailure

TDPfailure

478 SIPfailure MDPfailureMainfeedwaterpumpfailure

Turbinebreakfor

TDP

AccidentscenariosdevelopedbyMFManalysis(Result)

•  Groupofalldefinedaccidentscenarios

•  Group1(High-pressureinjectionfailure+secondarycoolingsystem

failure),415scenarios

•  Group2(High-pressureinjectionfailure+lossofcoolantaccident(L

OCA)),44scenarios

•  UnlimitedLOCA(e.g.hot-legbreak),39scenarios

•  PartialLOCA(e.g.steamgeneratortuberupture),5scenarios

•  Group3(SBO+turbinedrivensecondarycoolingsystemfailure,10

scenarios

•  Group4(Stationblackout(SBO)+LOCA),9scenarios

•  UnlimitedLOCA(e.g.hot-legbreak),8scenarios

•  PartialLOCA(e.g.u-tubebreak),1scenarios

•  ThehybridSafetyInjectionTank(H-SIT)wasinventedtopassivelyinjectcoolantintoareactorcoolant

system(RCS)underanypressureconditionwithoutdepressurization

8

Application of H-SIT system

Equalizingpipe

H-SIT

Pressurizer •  Inlow-pressureaccidents,suchlarge-breaklossofcoolantaccident,theH-SIT

systeminjectswaterusingthepressurefromnitrogengasasaconventional

accumulatorsinNPP.

•  Inhigh-pressureaccidents,itprovidesinventorymake-upbygravitational

forceafterthepressureoftheH-SITequalizeswithRCSpressurethrough

equalizingpipe.

1.  MFMmodelisreconstructedconsideringtheapplicationoftheH-SIT.

2.  AccidentscenariosthatareobtainedfrompreviousanalysisareinsertedintothemodifiedMFM

model.

9

Feasibility analysis of the H-SIT

•  Manytomanymapping

•  Manytomanymappingcanbeexplainedthatthesameendcanbe

realizedbymanyalternativemeans.

•  Causalinference

•  Additionalmeansnotonlybeusedtodirectlyachieveanobjective,

butalsobeusedtoenableotherfunctions,whichcanaffect

objective.

Manytomanymapping

Causalinference

3.  Alternativeways(=counter-measure)tosatisfytheobjectareidentifiedin

considerationoftwoapproaches.

10

Example of H-SIT application •  ReflectionofpredefinedaccidentscenariotoMFMmodel

•  Reactorcoolantgasventingvalve(RCGVV)stuckopen+SIP

inletvalvestuckclose

•  DeterminationofalternativemitigationwayswiththeH-SIT

bycausalreasoninginMFMmodel

•  High-pressureinjectionfromH-SITisapplied(tra37)

•  RCSdepressurization(obj1)keepssuccess.

>>Low-pressuresafetyinjection(LPSI)pumpscanbeusedto

injectwaterintothevessel(tra31andtra32arehigh).

>>Continuousdecayheatremovalispossible(tra38ishigh).

>>Stateofgoalchangesfromfailuretosuccess.

RCGVV Startingpoint


Startingpoint


Goalfailure

SIPinletvalve

Low-pressurepumps

=RCGVVstuckopen+SIPinletvalvestuckclosecanbemitigatedbyapplyingtheH-SIT

•  ConsequenceanalysisusingMFM

Startingpoint

Goalsuccess

H-SIT


Startingpoint


High-pressureinjectionbytheH-SIT

RCSdepressurizationissuccess

11

Application of Boolean equation

scenario Cutset

#1

#2

SolvingBooleanequation

•  Scenario2intable1canbecoveredbyapplyingmean3.

•  Insameway,allscenarioswhicharemitigatedbyapplyingtheH-SITcanbeidentified.

•  Mitigationcoveragecanbeestimatedbasedontotalnumberofmitigatedscenarios.

scenario Cutset

#1

#2

SolvingBooleanequation

•  BasedonconsequenceanalysisresultsfromMFManalysis,Booleanequationisrecalculatedto

determinethemitigatedaccidentscenarios.

•  MitigationcoverageestimationoftheH-SIT

•  Group1(High-pressureinjectionfailure+secondarycoolingsystemfailure)

•  249scenarioscanbemitigatedamong415scenarios,Mitigationcoverage=60%

•  Group2(High-pressureinjectionfailure+LOCA)

•  (UnlimitedLOCA),24scenarioscanbemitigatedamong39scenarios,Mitigationcoverage=61.5%

•  (PartialLOCA),3scenarioscanbemitigatedamong5scenarios,Mitigationcoverage=60%

•  Group3(SBO+turbinedrivensecondarycoolingsystemfailure),10scenarios

•  10scenarioscanbemitigatedamong0scenarios,Mitigationcoverage=0%

•  Group4(SBO+LOCA)

•  (UnlimitedLOCA),8scenarioscanbemitigatedamong0scenarios,Mitigationcoverage=0%

•  (PartialLOCA),1scenarioscanbemitigatedamong1scenarios,Mitigationcoverage=100%

12

Analysis results

13

Mitigation strategies with the H-SIT

Group2(High-pressureinjectionfailure+unlimitedLOCA)

Developmentoflong-termmitigationstrategywithSCPandH-SIT

Group2(High-pressureinjectionfailure+partialLOCA),

Group4(SBO+partialLOCA)

Developmentoflong-termmitigationstrategywithsecondarycoolingsystemandH-SITunderSGTR

Group3(SBO+turbinedrivencoolingsystemfailure)

Group4(SBO+unlimitedLOCA),

DevelopmentofmitigationstrategyforcopingtimeextensionwithH-SIT

Group1(High-pressureinjectionfailure+secondarycoolingsystemfailure)

Developmentoffeedandbleed(F&B)mitigationstrategywithH-SITunderlow-pressurecondition

mitigation coverage estimation of passive system s using ... · • after solving boolean equation...

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