ML112770237

LOCA Frequencies for STP GSI-191( Final)

ML112770237
Person / Time
Site:	South Texas
Issue date:	09/30/2011
From:	Chrun D, Kreslyon Fleming, Lydell B South Texas, KNF Consulting Services, Risk Management, Scandpower
To:	Balwant Singal Plant Licensing Branch IV
Singal, B K, NRR/DORL, 301-415-301
Shared Package
ML112770162	List: ML112770170 ML112770176 ML112770203 ML112770230 ML112770237 ML112770246 ML112770251
References
TAC ME5358, TAC ME5359, GSI-191
Download: ML112770237 (78)

Text

Development of LOCA Initiating Event Frequencies for South Texas Project GSI-191 Final Report for 2011 Work Scope Developed for South Texas Project Electric Generating Station by Karl N. Fleming KNF Consulting Services LLC Bengt O. Y. Lydell Danielle Chrun September 2011

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Table of Contents 1.

Introduction..........................................................................................................................................7 1.1 Background...................................................................................................................................7 1.2 Objectives......................................................................................................................................8 1.3 ReportGuide.................................................................................................................................8 2.

TechnicalApproachtoLOCAFrequencyQuantification.......................................................................9 2.1 BasicLOCAFrequencyModel.......................................................................................................9 2.2 StepbyStepProcedureforLOCAFrequencyEvaluation...........................................................11 3.

FailureRateDevelopment(Step1).....................................................................................................15 3.1 DefinitionofComponentTypes(Step1.1).................................................................................15 3.2 EvaluationScopefor2011..........................................................................................................18 3.3 FailureDataQuery(Step1.2)......................................................................................................18 3.4 ComponentPopulationExposure(Step1.3)...............................................................................20 3.4.1 ReactorYearsofServiceExperience...................................................................................20 3.4.2 ComponentExposureEstimatesforHotLegWelds...........................................................21 3.4.3 DegradationMechanismAssessment.................................................................................22 3.4.4 ComponentExposureforHotLegWelds............................................................................24 3.5 PriorDistributionsforHotLegWeldFailureRates(Step1.4)....................................................24 3.6 FailureRateBayesUpdates(Step1.5).......................................................................................24 3.7 FailureRateDistributionSynthesis(Steps1.6and1.7)..............................................................27 3.8 FailureRatesforOtherCalculationCases(Step1.7)..................................................................28 4.

ConditionalRuptureModeProbabilityModel(Step2)......................................................................34 4.1 OverviewofCRPModelApproach..............................................................................................34 4.2 UseofNUREG1829Data............................................................................................................36 4.3 ModelforDerivingConditionalProbabilitiesfromRuptureFrequencies..................................38 4.4 SelectComponentstoDefineCRPModelCategories(Step2.1)................................................39 4.5 UseofDatafromNUREG1829ExpertElicitation(Steps2.2and2.3)........................................41 4.6 Developmentof40YearLOCAFrequencyDistributions(Step2.4)...........................................41 4.7 DevelopExpertCompositeDistributionsfromNUREG1829(Step2.5).....................................47 4.8 BenchmarkofLydellsBaseCaseAnalysis(Step2.6)..................................................................50 4.9 SelectTargetLOCAFrequenciesfromNUREG1829Data(Step2.7)..........................................54 4.10 DevelopConditionalRuptureProbabilitiesfromTargetLOCAFrequencies(Step2.8)..............58

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4.11 BayesUpdateoftheConditionalProbabilityDistributions(Step2.9).......................................62 5.

LOCAFrequenciesforSTPGSI191Application(Step3)....................................................................65 5.1 WeldCountsandPipeSizesforEachComponent(Steps3.1and3.2).......................................65 5.2 ComponentLOCAFrequencyDistributions(Step3.3)................................................................65 5.3 ApplicationofMarkovModeltoAddressImpactofNDEProgram(Step3.4)...........................66 5.4 TotalLOCAFrequenciesforRISKMAN(Step3.6)........................................................................71 5.5 LOCAFrequencySummary..........................................................................................................76 6.

References..........................................................................................................................................77

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Figures

Figure21StepbyStepProcedureforLOCAFrequencyQuantification-Page1of2..............................13 Figure22StepbyStepProcedureforLOCAFrequencyQuantification-Page2of2..............................14 Figure31PIPExpDatabaseandRelationshiptoOtherDatabases[20].....................................................19 Figure32DamageandDegradationMechanismsinCommercialLightWaterReactorPlants................23 Figure33EventTreeModeltoRepresentUncertaintyinHotLegWeldExposureforThermalFatigue..25 Figure34ComparisonofMeanFailureRatesforCalculationCases.........................................................33 Figure41Category1LOCAFrequenciesforPWRPipingSystemsat25YearsofPlantOperation (ReproducedfromFigureL.13inNUREG1829).........................................................................................38 Figure42ComparisonofMixtureandGeometricMeanCompositeDistributions-RCSHotLeg...........49 Figure43ComparisonofMixtureandGeometricMeanCompositeDistributions-RCSSurgeLine.......49 Figure44BenchmarkingofLognormalDistributionstoLydellBaseCaseResults-HPIInjectionLine....51 Figure45BenchmarkingofLognormalDistributionstoLydellBaseCaseResults-RCSSurgeLine........51 Figure46BenchmarkingofLognormalDistributionstoLydellBaseCaseResults-RCSHotLeg.............52 Figure47ComparisonofExpertsGeometricMeanandLydellBaseCase-RCSHotLeg........................55 Figure48ComparisonofExpertsGeometricMeanandLydellBaseCase-RCSSurgeLine....................55 Figure49ComparisonofExpertsGeometricMeanandLydellBaseCaseHPILine................................56 Figure410ComparisonofLydellandSTPModelsforCRP-RCSHotLeg.................................................60 Figure411ComparisonofLydellandSTPModelsforCRP-RCSSurgeLine............................................60 Figure412ComparisonofLydellandSTPModelsforCRP-HPILine.......................................................61 Figure51LOCAFrequenciesvs.BreakSizeforBFWeldsinHotLeg(Category1A)................................69 Figure52LOCAFrequenciesvs.BreakSizeforBJWeldsinHotLegSubjecttoThermalFatigue(Category 1C)...............................................................................................................................................................69 Figure53ComparisonofMeanFrequenciesforHotLegWelds...............................................................70 Figure54ComparisonofWeldFailureRatesDeterminedbyMarkovModelforDifferentReliability IntegrityManagementApproaches............................................................................................................71 Figure55ComparisonofLOCAFrequenciesforPipes:STPvs.NUREG1829...........................................73 Figure56ComparisonofUncertaintyDistributionsforSTPPipeInducedLOCAandNUREG1829Total LOCAFrequencies.......................................................................................................................................74 Figure57ContributionstoMeanLOCACategoryFrequenciesbySystem................................................74 Figure58SystemContributionstoMeanLOCAInitiatingEventFrequencies..........................................75 Figure59SystemContributiontoLOCACategory6Frequencies.............................................................75

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Tables

Table21StepbyStepApproachtoLOCAFrequencyDevelopment........................................................12 Table31DefinitionofMajorPipingSystemComponentCases................................................................16 Table32DefinitionofSpecificComponentCategories.............................................................................17 Table33ResultsofClass1FailureDataQuerybySystemandComponent.............................................20 Table34ServiceExperiencebyWestinghouseTypePWRs......................................................................21 Table35EstimationofHotLegWeldsperReactor...................................................................................22 Table36DamageMechanismAssessmentforHotLegWelds..................................................................22 Table37PriorDistributionsforWeldFailureRatesbyDamageMechanism...........................................24 Table38ParametersofBayesUpdatesforHotLegWeldFailureRateCases.........................................26 Table39TotalFailureRatesforHotLegWeldCalculationCases.............................................................27 Table310ComponentPopulationExposureEstimatesforPipeFailureRates.........................................28 Table311DamageMechanismSusceptibilityMatrixforFailureRateDevelopment...............................30 Table312UncertaintyDistributionsforCalculationCaseFailureRates...................................................32 Table41NUREG1829andSTPPRALOCACategories...............................................................................36 Table42AssignmentofPipingSystemCategoriestoCRPModelCategories...........................................40 Table43NUREG1829ExpertDistributionsforHotLegLOCAFrequencies.............................................44 Table44CompositeDistributionsforNUREG1829ExpertsBasedonGeometricMeanMethod...........48 Table45LognormalDistributionsforFailureRatesandConditionalRuptureProbabilities(CRPs)

MatchingLydellsBaseCaseResults...........................................................................................................52 Table46LOCAFrequencyDistributionsfromBenchmarkingofLydellBaseCaseResults.......................53 Table47MixtureDistributionofGeometricMeanandLydellBaseCaseforTargetLOCAFrequencies..57 Table48ParametersofTargetLOCAFrequenciesSelectedforSTPModel..............................................59 Table49STPCRPDistributionPriorsDerivedfromTargetLOCAFrequencies.........................................61 Table410STPCRPDistributionsafterBayesUpdating............................................................................63 Table51LOCAFrequenciesvs.BreakSizeforHotLeg,SGInlet,ColdLeg,andSurgeLineComponent Categories1Athrough4B...........................................................................................................................67 Table52LOCAFrequenciesvs.BreakSizeforPressurizerandSmallBoreComponentCategories5A through6B..................................................................................................................................................67 Table53LOCAFrequenciesvs.BreakSizeforSafetyInjectionandRecirculationSystemCategories7A through7L...................................................................................................................................................68 Table54LOCAFrequenciesvs.BreakSizeforAccumulatorInjectionandCVCSCategories7Mthrough8F

....................................................................................................................................................................68 Table55ResultsforTotalPipeBreakInducedLOCAFrequencies............................................................73

Acronyms

ASME AmericanSocietyofMechanicalEngineers BJ ASMESectionXISimilarMetalWeld BF ASMESectionXIBimetallic Weld BC BranchConnectionWeld CRP ConditionalRuptureProbability CVCS ChemicalVolumeandControlSystem D&C DesignandConstructionDefects DEGB DoubleEndedGuillotineBreak DM Damage(Degradation)Mechanism ECCS EmergencyCoreCoolingSystem EPRI ElectricPowerResearchInstitute GM GeometricMean GSI GenericSafetyIssue HPI HighPressureInjection IGSCC IntergranularStressCorrosionCracking LOCA LossofCoolantAccident NPS NominalPipeSize PRA ProbabilisticRiskAssessment PWR PressurizedWaterReactor PWSCC PrimaryWaterStressCorrosionCracking PZR Pressurizer RCS ReactorCoolantSystem RIISI RiskInformedInserviceInspection SB SmallBore SIR SafetyInjectionandRecirculationSystems TASC ThermalStratification TF ThermalFatigue TT ThermalTransients SC StressCorrosionCracking TGSCC TransgranularStressCorrosionCracking VF Vibrationfatigue

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1. Introduction

1.1 Background

Thisreportdocumentstheanalysisoflossofcoolantaccident(LOCA)frequenciesinsupportofarisk informedevaluationofGenericSafetyIssue(GSI)191fortheSouthTexasProjectElectricGenerating Station(STPEGS)Units1and2.Thescopeofworkcoveredinthisreportistodevelopthelocationand breaksizedependentinitiatingeventfrequenciesandassociateduncertainties,andtoprovidetechnical supporttointerfacingtasksthatarenecessarytodeterminetherisksignificanceofdebrisinduced failuresofcorerecirculationheatremovalduringLOCAs.

Historically,probabilisticriskassessments(PRAs)haveincludedasmallsetofinitiatingevents characterizedbythephysicalsizesandthroughwallflowratesassociatedwithbreachesintheprimary reactorcoolantsystem(RCS)pressureboundary,commonlyknownasLOCAs.Considerationofthe locationofthebreachhaslargelybeenlimitedtothatassociatedwithsocalledexcessiveLOCAs,i.e.

breachesinthereactorpressurevesselthatexceedthecapabilitiesoftheemergencycorecooling systems(ECCSs)topreventcoredamage,andinterfacingsystemLOCAs(ISLs).ISLsrefertoevents wheretheintegrityoftheRCSpressureboundaryisbreachedthroughfailureofisolationvalveswhich separatetheRCSfromsafetysystemsoflowerdesignpressure.Theresultingoverpressurizationcould leadtoaLOCAwithleakflowpathbypassingthecontainmentandtherebydefeatingtherecirculation coolingfunctionsoftheECCS.IntypicalPRAs,theremainingLOCAsinsidethecontainmentare differentiatedonlywithrespecttosize,basedontherebeingdifferentsuccesscriteriaforpreventing coredamagefordifferentsizedLOCAs.ThedifferencesinsuccesscriteriaforthedifferentLOCAsizes relatetodifferencesinrequirementsforsecondarysideheatremoval,highpressureandlowpressure safetyinjection,andforimplementingreactorshutdown.

ThecurrentSTPEGSPRAmodelhasdifferentinitiatingeventsforbreacheswithequivalentbreaksizeof 0.5"to2.0",referredtoasSmallLOCAs,thosewithbreaksizesbetween2"and6",referredtoas MediumLOCAs,andthosewithbreaksizesfrom6"uptoandincludingadoubleendedbreakfromthe largestpipeintheRCS,knownasLargeLOCAs.TheVerySmallLOCAs,withbreaksizeslessthan0.5",are excludedbecausetheywouldbesmallenoughtobewithinthemakeupofthechemicalvolumeand controlsystem(CVCS),whoseoperationwouldbeexpectedtoprecludeasafetysystemactuationto mitigateaLOCA.

TheSTPRiskInformedGSI191ClosurestudyinvestigatesthesizeandlocationofLOCAsmorefinelyin ordertoassesstheriskofdebrisformationduringtheLOCAsthatcouldinterferewiththeoperationof theECCSsduringtherecirculationphaseafteranRCSbreach.Thesizeandlocationofthebreakcould influencetheamountofdebrisformationandthetimingandneedforactionstoinitiateorterminate containmentspraysandrecirculationcooling.ThepurposeofthisstudyistorevisetheLOCAinitiating eventfrequencyasneededtodeterminethemostrisksignificantbreaksizesandlocationsforthis genericsafetyissue.

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1.2 Objectives Theobjectivesofthisstudyareto:

DefineofasufficientsetofRCSpipingsystemfailurecategoriestosupporteachlocationtobe evaluatedfordebrisformation-tobeworkedoutwiththeintegratedteam.

Providefailureratesvs.breaksizeforallLOCAlocationswithinthescopeoftheevaluation.This includesafullquantificationofaleatoryandepistemicuncertaintiesthataddressesboth parameterandmodelinguncertainties.Thelocationsshallincludepipewelds,nonweld locationswithinthepiping,andnonpipecontributions,e.g.,ReactorCoolantPump(RCP)seals.

ProviderevisedestimatesoftheinitiatingeventfrequenciesforSmall,Medium,andLarge LOCAsforuseasinputstothePRAmodelforthisGSI191evaluation.

IncludetheresultsoftheRIISI(riskinformedinserviceinspection)evaluation,including damagemechanism(DM)assessmentresultsandwhichweldlocationsareselectedforinclusion fornondestructiveexaminations(NDE).

SupportthecalculationflowsheetinterfacesamongtheLOCAfrequency,debrisformation, thermalhydraulicsanalysis,andriskanalysistoensureproperintegration.

SupportprojectmeetingsandNRCmeetingsandassociatedreviews.

Incorporateinputfromindependentreviewsthatarebeingdonetosupporttheproject.

ThecurrentreportconsidersLOCAsinitiatedatornearthelocationofpipeandnozzlewelds.Arevision plannedfor2012willaddresspipefailuresatotherlocationsandnonpiperelatedfailuresintheRCS pressureboundary.

1.3 Report Guide ThetechnicalapproachtodeterminingLOCAfrequenciesissummarizedinSection2.Thisapproach makesuseofamodelthatexpressesLOCAinitiatingeventfrequenciesasafunctionofpipingsystem failureratesandconditionalprobabilitiesofpiperuptureoverarangeofbreaksizes.Themodelsand datausedtodevelopthepipingsystemfailureratesaredocumentedinSection3.Section4presentsthe approachthatwasselectedtoderivetheconditionalruptureprobability(CRP)vs.breaksize,givenpipe failure,togetherwithatechnicaldescriptionoftheresultingCRPmodels.TheLOCAfrequencyresults arepresentedinSection5.TheseresultsincludethosetobeusedatspecificlocationswithintheRCS pressureboundary,aswellastheSmall,Medium,andLargeLOCAfrequenciesforuseinthePRAmodel.

ComparisonswithgenericindustryestimatesofLOCAfrequenciesareincludedwiththeseresults.

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2. Technical Approach to LOCA Frequency Quantification 2.1 Basic LOCA Frequency Model ThetechnicalapproachtoestimatingLOCAinitiatingeventfrequenciesisbasedonthemodelexpressed byEquations(2.1)and(2.2)forestimatingthefrequencyofaLOCAofagivensize.Theparameterxis treatedasadiscretevariablerepresentingdifferentbreaksizeranges.Here,xtakesonvalues

{1,2,3,4,5,6}tocorrespondwiththeLOCAcategoriesdefinedinNUREG1829[1].Weshallusethe NUREG1829categorieswiththeunderstandingthatthesemayberedefinedlaterifnecessary.

i ix i

x m

LOCA F

)

(

(2.1) ik ik x

k ik ix I

F R

P

)

(

(2.2) where:

)

(

x LOCA F

FrequencyofLOCAofsizex,perreactorcalendaryear,subjectto epistemicuncertaintycalculatedviaMonteCarlo

i m

Numberofpipeweldsoftypei;eachtypedeterminedbypipesize, weldtype,applicabledamagemechanisms,andinspectionstatus (leaktestandNDE);nosignificantuncertainty

ix

Frequencyofruptureofcomponenttypeiwithbreaksizex,subject toepistemicuncertaintycalculatedviaMonteCarloorlognormal formulas

ik

Failurerateperweldyearforpipecomponenttypeiduetofailure mechanismk,subjecttoepistemicuncertaintydeterminedbyRIISI BayesmethodandEq.(2.3)below

)

(

ik x F R

P Conditionalprobabilityofruptureofsizexgivenfailureofpipe componenttypeiduetodamagemechanismk,subjecttoepistemic uncertaintydeterminedviaexpertelicitationusingNUREG1829data

ik I

Integritymanagementfactorforweldtypeiandfailuremechanismk, subjecttoepistemicuncertaintydeterminedbyMonteCarloand Markovmodel

Forapointestimateofthefailureratefortypeiandfailuremechanismk:

i i

ik ik ik ik ik T

N f

n n

(2.3) where:

ik n

Numberoffailuresinpipecomponent(i.e.,weld)typeiduetofailure mechanismk;verylittleepistemicuncertainty

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ik

Componentexposurepopulationforweldsoftypeisusceptibleto failuremechanismk,subjecttoepistemicuncertaintydeterminedby expertopinion

ikf Estimateofthefractionofthecomponentexposurepopulationfor weldtypeithatissusceptibletofailuremechanismk,subjectto epistemicuncertainty,estimatedfromresultsofRIISIforpopulation ofplantsandexpertopinion

i N

Estimateoftheaveragenumberofpipeweldsoftypeiperreactorin thereactoryearsexposureforthedataqueryusedtodeterminenik, subjecttoepistemicuncertainty,estimatedfromresultsofRIISIfor populationofplantsandexpertknowledgeofdamagemechanisms

iT Totalexposureinreactoryearsforthedatacollectionforcomponent typei;littleornouncertainty

ForaBayesestimate,apriordistributionforthefailurerateisupdatedusingnikandikwithaPoisson likelihoodfunction.

TheformulationofEquation(2.3)enablesthequantificationofconditionalfailurerates,giventhe knownsusceptibilitytothegivendamagemechanism.Whentheparameterfikisapplied,theunitsofthe failureratearefailuresperweldssusceptibletothedamagemechanism.Thisformulationofthefailure rateestimateisdonebecausethesusceptibledamagemechanismsareknownfromtheresultsofa previouslyperformedriskinformedinserviceinspectionevaluationforSTPEGS.Iftheparameterfik is setto1.0,thefailureratesbecomeunconditionalfailurerates,i.e.,independentofanyknowledge aboutthesusceptibilityofdamagemechanism,oralternativelythat100%ofthecomponentsinthe populationexposureestimateareknowntobesusceptible.

Thekeyinputsthatareneededtoprovidethepipefailurerateinformationinclude:

Identificationofwhichlocationswillbeinvestigatedfordebrisformation,thegroupingsof locationsthatwillbeperformedtosupporttheriskevaluation,andadefinitionofcomponent categoriesthatarerepresentativeofallpipefailurelocationswithintheSTPEGSClass1pressure boundary.

Countsofpipefailuresinapplicablenuclearindustrypipingsystems-essentiallyallthefailure datainASMEClass1and2pipingsystemsinPWRsinU.S.serviceexperienceandapplicable internationalplantswithsimilardesignsandintegritymanagementprograms-fromthePIPExp database.[2]

Pipeexposureestimates-quantityofpipeandpipeweldsandthereactoryearsofservice experiencethatproducedthefailurecountsidentifiedabove.Theseestimatesarebasedon informationcontainedinthePIPExpdatabaseaswellastheinformationavailableinrisk informedinserviceinspectionsubmittalstotheNRC,whichincludeanenumerationofweld countsindifferentcategoriesandtheresultsofdamagemechanismevaluations.

Estimatesofthefractionsofpipingsystemcomponentsintheservicedatathataresusceptible todifferentdamagemechanisms.TheseestimatesarebasedonNUREG1829andsupporting

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computerfilesthatprovideinformationonepistemicuncertaintyaboutpiperupture frequenciesvs.breaksizefordifferentpressureboundarycomponents.

STPRIISIevaluationreportandsupportingcalculationsprovidinginformationonapplicable damagemechanismsforeachweldandanidentificationofwhichweldsareselectedforNDE.

ResultsofinspectionreportsandotherevidenceofanypipefailureordegradationatSTPthat mayinfluencetheplantspecificfailurerates,aswellastheinformationneededtoestimate exposuredata.

TheintegritymanagementfactorIikofEquation(2.2)isquantifiedusingtheMarkovmodelforPiping ReliabilitythatwasdevelopedtosupporttheEPRIRIISIprojects.

Themethodologyoutlinedaboveandthemethodsanddatabasesthathavebeendevelopedto implementthisapproachwereoriginallydevelopedtosupporttheEPRIRIISImethodologythathas beenimplementedformanyoftheexistingNRClicensedplantsandseveralforeignplants.Thepartof thismethodologythatisrelevanttoestimatingLOCAfrequenciesisdescribedindetailinReference[3]

andhasbeenrecentlyappliedinEPRIsponsoredprojectstodeveloppipingsystemfailureratesforuse ininternalfloodingandhighenergylinebreakPRAs,asdocumentedinReferences[4]and[5].The originalEPRIstudythatwasresponsiblefordevelopingtheMarkovmodelandBayesmethodfor estimatingpipefailureratesandrupturefrequencieswasdocumentedinEPRITR110161[6],andan earlyversionofthepipefailureratedatabaseforbothconditionalandunconditionalpipefailurerates waspublishedinEPRITR111880[7].Anindependentreviewofthesereportswascarriedoutbythe UniversityofMaryland,whichvalidatedthemethodologythatwasdevelopedinthesereports.These methodsanddatawerethenusedaspartoftheEPRIRIISItechnicalapproachasdescribedintheEPRI RIISITopicalReport[9].TheNRCapprovedthesemethodsanddataforuseinappliedRIISIevaluations asdocumentedintheSafetyEvaluationReport(SER)[10].TheSERwassupportedbyanindependent reviewoftheBayesfailureratemethodandtheMarkovmodelbyLosAlamosNationalLaboratory[11],

whichprovidesasecondindependentreviewofthemethodology,includingavalidationoftheMarkov modelsolutions.

TheapplicationoftheMarkovmodelrequiresthedevelopmentofrathercomplexclosedformsolutions tothedifferentialequationssupportingtheMarkovmodel,whichwereoriginallydevelopedinTR 110161andarealsopublishedinReference[12].Usingtheseclosedformsolutions,itisstraightforward toquantifytheuncertaintiesintheresultinginspectionfactorsusingMonteCarlosimulationmethods viaMicrosoftExcel'andOracleCrystalBall',whichistheapproachbeingusedinthisSTPGSI191 evaluation.BayesupdatestepsintheanalysisofLOCAfrequencywereperformedusingtheRDAT Plus'Version1.5.8Program.

2.2 StepbyStep Procedure for LOCA Frequency Evaluation AstepbystepprocedureforevaluatingtheLOCAfrequenciesforeachlocationasafunctionofbreak sizeandcollectivelyforthedeterminationofSmall,Medium,andLargeLOCAfrequenciesforthePRA modeliscomprisedofthestepsinTable21anddepictedinFigures21and22.

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Table21StepbyStepApproachtoLOCAFrequencyDevelopment

1. FailureRateDevelopment 1.1 Determinecomponentandweldtypesi 1.2 Performdataqueryforfailurecountsn 1.3 EstimatecomponentexposureT 1.4 Developcomponentfailureratepriordistributionsforeachdamagemechanism(DM) 1.5 PerformBayesupdateforeachexposurecase(combinationofweldcountcaseandDM susceptibility[DMS]case) 1.6 Developmixturedistributiontocombineresultsfordifferentexposurehypothesesto yieldconditionalfailureratedistributionsikgivenSTPspecificapplicableDMs 1.7 Calculatetotalfailurerateoverallapplicabledamagemechanismsik

2. ConditionalRuptureProbability(CRP)DevelopmentP(RxFik) 2.1 Selectcomponentstodefineconditionalruptureprobability(CRP)modelcategories 2.2 ObtainexpertreferenceLOCAdistributionsfromNUREG1829 2.3 Obtainexpertmultiplierdistributionsfor40yrLOCAfrequenciesfromNUREG1829 2.4 Determine40yrLOCAdistributions(productofSteps2.2and2.3)foreachexpert,fitto lognormal 2.5 DeterminegeometricmeanofexpertdistributionsfromStep2.4(lognormal) 2.6a BenchmarkLydellBaseCaseAnalysisforselectedcomponents 2.6b DeterminefailureratedistributionforLydellBaseCaseAnalysisinNUREG1829;fitto lognormal 2.6c ApplyLydellCRPmodelfromBaseCaseAnalysis 2.6d DetermineLOCAfrequencydistributionfromLydellBaseCaseAnalysis 2.7 DeterminemixturedistributionofNUREG1829GM(fromStep2.5)andLydellLOCA frequency(fromStep2.6dtoobtainTargetLOCAfrequencydistributionforeachCRP categorycomponent 2.8 ApplyformulastocalculateCRPdistributionstobeusedaspriordistributionsforeach validcombinationofCRPcategoryandcomponent 2.9 ForeachcomponentinagivenCRPcategory,performBayes'updatewithevidenceof failureandrupturecountsfromservicedata

3. STPSpecificLOCAFrequencyDevelopment 3.1 Determineweldcountsandpipesizesforeachcomponentmi 3.2 IdentifywhichlocationsareinandoutoftheNDEprogram 3.3 CombinetheresultsofStep1andStep2forcomponentLOCAfrequencies 3.4 ApplyMarkovmodeltospecializerupturefrequenciesforNDEornoNDEIik 3.5 ProvidelocationbylocationLOCAfrequenciesvs.breaksizetoCASAGRANDEjx 3.6 ProvideSmall,Medium,andLargeLOCAfrequenciestoRISKMAN - F(LOCAx)

TheapplicationofSteps1,2,and3isdocumentedinSections3,4,and5,respectively.

QueryPIPExp DatabaseforPipe FailuresandPipe PopulationExposure foreachComponent Type STPPlantDesign Information IncludingRIISI EvaluationforSTP 1.2CountsofPipeFailuresand LOCAsforEachDMandComponent 1.3PipePopulationExposurefor eachDMandComponent 1.3UncertaintyDistributionsfor PipePopulationExposureInputs 1.4PriorDistributionsforeachDM andComponentFailureRate 1.5Upto9Bayes Updates,onefor eachexposure hypothesis 1.6Mixture Distributionto ObtainConditional FailureRategiven STPSpecificDMs 1.1ApplicableDMsforeach Component 3.1WeldCountsandPipeSizes 1.7Distributionfor theTotalConditional FailureRateoverAll ApplicableDMs 2.9BayesUpdated CRPDistributionfor EachComponent withFailureand LOCACount Evidence 2.8CRPModel CategoryPrior DistributionforEach LOCACategory (BreakSize)

From Page2 3.3Component LOCAFrequency Distribution=

ProductofFailure RatexCRP Distributions 3.6TotalLOCA Frequenciesfor EachLOCA Category forRISKMAN 3.5Component LOCAFrequencies vs.BreakSizefor CASAGRANDE 1.1Applicable Component(Weld)

Types 3.2IdentifyWhichLocationsare SubjectedtoNDE 3.4ApplyMarkov ModeltoAccount forImpactofNDE Program

Figure21StepbyStepProcedureforLOCAFrequencyQuantification-Page1of2

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Figure22StepbyStepProcedureforLOCAFrequencyQuantification-Page2of2

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3. Failure Rate Development (Step 1)

ThissectiondocumentsthefailureratedevelopmentforSTPEGSpipingsystems,whichcomprisesStep1 intheprocedureoutlinedinSection2.Asdescribedintheprevioussection,thisstepiscomposedofthe followingkeytasks:

1.1 Determinecomponentandweldtypes 1.2 Performdataqueryforfailurecounts 1.3 Estimatecomponentexposure 1.4 Developcomponentfailureratepriordistributionsforeachdamagemechanism(DM) 1.5 PerformBayesupdateforeachexposurecase(combinationofweldcountcaseandDM susceptibilitycase) 1.6 Developmixturedistributiontocombineresultsfordifferentexposurehypothesesto yieldconditionalfailureratedistributionsgivenSTPspecificapplicableDMs 1.7 CalculatetotalfailurerateoverallapplicableDMs 3.1 Definition of Component Types (Step 1.1)

Thefirstthreetasksoffailureratedevelopment(determinecomponenttypes,performdataqueryfor failurecounts,andestimationofcomponentexposure)areperformedasaniterativeprocess.Insights fromreviewingfailuredataareusedtoformulatecriteriafordefininghomogeneouspopulationsfor estimatingfailurerates.Theavailabledatafromwhichtoestimatecomponentexposuresalsoinfluences thecharacterizationofcomponenttypesinthesensethatsomegroupsofcomponentsmayexhibit unusuallyhighorlowincidenceoffailurescomparedtoothersimilarcomponents.Thefollowingcriteria wereusedtodeterminehomogeneouspipingcomponenttypes:

Pipematerials Pipesize Applicabledamageordegradationmechanisms1(DMs)

Unusualdistributionofcomponentfailures Inserviceinspectionprogramstatus(withinoroutsidethescopeofnondestructive examinations[NDEs])

Thefirststepindefiningcomponentcategorieswastodefinetheeightmajorpipingsystemcases, describedinTable31basedonthecriterialistedabove.Thesecaseswerethenfurthersubdividedto accountforspecificcombinationsofdamagemechanismsandpipesizes,asshowninTable32.This morerefinedsubdivisionformedthehomogeneouscomponentcategoriesthathavedistinctfailurepipe failureratesandrupturefrequencydistributions.The8systemcasesgiveriseto45component

1Thetermsdamagemechanismanddegradationmechanismareusedinterchangeablyinthisreport.

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calculationcases.Ingeneral,itisassumedthatthemaximumbreaksizeistheequivalentbreaksizeofa doubleendedguillotinebreak(DEGB)ofthepipe.IfDistheinsidediameterofthepipe,theDEGBsizeis D

2 Table31DefinitionofMajorPipingSystemComponentCases Case Description WeldType Damage Mechanism(DM)

Comment 1

RCSHotLegExcl.

SGInlet BF PWSCC,D&C DesignbasisLOCAlocation;BFweldhashigher failureratebutlocatedinsideRxcavity BJ TF,D&C 2

RCSColdLeg BF PWSCC,D&C Lowertemperaturesanddifferentpipesizes relativetohotleg BJ D&C 3

RCSHotLegSG Inlet BF PWSCC,D&C ThiscasedefinedtoaddressS/GInletnozzleto safeendweldthathasunusualfailurecount distribution[1]

4 PZRSurgeLine BF PWSCC,TF,D&C Includessurgelinefrombranchconnectionsand nozzlestopressurizersafeend;entiresurgeline subjectedtothermaltransientsduringstartup andshutdown BJ,BC TF,D&C 5

PZRMediumBore Piping BF PWSCC,TF,D&C Thisincludespressurizerspray,andreliefvalve pipingexcludingthepressurizersurgeline;BF weldsatSTPinthiscategoryhaveweld overlays[2]

BJ,BC TF,D&C 6

Class1SmallBore Piping BJ TF,D&C,TGSCC, VF ThisisalltheClass1pipingofsize2"andless andinsideisolationvalves 7

Class1Medium BoreSIRPiping BJ TF,D&C,IGSCC Safetyinjectionandresidualheatremoval(RHR) systemsinstandbyduringnormaloperation; Class1isinsidetheisolationvalves 8

Class1Medium BoreCVCSPiping BJ,BC TF,D&C,TGSCC, VF CVCS pipingwithinjectionandletdownflow duringnormaloperation BF ASMEXICategoryBFwelds(bimetallic)

BJ ASMEXICategoryBJwelds(singlemetal)

BC Branchconnectionwelds,BJweldsusedatbranchconnections CVCS Chemical,Volume,andControlSystem D&C DesignandConstructionDefects IGSCC IntergranularStressCorrosionCracking PWSCC PrimaryWaterStressCorrosionCracking PZR Pressurizer RCS ReactorCoolantSystem SIR SafetyInjectionandRecirculationSystems TF ThermalFatigue,includingthatduetothermaltransients(TT)andthermalstratification(TASC)

TGSCC TransgranularStressCorrosionCracking VF VibrationFatigue Notes:

[1]AnunusuallyhighincidenceoffailuresofthiscomponentwasobservedatJapaneseplantsfollowingSteamGenerator replacements.UntilitcanberuledoutforSTPitisincludedinthisstudy.

[2]NOCAE06002099(January30,2007):InspectionandMitigationofAlloy82/182PressurizerButtWelds,SouthTexas NuclearOperatingCompany.

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Table32DefinitionofSpecificComponentCategories System Case System Component Case Weld Type ApplicableDM STP Total No.of Welds PipeSize (in.)

DEGB Size(in.)

1 RCHotLeg 1A BF SC,D&C 4

29 41.0 1B BJ D&C 11 29 41.0 1C BJ TF,D&C 1

29 41.0 2

RCSGInlet 2

BF SC,D&C 4

29 41.0 3

RCColdLeg 3A BF SC,D&C 4

27.5 38.9 3B BJ 4

31 43.8 3C BJ D&C 12 27.5 38.9 3D BJ 24 31 43.8 4

RCSurge 4A BF SC,TF,D&C 1

16 22.6 4B BJ TF,D&C 7

16 22.6 4C BC 2

16 22.6 4D BJ 6

2.5 3.5 5

PZR 5A BJ TF,D&C 29 6

8.5 5B BJ 14 3

4.2 5C BJ D&C 53 4

5.7 5D BJ 4

3 4.2 5E BJ 29 6

8.5 5F BF SC,TF,D&C 0

6 8.5 5G BF SC,D&C 0

6 8.5 5H BF D&C(WeldOverlay) 4 6

8.5 5I BC D&C 2

4 5.7 5J BJ TF,D&C 2

2 2.8 6

SmallBore 6A BJ VF,SC,D&C 16 2

2.8 6B BJ 193 1

1.4 7

SIRLinesExcl.

Accumulator 7A BJ TF,D&C 21 12 17.0 7B BJ 9

8 11.3 7C BJ SC,TF,D&C 3

8 11.31 7D BJ SC,D&C 3

12 17.0 7E BJ,BC D&C 57 12 17.0 7F BJ 30 10 14.1 7G BJ,BC 42 8

11.3 7H BJ 23 6

8.49 7I BC 5

4 5.7 7J BC 9

3 4.24 7K BC 10 2

2.8 7L BJ 0

1.5 2.1

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System Case System Component Case Weld Type ApplicableDM STP Total No.of Welds PipeSize (in.)

DEGB Size(in.)

SIR Accumulator Lines 7M BJ SC,D&C 0

12 17.0 7N BJ TF,D&C 35 12 17.0 7O BJ,BC D&C 15 12 17.0 8

CVCS

8A BJ TF,VF,D&C 10 2

2.8 8B BJ 19 4

5.7 8C BJ VF,D&C 47 2

2.8 8D BJ 6

4 5.7 8E BC TF,D&C 4

4 5.7 8F BC D&C 1

4 5.7

Total 775

3.2 Evaluation Scope for 2011 TheevaluationthatisdocumentedinthisreportislimitedtotheASMEIIIClass1pipingsystempressure boundaryfailures;i.e.,nonisolableLOCAs.TheClass1boundaryconsistsofallhotleg,coldlegand crossoverlegpiping,pressurizersurge,spray,auxiliaryspray,reliefvalve,safetyvalveandventlines, andoneunit1drainline.ItalsoincludesbranchpipingtotheSafetyInjectionSystem(SIS),Chemical&

VolumeControlSystem(CVCS),andResidualHeatRemovalSystem(RHRS).Allpipingattachedtothe RCSloopsorpressurizervesselisconsideredClass1outtothesecondvalve.Class1SIS,CVCSandRHRS pipingbetweenthefirstandsecondvalveofftheRCSisdiscussedinlatersections.

IsolableLOCAs,seismicallyinducedLOCAs,andLOCAsduetofailuresofcomponentsotherthanpipes willbeconsideredforthe2012workscope,asnecessarytocharacterizedebrisinducedcoredamage risks.Alsoexcludedinthecurrentscopearesteamlineandfeedwaterlinebreaksinsidethe containmentthatcouldleadtoaneedtoimplementrecirculationcoolingand/orcontainmentspray actuationaswellnonpipingpassivecomponentfailures.Ifthosebreaklocationsareregardedas significanttoGSI191,theywillalsobeaddressedin2012.

3.3 Failure Data Query (Step 1.2)

Thisstudyusestheterm"pipefailure"toincludeanyconditionthatleadstorepairorreplacementof theaffectedpipingcomponent.ThisincludesflawsthatexceedASMEcriteriaforrepairorreplacement, cracks,leaks,and,iftheywereobservedtooccur,piperuptures.Thefailuredataqueryfoundthemost severetypeofpipefailuretobeleakwithleakflowratelessthan10gpm.Nonpipefailuresthatcan produceaLOCAaretobeaddressedin2012.Insightsfromreviewofserviceexperienceclearlyshow thatforfailuresinASMEClass1pipingsystems,withtheexceptionofleaksfromvalvesandseals,piping systemfailuresoccuralmostexclusivelyatornearwelds.Infact,theresultsofourdataqueryshowthat 100%oftheexperiencedpipefailuresoccuratornearaweld.SincetheweldsinaClass1pressure boundaryarerelativelyevenlydistributedaroundthepipingsystems,identifyingthefailurelocationsat ornearweldsalsoprovidesforarepresentativesetofpipefailurelocations.Hence,allpipefailuresthat

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significantlycontributetoLOCAfrequenciesmaybeassumedtooccuratornearwelds.Thisassumption willbereplacedbyanexplicitaccountingfornonpipeinducedLOCAsin2012.

AtSTP,thereareapproximately775weldlocationswithintheClass1RCSpressureboundaryincluding approximately200weldlocationsinsmallborepipe(2).Hence,modelingpipefailuresattheseweld locationsusingthe45componentcategoriesinTable32willfacilitatetheanalysisofLOCAsatlarge numberpipefailurelocations.

ThesourceoftheanalyzedpipefailuredataisthePIPExpdatabase[2]whichisdepictedinFigure31.

ThefailuredataquerywasperformedonWestinghouse,MitsubishiHeavyIndustries(MHI),and FramatomePWRplantoperatingexperiencefrom1970through2010andincludedASMEClass1piping systems.ThisgenerallyincludesRCSpipingandsystemsthatinterfacewiththeRCSinsidetheisolation valvesthatnormallyseparatetheRCSfrominterfacingASMEClass2piping.Interfacingsystemsinclude theemergencycorecooling,residualheatremoval,chemicalvolumeandcontrolsystem,andvarious othersystemsincludingReactorPressureVessel(RPV)headventsandinstrumentationlines.Class1 pipingserviceexperiencewithBabcoxandWilcox,CombustionEngineering,andKWU/SeimensPWR plantswasnotconsideredonthebasisofdifferentmaterialsanddegradationsusceptibilitiesrelativeto WestinghousePWRsandthosederivedfromtheWestinghousedesign.Acontributingfactortothis decisionisthatthereissufficientdatafromWestinghousetypeplantstomeettheneedsofthisstudy.

SKI R&D Project 1994-1998 SOAR on piping reliability analysis as it relates to PSA (SKI Report 95:58)

Basis for deriving pipe failure parameters from service data (SKI Report 97:26; PIPExp Database Project (1999 - to date) - independent of SKI Active maintenance program (weekly updates);

QA program - extensive data validation; PIPExp-1999 (12-31-1999)

PIPExp-2000 (12-31-2000)

PIPExp-2001 (12-31-2001)

PIPExp-2002 (12-31-2002)

PIPExp-2003 (12-31-2003)

PIPExp-2011 (08-31-2011) 8287 db records (pipe) 566 water hammer records (w/o structural failure)

OECD/NEA OPDE Project (2002-2011)

Based on SKI-PIPE (1998);

Validation of selected records by National Coordinators; Harmonized db-structure; OPDE-2003 (12-31-2003)

OPDE-2011:1 (05-31-2011)

Figure31PIPExpDatabaseandRelationshiptoOtherDatabases[20]

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TheresultsofthefailuredataqueryareshowninTable33.Becauseroughlyhalfofthecurrentfleetof operatingplantsweredesignedandbuiltpriortothedevelopmentofASMEnuclearpipingcodes,much ofthispipewasoriginallydesignedtoB31.1designcodes,andtheninspectionandISIrequirementsfor Class1pipingwereretrofittedintotheseplants.Sofromadesignandmaterialsperspective,theLOCA sensitivepipingactuallyreflectsamixtureofB31.1andClass1pipe.

Table33ResultsofClass1FailureDataQuerybySystemandComponent System Case System Event Type Nominal Pipe Size Failure Count by DM - Weld Locations Totals D&C SC PWSCC TF V-F 1

RCS Hot Leg Crack 32" 5

5 RCS Hot Leg Leak 32" 1

1 2

RCS Cold Leg Crack 32" 3

3 3

S/G Inlet Crack 32" 19 1

18 4

PZR-Surge Crack 16" 3

3 5

PZR-PORV Crack 4" ø 10" 2

2 PZR-SPRAY Crack 4" ø 10" 2

2 PZR-SPRAY Leak 4" ø 10" 1

1 PZR-SRV Crack 4" ø 10" 6

1 5

PZR-SRV Leak 4" ø 10" 1

1 6

CVCS Crack 1"

1 1

CVCS Leak 1"

6 1

5 Safety Injection Leak 1"

2 2

PZR-Sample/Instr.

Crack 2"

5 1

2 2

PZR-SPRAY Crack 1"

1 1

PZR-SPRAY Leak 1"

3 1

1 1

RCS Crack 2"

14 1

3 2

1 7

RCS Leak 2"

62 12 10 2

2 36 RHR Leak 1"

6 1

5 S/G System Crack 1"

2 1

1 S/G System Leak 1"

4 2

2 7

Safety Injection Crack 4" ø 12" 3

1 2

Safety Injection Leak 4" ø 12" 3

3 RHR Crack 4" ø 12" 1

1 8

CVCS Crack 2" ø 4" 1

1 CVCS Leak 2" ø 4" 6

1 5

Total 163 23 21 46 9

64

3.4 Component Population Exposure (Step 1.3) 3.4.1 ReactorYears of Service Experience Pipecomponentexposureisevaluatedinthecurrentanalysisintermsofpipeweldsinthedataquery.

Thisisestimatedfromacombinationofreactoryearsofserviceexperienceandanestimateofthetotal numberofweldsperplant.Inprinciple,thenumberofweldsperplantisknownbutisseldomfoundin publicdomainreferences.Inaddition,thereisusuallysignificantplanttoplantvariabilityinthenumber ofweldsfordifferentcomponents.Toaddressthis,thecomponentexposure,i.e.,totalweldyearsof

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experienceresponsiblefortheidentifiedfailures,istreatedasanuncertainparameterinfailurerate development.Inaddition,tosupporttheestimationoffailureratesfromdifferentdamagemechanisms, itisnecessarytoestimatethefractionoftheexposurethatissusceptibletoagivendamagemechanism, whichisalsouncertain.ResultsofpublishedreportsonRIISIevaluationsprovidedthebasisforboth weldcountandfractionsusceptibleestimates.

ThereactoryearsofserviceexperiencebyreactortyperesponsibleforthefailuresinTable23arelisted inTable34.

Table34ServiceExperiencebyWestinghouseTypePWRs WE Type Rx Reactor-Calendar Years Initial Grid Connection Initial Criticality 2-Loop 570.1 581.4 3-Loop 2052.6 2096.1 4-Loop 1193.9 1236.5 Total 3816.6 3914.0

Forthepurposesoffailurerateestimation,reactorcalendaryearswasbasedontheinitialgrid connection.

3.4.2 Component Exposure Estimates for Hot Leg Welds Toillustratethedetailedapproachtofailureratedevelopment,thepipingcomponentsforthehotleg areexamined.AsshowninTable32,thehotleghastwotypesofwelds:BF(bimetallic)weldsandBJ (singlemetalwelds).Toestimatefailureratesrequiresestimatingthenumberofweldsinthereactor populationthatcorrespondstothereactoryearsinthedataquery.Forthispurpose,theauthorsofthis reportfromScandpowerreviewedisometricdrawingsforaselectedsampleofPWRplantsand determinedfromthissampleabestestimate,upperbound,andlowerboundofweldcountsperreactor inthedatabase.Thesethreeestimateswereusedtodefineathreepointdiscretedistributionto characterizetheuncertaintyinthetotalreactoryearpopulationthatwasqueriedforfailurecounts.This approachwasdevelopedtosupportpipefailureratedevelopmentfortheEPRIRIISIprogram[7]aspart oftheoverallBayesmethodforpipefailurerateestimation.ThiswasreviewedbyLANL(LosAlamos NationalLaboratory)fortheNRC[11]andapprovedforuseinRIISIevaluationsbytheNRC[10].

AsshowninTable34,thereactoryearpopulationisdistributedamong2loop,3loop,and4loopPWR plants.Forcomponentslikethehotlegandcoldlegwelds,thenumberofweldsperplantmaybe reasonablyassumedtobeproportionaltothenumberofcoolantloops.Thereviewofisometric drawingsat10PWRreactorsproducedthehotlegweldestimatesthatarepresentedinTable35.This samplewasusedtodeterminetheaveragenumberofweldsperloop,theminimum,andthemaximum.

Thisinformationisusedtocharacterizetheuncertaintyintheexposuretermsasdescribedinthe sectionsbelow.

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Table35EstimationofHotLegWeldsperReactor Plant PWR Type NPS29WeldPopulation BFWelds BJWelds BF Welds/loop BJ Welds/loop Braidwood1 4Loop 8

12 2

3 Braidwood2 4Loop 8

12 2

3 Byron1 4Loop 8

12 2

3 Byron2 4Loop 8

11 2

2.75 Kewaunee 2Loop 4

6 2

3 Koeberg1 3Loop 3

9 1

3 Koeberg2 3Loop 3

9 1

3 STP1 4Loop 8

8 2

2 STP2 4Loop 8

8 2

2 V.C.Summer 3Loop 6

6 2

2 Average 1.8 2.68 Min 1

2 Max 2

3

3.4.3 Degradation Mechanism Assessment AswasdeterminedinthedevelopmentoffailureratesfortheEPRIRIISIevaluations,itisassumedthat allweldsaresubjecttodesignandconstructiondefects.Insightsfromserviceexperienceindicatethat certainweldtypesarealwayssusceptibletoaspecificDM,whereasinsomecasesaDMcanberuled outgenericallyforagivenweldtype.Inothercases,thereisuncertaintyonhowmanyweldsinthe reactoryearpopulationthatwasqueriedforthefailurecountsaresusceptibletoagivenDM.The evaluationofDMsusceptibilityforthehotlegweldsisshowninTable36.

Table36DamageMechanismAssessmentforHotLegWelds Calc.

Case System Location Confidence Level WeldSusceptibilityFractions CF D&C ECSCC Fretting IGSCC PWSCC TF TGSCC VF 1A RCHotLeg BF(Un mitigated)

Low N/A 1

N/A N/A N/A 1

N/A N/A N/A Medium N/A 1

N/A N/A N/A 1

N/A N/A N/A High N/A 1

N/A N/A N/A 1

N/A N/A N/A 1B,1C BJ Low N/A 1

N/A N/A N/A N/A 0.01 N/A N/A Medium N/A 1

N/A N/A N/A N/A 0.02 N/A N/A High N/A 1

N/A N/A N/A N/A 0.08 N/A N/A

Thedamagemechanismassessmentisbasedoninsightsfromserviceexperience,resultsofcompleted RIISIevaluationsforWestinghousetypePWRs,andunderstandingoftheDMcriteriathatwere developedfortheEPRIRIISIevaluation[9].Othersourcesofinformationthatwereavailabletoassess damagemechanismsincludetheExpertPanelReportonProactiveMaterialsDegradationAssessment (NUREG/CR6923)[16],SCAPSCCWorkingGroup[17][18],OECDNuclearEnergyAgencytopicalreport onthermalfatigue[19].Dissimilarmetalwelds(CategoryBFwelds)areknowntobesusceptibleto primarywaterstresscorrosioncracking(PWSCC).Onlyasmall,albeituncertainfractionoftheBJwelds

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aresusceptibletothermalfatigueandbotharesusceptibletodesignandconstructiondefects.Forthe PhaseIscopeweldpopulationandbecauseoftheuniqueconjointconditionsfordegradationthatare associatedwiththePWRprimarysystemoperatingenvironment,allotheridentifieddamage mechanismsidentifiedinFigure32canberuledout.Serviceinduceddegradationofreactor componentsresultsfromsynergiesamongmaterialcharacteristics,stressandenvironmentconditions.

IllustratedinFigure32arefourcategoriesofdegradationmechanismsandtheirfailurepotential.The fourcategoriesare:

1) stresscorrosioncracking(SCC)mechanisms,

2) flowassistedmechanisms,

3) corrosionmechanisms,and

4) fatiguemechanisms.

InorderforSSCorfatiguemechanismstodevelopintostructuraldegradationorfailureacrackinitiation mustoccurandthengrowintoasurfaceconnectedcrackandbeyond.Designandconstruction(D&C) defectsoftentimesprovideforcrack/flawinitiation,butnotforcrack/flawgrowth.

Inadditiontotheabovegenericindustryinputstoassessmentofdegradationmechanisms,thestudy alsobenefittedfromaplantspecificriskinformedinserviceinspection(RIISI)evaluationofClass1 pipingthatwasperformedforSTPin2001[21].Thisevaluationincludedadeterministicengineering evaluationofalltheClass1pipeweldsagainstscreeningcriteriathatweredevelopedbyEPRIforusein RIISIevaluations.ThesescreeningcriteriaandtheirtechnicalbasesaredocumentedintheEPRIRIISI TopicalReport[9]whichwasapprovedbytheNRCforuseinappliedRIISIevaluations[10].TheRIISI applicationatSTPwasalsoapprovedbytheNRC.

Figure32DamageandDegradationMechanismsinCommercialLightWaterReactorPlants PSI / ISI Recordable /

Rejectable Flaw Crack - Part Through-Wall (Surface Connected)

Crack - Through-Wall (No Active Leakage)

Active Leakage (< TS Limit)

Active Leakage ( TS Limit)

Structural Failure

("Significant" Through-Wall Flow Rate)

FLAW INITIATION Construction / Fabrication Defect Design Error Maintenance / Repair Error Programmatic / Procedural Error Welding Error Corrosion Fatigue High-Cycle Fatigue Low Cycle Fatigue Thermal Fatigue (TT, TASCS)

Crevice/Pitting Corrosion Galvanic Corrosion General Corrosion MIC - Microbiologically Influenced Corrosion Steam Jet Impingement Erosion Erosion-Corrosion Erosion-Cavitation FAC - Flow-Accelerated Corrosion ECSCC - Cl Induced SCC (ID/OD)

TGSCC PWSCC - Inconel SICC - Strain Induced Corrosion Cracking IGSCC - Stabilized Austenitic SS IGSCC-PWR - Unstabilized Austenitic SS IGSCC-BWR - Unstabilized Austenitic SS Observed Failures D&C (Damage State)

FLAW GROWTH FAILURE ISI / Visual Inspection / Walkdown Inspection / Leak Detection / CR Indication STRESS CORROSION CRACKING PIPE DAMAGE & DEGRADATION / FAILURE MANIFESTATIONS FATIGUE CORROSION FLOW-ASSISTED DEGR.

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3.4.4 Component Exposure for Hot Leg Welds Theuncertaintyincomponentexposureisdeterminedbytheuncertaintyinthecomponent'sweldsper reactorandbythefractionofthoseweldsthataresusceptibletothevariousDMs.Table35showed thatforthehotlegwelds,thereisuncertaintyinthecomponentsperreactorforbothBFandBJwelds.

InadditionthereisuncertaintyinBJweldsusceptibilityforthermalfatigue.Basedonthemethodology developedintheEPRIRIISIprogram,eachofthesesourcesofuncertaintyarecharacterizedbythree pointdiscretedistributions.FortheBJweldspronetothermalfatigue,thereareninecombinationsof exposurederivedfromthetwothreepointdistributions,asshowninFigure33.

3.5 Prior Distributions for Hot Leg Weld Failure Rates (Step 1.4)

PriordistributionsforeachDMweredevelopedforthefailureratedevelopmentintheEPRIRIISI programinReference[7],basedonearlyestimatesofpipefailurerates,engineeringjudgment,and insightsfromreviewofservicedata.ThisispartofthemethodologythatwasreviewedbyLANL[11]and approvedbytheNRC[10]forRIISIevaluationsusingtheEPRIRIISImethodology[9].Theapplicable priordistributionsforthehotlegweldsandotherClass1weldssubjecttothesesameDMsare presentedinTable37.Theseareverybroaddistributions,alllognormalwithrangefactorsof100.As such,theyonlyweaklyinfluencetheposteriordistributionsduringtheBayesupdatingprocess.

Table37PriorDistributionsforWeldFailureRatesbyDamageMechanism DamageMechanism PriorDistribution Distribution Type FailureRateperWeldYr Range Factor Mean Median StressCorrosionCracking Lognormal 4.27E05 8.48E07 100 DesignandConstructionErrors Lognormal 2.75E06 5.46E08 100 ThermalFatigue Lognormal 1.34E05 2.66E07 100 3.6 Failure Rate Bayes Updates (Step 1.5)

ThenextstepintheLOCAfrequencyquantificationprocedureistoperformBayesupdatesforeach component/DM/populationexposureestimatethatsupportsthecalculation.Thepriordistributions usedinthisassessmentarebasedonthosethatweredevelopedinReference[7]foruseintheEPRIRI ISIevaluationsthatfollowedthemethodologyintheEPRIRIISITopicalReport[9],whichwasreviewed bytheNRCandLANLasdocumentedinReferences[10]and[11].Theevidencefortheupdatesisbased onthreefailuresofBFsurgelineweldsduetoPWSCC,andzerofailuresforboththebranchconnection andBJweldsforthesurgeline.Theparametersofthepriorandupdateddistributionsforallthecases thatwereneededtosupportthesurgelineweldsarelistedinTable27.Thefailuredataqueryyieldeda totalofsixpipefailuresforhotlegwelds,allofwhichfailureswereatBFweldsandcausedbyprimary waterstresscorrosioncracking.

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Figure33EventTreeModeltoRepresentUncertaintyinHotLegWeldExposureforThermalFatigue Welds/Loop Number Number/Average Welds/Loop Loops Rx-yrs Weld-yrs Average 2.675 1

2.675 2

570 3,050 Minimum 2

0.75 2.675 3

2,053 16,472 Maximum 3

1.12 2.675 4

1,194 12,775 32,297 Weld Count Uncertainty Fraction of B-J Welds Susceptible to Thermal Fatigue Exposure Case Probability Exposure Multiplier p=.25 0.0625 0.08972 2,898 weld-yrs High (.08 x Base) p=.25 p=.50 0.125 0.02243 724 weld-yrs High (1.12 x Base)

Medium (.02 x Base) p=.25 0.0625 0.011215 362 weld-yrs Low (.01 x Base) p=.25 0.125 0.08 2,584 weld-yrs High (.08 x Base) p=.50 p=.50 0.25 0.02 646 weld-yrs Medium (1.0 x Base)

Medium (.02 x Base) p=.25 0.125 0.01 323 weld-yrs Low (.01 x Base) p=.25 0.0625 0.059813 1,932 weld-yrs High (.08 x Base) p=.25 p=.50 0.125 0.014953 483 weld-yrs Low (0.75 x Base)

Medium (.02 x Base) p=.25 0.0625 0.007477 241 weld-yrs Low (.01 x Base)

Exposure Base Exposure

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Table38ParametersofBayesUpdatesforHotLegWeldFailureRateCases WeldTypeand DM (3)

WeldCount Case DM Susceptibility Case PriorDistribution (1)

Evidence (2)

BayesPosteriorDistribution (1)

Type Median RF Failures Exposure Mean 5%tile 50%tile 95%tile RF (4)

HotLegBFSC Low Base Lognormal 8.48E07 100 6

12,074 4.32E04 1.78E04 4.05E04 7.78E04 2.1 Medium Base Lognormal 8.48E07 100 6

21,732 2.43E04 1.01E04 2.29E04 4.37E04 2.1 High Base Lognormal 8.48E07 100 6

24,147 2.20E04 9.10E05 2.06E04 3.94E04 2.1 HotLegBFDC Low Base Lognormal 5.46E08 100 0

12,074 1.02E06 5.34E10 5.16E08 4.05E06 87.1 Medium Base Lognormal 5.46E08 100 0

21,732 8.31E07 5.28E10 5.01E08 3.54E06 81.9 High Base Lognormal 5.46E08 100 0

24,147 8.31E07 5.28E10 5.01E08 3.54E06 81.9 HotLegBJTF Low Low Lognormal 2.66E07 100 0

241 8.88E06 2.65E09 2.64E07 2.53E05 97.6 Medium Low Lognormal 2.66E07 100 0

323 8.41E06 2.65E09 2.63E07 2.49E05 97.0 High Low Lognormal 2.66E07 100 0

362 8.22E06 2.65E09 2.63E07 2.47E05 96.7 Low Medium Lognormal 2.66E07 100 0

483 7.74E06 2.64E09 2.62E07 2.43E05 95.8 Medium Medium Lognormal 2.66E07 100 0

646 7.25E06 2.64E09 2.61E07 2.37E05 94.8 High Medium Lognormal 2.66E07 100 0

724 7.05E06 2.64E09 2.60E07 2.35E05 94.3 Low High Lognormal 2.66E07 100 0

1,932 5.38E06 2.61E09 2.54E07 2.06E05 88.9 Medium High Lognormal 2.66E07 100 0

2,584 4.90E06 2.60E09 2.51E07 1.96E05 86.7 High High Lognormal 2.66E07 100 0

2,898 4.72E06 2.59E09 2.50E07 1.91E05 85.8 HotLegBJDC Low Base Lognormal 5.46E08 100 0

24,147 7.99E07 5.26E10 4.98E08 3.45E06 80.9 Medium Base Lognormal 5.46E08 100 0

32,297 7.14E07 5.22E10 4.87E08 3.17E06 77.9 High Base Lognormal 5.46E08 100 0

36,221 6.82E07 5.20E10 4.83E08 3.06E06 76.7 Notes:

(1)Failureratesexpressedinfailuresperweldyear.

(2)Exposureexpressedinweldyears.

(3)DM=DamageMechanism;SC=stresscorrosioncracking;TF=thermalfatigue;DC=designandconstructiondefects.

(4)RF=RangeFactor=SQRT(95%tile/5%tile).

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3.7 Failure Rate Distribution Synthesis (Steps 1.6 and 1.7)

ThetotalweldfailureratesarecalculatedusingaMonteCarloposteriorweightingtechniqueto combinethedistributionsfromthedifferentweldcountandDMsusceptibilityhypothesesandthen summingthecontributionsfromapplicableDMs.Theresultisoftenreferredtoasamixture distribution.ForBJwelds,thefailurerateforthermalfatiguewasdevelopedbyMonteCarlosampling fromadiscretedistributiondefinedbyprobabilitiesandexposurecasesinFigure33todetermine whichofthelognormaldistributionsforBJTFfromTable38tosampleforthattrial.Repeatingthis processovermanytrials(100,000trialsusedforallMonteCarlocalculationsinthisreport)yieldsa singledistributionfortheBJweldfailurerateduetothermalfatigue.Thissinglefailurerate incorporatesaprobabilisticallyweightedcontributionfromeachsupportingweldcountandDM susceptibilityhypothesis.FortheBJweldfailurerateduetodesignandconstruction(D&C)defects, onlythreecasesarerequiredtomodeluncertaintyintheweldcountsbecauseallweldsareassumedto besusceptibletoD&C.ThenthetotalfailurerateforBJweldsduetothermalfatigue(Case1C)is calculatedbysummingthecontributionsfromTFandD&C.ForBJweldsthatarenotsusceptibleto thermalfatigue(asdeterminedatSTPintheRIISIevaluation),onlytheD&Ccontributionapplies.For theBFwelds,thereisnosignificantuncertaintyforDMsusceptibility.Henceonlythethreecasesfor weldcountuncertaintyneedtobecombinedfortheSCcontributiontotheBFfailurerate,aswellas threecasesfortheD&Cfailurerate,andthentheSCandD&Ccontributionsaresummedtoobtainthe totalBFweldfailurerateforCase1A.Itissignificantthatthemeanfailureratesforthethree calculationcasesspanmorethantwoordersofmagnitude,fromBJweldsthatarenotsubjectto thermalfatigueonthelowside,totheBFweldsonthehighside.TheuncertaintyintheBFweldfailure rate(Case1A)asmeasuredbytherangefactorisrelativelysmallduetothesignificantnumberofpipe failuresinthesewelds.TherangefactorsaremuchhigherfortheBJweldcases(1Band1C)because therewerezerofailures.Inthesesituations,thelargerangefactorusedinthepriordistributionhasa muchlargerinfluenceontheposteriordistributionparameters.Theseresultsareexpectedduetothe propertiesofBayesupdating.

Table39TotalFailureRatesforHotLegWeldCalculationCases Calculation Case Weld Type DM FailureRateDistribution(failuresperweldyear)

Mean 5%tile 50%tile 95%tile RF 1A BF SC+D&C 2.73E04 1.04E04 2.33E04 5.78E04 2.4 1B BJ D&C 1.44E06 5.27E10 4.12E08 3.19E06 77.8 1C TF+D&C 1.07E05 1.79E08 5.79E07 2.83E05 39.8

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3.8 Failure Rates for Other Calculation Cases (Step 1.7)

Thissectionpresentsinformationthatcanbeusedtoderivetheresultsforthefailureratedistributions fortheremainingCalculationCasesinTable32.Theprocessoutlinedintheprevioussectionwas repeatedforallthecasesinTable32.Actualweldcountsfromthe10PWRunitsinTable35wereused tocharacterizetheuncertaintyintheweldpopulationperplantusingtheaveragevaluefromthe sampleasthebestestimate,theminimuminthesampleasthelowerbound,andthemaximuminthe sampleastheupperbound.Table310providesasummaryofthebestestimate,upperbound,and lowerboundweldyearsestimatedforeachcomponenttype.Asseeninthistable,thepopulation exposureaccountedforinthisfailureratedevelopmentisseveralmillioncomponentyearsof experience.

Table310ComponentPopulationExposureEstimatesforPipeFailureRates System Case System Component Case Weld Type Best Estimate Upper Bound Lower Bound 1

RCSHotLeg 1A BF 21,732 24,147 12,074 1B,1C BJ 32,297 36,221 24,147 2

RCSSGInlet 2

BF 12,074 12,074 12,074 3

RCSColdLeg 3A BF 22,315 24,794 12,397 3B BJ 123,764 177,279 99,177 4

RCSSurge 4A BF 3,914 3,914 3,914 4B BJ 27,007 54,013 13,503 4C BC 7,828 7,828 7,828 5

PZR 5A-5D BJ 351,127 496,158 286,245 5E-5G BF 19,083 19,083 19,083 6

SB 6A-6B BJ 744,237 1,144,980 366,394 7

SIRLinesExcl.Accumulator 7A-7L BJ 590,797 637,190 507,518 SIRAccumulatorLines 7M-7O BJ 175,067 277,693 132,810 8

CVCS 8A-8D BJ 562,348 627,324 403,018 8E,8F BC 81,393 90,797 58,332 TotalEstimatedWeldYrs 2,774,983 3,633,494 1,958,513

Table311presentstheDMsusceptibilitymatrixforthedevelopmentoffractionofthecomponent populationsusceptibletoeachDM.Thisisbasedontheresultsofthefailuredataquery,EPRIcriteriafor screeningforDMsusceptibility,andinsightsfromreviewofpipefailuredatainthisandpreviouspipe failureratestudiesperformedbytheauthors.

Table312andFigure34presenttheresultsofthefailurerateuncertaintyanalysisthatsupportsallthe calculationcases.Theseexhibitsshowthatthemeanfailureratesspanmorethanthreeordersof magnitude.Theyalsoindicatethatbimetallicwelds(BF)tendtohavemuchhigherfailureratesthanBJ orBranchConnection(BC)welds.ThisisduetothesusceptibilityofBFweldstoPWSCC,ahigher incidenceoffailuresforthisDMintheservicedata,andasmallercomponentexposurepopulationthan

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thatoftheBJandBCwelds.AtSTP,therehasbeensomecrackingobservedinthePressurizerBF welds,whichhasbeenmitigatedthroughapplicationofweldoverlays.Thefailureratesforthesewelds (Case5G)isestimatedbyusingthefailurerateforD&Cdefectsthatisassumedtoapplytotheseweld overlays.Thisisviewedasaconservativeassumptionbecausenocreditistakenforthecapabilityofthe underlyingcrackedmaterialtoinhibitaruptureiftheoverlayweldwouldfail.Therearefewerdistinct failureratesthancalculationcasesbecausetheadditionalcalculationcasesaredifferentiatedonlyby pipesize.Forexample,thisappliestoCases3Aand3B.WhenwedeveloptheLOCAfrequenciesvs.

breaksizeinthefollowingsections,eachofthesecaseswillhaveadifferentmaximumbreaksize,but theyotherwisewillexhibitanidenticalfrequencyvs.breaksizecurve.

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Table311DamageMechanismSusceptibilityMatrixforFailureRateDevelopment System Location Confidence Level WeldSusceptibilityFractions CF D&C ECSCC Fretting IGSCC PWSCC TF TGSCC VF RCHotLeg BF(Un mitigated)

Low N/A 1

N/A N/A N/A 1

N/A N/A N/A Medium N/A 1

N/A N/A N/A 1

N/A N/A N/A High N/A 1

N/A N/A N/A 1

N/A N/A N/A BJ Low N/A 1

N/A N/A N/A N/A 0.01 N/A N/A Medium N/A 1

N/A N/A N/A N/A 0.02 N/A N/A High N/A 1

N/A N/A N/A N/A 0.08 N/A N/A RCColdLeg BF Low N/A 1

N/A N/A N/A N/A N/A N/A N/A Medium N/A 1

N/A N/A N/A N/A N/A N/A N/A High N/A 1

N/A N/A N/A N/A N/A N/A N/A BJ Low N/A 1

N/A N/A N/A N/A N/A N/A N/A Medium N/A 1

N/A N/A N/A N/A N/A N/A N/A High N/A 1

N/A N/A N/A N/A N/A N/A N/A RCHotLeg/SG Inlet BF Low N/A 1

N/A N/A N/A 1

N/A N/A N/A Medium N/A 1

N/A N/A N/A 1

N/A N/A N/A High N/A 1

N/A N/A N/A 1

N/A N/A N/A PressurizerSurge Line BF Low N/A 1

N/A N/A N/A 1

1 N/A N/A Medium N/A 1

N/A N/A N/A 1

1 N/A N/A High N/A 1

N/A N/A N/A 1

1 N/A N/A BJ Low N/A 1

N/A N/A N/A N/A 1

N/A N/A Medium N/A 1

N/A N/A N/A N/A 1

N/A N/A High N/A 1

N/A N/A N/A N/A 1

N/A N/A RCHLBranch Connection Low N/A 1

N/A N/A N/A N/A 1

N/A N/A Medium N/A 1

N/A N/A N/A N/A 1

N/A N/A High N/A 1

N/A N/A N/A N/A 1

N/A N/A Pressurizer PRV/SRV&Spray Lines BF (Unmitigated)

Low N/A 1

N/A N/A N/A 1

0.01 N/A N/A Medium N/A 1

N/A N/A N/A 1

0.04 N/A N/A High N/A 1

N/A N/A N/A 1

0.20 N/A N/A BJ Low N/A 1

N/A N/A 0.01 N/A 0.01 N/A N/A Medium N/A 1

N/A N/A 0.02 N/A 0.04 N/A N/A High N/A 1

N/A N/A 0.08 N/A 0.20 N/A N/A

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System Location Confidence Level WeldSusceptibilityFractions CF D&C ECSCC Fretting IGSCC PWSCC TF TGSCC VF SmallBore BJ Low N/A 1

N/A N/A 1

N/A N/A N/A 1

Medium N/A 1

N/A N/A 1

N/A N/A N/A 1

High N/A 1

N/A N/A 1

N/A N/A N/A 1

SIR-Medium Bore BJ Low N/A 1

N/A N/A 0.01 N/A 0.01 N/A N/A Medium N/A 1

N/A N/A 0.05 N/A 0.04 N/A N/A High N/A 1

N/A N/A 0.25 N/A 0.20 N/A N/A CF1 Low N/A 1

N/A N/A 0.01 N/A 0.01 N/A N/A Medium N/A 1

N/A N/A 0.05 N/A 0.04 N/A N/A High N/A 1

N/A N/A 0.25 N/A 0.20 N/A N/A SIR-LargeBore (Accumulator lines)

BJ Low N/A 1

N/A N/A N/A N/A 0.01 N/A N/A Medium N/A 1

N/A N/A N/A N/A 0.04 N/A N/A High N/A 1

N/A N/A N/A N/A 0.20 N/A N/A CV BJ Low N/A 1

N/A N/A N/A N/A 0.01 N/A 1

Medium N/A 1

N/A N/A N/A N/A 0.04 N/A 1

High N/A 1

N/A N/A N/A N/A 0.20 N/A 1

CF1 Low N/A 1

N/A N/A N/A N/A 1

N/A N/A Medium N/A 1

N/A N/A N/A N/A 1

N/A N/A High N/A 1

N/A N/A N/A N/A 1

N/A N/A CF CorrosionFatigue D&C Design&ConstructionFlaws ECSCC ExternalChlorideinducedSCC IGSCC IntergranularSCC PWSCC PrimaryWaterSCC SCC StressCorrosionCracking TF ThermalFatigue TGSCC TransgranularSCC VF VibrationFatigue

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Table312UncertaintyDistributionsforCalculationCaseFailureRates System Case System Calculation Case Weld Type ApplicableDamage Mechanisms FailureRateDistribution (FailuresperWeldYear)

RF Mean 5%tile 50%tile 95%tile 1

RCHotLeg 1A BF SC,D&C 2.73E04 1.04E04 2.33E04 5.78E04 2.4 1B BJ D&C 1.44E06 5.27E10 4.12E08 3.19E06 77.8 1C BJ TF,D&C 1.07E05 1.79E08 5.79E07 2.83E05 39.8 2

RCSGInlet 2

BF SC,D&C 1.42E03 9.22E04 1.37E03 2.06E03 1.5 3

RCColdLeg 3A,3B BF SC,D&C 1.25E04 2.99E05 9.34E05 3.17E04 3.3 3C,3D BJ D&C 2.39E06 2.14E08 4.35E07 8.84E06 20.3 4

RCSurge 4A BF SC,TF,D&C 5.19E04 1.26E04 4.04E04 1.28E03 3.2 4B BC TF,D&C 8.06E06 1.80E08 5.39E07 2.24E05 35.3 4C BJ TF,D&C 4.52E06 1.51E08 4.04E07 1.40E05 30.4 5

Pressurizer 5A,5B BJ TF,D&C 6.29E06 1.63E07 1.32E06 1.61E05 10.0 5C,5D BJ D&C 1.61E06 7.31E08 6.59E07 5.93E06 9.0 5E BF SC,TF,D&C 4.80E04 2.59E04 4.49E04 7.83E04 1.7 5F BF SC,D&C 4.69E04 2.56E04 4.43E04 7.68E04 1.7 5G BF D&C(WeldOverlay) 8.72E07 5.29E10 5.05E08 3.66E06 83.2 6

SmallBore 6A,6B BJ VF,SC,D&C 1.23E04 7.03E05 1.11E04 2.02E04 1.7 7

SIRExcl.

Accumulator 7A,7B BJ TF,D&C 2.59E04 2.17E05 1.50E04 8.81E04 6.4 7C BJ SC,TF,D&C 2.91E04 3.06E05 1.78E04 9.37E04 5.5 7D BJ SC,D&C 3.32E05 1.24E06 9.38E06 1.25E04 10.1 7E-7L BJ,BC D&C 1.07E06 5.61E08 4.64E07 3.89E06 8.3 SIR Accumulator Lines 7M BJ SC,D&C 3.32E05 1.24E06 9.38E06 1.25E04 10.1 7N BJ TF,D&C 6.72E06 1.42E08 3.90E07 1.66E05 34.2 7O BJ,BC D&C 5.45E07 4.61E10 2.72E08 1.60E06 59.0 8

CVCS 8A,8B BJ TF,VF,D&C 5.33E06 2.43E07 1.49E06 1.43E05 7.7 8C,8D BJ VF,D&C 1.76E06 1.37E07 8.61E07 6.01E06 6.6 8E BC TF,D&C 7.75E06 3.03E07 2.76E06 2.80E05 9.6 8F BC D&C 1.07E06 5.61E08 4.64E07 3.89E06 8.3

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Figure34ComparisonofMeanFailureRatesforCalculationCases

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4. Conditional Rupture Mode Probability Model (Step 2) 4.1 Overview of CRP Model Approach Thissectiondocumentsthedevelopmentoftheconditionalruptureprobabilities(CRPs)givenpipe failureforanappropriaterangeofpipebreaksizesforeachcomponent.Thecomponentstobecovered bythisanalysisaredeterminedbytheComponentCategoriesinTable23.Inaccordancewiththestep bystepapproachtoLOCAfrequencydeterminationpresentedinSection2,thissectioncoversthe followingkeytasksofStep2,ConditionalRuptureProbability(CRP)Development[P(RxFik)inEquation (2.2)]:

2.1 Selectcomponentstodefineconditionalruptureprobability(CRP)modelcategories 2.2 ObtainexpertreferenceLOCAdistributionsfromNUREG1829 2.3 Obtainexpertmultiplierdistributionsfor40yrLOCAfrequenciesfromNUREG1829 2.4 Determine40yrLOCAdistributions(productofSteps2.2and2.3)foreachexpert,fitto lognormal 2.5 2.6a DeterminegeometricmeanofexpertdistributionsfromStep2.4(lognormal)

BenchmarkLydellBaseCaseAnalysisforselectedcomponents 2.6b DeterminefailureratedistributionforLydellBaseCaseAnalysisinNUREG1829;fitto lognormal 2.6c ApplyLydellCRPmodelfromBaseCaseAnalysis 2.6d DetermineLOCAfrequencydistributionfromLydellBaseCaseAnalysis 2.7 DeterminemixturedistributionofNUREG1829GM(fromStep2.5)andLydellLOCA frequency(fromStep2.8)toobtainTargetLOCAFrequencyDistributionforeachCRP categorycomponent 2.8 ApplyformulastocalculateCRPdistributionstobeusedaspriordistributionsforeach componentassignedtoeachCRPcategory 2.9 ForeachcomponentinagivenCRPcategory,performBayes'updatewithevidenceof failureandrupturecountsfromservicedata.

ThegoalofthissectionistoestablishasetofCRPsvs.breaksizeforeachComponentCategoryinTable 32.ForeachComponentCategory,thebreaksizestobeconsideredrangefromanequivalentbreaksize of0.5"tothebreaksizecorrespondingtoadoubleendedguillotinebreak(DEGB)ofthepipe.Thelower boundisbasedonthelowerboundoftheSmallLOCAinitiatingeventintheSTPPRAmodel,which coversbreaksintherangeof0.5"to2.0".ThebreaksizeforaDEGBisassumedtobe D

2

,whereDis theinsidediameterofthepipe.(Thiscomesfromthefactthatanoffsetruptureeffectivelydoublesthe flowarea,whichwouldbeequivalenttoincreasingthebreaksizediameterofasinglebreakbythe factor 2.)Thismodelofmaximumbreaksize,asisthatforaDEGBforallClass1pipes,isconservative forpipelocationswithaclosedendononesideofthebreak,whichwouldbethecaseformostbranch connectionweldsinthesafetyinjectionandrecirculationsystempiping.

ResultsforLOCAfrequenciesateachlocationcangenerallybedepictedasacurveofCRPvs.breaksize.

However,thisstudygeneratesafamilyofcurvesduetotheepistemicuncertaintyinestimatingtheCRP foreachcomponent.Thisyieldsbothameancurveandvariouscurvesrepresentingdifferentpercentiles

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oftheLOCAfrequencyuncertaintydistributions.Inthisreport,resultsarepresentedintermsofmeans, 5%tiles,50%tiles(medians),and95%tiles.

ThetechnicalapproachtoCRPdevelopmentusedherehasbeenstructuredtocapturethecurrentstate ofknowledgeofLOCAfrequencies.ThestepstoderivingCRPsforeachcomponentarebasedonthe followingstrategyforLOCAfrequencyestimation.Itwasastudyobjectivetomakeuseofinformation onLOCAfrequenciesinNUREG1829[1],whichreasonablycapturesthecurrentstateofknowledge amongpipingsystemreliabilityexpertsonLOCAfrequencies.Theexpertelicitationthatisdocumented inthisreportcapturedinputsfromexpertsrepresentingtwoschoolsofthoughtonhowtobestquantify pipebreakfrequencies:onebasedonstatisticalanalysisofservicedataandsimplemodels,andanother basedonprobabilisticfracturemechanicsapproaches.The12expertsthatparticipatedinthisexpert elicitationprovidedabalancedperspectiveonthesetwoapproachesandproducedestimatesofthe LOCAfrequenciesvs.breaksizeforuseinriskinformedevaluations.NUREG1829includedsomebase caseanalysesthatwereperformedonselectedcomponentstoinformtheexpertelicitation.Onesetof thesebasecaseanalyseswasperformedbyBengtLydell,whoisacoauthorofthisreport.Lydell performedhisbasecaseanalysisusingamethodologythatisverysimilartothatusedinthisstudyand producedasetofLOCAresultswithaquantificationofepistemicresultsforasetofPWRcases,namely thehotleg,thesurgeline,andahighpressureinjectionsystemline.Inadditiontothesebasecase analyses,nineoftheparticipatingexpertsprovidedindividualdistributionsforLOCAfrequenciesfora rangeofcomponents,includingthecomponentscoveredinthebasecaseanalyses.Thetechnical approachtoCRPmodeldevelopmentwasdesignedtomakeuseofbothsetsofinformationdeveloped inNUREG1829,namely,thebasecaseanalysesandtheinputsprovidedbythenineexpertsand documentedinReference[14].

OurapproachtodevelopingCRPsistoestablishasetoftargetLOCAfrequenciesthatcapturesthe epistemicuncertaintiesdevelopedforNUREG1829.Inputsfromthenineexpertswhoprovidedinputs atthecomponentlevelarecollectedinSteps2.2and2.3andusedtorecreatetheirrespectiveLOCA frequencydistributionsinStep2.4.Acompositedistributionofthesenineexpertdistributionsis developedusingageometricmeanmethodsimilartothatusedinNUREG1829inStep2.5.Inparallel withthesesteps,theLydellBaseCaseAnalysisforthesesamecomponentsisbenchmarkedand deconstructedinStep2.6andisusedtoprovideanalternativemodeltothetargetLOCAfrequenciesfor thesecomponents.InStep2.7,theLOCAfrequencydistributionsprovidedbyLydellandthegeometric meancompositedistributionsfromStep2.5arecombinedtoproducethetargetLOCAfrequency distribution.InStep2.8,formulasareusedtoderivetheequivalentCRPdistributions.TheseCRP distributionsserveaspriordistributionsforthefinalstepintheCRPmodeldevelopment,Step2.9,in whichBayesupdatesoftheCRPdistributionsareperformedforeachcomponentcategory.

ToappropriatelyapplytothisstudytheinformationfromNUREG1829andthesupportinginputsand analyses,thefollowingdifferencesbetweenthatstudyandthisstudyneedtobeunderstood.

NUREG1829wasmeanttodevelopestimatesofPWRandBWRtotalLOCAfrequenciesforgeneric applicationtoU.S.nuclearpowerplants.Incontrast,thisstudyisintendedtodevelopplantspecific estimatesofLOCAfrequenciesnotonlyforaplantasawholebutfornumerouslocationswithina

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plant.ThisismadepossiblebythemodelingassumptionthatLOCAfrequenciescanbeestimatedas theproductofapipefailurerateandaCRP.

ThePWRLOCAfrequenciesaddressplanttoplantvariabilityindesigncharacteristicssuchas numberofcoolantloops,pipingsystemdesigns,andconfigurations,whereasthisstudyfocusesona specific4loopPWRwiththreetrainsofemergencycorecoolingsysteminterfacepipingthatis uniquetoSTP.

ThisstudyhasbenefittedfromseveralhundredreactoryearsofservicedataonPWRpipingsystems thatwerenotavailablewhenthetechnicalinputstoNUREG1829werecreated.

4.2 Use of NUREG1829 Data TheexpertelicitationthatwasperformedanddocumentedinNUREG1829[1]providedestimatesof thefrequenciesforLOCAsbasedonasetofLOCAcategoriesselectedtospanthebreaksizesandleak ratesthatarenormallymodeledinPWRandBWRPRAs.TheestimatesprovidedinNUREG1829 includedbothpipefailuresandnonpipefailures.However,onlypipefailuresarewithinthescopeof thisstudy.LOCAscausedbynonpipefailureswillbeaddressedin2012.TheLOCAcategoriesforPWRs usedinNUREG1829aresummarizedinTable41.SincethelargestpipesinaPWRreactorcoolant system,whichcorrespondtothecoldlegpiping,areontheorderof31nominalpipesize(NPS),the NUREG1829LOCAcategoriesdonotdifferentiateaDEGBfromasinglebreakofthelargestpipeinthe system.TheeffectiveDEGBsizeofacoldlegpipeof31NPSwouldbeabout44.

Table41NUREG1829andSTPPRALOCACategories LOCA Category STPPRACategory Effective BreakSize (in.)

FlowRate (gpm) 1 SmallLOCA(1) 0.5 100 2

MediumLOCA(1) 1.5 1,500 3

LargeLOCA 3

5,000 4

6.75 25,000 5

14 100,000 6

31.5 500,000 Note:

(1)IntheSTPPRA,thebreakpointbetweenSmallandMediumLOCAsisactually2, andthebreakpointbetweenMediumandLargeLOCAsis6.

TheapproachtousinginformationinNUREG1829todevelopestimatesoftheconditionalprobabilityof piperupturesisbasedonthefollowingobservationsandinformationpresentedinthatdocument.

Basecaseresultsarepresentedinthereportforthreewelldefinedpipingcomponentsfor PWRs,namely,hotlegpiping,pressurizersurgelinepiping,andhighpressureinjectionpiping, whichcomprisepartoftheASMEClass1pressureboundary.Foreachcomponent,four independentestimateswereprovidedforeachapplicableLOCAcategory:twoestimatesbased onastatisticalanalysisofservicedataandsimplemodelssimilartothosethatwillbeusedin theSTPGSI191evaluation,andtwoestimatesbasedonprobabilisticfracturemechanics

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analyses.Thesebasecaseresultswereprovidedasinputtotheexperts,andsomeexpertschose tousethemasanchorsfortheirrespectiveinputs.Thebasecaseresultsaresummarizedin Section4ofNUREG1829aswellasinthesupportingappendicesofthatdocument.

Aspartoftheelicitation,mostoftheexpertsprovidedinputtotheestimationofLOCA frequenciesforspecificcomponentsontheRCSpressureboundary,includingthecomponents thatwereevaluatedinthebasecaseresultsaswellasessentiallyallthemajorcomponentson theClass1pressureboundary.Selectedcomponentlevelresultsofthiselicitationarefoundin AppendixLofNUREG1829.ForPWRs,theseresultsarepresentedforLOCACategories1,3,and 5.AnexampleoftheformofthisinformationforLOCACategory1isshowninFigure41.There isalsocomponentlevelexpertelicitationinformationpresentedinthatappendixforhotleg pipingforLOCACategory6.TheNUREG1829supportinginformationthatwasjustrecently releasedhasadditionalinformationoncomponentlevelLOCAestimatesforLOCAfrequencies thatcoversallapplicableLOCAcategoriesforeachcomponent[14].

IntheevaluationofservicedatathatwasperformedinsupportofNUREG1829,whichincludes thebasecaseanalysesperformedbyBillGalleanandBengtLydell,noneofthereviewedservice datainvolvedtheoccurrenceofanyLOCAs.TheservicedatawehavecollectedinTable33for thesesystems,encompassingatotalof166pipefailures,includeflaws,cracks,andrathersmall leaks,butnoleaksthatwouldconstituteevenaSmallLOCA,whichcorrespondstoLOCA Category1.ThepiperupturemodelsusedinthebasecasestudiesofGalleanandLydell,aswell astheoneusedinthisstudy,assumethateachpipefailureisaprecursortoaLOCA.Eachof thesemodelsstartswithanestimateofthefailurerate,whichincludesallpipefailuresrequiring repairorreplacement.Themodelintegratesthefailurerates,whichareestimatedusingservice data,withthemoresignificantpipefailuresthatproduceLOCAs.Thisisaccomplishedby definingtheconditionalprobabilityofabreakofagivensizegivenapipefailure.Anotherwayto lookatthismodelisthatpipefailuresareassumedtorepresentchallengestothesystemand thatuponeachchallenge,thereisaprobabilityofexperiencingabreakofagivensize.By consideringthefullrangeofdifferentbreaksizes,alltheLOCAfrequencycategoriescanbe quantified.

ThepipebreakfrequencymodeldescribedinSection2andEquations(2.1)and(2.2)providethe capabilitytoestimatefailureratesateachlocationintheClass1pipingsystempressure boundary,whichisneededforthisGSI191riskinformedevaluation.ConversionoftheLOCA frequencyinputsinNUREG1829fromaLOCAfrequencybasistoaconditionalprobabilityof LOCAbasiswasnecessitatedbythismodel.ThisrequiredestablishingtargetLOCAfrequencies forkeycomponentsandthenderivingtheequivalentCRPmodelthatwhencombinedwiththe failureratemodelwillproducethesametargetLOCAfrequencies.

Basedontheaboveinformationandinsights,wewilluseinformationfromNUREG1829toconvert informationthatwaspresentedintheformofLOCAfrequenciesvs.LOCAcategory,toconditional probabilitiesvs.breaksize.ThisapproachisappliedtothefourPWRcomponentsthatwereincludedin thebasecaseresultsaswellasintheexpertelicitation:theRCShotleg,theRCScoldleg,theRCSsurge line,andtheHPIinjectionline.ThesespanarepresentativerangeofnominalpipesizesonthePWR Class1pressureboundaryof30",30,14,and3.75,respectively.

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Figure41Category1LOCAFrequenciesforPWRPipingSystemsat25YearsofPlantOperation (ReproducedfromFigureL.13inNUREG1829) 4.3 Model for Deriving Conditional Probabilities from Rupture Frequencies Themodelusedtoconvertinformationonunconditionalrupturefrequenciestoconditionalfailure probabilitiesmakesuseofthebasecaseresultsofLydellforeachofthefourselectedPWRcomponents (hotleg,coldleg,surgeline,HPinjectionline)andthefollowingequation:

)

(

)

(

F R

P m

LOCA F

j l

l l

j

(4.1)

Where:

)

(

j LOCA F

UnconditionalfrequencyofLOCACategoryjduetopipefailuresin selectedcomponent,perreactorcalendaryear

l m

Numberofpipeweldsoftypelinselectedcomponenthavingthe samefailurerate

l Failurerateperweldyearforpipeweldtype lwithintheselected componentinLydellsBaseCaseAnalysisfromAppendixDinNUREG 1829

)

(

F R

P j

Conditionalruptureprobability(CRP)inLOCACategoryjgivenfailure inselectedcomponent

Eachterminthismodelissubjecttoepistemicuncertainty,whichistobeestimated.Therefore,this modelandthebasecaseanalysisofthefailureratesfromLydellareusedtoderiveepistemic uncertaintiesfortheCRPsineachLOCAcategory.ThisproducesasetoftargetLOCAfrequency distributionparametersthathavebeenselectedtoincorporatetheepistemicuncertaintiesdevelopedin NUREG1829.Thisapproachmakesuseoftherebeingatechnicalbasisforthefailurerateestimates

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fromservicedataandawellreviewedandextensivelyappliedBayesuncertaintyanalysismethod.

TheseestimateswerepartoftheinformationthatwasavailabletoeachNUREG1829experttoanchor hisinputs.SincetherehavebeennoCategory1,2,3,4,5,or6LOCAs,theexpertelicitationresultsofall theexpertsconstituteanextrapolationfromtheexistingservicedata.Therefore,ourapproachsimply assumesthatthevariabilityintheexpertelicitationinputsforLOCAfrequencyrepresentstheepistemic uncertaintyintheLOCAfrequencyforeachcomponent.Thisepistemicuncertaintyisthenassumedto resultfromthecombinationoftheepistemicuncertaintyinthefailurerateandtheepistemic uncertaintyintheconditionalprobabilityofeachLOCAcategory.

ThismodelissomewhatsimplifiedfromtheLydellBaseCaseAnalysisinAppendixDofNUREG1829.

LydellsBaseCaseAnalysisusesdifferentconditionalLOCAcategoryprobabilitiesfordifferentloading conditionsandthencombinesthemtoproducehisbasecaseresults.So,aspartofStep2.6,weshall deriveanequivalentconditionalprobabilitymodelusingequationsdescribedinthefollowinginorderto benchmarkthismodelagainsttheslightlydifferentmodelofLydell.Thenweshalladjusttheepistemic uncertaintiesintheconditionalprobabilityofaLOCAinamannerthatmatchestargetLOCAfrequencies thataresettoincorporatethevariabilityamongexpertsestimatesinNUREG1829.

4.4 Select Components to Define CRP Model Categories (Step 2.1)

Asshownintheprevioussection,45failureratecategorieswereusedtocharacterizethepipefailure ratesfor775distinctweldlocationsforalltheClass1pipingsystemsatSTP.Thefailureratecategories coverallcombinationsofsystems,weldtypes,damagemechanisms,andpipesizesthataredefinedby thecomponentcategories.InordertoestimateCRP,thefollowingCRPModelcategorieswereselected:

HotLegCRPmodel ColdLegCRPmodel SurgeLineCRPmodel HighPressureInjectionCRPmodel Thisselectionwasbasedonthefollowingconsiderations:

TherearesufficientdatainNUREG1829andsupportinginputdatatosupportestimationofthe CRPsandtheassociatedepistemicuncertaintiesusingthetechnicalapproachadoptedinthisstudy.

Theabovecategoriesprovideauniquemodelforallthecategorieswithlargepipesizes,i.e.,those withpipediametersatleast12,whichareexpectedtobethemostpronetodebrisgeneration.

Furtherdetailinthetreatmentofsmallerpipesisnotwarrantedforthisapplication,norisit supportedbysufficientpipefailuredata.

TheSGInletcategoriesareaspecialcaseoftheweldsinthehotlegandconstituteaseparate categorysolelytocaptureanyoutliersinthefailureratedata.Theconditionalprobabilityofpipe rupturefortheSGInletisnotexpectedtodifferfromthatfortheotherweldsinthehotleg.

TheHighPressureInjectionCRPcategoryisrepresentativeofthemediumandsmallborepipewith pipediameterupto12.Theyareallstainlesssteellinesconnectedtothelargerpipesizesandare subjecttoasimilarrangeofDMs.Thiscategoryincludesbothbimetallic(BF)andsimilarmetal(BJ andBC)weldsandcoversafullrangeofDMsthatarefoundinClass1piping.

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Incombinationwiththe45uniquefailureratecasesdevelopedinSection3,theaboveCRPmodel categoriesprovideareasonablycompletesettocharacterizetheLOCAfrequenciesinall775weld locationsinTable33.

TheabovefourmodelswillbeusedtodeveloppriordistributionsfortheCRPepistemic uncertainties.ApplyingthemtospecificcomponentswillentailtheBayes'updateinStep2.9,in whichthenumberoffailuresandrupturesforeachfailureratecasewillbeusedastheevidencefor updatingthesebasepriors.Hence,thefourCRPmodelswillactuallyproduceeightdifferentsetsof CRPs,oneforeachsystem.Thesewillbeexpandedfurthertoapplytodifferentpipesizes,where themaximumbreaksizeforeachpipesizeissettotheDEGBsize.

AsummaryofthemappingofCRPmodelcategoriestothepipingsystemcategoriesisshowninTable4 2

Table42AssignmentofPipingSystemCategoriestoCRPModelCategories Case Description WeldType Damage Mechanism(DM)

CRPModelandBayesUpdateEvidence 1

RCSHotLegExcl.

SGInlet BF PWSCC,D&C HotLegCRPModel, updatedwith0rupturesin6failures BJ TF,D&C 2

RCSColdLeg BF PWSCC,D&C ColdLegCRPModel, updatedwith0rupturesin3failures BJ D&C 3

RCSHotLegSG Inlet BF PWSCC,D&C HotLegCRPModel, updatedwith0rupturesin19failures 4

PZRSurgeLine BF PWSCC,TF,D&C SurgeLineCRPModel, updatedwith0rupturesin3failures BJ,BC TF,D&C 5

PZRMediumBore Piping BF PWSCC,TF,D&C HPICRPModel, updatedwith0rupturesin12failures BJ,BC TF,D&C 6

Class1SmallBore Piping BJ TF,D&C,TGSCC,VF HPICRPModel, updatedwith0rupturesin106failures 7

Class1Medium BoreSIRPiping BJ TF,D&C,IGSCC HPICRPModel, updatedwith0rupturesin14failures 8

Class1Medium BoreCVCSPiping BJ,BC TF,D&C,TGSCC,VF HPICRPModel Updatedwith0rupturesin14failures BF ASMECategoryBFwelds(bimetallic)

BJ ASMECategoryBJwelds(singlemetal)

BC BranchConnectionWeld,BJweldsusedatbranchconnections CVCS Chemical,Volume,andControlSystem D&C DesignandConstructionDefects IGSCC IntergranularStressCorrosionCracking PWSCC PrimaryWaterStressCorrosionCracking PZR Pressurizer

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Case Description WeldType Damage Mechanism(DM)

CRPModelandBayesUpdateEvidence RCS ReactorCoolantSystem SIR SafetyInjectionandRecirculationSystems TF ThermalFatigue TGSCC TransgranularStressCorrosionCracking VF VibrationFatigue

4.5 Use of Data from NUREG1829 Expert Elicitation (Steps 2.2 and 2.3)

TheexpertelicitationthatwasperformedforNUREG1829includedarequestforestimatesofLOCA frequenciesforspecificpipeandnonpiperelatedcomponents[14].Nineexpertsprovidedinputatthis level,andSteps2.1through2.5involveanalysisofthesedataforselectedcomponents,namelythehot leg,coldleg,surgeline,andHPIlinecomponentsinPWRs.Onesetofnumbersprovidedbytheexperts wasLOCAfrequenciesbyLOCAcategoryintermsofamidvalue(Mid),anupperbound(UB),anda lowerbound(LB),withtheunderstandingthatthosewouldbeinterpretedasmedians,95%tiles,and 5%tilesofalognormaluncertaintydistribution.Forsymmetricinputs(i.e.,whenUB/Mid=Mid/LB),

whichwereprovidedinmostcases,thesedistributionswereassumedtobelognormaldistributions.For asymmetricinputsprovidedbytheexperts,aspecificsplitlognormaldistributionwasassumed.

ThefirstsetofLOCAfrequencieswasfortheexistingfleetofplants,whichinvolvesamixtureofplant agesandanaverageplantageofabout25yearsatthetimetheelicitationwasperformed.Theexperts providedmultipliersfornormalizingtheseLOCAfrequenciestoplantagesof25years,40years,and60 yearspriortotheoccurrenceofaLOCA.ThesemultipliersenabledtheexpertstoexpresswhetherLOCA frequenciescouldbeaffectedbyagingeffectsandwhethersucheffectsmightbemitigated.Thisstudyis intendedtodevelopLOCAfrequenciesthatwillbevalidoverthe40yearsofthecurrentplantlicense.

Therefore,onlythe40yearvaluesareusedhere.

TheexpertelicitationinputsforthehotlegpipesareprovidedinTable43.Thenineexpertsarelabeled AthroughL,withD,F,andKunassigned.Thedatahighlightedinyellowarecopieddirectlyfromthe questionnairesheetsinReference[14].Similartablesweredevelopedforthecoldleg,surgeline,and HPIline(thevariantoftheHPIlinewithvolumeinjectionwasselectedforconsistencywiththeLydell HPIBaseCaseAnalysisinAppendixDofNUREG1829).ThiscompletesSteps2.2and2.3foreachCRP modelcomponent.

4.6 Development of 40Year LOCA Frequency Distributions (Step 2.4)

InStep2.4,theLOCAFrequenciesforSystemdistributionsaremultipliedbythe40yearmultiplier distributions,toobtainthe40yearLOCAfrequencydistributions.Thisisstraightforwardbecausethe productoftwolognormaldistributionsisalsoalognormaldistribution.

Whenthetwoinputdistributionsarelognormal,theparametersofthelognormaldistributionforthe 40yearLOCAfrequenciescanbedirectlycomputedusingthefollowingformulas.

YM Base YLF median median median 40 40

(4.2)

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YLF e

RF YLF 40 645

.1 40

(4.3)

Where:

2 40 2

40 645

.1

)

ln(

645

.1

)

ln(

YM Base YLF RF RF

(4.4)

YLF median40 Medianofthelognormaldistributionforthe40yearLOCAfrequency, evaluatedforeachcombinationofexpertandLOCACategory

Base median MedianofthelognormaldistributionforthebaseLOCAfrequency (LOCAFrequencyforSystemprovidedbyeachexpertforeachLOCA Category)

YM median40 Medianofthelognormaldistributionforthe40yearmultiplier providedbyeachexpertforeachLOCACategory

YLF RF40 Rangefactorofthelognormaldistributionforthe40yearLOCA frequency,equaltoSQRT(95%tile/5%tile)ofthelognormal distribution

YLF 40

Logarithmicstandarddeviationforthelognormaldistributionforthe 40yearLOCAfrequency,evaluatedforeachcombinationofexpert andLOCACategory

Base RF RangefactorofthelognormaldistributionforthebaseLOCA frequencyprovidedbyeachexpertforeachLOCACategory

YM RF40 Rangefactorofthelognormaldistributionforthe40yearmultiplier providedbyeachexpertforeachLOCACategory

Whentheexpertsprovidedasymmetricinputs,NUREG1829utilizedasplitlognormalformulationfor calculatingthe40yearLOCAfrequencydistributions.Inthisstudy,theinputsprovidedbytheexperts werefittolognormalsbypreservingthemediansandthe95%tilesoftheinputdistributions,while ignoringtheasymmetriesontheleftsideofthedistributions.Analternativeprocedurewasalsotested, inwhichthemedianandtherangefactordefinedasthesquarerootoftheratioofthe95%tiletothe 5%tilewerepreservedintheinputdistributions,whichwereagainassumedtobelognormal.Inhis independentreviewofanearlierdraftofthisreport,Dr.AliMoslehrecommendedtheformer procedure,whichwasadoptedinthisreport.Theadoptedapproachretainsthesimplicityofusing lognormalsinlieuofthemorecomplicatedsplitlognormals,retainstheidentificationofthebest estimateswiththemediansofthedistributions,andbypreservingthe50thandhigherpercentilesis moreeffectiveinpreservingthemeansoftheunderlyinginputdistributions.

InTable43,thefirstprocedureisappliedasindicatedintheblueshadedcells.TheRF95valueswere calculatedbasedonUB/MidforthebaseLOCAfrequenciesandthe40yearmultipliers,andtheRF95 valuesforthe40yearLOCAfrequencieswerecalculatedfromEquation(4.4).

Asaresultoftheaboveprocedure,thereisasinglelognormaldistributiondefinedforeachLOCA categoryfrequencyat40yearsofoperation.Thisdistributionisapplicabletoeachcomponentprovided

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byeachofthe9expertswhoprovidedcomponentlevelinputsinReference[14].Insomecases,experts providedfixedvaluesforoneparameter(baseLOCAfrequencyormultiplier)andadistributionforthe other,inwhichcasethedistributionforthe40yearLOCAfrequencywasfoundsimplybyscalingthe provideddistributionparameterswiththesuppliedfixedvalues.TheresultsinthelastcolumnofTable 43reflecttheexecutionofStep2.4forthehotleg.

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Table43NUREG1829ExpertDistributionsforHotLegLOCAFrequencies ExpertID LOCACategory LOCAFrequencyforSystem[1]

(PerReactorCalendarYear) 40YrMultiplier[1]

40YrLOCAFrequency[1]

(PerReactorCalendarYear)

LB Mid UB RF95=UB/Mid[2]

LB Mid UB RF95=UB/Mid[2]

Mid[3]

RF95[4]

A 1(>100) 5.33E08 1.60E07 4.80E07 3.00E+00 1.00E+00 1.00E+00 1.00E+00 1.00E+00 1.60E07 3.00E+00 2(>1,500) 5.33E08 1.60E07 4.80E07 3.00E+00 1.50E02 3.00E01 5.85E01 1.95E+00 4.80E08 3.62E+00 3(>5,000) 5.33E08 1.60E07 4.80E07 3.00E+00 5.00E03 1.00E01 1.95E01 1.95E+00 1.60E08 3.62E+00 4(>25,000) 5.33E08 1.60E07 4.80E07 3.00E+00 1.50E03 3.00E02 5.85E02 1.95E+00 4.80E09 3.62E+00 5(>100,000) 5.33E08 1.60E07 4.80E07 3.00E+00 5.00E04 1.00E02 1.95E02 1.95E+00 1.60E09 3.62E+00 6(>500,000) 5.33E08 1.60E07 4.80E07 3.00E+00 1.50E04 3.00E03 5.85E03 1.95E+00 4.80E10 3.62E+00 B

1(>100) 3.00E07 3.00E07 3.00E07 1.00E+00 1.00E01 1.00E+00 1.00E+01 1.00E+01 3.00E07 1.00E+01 2(>1,500) 1.20E07 1.20E07 1.20E07 1.00E+00 1.00E01 1.00E+00 1.00E+01 1.00E+01 1.20E07 1.00E+01 3(>5,000) 4.80E08 4.80E08 4.80E08 1.00E+00 1.00E01 1.00E+00 1.00E+01 1.00E+01 4.80E08 1.00E+01 4(>25,000) 1.92E08 1.92E08 1.92E08 1.00E+00 1.00E01 1.00E+00 1.00E+01 1.00E+01 1.92E08 1.00E+01 5(>100,000) 7.68E09 7.68E09 7.68E09 1.00E+00 1.00E01 1.00E+00 1.00E+01 1.00E+01 7.68E09 1.00E+01 6(>500,000) 3.07E09 3.07E09 3.07E09 1.00E+00 1.00E01 1.00E+00 1.00E+01 1.00E+01 3.07E09 1.00E+01 C

1(>100) 6.00E07 6.00E07 6.00E07 1.00E+00 3.00E02 1.00E+00 3.00E+01 3.00E+01 6.00E07 3.00E+01 2(>1,500) 5.00E08 5.00E08 5.00E08 1.00E+00 3.00E02 1.00E+00 3.00E+01 3.00E+01 5.00E08 3.00E+01 3(>5,000) 2.00E08 2.00E08 2.00E08 1.00E+00 3.00E02 1.00E+00 3.00E+01 3.00E+01 2.00E08 3.00E+01 4(>25,000) 3.00E09 3.00E09 3.00E09 1.00E+00 5.00E02 1.67E+00 1.67E+02 1.00E+02 5.01E09 1.00E+02 5(>100,000) 1.00E09 1.00E09 1.00E09 1.00E+00 6.00E02 2.00E+00 2.00E+03 1.00E+03 2.00E09 1.00E+03 6(>500,000) 2.00E10 2.00E10 2.00E10 1.00E+00 6.00E02 2.00E+00 2.00E+03 1.00E+03 4.00E10 1.00E+03 E

1(>100) 3.07E07 9.22E07 2.77E06 3.00E+00 3.33E04 2.83E02 3.33E01 1.18E+01 2.61E08 1.49E+01 2(>1,500) 3.07E07 9.22E07 2.77E06 3.00E+00 3.33E04 2.83E02 3.33E01 1.18E+01 2.61E08 1.49E+01 3(>5,000) 3.07E07 9.22E07 2.77E06 3.00E+00 3.33E04 2.83E02 3.33E01 1.18E+01 2.61E08 1.49E+01 4(>25,000) 3.67E09 1.10E08 3.30E08 3.00E+00 1.00E03 1.00E01 1.50E+00 1.50E+01 1.10E09 1.86E+01 5(>100,000) 1.27E09 3.80E09 1.14E08 3.00E+00 1.00E04 5.00E02 1.00E+00 2.00E+01 1.90E10 2.43E+01

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ExpertID LOCACategory LOCAFrequencyforSystem[1]

(PerReactorCalendarYear) 40YrMultiplier[1]

40YrLOCAFrequency[1]

(PerReactorCalendarYear)

LB Mid UB RF95=UB/Mid[2]

LB Mid UB RF95=UB/Mid[2]

Mid[3]

RF95[4]

6(>500,000) 4.33E10 1.30E09 3.90E09 3.00E+00 1.00E04 3.00E02 3.00E+00 1.00E+02 3.90E11 1.14E+02 G

1(>100) 5.13E08 1.54E07 4.62E07 3.00E+00 1.00E01 1.14E+00 1.00E+01 8.77E+00 1.76E07 1.14E+01 2(>1,500) 7.50E09 2.25E08 6.75E08 3.00E+00 1.00E01 1.14E+00 1.00E+01 8.77E+00 2.57E08 1.14E+01 3(>5,000) 2.78E09 8.33E09 2.50E08 3.00E+00 1.00E01 1.14E+00 1.00E+01 8.77E+00 9.50E09 1.14E+01 4(>25,000) 9.50E10 2.85E09 8.55E09 3.00E+00 1.00E01 1.14E+00 1.00E+01 8.77E+00 3.25E09 1.14E+01 5(>100,000) 1.71E10 8.53E10 4.27E09 5.01E+00 1.00E01 1.14E+00 1.00E+01 8.77E+00 9.72E10 1.49E+01 6(>500,000) 1.58E11 1.58E10 1.58E09 1.00E+01 1.00E01 1.14E+00 1.00E+01 8.77E+00 1.80E10 2.37E+01 H

1(>100) 1.48E07 4.45E07 1.34E06 3.01E+00 2.50E+00 2.50E+01 2.50E+02 1.00E+01 1.11E05 1.28E+01 2(>1,500) 2.03E08 6.10E08 1.83E07 3.00E+00 1.00E+00 1.00E+01 1.00E+02 1.00E+01 6.10E07 1.28E+01 3(>5,000) 7.33E09 2.20E08 6.60E08 3.00E+00 5.00E01 5.00E+00 5.00E+01 1.00E+01 1.10E07 1.28E+01 4(>25,000) 2.60E09 7.80E09 2.34E08 3.00E+00 5.00E01 5.00E+00 5.00E+01 1.00E+01 3.90E08 1.28E+01 5(>100,000) 8.83E10 2.65E09 7.95E09 3.00E+00 5.00E01 5.00E+00 5.00E+01 1.00E+01 1.33E08 1.28E+01 6(>500,000) 2.93E10 8.80E10 2.64E09 3.00E+00 5.00E01 5.00E+00 5.00E+01 1.00E+01 4.40E09 1.28E+01 I

1(>100) 4.00E11 2.00E09 1.00E07 5.00E+01 5.00E01 5.00E01 5.00E01 1.00E+00 1.00E09 5.00E+01 2(>1,500) 4.00E11 2.00E09 1.00E07 5.00E+01 5.00E01 5.00E01 5.00E01 1.00E+00 1.00E09 5.00E+01 3(>5,000) 4.00E11 2.00E09 1.00E07 5.00E+01 5.00E01 5.00E01 5.00E01 1.00E+00 1.00E09 5.00E+01 4(>25,000) 4.00E11 2.00E09 1.00E07 5.00E+01 5.00E01 5.00E01 5.00E01 1.00E+00 1.00E09 5.00E+01 5(>100,000) 4.00E11 2.00E09 1.00E07 5.00E+01 5.00E01 5.00E01 5.00E01 1.00E+00 1.00E09 5.00E+01 6(>500,000) 4.00E11 2.00E09 1.00E07 5.00E+01 5.00E01 5.00E01 5.00E01 1.00E+00 1.00E09 5.00E+01 J

1(>100) 9.25E12 9.80E11 2.88E09 2.94E+01 3.19E+01 3.19E+01 3.19E+01 1.00E+00 3.13E09 2.94E+01 2(>1,500) 5.78E13 1.03E11 7.61E10 7.39E+01 5.24E+01 5.24E+01 5.24E+01 1.00E+00 5.40E10 7.39E+01 3(>5,000) 1.40E13 3.21E12 3.38E10 1.05E+02 6.04E+01 6.04E+01 6.04E+01 1.00E+00 1.94E10 1.05E+02 4(>25,000) 1.53E14 4.82E13 9.75E11 2.02E+02 7.50E+01 7.50E+01 7.50E+01 1.00E+00 3.62E11 2.02E+02 5(>100,000) 2.42E15 6.99E14 1.93E11 2.76E+02 9.81E+01 9.81E+01 9.81E+01 1.00E+00 6.86E12 2.76E+02 6(>500,000) 1.44E17 6.28E16 7.56E13 1.20E+03 1.14E+02 1.14E+02 1.14E+02 1.00E+00 7.16E14 1.20E+03

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ExpertID LOCACategory LOCAFrequencyforSystem[1]

(PerReactorCalendarYear) 40YrMultiplier[1]

40YrLOCAFrequency[1]

(PerReactorCalendarYear)

LB Mid UB RF95=UB/Mid[2]

LB Mid UB RF95=UB/Mid[2]

Mid[3]

RF95[4]

L 1(>100) 2.62E06 9.60E06 3.52E05 3.67E+00 1.27E01 1.27E01 1.27E01 1.00E+00 1.22E06 3.67E+00 2(>1,500) 1.58E06 6.34E06 2.53E05 3.99E+00 1.27E01 1.27E01 1.27E01 1.00E+00 8.05E07 3.99E+00 3(>5,000) 3.84E07 1.92E06 9.60E06 5.00E+00 4.19E01 4.19E01 4.19E01 1.00E+00 8.04E07 5.00E+00 4(>25,000) 1.54E07 7.68E07 3.84E06 5.00E+00 1.01E+00 1.01E+00 1.01E+00 1.00E+00 7.76E07 5.00E+00 5(>100,000) 6.40E08 3.20E07 1.60E06 5.00E+00 2.41E+00 2.41E+00 2.41E+00 1.00E+00 7.71E07 5.00E+00 6(>500,000) 3.20E11 3.20E10 3.20E09 1.00E+01 2.61E+00 2.61E+00 2.61E+00 1.00E+00 8.35E10 1.00E+01 Notes:

[1]DatashadedinyellowaretakenfromNUREG1829expertquestionnairesinReference[14].DatashadedinbluewerecalculatedinthisstudyperNotes[2]through[4].

[2]RF=RangeFactorofalognormaldistributiondefinedbytheMidvalueasthemedianandbytheUBvalueasthe95%tile.

[3]Medianofalognormaldistributionforthe40yearLOCAfrequencycreatedbytheproductoftwolognormaldistributions:themediansofthelognormaldistributionsfor LOCAfrequencyforsystemandthe40yearmultiplier(seeEquation[4.1]).

[4]RangeFactorofthe40yearLOCAfrequencylognormaldistribution(seeEquation[4.2]).

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4.7 Develop Expert Composite Distributions from NUREG1829 (Step 2.5)

Inthisstep,thenineexpertdistributionsfor40yearLOCAfrequenciesobtainedinStep2.4are combinedintoasinglecompositedistribution.

NUREG1829discussedtwoapproachesfordevelopingexpertcompositedistributions:theMixture DistributionMethodandtheGeometricMeanMethod.NUREG1829adoptedthelatterapproach, whereasthisstudyevaluatedbothapproaches,brieflydescribedbelow.

MixtureDistributionMethod TheexpertelicitationinputsheetsthatarefoundinReference[14]furnishedeachexpertwithinputon theLOCAfrequenciesineachofthesixapplicableLOCAcategoriesforeachcomponentintheRCS pressureboundary,thesamecomponentsasshowninFigure41.

AsinglemixturedistributionwasdevelopedforeachcombinationofcomponentandLOCAcategoryby combiningthe40yearLOCAfrequencydistributionsprovidedbyeachexpert.Asinglemixture distributionwasdevelopedbysamplingadiscretedistributiononeachMonteCarlotrialtodetermine whichexpertslognormaldistributionforthe40yearLOCAfrequencytobesampledforthattrial.The discretedistributionhasavalueforeachexpert,witheachvalue'sbeingassignedthesameprobability inordertogiveallexpertsequalweight.Intheseveralcaseswhereexpertsdidnotprovideinputsfor eachLOCAcategory,themixturedistributionwasdevelopedonlyforthoseexpertsprovidinginputsfor thatcategory.Inallcases,aminimumofsevenexpertsprovidedinput,andthevastmajorityofcases hadnine.ThismethodisdiscussedinNUREG1829butwasrejectedinfavoroftheGeometricMean method.

GeometricMeanMethod WhenthismethodwasusedinNUREG1829,itwasorientedtowardthecalculationofthetotalLOCA frequencyratherthantheLOCAfrequencyformanylocations.AnothercontrastwastheuseinNUREG 1829ofsplitlognormals,whereasthisstudyusedlognormalfittingbasedonpreservingmediansand 95%tiles.Inthisstudy,asinglelognormaldistributionforeachcomponentandeachLOCAcategorywas definedbytakingthegeometricmeanofthemediansoftheexpertslognormaldistributionsasthe compositedistributionmedian,andthegeometricmeansoftherangefactorsoftheexpertslognormal distributionsforthe40yearLOCAfrequenciesasthecompositedistributionrangefactor.Aswiththe MixtureMethod,inthisstudytheinputlognormaldistributionsprovidedbytheexpertswerefitto lognormaldistributionbymatchingthe50thand95thpercentiles.Asummaryofthederivedcomposite distributionparametersisprovidedinTable44,whichcompletesStep2.5ofourLOCAfrequency procedure.

AcomparisonoftheresultingcompositedistributionsusingbothmethodsisprovidedinFigures42 and43,fortheRCShotlegandRCSsurgeline,respectively.Asseeninthesefigures,thecomposite distributionsgeneratedbytheMixtureDistributionmethodproducemuchbroaderrangesof uncertaintythanthoseobtainedbytheGeometricMeanmethod.AsdiscussedinNUREG1829and

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confirmedbyourstudy,theupperandlowerboundsofthemixturedistributionsareheavilyinfluenced bytheexperts'extremehighsideandlowsideinputs,respectively,whereasthedistributionpercentiles fromtheGeometricMeanmethodmorefairlyrepresenttheexpertsinputs.However,intheselection oftargetLOCAfrequencies,thisstudydepartsfromNUREG1829byemployingboththeGeometric MeanModelofLOCAfrequenciesandarecreationoftheLydellBaseCaseAnalysisinNUREG1829 AppendixDforthesamegroupofcomponents.

Table44CompositeDistributionsforNUREG1829ExpertsBasedonGeometricMeanMethod

Component LOCA Cat.

Break Size (Inches)

GeometricMeanDistributionParameters EventsperReactorCalendarYear Mean 5%tile 50%tile 95%tile RF HotLeg 1

0.5 4.08E07 9.32E09 1.21E07 1.57E06 13.0 2

1.5 1.28E07 2.25E09 3.34E08 4.95E07 14.8 3

3 6.51E08 1.01E09 1.59E08 2.52E07 15.8 4

6.75 2.59E08 2.49E10 4.96E09 9.88E08 19.9 5

14 1.50E08 6.70E11 1.90E09 5.37E08 28.3 6

31.5 3.16E09 4.84E12 2.18E10 9.78E09 45.0 ColdLeg 1

0.5 1.47E07 3.27E09 4.30E08 5.66E07 13.2 2

1.5 5.20E08 9.07E10 1.35E08 2.01E07 14.9 3

3 2.19E08 3.33E10 5.31E09 8.48E08 16.0 4

6.75 7.85E09 7.41E11 1.49E09 2.99E08 20.1 5

14 4.54E09 1.94E11 5.60E10 1.62E08 28.9 6

31.5 1.10E09 1.56E12 7.23E11 3.36E09 46.4 SurgeLine 1

0.5 3.60E07 1.33E08 1.34E07 1.35E06 10.1 2

1.5 1.26E07 3.46E09 4.09E08 4.83E07 11.8 3

3 6.45E08 1.29E09 1.79E08 2.49E07 13.9 4

6.75 1.92E08 2.47E10 4.28E09 7.41E08 17.3 5

14 2.72E09 4.22E11 6.66E10 1.05E08 15.8 HPILine 1

0.5 1.27E05 6.40E07 5.45E06 4.65E05 8.5 2

1.5 4.58E06 1.51E07 1.62E06 1.74E05 10.7 3

3 7.21E07 1.53E08 2.06E07 2.78E06 13.5 4

6.75 1.29E07 1.41E09 2.64E08 4.95E07 18.8 5

14 3.03E08 3.30E10 6.20E09 1.16E07 18.8

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Figure42ComparisonofMixtureandGeometricMeanCompositeDistributions-RCSHotLeg

Figure43ComparisonofMixtureandGeometricMeanCompositeDistributions-RCSSurgeLine

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4.8 Benchmark of Lydells Base Case Analysis (Step 2.6)

ThisstepestablishesinputstotheselectionoftargetLOCAfrequenciesfromtheLydellBaseCase Analysis.AsecondarypurposeistoestablishthecorrespondingfailurerateandCRPdistributionsthat areresponsiblefortheBaseCaseresults.ThefailureratedistributionparameterswillbeusedinStep 2.8toconvertthetargetLOCAfrequencydistributionstoCRPdistributions.

UsingthesameMicrosoftExcel'andOracleCrystalBall'filesthatLydellusedtodevelophisBaseCase results,thesimplifiedmodelofEquation(4.1)wasappliedtothesamefailurerateestimatesthatLydell derivedanddocumentedinAppendixDofNUREG1829,assumingalognormaldistributionforthe conditionalLOCAcategoryprobabilityforeachcomponent.Thisresultedinlognormalparametersthat essentiallyreproduceLydellsAppendixDresults,asshowninFigures44,45,and46,fortheHPI injectionline,RCSsurgeline,andRCShotleg,respectively.TheCRPdistributionparameterswere obtainedbyfirstdevelopingtheLOCAfrequenciesandthencalculatingtheCRPdistributionparameters usingformulasforcalculatingtheparametersfortheproductoftwolognormaldistributions-similarto Equations(4.2)and(4.3).ThefigurescomparingtheBaseCaseresultsfromAppendixDinNUREG1829 withtheresultsobtainedusingtheequivalentlognormaldistributionsindicateexcellentagreement.The underlyinglognormaldistributionparametersfortheconditionalLOCAprobabilitiesinTable45appear totheauthorstobereasonable,i.e.theyareneitherverylargenorverysmall.Theconditional probabilityofagivenbreaksizeisindicatedtobeinverselyproportionaltopipesizewhichisin agreementwithpreviousestimatesofLOCAfrequencies.

TheuncertaintydistributionparametersfortheLOCAfrequenciesfromthisreconstructionoftheLydell BaseCaseresultsareshowninTable46.ThiscompletesStep2.6oftheLOCAfrequencyprocedure.

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Figure44BenchmarkingofLognormalDistributionstoLydellBaseCaseResults-HPIInjectionLine

Figure45BenchmarkingofLognormalDistributionstoLydellBaseCaseResults-RCSSurgeLine

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Figure46BenchmarkingofLognormalDistributionstoLydellBaseCaseResults-RCSHotLeg Table45LognormalDistributionsforFailureRatesandConditionalRuptureProbabilities(CRPs)

MatchingLydellsBaseCaseResults Component LOCA Category BreakSize (in.)

Mean 5%tile Median 95%tile Range Factor RCS-HotLeg FailureRate 3.46E04 1.01E05 1.15E04 1.32E03 11.4 1

.5 1.67E03 9.49E05 7.55E04 6.01E03 8.0 2

1.5 1.18E04 5.38E06 4.85E05 4.37E04 9.0 3

3 4.73E05 2.13E06 1.93E05 1.75E04 9.1 4

6.75 1.76E05 7.71E07 7.09E06 6.52E05 9.2 5

14 6.59E06 2.97E07 2.69E06 2.43E05 9.1 6

31.5 3.23E06 1.38E07 1.28E06 1.20E05 9.3 RCS-ColdLeg FailureRate 1.73E04 5.04E06 5.77E05 6.61E04 11.4 1

.5 1.67E03 9.49E05 7.55E04 6.01E03 8.0 2

1.5 1.18E04 5.38E06 4.85E05 4.37E04 9.0 3

3 4.73E05 2.13E06 1.93E05 1.75E04 9.1 4

6.75 1.76E05 7.71E07 7.09E06 6.52E05 9.2 5

14 6.59E06 2.97E07 2.69E06 2.43E05 9.1 6

31.5 3.23E06 1.38E07 1.28E06 1.20E05 9.3

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Component LOCA Category BreakSize (in.)

Mean 5%tile Median 95%tile Range Factor RCS-Surge Line FailureRate 1.33E05 5.55E07 5.25E06 4.96E05 9.5 1

.5 7.65E03 1.46E03 5.52E03 2.08E02 3.8 2

1.5 6.70E04 9.19E05 4.31E04 2.02E03 4.7 3

3 2.62E04 3.59E05 1.68E04 7.89E04 4.7 4

6.75 9.81E05 1.21E05 6.08E05 3.04E04 5.0 5

14 3.62E05 5.17E06 2.36E05 1.08E04 4.6 HPI FailureRate 1.33E03 4.27E05 4.65E04 5.07E03 10.9 1

.5 1.18E02 2.32E03 8.59E03 3.18E02 3.7 2

1.5 1.75E03 2.69E04 1.17E03 5.11E03 4.4 3

3 6.97E04 1.03E04 4.61E04 2.06E03 4.5

Table46LOCAFrequencyDistributionsfromBenchmarkingofLydellBaseCaseResults

Component LOCA Cat.

Break Size(in.)

LydellBaseCaseDistributionParameters EventsperReactorCalendarYear Mean 5%tile 50%tile 95%tile RF HotLeg 1

0.5 6.65E07 3.55E09 9.39E08 2.14E06 24.6 2

1.5 4.87E08 2.10E10 6.15E09 1.49E07 26.6 3

3 1.83E08 8.33E11 2.42E09 5.95E08 26.7 4

6.75 6.99E09 3.03E11 8.93E10 2.21E08 27.0 5

14 2.55E09 1.16E11 3.29E10 8.29E09 26.7 6

31.5 1.26E09 5.44E12 1.58E10 4.04E09 27.3 ColdLeg 1

0.5 3.33E07 1.78E09 4.70E08 1.07E06 24.6 2

1.5 2.44E08 1.05E10 3.08E09 7.45E08 26.6 3

3 9.15E09 4.17E11 1.21E09 2.98E08 26.7 4

6.75 3.50E09 1.52E11 4.47E10 1.11E08 27.0 5

14 1.28E09 5.80E12 1.65E10 4.15E09 26.7 6

31.5 6.30E10 2.72E12 7.90E11 2.02E09 27.3 SurgeLine 1

0.5 1.14E07 2.13E09 2.36E08 3.94E07 13.6 2

1.5 9.60E09 1.48E10 1.88E09 3.46E08 15.3 3

3 3.84E09 5.78E11 8.50E10 1.35E08 15.3 4

6.75 1.44E09 2.01E11 2.77E10 5.06E09 15.9 5

14 5.31E10 8.23E12 1.01E10 1.87E09 15.1 HPILine 1

0.5 1.60E05 2.62E07 3.93E06 6.09E05 15.2 2

1.5 2.33E06 3.30E08 5.40E07 9.02E06 16.5 3

3 9.22E07 1.28E08 2.14E07 3.59E06 16.7

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4.9 Select Target LOCA Frequencies from NUREG1829 Data (Step 2.7)

InselectingthetargetLOCAfrequencies,fouroptionswereconsidered.

Option1:useonlytheLydellBaseCaseresults Option2:useonlytheExperts'MixtureDistributionresults Option3:useonlytheExpertsGeometricMeanresults Option4:useahybridoftheExperts'GeometricMeanandLydellBaseCaseresults Option1wouldbeconsistentwiththeSTPapproachtoLOCAfrequencyassessmentbutwouldnotbe makingfulluseoftheexpertelicitationresultsofNUREG1829.Option2wouldbemakinguseofthe expertelicitationbutwouldproduceunreasonablylargespreadsbetweentheupperandlower percentiles,whichwouldoveremphasizethemostextremeexpertinputs.Option3wouldbesuperiorto Options1and2inthatitwouldbetterrepresentthediverseinputsoftheexpertpanelandwould includetheinputofLydell.Theoptionselected,Option4,isahybridofOptions1and3andiscomprised ofamixturedistributionoftheLOCAfrequenciesproducedbythoseoptions.

Option4placesequalweightontheLydellBaseCaseresultsandtheExpertGeometricMeanresults.

Thisoption'smixturedistributionwasdevelopedbyMonteCarlosimulation,whichinvolvedabinary variabletoselecteitherLydellBaseCaseresultsorExpertGeometricMeanresults,afterwhicha randomsamplewasobtainedfromthatselecteddistribution.Theuseofthemixturedistribution methodtoprovideacompositetargetLOCAdistributionwasrecommendedbyDr.AliMosleh,who performedanindependentreviewofanearlierdraftwhereadifferentmethodwasusedtodevelopthe hybridofthetwoLOCAfrequencymodels.Intheearlierapproach,ahybriddistributionwasconstructed usingtheworstcase95%tilesand5%tilesofthedistributionsfromOptions1and3,andthe95%tileand 5%tilewerethenselectedfromthathybriddistribution.

Option4ispreferredoverOption3asitexhibitsalargerdegreeofepistemicuncertaintywhile providingmeanvaluesthatareveryclosetothoseofOption3.ThesetargetLOCAfrequenciesareused inthenextsteptoderiveCRPsforLOCAsineachoftheLOCAbreaksizecategoriesgivenapipefailure.

TheparametersofthetargetLOCAfrequencydistributionsfortheHotLeg,ColdLeg,SurgeLine,andHPI LineselectedusingthismethodwereshowninTable211.Figures47,48and49comparethe resultingtargetLOCAfrequenciesandthoseforOption3,fortheRCSHotLeg,SurgeLine,andHPILine, respectively.Theneteffectistoincreasetheuncertaintywithslightreductionsinthemeanand95%tile andlargerreductionsforthe5%tilescomparedtoOption3fortheHotLegandSurgeLine.Inthecaseof theHPIline,theLydellBaseCasewasforasmallpipesizesoonlyCategories1,2,and3wereincluded.

HencethetargetLOCAfrequenciesforCategories4and5arethesameasthosefortheGMmethodand theimpactofincorporatingtheLydellBaseinputstothemixturedistributionismuchsmallerforthis casewhencomparedtothehotlegandsurgeline.Thecoldlegresultsareverysimilartothehotleg resultsexceptthatthefrequenciesarescaleddownsomewhat.ThiscompletesStep2.7.

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Figure47ComparisonofExpertsGeometricMeanandSTPTargetLOCAModelHotLeg

Figure48ComparisonofExpertsGeometricMeanandSTPTargetLOCAModel-SurgeLine

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Figure49ComparisonofExpertsGeometricMeanandSTPTargetLOCAModelHPILine

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Table47MixtureDistributionofGeometricMeanandLydellBaseCaseforSTPTargetLOCA Frequencies

Component LOCA Cat.

Break Size(in.)

TargetLOCAFrequency DistributionParameters EventsperReactorCalendarYear Mean 5%tile 50%tile 95%tile RF HotLeg 1

0.5 5.07E07 5.39E09 1.05E07 1.83E06 18.4 2

1.5 8.22E08 4.29E10 1.49E08 3.30E07 27.7 3

3 4.10E08 1.68E10 6.47E09 1.60E07 30.9 4

6.75 1.57E08 5.65E11 2.09E09 6.07E08 32.8 5

14 8.69E09 2.09E11 7.64E10 2.93E08 37.4 6

31.5 2.11E09 5.01E12 1.79E10 6.63E09 36.4 6D[1]

44.5 1.05E09 2.72E12 9.80E11 3.52E09 36.0 ColdLeg 1

0.5 2.28E07 2.36E09 4.32E08 8.08E07 18.5 2

1.5 3.71E08 2.09E10 6.63E09 1.43E07 26.1 3

3 1.53E08 8.09E11 2.62E09 5.92E08 27.1 4

6.75 5.38E09 2.68E11 8.13E10 2.03E08 27.5 5

14 2.72E09 8.97E12 2.94E10 9.45E09 32.5 6

31.5 8.03E10 2.05E12 7.27E11 2.64E09 35.8 6D 44.5 4.63E10 1.10E12 4.10E11 1.53E09 37.4 SurgeLine 1

0.5 2.34E07 3.55E09 6.60E08 9.35E07 16.2 2

1.5 6.78E08 2.72E10 1.04E08 2.83E07 32.3 3

3 3.33E08 1.05E10 4.04E09 1.38E07 36.2 4

6.75 1.05E08 3.52E11 1.14E09 4.06E08 34.0 5

14 1.61E09 1.35E11 2.84E10 6.17E09 21.4 5D[2]

19.8 6.53E10 8.56E12 1.47E10 2.52E09 17.2 HPILine 1

0.5 1.39E05 3.88E07 4.73E06 5.26E05 11.6 2

1.5 3.51E06 5.50E08 9.78E07 1.37E05 15.8 3

3 8.11E07 1.41E08 2.11E07 3.11E06 14.9 4

6.75 1.29E07 1.41E09 2.64E08 4.95E07 18.8 5

14 3.03E08 3.30E10 6.20E09 1.16E07 18.8 Notes:

[1]LOCACategory6Disintroducedinthisstudytodenoteadoubleendedbreakofa31.5in.pipe

[2]LOCACategory5Disintroducedinthisstudytodenoteadoubleendedbreakofa14in.pipe

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4.10 Develop Conditional Rupture Probabilities from Target LOCA Frequencies (Step 2.8)

ThisstepusesthetargetLOCAfrequenciesfromStep2.7andinformationfromtheLydellBaseCase resultsontheunderlyingfailureratesforeachcomponent,toderiveaCRPmodelthatwhenlinkedwith theLydellBaseCasefailureratemodel,willreproducethetargetLOCAfrequenciesthatweredeveloped inStep2.7.TheLydellfailurerateanalysisthatwasperformedinAppendixDofNUREG1829usedthe samemethodologyforfailureratedevelopmentasusedhere,usinganearliersetofPIPExpfailuredata.

TheresultsforhisBaseCasefailureratesforthecomponentsassociatedwiththetargetLOCA frequenciesareshowninTable48.ThisincludesthethreePWRcomponentsanalyzedinNUREG1829 aswellastheRCScoldleg,whoseresultshavebeendevelopedusingasetofassumptionsthatare comparabletothatusedfortheRCShotleg.Inordertoderivethemodelforconditionalprobabilityof rupture,theLydellfailurerateswerefittolognormaldistributionsbymatchingthe5thand95th percentilesandtherangefactorcalculatedfromthesepercentiles.

SincetheuseoflognormaldistributionsenablestheLOCAfrequencytobeexpressedastheproductofa lognormallydistributedfailurerateandalognormallydistributedCRP,theparametersoftheCRP distributionsmaybecalculateddirectly.UsingthesamemethodologyasusedinEquations(4.2,(4.3),

and(4.4),thefollowingrelationsareestablished.

FR TLF CRP median median median k

k

(4.5) k CRP k

e RFCRP

645

.1

(4.6) where 2

2 645

.1

)

ln(

645

.1

)

ln(

FR TLF CRP RF RF k

k

(4.7)

k CRP median Medianofthelognormaldistributionfortheconditionalprobability ofpiperuptureinLOCACategorykgivenpipefailure

k TLF median MedianofthelognormaldistributionforthetargetLOCAfrequency forLOCACategoryk

FR median Medianofthelognormaldistributionforthepipefailurerate

k CRP RF Rangefactorofthelognormaldistributionfortheconditional probabilityofpiperuptureinLOCACategorykgivenpipefailure, equaltoSQRT(95%tile/5%tile)ofthelognormaldistribution

k CRP

Logarithmicstandarddeviationforthelognormaldistributionforthe conditionalprobabilityofpiperuptureinLOCACategorykgivenpipe failure

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k TLF RF RangefactorofthelognormaldistributionforthetargetLOCA frequencyforLOCACategoryk

FR RF Rangefactorofthelognormaldistributionforthepipefailurerate

ThemediansandrangefactorsoftheCRPdistributionswerecomputedfromthemediansandrange factorsofthetargetLOCAfrequencydistributionsusingtheaboveformulas.Then,usingtheproperties ofthelognormaldistribution,theremainingparametersofthedistributionsmaybedirectlycomputed.

Table48ParametersofTargetLOCAFrequenciesSelectedforSTPModel Component LOCA Category Break Size(in.)

CumulativeLOCAFrequency[1],

perReactorCalendarYear RF[2]

Mean 5%tile 50%tile 95%tile HotLeg 1

0.5 4.45E07 3.55E09 7.72E08 1.68E06 21.7 2

1.5 1.95E07 2.10E10 1.09E08 5.68E07 52.0 3

3 1.05E07 8.33E11 4.89E09 2.87E07 58.7 4

6.75 3.75E08 3.03E11 1.77E09 1.03E07 58.3 5

14 2.02E08 1.16E11 7.75E10 5.17E08 66.8 6

31.5 2.41E09 5.44E12 2.08E10 7.94E09 38.2 ColdLeg 1

0.5 1.52E07 1.78E09 3.22E08 5.85E07 18.2 2

1.5 7.47E08 1.05E10 4.89E09 2.28E07 46.6 3

3 3.17E08 4.17E11 1.99E09 9.55E08 47.9 4

6.75 1.00E08 1.52E11 6.85E10 3.09E08 45.2 5

14 5.27E09 5.80E12 2.99E10 1.54E08 51.5 6

31.5 7.60E10 2.72E12 8.51E11 2.66E09 31.3 SurgeLine 1

0.5 3.85E07 2.13E09 5.48E08 1.41E06 25.7 2

1.5 1.94E07 1.48E10 8.84E09 5.27E07 59.7 3

3 1.10E07 5.78E11 4.00E09 2.77E07 69.2 4

6.75 2.86E08 2.01E11 1.24E09 7.64E08 61.7 5

14 3.01E09 8.23E12 2.89E10 1.02E08 35.2 HPILine 1

0.5 1.57E05 2.62E07 3.99E06 6.09E05 15.2 2

1.5 5.31E06 3.30E08 8.05E07 1.96E05 24.4 3

3 9.30E07 1.28E08 2.14E07 3.59E06 16.7 4

6.75 1.36E07 1.34E09 2.64E08 5.17E07 19.6 5

14 3.19E08 3.16E10 6.20E09 1.22E07 19.6 Notes:

[1]FrequencyofLOCAwithbreaksizegreaterthanorequaltotheindicatedvalue.

[2]RF=SQRT(95%tile/5%tile).

ComparisonsoftheSTPModelCRPdistributionswiththoseusedintheLydellBaseCaseareshownin Figures411,412,and413.Thenetresultoftheprocedureistoproducesomewhatmorepessimistic CRPvalueswithlargerepistemicuncertaintiesthanthoseusedintheLydellBaseCaseAnalysis.This completesStep2.8oftheLOCAfrequencyprocedure.

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Figure410ComparisonofLydellandSTPModelsforCRP-RCSHotLeg

Figure411ComparisonofLydellandSTPModelsforCRP-RCSSurgeLine

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Figure412ComparisonofLydellandSTPModelsforCRP-HPILine Table49STPCRPDistributionPriorsDerivedfromTargetLOCAFrequencies Component LOCA Category Break Size(in.)

ConditionalRuptureProbabilityDistributionParameters Median Mean 5th Percentile 95th Percentile Range Factor[1]

HotLeg 1

0.5 1.46E03 1.84E04 9.10E04 4.50E03 4.9 2

1.5 3.31E04 1.35E05 1.29E04 1.23E03 9.6 3

3 1.65E04 5.01E06 5.61E05 6.28E04 11.2 4

6.75 5.74E05 1.49E06 1.81E05 2.20E04 12.2 5

14 2.49E05 4.54E07 6.62E06 9.65E05 14.6 6

31.5 5.84E06 1.06E07 1.55E06 2.26E05 14.6[4]

6D[2]

44.5 3.20E06 5.82E08 8.49E07 1.24E05 14.6[4]

ColdLeg 1

0.5 1.20E03 1.50E04 7.48E04 3.72E03 5.0 2

1.5 2.74E04 1.31E05 1.15E04 1.00E03 8.7 3

3 1.13E04 4.92E06 4.54E05 4.18E04 9.2 4

6.75 3.58E05 1.49E06 1.41E05 1.33E04 9.5 5

14 1.59E05 4.25E07 5.09E06 6.10E05 12.0 6

31.5 4.48E06 9.17E08 1.26E06 1.73E05 13.7 6D[2]

44.5 2.67E06 4.88E08 7.10E07 1.03E05 14.6

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Component LOCA Category Break Size(in.)

ConditionalRuptureProbabilityDistributionParameters Median Mean 5th Percentile 95th Percentile Range Factor[1]

SurgeLine 1

0.5 2.08E02 2.42E03 1.26E02 6.53E02 5.2 2

1.5 7.24E03 1.40E04 1.98E03 2.80E02 14.1 3

3 3.28E03 4.68E05 7.70E04 1.27E02 16.4 4

6.75 9.24E04 1.32E05 2.17E04 3.57E03 16.4[4]

5 14 2.30E04 3.29E06 5.41E05 8.90E04 16.4[4]

5D[3]

19.8 1.19E04 1.70E06 2.80E05 4.60E04 16.4[4]

HPILine 1

0.5 1.08E02 5.77E03 1.02E02 1.80E02 1.8 2

1.5 3.00E03 5.27E04 2.10E03 8.39E03 4.0[4]

3 3

6.45E04 1.13E04 4.53E04 1.81E03 4.0 4

6.75 9.67E05 1.03E05 5.67E05 3.11E04 5.5 5

14 2.27E05 2.43E06 1.33E05 7.30E05 5.5[4]

Notes:

[1]RangeFactor=SQRT(95%tile/5%tile).

[2]6Dcorrespondstoadoubleendedbreakofa31.5pipe.

[3]5Dcorrespondstoadoubleendedbreakofa14pipe.

[4]RangefactorsadjustedupwardstoensurenoRFdecreasewithdecreasingLOCAfrequency.

4.11 Bayes Update of the Conditional Probability Distributions (Step 2.9)

Theconditionalprobabilitymodelsdevelopedintheprevioussectionareusedasthebasisforaprior distribution,whichwethenupdatewiththeevidencefromtheservicedataonthenumberof experiencedpipefailureswithnoLOCAsforeachsystem.DuringtheBayesupdating,thelognormal distributionsdevelopedinStep2.8asthepriordistributions,weretruncatedtoavoidCRPvaluesgreater than1.0.However,thistruncationonlyimpactstheextremerighthandtailsofthedistributionand thereforedoesnotsignificantlyaffectthemajorquotedparameters(mean,median,5%tile,and 95%tile).TheBayesupdateswereperformedusingRDATPlus'Version1.5.8(Build1691)software.

ThetruncatedlognormaldistributionsdescribedinTable49wereusedaspriordistributionsandthen updatedwith0LOCAsineachLOCAcategoryoutofthenumberofobservedfailuresforeachsystem.

TheresultsaresummarizedinTable410.ThefinalBayesupdateddistributionsfortheCRP distributionsinTable410showasmalldecreaserelativetothevaluesinTable49.ThiscompletesStep 2.9andallthestepsassociatedwithdevelopingtheCRPmodelfortheSTPLOCAfrequencies.

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Table410STPCRPDistributionsafterBayesUpdating Component Bayes Update Evidence LOCA Category Break Size(in.)

ConditionalRuptureProbabilityDistributionParameters Mean 5%tile Median 95%tile RF[1]

HotLeg 0Ruptures/

6Failures; HotLegCRP Model 1

0.5 1.43E03 1.85E04 9.04E04 4.39E03 4.9 2

1.5 3.28E04 1.34E05 1.29E04 1.23E03 9.6 3

3 1.64E04 5.01E06 5.60E05 6.25E04 11.2 4

6.75 5.74E05 1.48E06 1.81E05 2.20E04 12.2 5

14 2.49E05 4.53E07 6.62E06 9.66E05 14.6 6

31.5 5.85E06 1.06E07 1.55E06 2.26E05 14.6 6D[2]

44.5 3.20E06 5.82E08 8.49E07 1.24E05 14.6 HotLegatSG Inlet 0Ruptures/

19Failures; HotLegCRP Model 1

0.5 1.39E03 1.84E04 8.91E04 4.25E03 4.8 2

1.5 3.22E04 1.34E05 1.28E04 1.20E03 9.5 3

3 1.61E04 5.00E06 5.58E05 6.18E04 11.1 4

6.75 5.70E05 1.48E06 1.81E05 2.19E04 12.2 5

14 2.35E05 4.29E07 6.26E06 9.11E05 14.6 6

31.5 5.84E06 1.06E07 1.55E06 2.26E05 14.6 6D[2]

44.5 3.20E06 5.82E08 8.49E07 1.24E05 14.6 ColdLeg 0Ruptures/

3Failures; ColdLegCRP Model 1

0.5 1.20E03 1.49E04 7.46E04 3.71E03 5.0 2

1.5 2.72E04 1.32E05 1.15E04 9.97E04 8.7 3

3 1.13E04 4.93E06 4.54E05 4.17E04 9.2 4

6.75 3.60E05 1.48E06 1.41E05 1.34E04 9.5 5

14 1.59E05 4.24E07 5.09E06 6.11E05 12.0 6

31.5 4.47E06 9.20E08 1.26E06 1.73E05 13.7 6D[2]

44.5 2.68E06 4.86E08 7.10E07 1.04E05 14.6 SurgeLine 0Ruptures/

3Failures; SurgeLine CRPModel 1

0.5 1.89E02 2.36E03 1.20E02 5.81E02 5.0 2

1.5 6.09E03 1.38E04 1.91E03 2.46E02 13.3 3

3 2.92E03 4.66E05 7.56E04 1.18E02 15.9 4

6.75 8.86E04 1.32E05 2.16E04 3.49E03 16.2 5

14 2.27E04 3.30E06 5.40E05 8.83E04 16.4 5D[3]

19.8 1.18E04 1.71E06 2.80E05 4.58E04 16.4 CVCSLine 0Ruptures/

14Failures; HPICRP Model 1

0.5 1.07E02 5.59E03 1.00E02 1.79E02 1.8 2

1.5 2.88E03 5.17E04 2.05E03 7.97E03 3.9 3

3 6.40E04 1.13E04 4.50E04 1.79E03 4.0 4

6.75 9.68E05 1.03E05 5.66E05 3.11E04 5.5 5

14 2.27E05 2.42E06 1.33E05 7.31E05 5.5

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Component Bayes Update Evidence LOCA Category Break Size(in.)

ConditionalRuptureProbabilityDistributionParameters Mean 5%tile Median 95%tile RF[1]

SafetyInjection Recirculation (SIR)Lines 0Ruptures/

14Failures; HPICRP Model 1

0.5 1.07E02 5.59E03 1.00E02 1.79E02 1.8 2

1.5 2.88E03 5.17E04 2.05E03 7.97E03 3.9 3

3 6.40E04 1.13E04 4.50E04 1.79E03 4.0 4

6.75 9.68E05 1.03E05 5.66E05 3.11E04 5.5 5

14 2.27E05 2.42E06 1.33E05 7.31E05 5.5 Pressurizer Lines 0Ruptures/

12Failures; HPICRP Model 1

0.5 1.07E02 5.60E03 1.00E02 1.80E02 1.8 2

1.5 2.89E03 5.18E04 2.05E03 8.03E03 3.9 3

3 6.41E04 1.13E04 4.51E04 1.79E03 4.0 4

6.75 9.68E05 1.03E05 5.66E05 3.11E04 5.5 5

14 2.27E05 2.42E06 1.33E05 7.31E05 5.5 SmallBore 0Ruptures/

79Failures; HPICRP Model 1

0.5 8.21E03 1.10E02 2.26E03 2.91E02 3.6 2

1.5 1.67E03 3.60E03 2.05E04 1.30E02 8

3 3

4.57E04 1.02E03 5.53E05 3.72E03

8.2 Notes

[1]RangeFactor=SQRT(95%tile/5%tile).

[2]6Dcorrespondstoadoubleendedbreakofa31.5pipe.

[3]5Dcorrespondstoadoubleendedbreakofa16pipe.

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5. LOCA Frequencies for STP GSI191 Application (Step 3)

ThissectiondocumentsthequantificationofLOCAfrequenciesforinputtotheCASAGRANDEmodelfor evaluationofdebrisinducedfailuresoftherecirculationcoolingfunctionandtotheRISKMANmodelfor evaluationofthechangestocoredamagefrequencyandlargeearlyreleasefrequencyfortheGSI191 application.InaccordancewiththestepbystepapproachtoLOCAfrequencydeterminationpresented inSection2,thissectioncoversthefollowingkeytasks:

3. STPSpecificLOCAFrequencyDevelopment 3.1 Determineweldcountsandpipesizesforeachcomponentmi 3.2 IdentifywhichlocationsareinandoutoftheNDEprogram 3.3 CombinetheresultsofStep1andStep2forcomponentLOCAfrequencies 3.4 ApplyMarkovModeltospecializerupturefrequencies(Iik)forNDEornoNDE 3.5 ProvidelocationbylocationLOCAfrequenciesvs.breaksizetoCASAGRANDE-jx 3.6 ProvideSmall,Medium,andLargeLOCAfrequencies(F(LOCAx)) toRISKMAN 5.1 Weld Counts and Pipe Sizes for Each Component (Steps 3.1 and 3.2)

Adetailedreviewofthepipingsystemisometricdiagramswasperformedtoestablishthepipesizesand weldcountsforeachofthecomponentcategorieslistedinTable32.Thisreviewwasdone independentlybythegroupatAlionthatdevelopedtheCADmodeloftheSTPLOCAsensitivepiping systemsandcontainment,andbyanothergroupatScandpowerthatpreparedadatabaseofSTPpiping systemcomponentsandsupportingdesigninformation[15].Thisdatabaseidentifieswhichweldsare beinginspectedintheNDEprogrambothbeforeandaftertheimplementationofriskinformedin serviceinspectionatSTP.

5.2 Component LOCA Frequency Distributions (Step 3.3)

TheLOCAfrequenciesforeachcomponentcategoryweredevelopedbycombiningtheresultsforthe failurerateuncertaintydistributionsdevelopedinStep1anddocumentedinSection3,withtheresults fortheconditionalruptureprobabilitydistributionsdevelopedinStep2anddocumentedinSection4.

Thiswasdoneusingtwomethods:Method1isMonteCarlosimulationviaEquation(2.2),andMethod2 istheuseofformulasforcomputingtheparametersofthearithmeticproductoftwolognormal distributions.TheresultsofMethod2areregardedastheofficialresults,asthesearenotinfluencedby anyMonteCarlosamplinguncertaintyandareexactundertheassumptionthatboththefailurerateand CRPdistributionsarelognormal.Ingeneral,theresultsofMethod1and2wereinexcellentagreement, whichfacilitatedcheckingtheresultsanddebuggingthespreadsheets(smalldifferencesinthesecond significantfigure).TheuncertaintiesinthefrequencyofLOCAvs.breaksizereflecttheuncertaintiesin thefailurerateestimationaswellasintheCRPmodelestimates.

ThecomponentLOCAfrequencyvs.breaksizedistributionsforeachofthe41componentcategoriesare foundinTables51through54.Thesetableshavebeencustomizedtofitthevariouspipesizesthatare reflectedinthecomponentcategorydefinitions.Thelastentryinthetableistheestimatedfrequencyof adoubleendedbreakofthepipe.TheLOCAfrequenciesfortheotherentriesarecumulative frequencies,i.e.,frequenciesofabreakequaltoorgreaterthantheindicatedbreaksize.

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InconvertingfromLOCAcategorytobreaksizeintheCRPmodel,thefrequenciesforbreaksizesother thanthoseindicatedinTable41weredevelopedusinglinearinterpolationandextrapolationonalog frequencyvs.logbreaksizecurve.Thisapproachisjustifiedbythetrendsofthefrequenciesvs.break sizecurvesonaloglogplotbeingwellbehavedandshowinglimitedcurvature.Theshapeofthese curvesisdrivenbytheassumptionsunderlyingtheCRPmodel.

TheMonteCarlocalculationswerecarriedoutusingCrystalBall'Version11.1.2.1.000(32bit)and MicrosoftExcelOfficeProfessional2010Version14.0.6106.5005.StraightMonteCarloratherthanLatin Hypercubewasused,with100,000trials.TheCRPdistributionsderivedfromeachoftheCRP componentcategories(hotleg,coldleg,surgeline,HPIline)wereassumedtocorrelatefully,i.e.,to haveacorrelationcoefficientof+1.0.TheMonteCarloanalysisforthefailureratedevelopmentand LOCAfrequencyanalysiswerefullyintegratedratherthandoneinstages.

PlotsoftheLOCAfrequenciesvs.breaksizeforhotlegcomponentsareshowninFigures51,52,and5 3.Thefirsttwofiguresshowtheepistemicuncertaintiesforcomponentcategories1A(BFweldsinhot legsubjecttostresscorrosioncrackinganddesign&constructiondefects)and1C(BJweldsinhotleg susceptibletothermalfatigueanddesign&constructiondefects).Asseeninthesefigures,theratios betweenthe95thand5thpercentilesaretwotothreeordersofmagnitude,indicatinggreatuncertainty.

InFigure53,themeanLOCAfrequenciesforthethreetypesofhotlegwelds(BF,andBJwithand withoutthermalfatigue)arecompared.ThereissignificantvariabilityinLOCAfrequenciesacrossthese categories.TheresultsforthesecasesareparallelbecausetheyusethesameCRPmodel.Hencethe variabilityissourcedtothevariabilityinthefailurerates,whosedetailswerepresentedinSection4.

ThefourBFweldsinthepressurizeratSTP(excludingtheBFweldinthesurgelineatthepressurizer) havebeenrepairedusingweldoverlaystoaddressobservedcracking.Priortoapplicationoftheseweld overlays,theseweldswereinCategories5Fand5GinTable32.TheyarenowassignedtoCategory5H.

TheLOCAfrequencymodelusedfortheseweldsistoapplythepressurizerfailureratefordesign&

constructiondefectstotheweldoverlayitself,undertheassumptionthattheunderlyingcracksand associateddamagemechanismshavebeenadequatelymitigatedbytheoverlay.

5.3 Application of Markov Model to Address Impact of NDE Program (Step 3.4)

Alltheresultspresentedtothispointhaveincludedtheeffectsofpipinginspectionsandintegrity managementprogramsonlyimplicitly.ThisisbecausethefailureratedataandinputsfromNUREG1829 thatformthebasisforourconditionalprobabilityoftheLOCAmodelhavebeenbasedonananalysis thathasimplicitlyreflectedtheeffectsoftheindustryreliabilityintegritymanagement(RIM)programs.

Suchprogramsincludetestingandmonitoringforleaksaswellasnondestructiveexaminationsthatare performedinthevariousISIprogramsonaperiodicbasis.Hence,theLOCAfrequenciesdevelopedfor STPcomponentcategoriesinStep3.3reflectanaveragingoftheeffectsoftheseRIMprograms.For Class1welds,thereisavariabilityinRIMbecauseonlyarelativelysmallfractionoftheweldpopulation issubjectedtoNDE(approximately10%),whereasalltheClass1weldsbenefitfromthesame100%

coverageofleaktesting.

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Table51LOCAFrequenciesvs.BreakSizeforHotLeg,SGInlet,ColdLeg,andSurgeLineComponentCategories1Athrough4B

Table52LOCAFrequenciesvs.BreakSizeforPressurizerandSmallBoreComponentCategories5Athrough6B

Calc.Case System SizeCase(in.)

DEGB(in.)

WeldType DM No.Welds X,BreakSize (in.)

F(LOCAX)

X,BreakSize (in.)

F(LOCAX)

X,BreakSize (in.)

F(LOCAX)

X,BreakSize (in.)

F(LOCAX)

X,BreakSize (in.)

F(LOCAX)

X,BreakSize (in.)

F(LOCAX)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.)

0.50 4.02E07 0.50 1.95E09 0.50 1.25E08 0.50 1.98E06 0.50 1.51E07 0.50 1.51E07 0.50 2.79E09 0.50 2.79E09 0.50 9.75E06 0.50 7.44E08 0.50 1.21E07 0.50 7.44E08 1.50 9.25E08 1.50 4.49E10 1.50 2.87E09 1.50 4.59E07 1.50 3.43E08 1.50 3.43E08 1.50 6.33E10 1.50 6.33E10 1.50 3.30E06 1.50 2.52E08 1.50 4.11E08 1.50 2.52E08 2.00 6.92E08 2.00 3.36E10 2.00 2.15E09 2.00 3.45E07 2.00 2.38E08 2.00 2.38E08 2.00 4.39E10 2.00 4.39E10 2.00 2.43E06 2.00 1.85E08 2.00 3.02E08 2.00 1.85E08 3.00 4.61E08 3.00 2.24E10 3.00 1.43E09 3.00 2.31E07 3.00 1.42E08 3.00 1.42E08 3.00 2.62E10 3.00 2.62E10 3.00 1.58E06 3.00 1.20E08 3.00 1.97E08 3.00 1.20E08 4.00 3.19E08 4.00 1.55E10 4.00 9.90E10 4.00 1.60E07 4.00 9.49E09 4.00 9.49E09 4.00 1.75E10 4.00 1.75E10 4.00 1.03E06 4.00 7.82E09 4.00 1.28E08 3.54 9.42E09 6.00 1.89E08 6.00 9.19E11 6.00 5.89E10 6.00 9.52E08 6.00 5.39E09 6.00 5.39E09 6.00 9.95E11 6.00 9.95E11 6.00 5.58E07 6.00 4.26E09 6.00 6.94E09 6.75 1.61E08 6.75 7.83E11 6.75 5.01E10 6.75 8.12E08 6.75 4.53E09 6.75 4.53E09 6.75 8.36E11 6.75 8.36E11 6.75 4.68E07 6.75 3.57E09 6.75 5.82E09 14.00 7.01E09 14.00 3.40E11 14.00 2.18E10 14.00 3.35E08 14.00 2.01E09 14.00 2.01E09 14.00 3.70E11 14.00 3.70E11 14.00 1.18E07 14.00 9.03E10 14.00 1.47E09 20.00 3.70E09 20.00 1.80E11 20.00 1.15E10 20.00 1.81E08 20.00 1.15E09 20.00 1.15E09 20.00 2.11E11 20.00 2.11E11 16.00 9.19E08 16.00 7.02E10 16.00 1.15E09 29.00 1.90E09 29.00 9.24E12 29.00 5.92E11 29.00 9.57E09 27.50 6.96E10 27.50 6.96E10 27.50 1.28E11 27.50 1.28E11 20.00 6.14E08 20.00 4.69E10 20.00 7.65E10 31.50 1.64E09 31.50 7.97E12 31.50 5.11E11 31.50 8.30E09 31.50 5.63E10 31.50 5.63E10 31.50 1.04E11 31.50 1.04E11 22.63 4.77E08 22.63 3.64E10 22.63 5.93E10 41.01 1.04E09 41.01 5.03E12 41.01 3.22E11 41.01 5.24E09 38.89 4.12E10 43.80 3.38E10 38.89 7.60E12 43.80 6.23E12 HotLeg 29 41.01 BJ TF,D&C 4A 3D 4B SurgeLine 16 22.63 BJ TF,D&C 4C SurgeLine 16 22.63 31 43.84 BF SC,D&C 4

ColdLeg 3A 27.5 ColdLeg 31 43.84 BJ 1A 29 41.01 BF 38.89 BF SC,D&C 4

2 SGInlet 29 41.01 BF SC,D&C 4

D&C 11 SC,D&C BC D&C SurgeLine 16 22.63 BF SC,TF,D&C HotLeg HotLeg 12 24 1

2 TF,D&C 29 41.01 BJ 1

4 SurgeLine 3.54 4D 2.5 BJ TF,D&C 6

7 1B 1C 3C ColdLeg 27.5 38.89 BJ D&C 3B ColdLeg Calc.Case System SizeCase(in.)

DEGB(in.)

WeldType DM No.Welds X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX) 0.50 4.59E08 0.50 4.59E08 0.50 1.72E08 0.50 1.72E08 0.50 1.72E08 0.50 5.09E06 0.50 5.01E06 0.50 1.74E08 0.50 1.72E08 0.50 4.59E08 0.5 1.22E06 0.5 1.22E06 0.75 2.76E08 0.75 2.76E08 0.75 1.03E08 0.75 1.03E08 0.75 1.03E08 0.75 3.06E06 0.75 3.01E06 0.75 1.05E08 0.75 1.03E08 0.75 2.76E08 0.75 7.18E07 0.75 7.18E07 1.00 1.96E08 1.00 1.96E08 1.00 7.33E09 1.00 7.33E09 1.00 7.33E09 1.00 2.17E06 1.00 2.13E06 1.00 7.42E09 1.00 7.33E09 1.00 1.96E08 1

5.00E07 1

5.00E07 1.50 1.24E08 1.50 1.24E08 1.50 4.64E09 1.50 4.64E09 1.50 4.64E09 1.50 1.38E06 1.50 1.35E06 1.50 4.70E09 1.50 4.64E09 1.50 1.24E08 1.4 3.30E07 1.4 3.30E07 2.00 6.64E09 2.00 6.64E09 2.00 2.49E09 2.00 2.49E09 2.00 2.49E09 2.00 7.36E07 2.00 7.24E07 2.00 2.52E09 2.00 2.49E09 2.00 6.64E09 1.5 3.08E07 3.00 2.75E09 3.00 2.75E09 3.00 1.03E09 3.00 1.03E09 3.00 1.03E09 3.00 3.05E07 3.00 3.00E07 3.00 1.04E09 3.00 1.03E09 2.83 3.13E09 1.99 1.75E07 4.24 1.30E09 4.24 1.30E09 4.24 4.87E10 4.24 4.87E10 4.24 4.87E10 4.24 1.44E07 4.24 1.42E07 4.24 4.94E10 4.24 4.87E10 2.0 1.73E07 5.66 6.26E10 5.66 2.34E10 5.66 2.34E10 5.66 6.94E08 5.66 6.83E08 5.66 2.37E10 5.66 2.34E10 2.8 8.66E08 6.00 5.47E10 6.00 2.05E10 6.00 6.06E08 6.00 5.96E08 6.00 2.07E10 6.75 4.16E10 6.75 1.56E10 6.75 4.61E08 6.75 4.54E08 6.75 1.58E10 8.49 2.64E10 8.49 9.89E11 8.49 2.93E08 8.49 2.88E08 8.49 1.00E10 16 6B SmallBore 1

1.41 BJ VF,SC,D&C 193 6A SmallBore 2

2.83 BJ VF,SC,D&C 29 5H Pressurizer 6

8.49 BF D&C(WeldOverlay) 4 5E Pressurizer 6

8.49 BJ D&C SC,TF,D&C 0

5G Pressurizer 6

8.49 BF SC,D&C 0

5F 5C Pressurizer 4

5.66 BJ D&C 53 BJ TF,D&C 5A Pressurizer 6

8.49 29 5B Pressurizer 3

4.24 BJ TF,D&C 14 5J Pressurizer 2

2.83 BJ TF,D&C 2

5D Pressurizer 3

4.24 BJ D&C 4

Pressurizer 6

8.49 5I Pressurizer 4

5.66 BC D&C 2

BF

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Table53LOCAFrequenciesvs.BreakSizeforSafetyInjectionandRecirculationSystemCategories7Athrough7L

Table54LOCAFrequenciesvs.BreakSizeforAccumulatorInjectionandCVCSCategories7Mthrough8F Calc.Case System SizeCase(in.)

DEGB(in.)

WeldType DM No.Welds X,Break Size(in.)

F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX) 0.50 2.78E06 0.50 2.78E06 0.50 3.10E06 0.50 3.54E07 0.50 1.14E08 0.50 1.14E08 0.50 1.14E08 0.50 1.14E08 0.50 1.14E08 0.50 1.14E08 0.50 1.14E08 0.50 1.14E08 0.75 1.67E06 0.75 1.67E06 0.75 1.86E06 0.75 2.12E07 0.75 6.84E09 0.75 6.84E09 0.75 6.84E09 0.75 6.84E09 0.75 6.84E09 0.75 6.84E09 0.75 6.84E09 0.75 6.84E09 1.00 1.18E06 1.00 1.18E06 1.00 1.32E06 1.00 1.51E07 1.00 4.85E09 1.00 4.85E09 1.00 4.85E09 1.00 4.85E09 1.00 4.85E09 1.00 4.85E09 1.00 4.85E09 1.00 4.85E09 1.50 7.48E07 1.50 7.48E07 1.50 8.34E07 1.50 9.54E08 1.50 3.07E09 1.50 3.07E09 1.50 3.07E09 1.50 3.07E09 1.50 3.07E09 1.50 3.07E09 1.50 3.07E09 1.50 3.07E09 2.00 4.01E07 2.00 4.01E07 2.00 4.48E07 2.00 5.12E08 2.00 1.65E09 2.00 1.65E09 2.00 1.65E09 2.00 1.65E09 2.00 1.65E09 2.00 1.65E09 2.00 1.65E09 2.00 1.65E09 2.83 1.67E07 2.83 1.67E07 2.83 1.86E07 2.83 2.13E08 2.83 6.85E10 2.83 6.85E10 2.83 6.85E10 2.83 6.85E10 2.83 6.85E10 2.83 6.85E10 2.83 6.85E10 4.00 8.50E08 4.00 8.50E08 4.00 9.48E08 4.00 1.08E08 4.00 3.49E10 4.00 3.49E10 4.00 3.49E10 4.00 3.49E10 4.00 3.49E10 4.00 3.49E10 4.24 7.41E08 4.24 7.41E08 4.24 8.26E08 4.24 9.45E09 4.24 3.04E10 4.24 3.04E10 4.24 3.04E10 4.24 3.04E10 4.24 3.04E10 4.24 3.04E10 5.66 3.79E08 5.66 3.79E08 5.66 4.23E08 5.66 4.84E09 5.66 1.56E10 5.66 1.56E10 5.66 1.56E10 5.66 1.56E10 5.66 1.56E10 6.00 3.31E08 6.00 3.31E08 6.00 3.70E08 6.00 4.23E09 6.00 1.36E10 6.00 1.36E10 6.00 1.36E10 6.00 1.36E10 6.75 2.52E08 6.75 2.52E08 6.75 2.81E08 6.75 3.22E09 6.75 1.04E10 6.75 1.04E10 6.75 1.04E10 6.75 1.04E10 7.20 2.22E08 7.20 2.22E08 7.20 2.48E08 7.20 2.83E09 7.20 9.12E11 7.20 9.12E11 7.20 9.12E11 7.20 9.12E11 8.49 1.60E08 8.49 1.60E08 8.49 1.79E08 8.49 2.04E09 8.49 6.58E11 8.49 6.58E11 8.49 6.58E11 8.49 6.58E11 10.00 1.16E08 10.00 1.16E08 10.00 1.29E08 10.00 1.47E09 10.00 4.75E11 10.00 4.75E11 10.00 4.75E11 11.31 9.11E09 11.31 9.11E09 11.31 1.02E08 11.31 1.16E09 11.31 3.74E11 11.31 3.74E11 11.31 3.74E11 14.14 5.93E09 14.14 7.56E10 14.14 2.44E11 14.14 2.44E11 16.97 4.05E09 16.97 5.16E10 16.97 1.66E11 SIR 4.24 D&C 9

7K 2

BC D&C 10 SIR SIR 2.83 2.12 23 5.66 SIR BC D&C 7I 4

5 SIR 8.49 D&C 7H 6

BJ 7L 1.5 BJ D&C 0

7J 3

BC 30 BC,BJ 11.31 D&C 7G SIR 8

42 D&C 14.14 SIR 7F 10 BJ 3

16.97 7E SIR 12 BC,BJ D&C 57 SC,D&C 3

8 11.31 BJ SIR 7C SC,TF,D&C 7D SIR 12 16.97 BJ 21 11.31 BJ TF,D&C 7B SIR 8

9 BJ 16.97 7A SIR 12 TF,D&C Calc.Case System SizeCase(in.)

DEGB(in.)

WeldType DM No.Welds X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.)

F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX)

X,Break Size(in.) F(LOCAX) 0.50 3.54E07 0.50 5.18E08 0.50 6.26E09 0.50 4.28E08 0.50 4.28E08 0.50 1.87E08 0.50 1.87E08 0.50 7.98E08 0.50 1.87E08 0.75 2.12E07 0.75 3.11E08 0.75 3.75E09 0.75 2.57E08 0.75 2.57E08 0.75 1.12E08 0.75 1.12E08 0.75 4.79E08 0.75 1.12E08 1.00 1.51E07 1.00 2.21E08 1.00 2.66E09 1.00 1.82E08 1.00 1.82E08 1.00 7.97E09 1.00 7.97E09 1.00 3.40E08 1.00 7.97E09 1.50 9.54E08 1.50 1.40E08 1.50 1.69E09 1.50 1.15E08 1.50 1.15E08 1.50 5.04E09 1.50 5.04E09 1.50 2.15E08 1.50 5.04E09 2.00 5.12E08 2.00 7.49E09 2.00 9.04E10 2.00 6.03E09 2.00 6.03E09 2.00 2.64E09 2.00 2.64E09 2.00 1.12E08 2.00 2.64E09 2.83 2.13E08 2.83 3.12E09 2.83 3.76E10 3.00 2.42E09 3.00 2.42E09 3.00 1.06E09 3.00 1.06E09 3.00 4.51E09 3.00 1.06E09 4.00 1.08E08 4.00 1.67E09 4.00 2.02E10 4.00 1.26E09 4.00 5.49E10 4.00 2.34E09 4.00 5.49E10 4.24 9.45E09 5.66 7.09E10 5.66 8.55E11 5.66 5.77E10 5.66 2.52E10 5.66 1.08E09 5.66 2.52E10 5.66 4.84E09 6.00 6.19E10 6.00 7.47E11 6.00 4.23E09 6.80 4.71E10 6.80 5.69E11 6.75 3.22E09 7.20 4.14E10 7.20 5.00E11 7.20 2.83E09 10.00 2.16E10 10.00 2.61E11 8.49 2.04E09 14.14 1.11E10 14.14 1.34E11 10.00 1.47E09 16.97 7.56E11 16.97 9.12E12 11.31 1.16E09 14.14 7.56E10 16.97 5.16E10 D&C 8E 4

8F 1

CVCS 4

4 5.66 5.66 BC BC BJ VF,D&C VF,D&C 47 6

CVCS TF,D&C 19 8C 8D CVCS CVCS 2

4 2.83 5.66 BJ 8B CVCS 4

5.66 BJ TF,VF,D&C 15 8A CVCS 2

2.83 BJ TF,VF,D&C 10 7O ACC 12 16.97 BC,BJ D&C 0

7N ACC 12 16.97 BJ TF,D&C 35 16.97 7M ACC 12 BJ SC,D&C

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Figure51LOCAFrequenciesvs.BreakSizeforBFWeldsinHotLeg(Category1A)

Figure52LOCAFrequenciesvs.BreakSizeforBJWeldsinHotLegSubjecttoThermalFatigue (Category1C)

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Figure53ComparisonofMeanFrequenciesforHotLegWelds AnexampleofthekindofchangeinLOCAfrequenciesthatcanresultfromlocationbylocationchanges inthepipeinspectionandleakmonitoringprogramisshowninFigure54foranRCSweldsubjectto stresscorrosioncracking[13].Asseeninthisfigure,thefrequencyofapipebreakmayvarybymore thananorderofmagnitudebasedonthereliabilityintegritymanagementprogram,allotherfactors beingequal.

TheapplicationoftheMarkovmodeltoSTPcomponentsisdeferreduntilmoreinformationisavailable toidentifywhichlocationsarerisksignificantwithrespecttodebrisformation.Becausethenumberof inputparametersneededtoquantifytheMarkovmodelissignificant,itisimpracticaltoapplythat modeltoall41uniquecomponentcategoriesatSTP.TheanalysispresentedinFigure54wouldbe representativeofBFweldsinthelargeborepipes,suchasCategories1A,2,3A,and3B.Whenthe MarkovmodelisappliedtoSTPcomponents,theLOCAfrequenciesforthoseweldsnotsubjectedto NDEwillbeincreasedbyasmallandnotsignificantamount,andtheLOCAfrequenciesforthose subjectedtoNDEwillbedecreasedbyfactorsrangingfrom3to10.Thiswillalsoprovideanopportunity tomodifytheselectionsofweldsfortheNDEprogramtooffsetsignificantriskimpactsthatare associatedwithdebrisinducedfailureofrecirculationcooling.BecauseStep3.4intheLOCAfrequency procedureisdeferred,theresultstobeusedinthe2011GSI191evaluationwillnotreflectweldtoweld variationsduetotheweldsincludedandexcludedfromtheNDEprogram.

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Figure54ComparisonofWeldFailureRatesDeterminedbyMarkovModelforDifferentReliability IntegrityManagementApproaches 5.4 Total LOCA Frequencies for RISKMAN (Step 3.6)

ThetotalLOCAfrequencieswerecalculatedusingEquation(2.1)bymultiplyingthenumberof componentsineachcategorybytheLOCAfrequenciespercategoryfromStep3.3.Thiswasdoneusing twomethods.Method1isameanpointestimateinwhichthemeansofthefailurerate,meansofthe CRPmodeldistributions,andweldcountsweremultipliedonanExcelspreadsheet.Method2wasan integratedMonteCarlosimulationthatincludedthestepsinthefailureratedevelopment,application oftheCRPlognormaldistributions,andweldcounts.Asnotedearlier,theCRPdistributionswithinaCRP componentcategoryweretreatedasfullycorrelatedintheMonteCarlocalculations.Theresultsare summarizedinTable55.

InFigure55,theSTPmeanpipeinducedLOCAfrequenciesarecomparedagainsttheresultsfrom NUREG1829forpipeinducedLOCAs.Asseeninthiscomparison,theresultsareinexcellentagreement forCategories1and4andwithinafactorof3ofeachotheroverthewholerangeofLOCAcategories.

ForCategories2and3,theSTPresultstracksomewhatlower,whereasforCategories5and6,theSTP resultstracksomewhathigher.Toconductasensitivitystudy,acaseisplottedwiththecontributions fromtheSGinletremovedtoinvestigatetheimpactofthisoutliercomponentthatwasobservedin thefailuredata.Therewasanunusuallyhighincidenceoffailuresatthisweldlocation(19failuresvs.6

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failuresfortheentireremaininghotlegweldsinthedatabase),alloccurringinJapanesePWRsfollowing steamgeneratorreplacement.Whentheseoutliercontributionsareremoved,theCategory5and6 resultsfromSTPandNUREG1829areinexcellentagreement.

Figure55isbasedonmeanvalues,whereasFigure56comparestheuncertaintydistributionresults, withthecaveatthattheSTPresultsareforpipeinducedLOCAsandthattheNUREG1829datainthis figureincludebothpipeandnonpipeinducedLOCAs.WhilethereisinformationinNUREG1829that breaksdownpipeandnonpipecontributions,whichisusedinFigure55,thereisnoinformationon uncertaintydistributionsforthepipeonlycontributions.However,itisreasonablethattheuncertainties calculatedforSTParesomewhatsmallerthanthoseestimatedinNUREG1829,giventhattheSTP resultsareforaspecificplantandNUREG1829reflectstheuncertaintyandvariabilityforentirefleetof USPWRplants.

Figures57and58presentthemajorcontributionstoLOCAfrequencybysystem,usingalogarithmic scaleontheYaxis.Alinearperspective(i.e.notwiththedistortionoflogarithmicscales)onthe contributionstoCategory6LOCAfrequenciesisprovidedinFigure59,whichshowsthattheSGInletB Fweldscontributeabout74%tothetotalCategory6LOCAfrequency.

WhenmakingcomparisonswithNUREG1829,thefollowingdifferencesbetweenthatandthepresent studyshouldbetakenintoaccount:

NUREG1829resultsarefromagenericstudyforthepopulationofPWRsintheU.S.This includes2loop,3loop,and4loopPWRplants,almostallofwhichhaveonlytwotrainsof ECCSsconnectedtothelooppiping.ThebasecaseanalysesthatwereperformedinNUREG 1829thatwereavailableforuseasanchorsfortheexpertelicitationwerefora3loopPWR plant.Thisdocument'sresultsarespecifictoSTP,a4loopPWRplantwithinterfacingpipingfor threetrainsofECCSs.

NUREG1829resultsareproducedfromexpertelicitation.TheSTPresultshaveutilizedNUREG 1829informationtodeveloptheCRPdistributions,buthavebeencalculatedusingadifferent methodologyandbasedongenericpipefailureinformationfromthePIPExpdatabaseandfrom STPspecificweldcounts,pipesizes,anddamagemechanisms.

Giventhedifferences,itisinterestingthattheresultsaresocomparableinmagnitude.Thatthetotal LOCAfrequenciescalculatedforSTParecomparabletotheNUREG1829resultsprovidesasanitycheck onthemethodologyusedinthisstudyanditsapplicationtoSTP.Morespecificallythiscomparison showsthatassumptionsmadeinusingNUREG1829datatodeveloptheCRPdistributions,in combinationofthefailureratetreatmentandLOCAfrequencymethodology,haveproducedasetof resultsthatdonotdifferappreciablyfromthepipeinducedLOCAfrequenciesinNUREG1829.

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Table55ResultsforTotalPipeBreakInducedLOCAFrequencies LOCA Category[1]

Break Size(in.)

Point Estimate[2]

LOCAFrequencyperReactorCalendarYear Range Factor[3]

Mean 5%tile 50%tile 95%tile SmallLOCA 0.5to2.0 3.59E04 3.54E04 1.42E04 3.11E04 7.03E04 2.2 MediumLOCA 2.0to6.0 2.01E05 2.00E05 1.44E06 1.14E05 6.53E05 6.7 LargeLOCA

>6.0 2.29E06 2.09E06 1.80E07 9.53E07 7.18E06 6.3 Category1 0.5 3.82E04 3.76E04 1.57E04 3.30E04 7.39E04 2.2 Category2 1.5 3.91E05 3.90E05 7.00E06 2.37E05 1.18E04 4.1 Category3 3

9.24E06 9.09E06 1.07E06 5.04E06 2.94E05 5.2 Category4 6.75 1.84E06 1.82E06 2.00E07 9.69E07 5.83E06 5.4 Category5 14 4.40E07 4.31E07 4.45E08 2.25E07 1.39E06 5.6 Category6 0.5 4.48E08 4.50E08 1.61E09 1.44E08 1.65E07 10.1 Notes:

[1]Small,Medium,andLargeLOCAcategoriesconsistentwithSTPPRAmodel;Categories16definedinNUREG1829(seeTable41).

[2]PointestimateobtainedwithmeanfailurerateandCRPlognormaldistributionsandweldcounts.

[3]RangeFactor=SQRT(95%tile/5%tile).

Figure55ComparisonofLOCAFrequenciesforPipes:STPvs.NUREG1829

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Figure56ComparisonofUncertaintyDistributionsforSTPPipeInducedLOCAandNUREG1829Total LOCAFrequencies

Figure57ContributionstoMeanLOCACategoryFrequenciesbySystem

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Figure58SystemContributionstoMeanLOCAInitiatingEventFrequencies

Figure59SystemContributiontoLOCACategory6Frequencies

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5.5 LOCA Frequency Summary ThetechnicalapproachtoestimationofLOCAfrequenciesfortheSTPGSI191projecthasbeen describedinsection5,withresultsforeachstep.Thespecificcapabilitiesthathavebeendemonstrated include:

ThecapabilitytoestimateLOCAfrequenciesasafunctionofbreaksizeateachlocation.

ThecapabilitytoutilizeinformationfromNUREG1829tocharacterizeepistemicuncertainty associatedwithLOCAfrequencies.

AmethodthatincorporatesviaBayesuncertaintyanalysistheservicedataonpipefailuresand componentexposures.

Aquantificationofepistemicuncertaintiesassociatedwithestimatingtheinputparametersin themodelequations,includingbothparametricandmodelingsourcesofuncertainty.

Thecapabilitytoquantifytheimpactsofinformationondegradationmechanismsusceptibility ateachlocation,basedoninsightsfromservicedataandresultsofRIISIevaluation.

TheresultsthathavebeengeneratedforLOCAspecificaswellastotalLOCAfrequenciesarereasonable andconsistentwiththosedevelopedinpreviousstudies.

PriortocompletionoftheLOCAfrequencytaskforGSI191,thefollowingissuesneedtobeandwillbe addressedinafutureupdateofthisreport.

NonisolatableLOCAscausedbyfailuresofnonpipecomponentsneedtobeaddressed.These includecontrolroddrivestandpipes,instrumentlines,andothercomponentsweldedtothereactor pressurevessel,pumpandvalvebodies,pressurizersafetyandreliefvalveleaks,andreactorcoolant pumpseals.

IsolatableLOCAsneedtobeaddressed.TheseinvolvefailuresinClass2pipingsystemsthatcanbe isolated,includingCVCSchargingandletdownlines,RCPsealreturnlines,etc.

Pipebreaksinsteamandfeedwaterlinesinsidethecontainmentthatcouldgeneratedebrisand leadtoaneedforrecirculationcoolingand/orcontainmentsprayactuationneedtobeaddressed.

ExecutionofStep3.4toapplytheMarkovmodeltoevaluatetheimpactofinspectedandnon inspectedNDElocationsontheLOCAfrequenciesneedstobecompleted.

Thecurrentstudyisbasedonroughestimatesofweldcountsandpipesizesforsmallborepipes.If smallborepipesarefoundtocontributesignificantlytotheriskofdebrisinducedECCSfailures, moredetailedreviewofthesmallborepipingconfigurationsneedstobecompleted.

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6. References

[1]

Tregoning,R.,L.Abramson,andP.Scott,EstimatingLossofCoolantAccident(LOCA)

FrequenciesthroughtheElicitationProcess,NUREG1829,U.S.NuclearRegulatory Commission,Washington,DC,April2008.

[2]

Lydell,B.O.Y.,PIPExp/PIPE2010:MonthlySummaryofDatabaseContent(Statusasof31 July2011),SigmaPhaseInc.,VailAZ.Monthlysummaryreportshavebeenissuedsince January1999.

[3]

Fleming,K.N.andB.O.Y.Lydell,DatabaseDevelopmentandUncertaintyTreatmentfor EstimatingPipeFailureRatesandRuptureFrequencies,ReliabilityEngineeringandSystem Safety,86:227-246,2004.

[4]

Fleming,K.N.andB.O.Y.Lydell,PipeRuptureFrequenciesforInternalFloodingPRAs, Revision1.EPRI,PaloAlto,CA:2006.1013141.

[5]

Fleming,K.N.andB.O.Y.Lydell,PipeRuptureFrequenciesforInternalFloodingPRAs, Revision2.EPRI,PaloAlto,CA:2010.1021086.

[6]

Fleming,K.N.etal.,PipingSystemReliabilityandFailureRateEstimationModelsforUsein RiskInformedInServiceInspectionApplications,EPRI,PaloAlto,CA:1998.TR110161.

[7]

Fleming,K.N.andT.J.Mikschl,PipingSystemFailureRatesandRuptureFrequenciesforUse inRiskInformedInServiceInspectionApplications,EPRI,PaloAlto,CA:1999.TR111880.

[8]

Mosleh,A.andF.Groen,TechnicalReviewoftheMethodologyofEPRITR110161, UniversityofMarylandreportforEPRI,publishedasanAppendixtoEPRITR110161 (Reference[6]).

[9]

ElectricPowerResearchInstitute,RevisedRiskInformedInServiceInspectionProcedure, EPRI,PaloAlto,CA:1999.TR112657,Rev.BA.

[10] U.S.NuclearRegulatoryCommission,SafetyEvaluationReportRelatedtoRevisedRisk InformedInServiceInspectionEvaluationProcedure:EPRITR112657,Rev.B,July1999, Washington,DC,1999.PublishedasaforwardtoTR112657(Reference[9]).

[11] Martz,H.,Final(Revised)ReviewoftheEPRIProposedMarkovModeling/BayesianUpdating MethodologyforUseinRiskInformedInServiceInspectionofPipinginCommercialNuclear PowerPlants,LosAlamosNationalLaboratory,June1999.TSA1/99164.

[12] Fleming,K.N.,MarkovModelsforEvaluatingRiskInformedInServiceInspectionStrategies forNuclearPowerPlantPipingSystems,ReliabilityEngineeringandSystemSafety,83(1):27-45,2004.

[13] Fleming,K.N.etal.,TreatmentofPassiveComponentReliabilityinRiskInformedSafety MarginCharacterization-FiscalYear2010StatusReport,INL/EXT1020013,reportprepared byPacificNorthwestNationalLaboratoryfortheU.S.DepartmentofEnergy,September2010.

[14] U.S.NuclearRegulatoryCommission,SupportinginformationforNUREG1829(Reference[1])

onIndividualExpertsEstimatesofLOCAFrequenciesforSpecificComponentsandLOCA Categories,availableonADAMSAccessionNumbersML080560008,ML080560010, ML080560011,ML080560013.

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[15] ScandpowerRiskManagement,Inc.,GSI191ComponentDatabase,MicrosoftAccess DatabaseofSouthTexasProjectComponentsconsideredinLOCAFrequencyAnalysis, September16,2011.

[16] Andresen,P.L.etal,2007.ExpertPanelReportonProactiveMaterialsDegradation Assessment,NUREG/CR6923,U.S.NuclearRegulatoryCommission,Washington(DC).

[17] OECDNuclearEnergyAgency,2011.TechnicalBasisforCommendablePracticesonAgeing Management-SCCandCableAgeingProject(SCAP),NEA/CSNI/R(2010)5,IssylesMoulineaux (France).

[18] Scott,P.M.,2010.PrimaryWaterStressCorrosionCrackingofNickelbaseAlloys,Technical ReportPreparedfortheSCAPSCCWorkingGroup,NoisyleRoi(France).

[19] OECDNuclearEnergyAgency,1998.Proc.SpecialistsMeetingonExperiencewithThermal FatigueinLWRPipingCausedbyMixingandStratification,NEA/CSNI/R(1998)8,Issyles Moulineaux(France).

[20] Lydell,B.andOlsson,A.,2008.ReliabilityDataforPipingComponentsinNordicNuclearPower Plants."RBook"ProjectPhaseI,SKIReport2008:1,SwedishnuclearPowerInspectorate, Stockholm(Sweden).

[21] Letter,datedDecember30,1999,assupplementedApril17,2000,T.J.Jordan(SouthTexas Project,Units1and2,Manager,SystemsEngineering),toU.S.NuclearRegulatory Commission,containingRiskInformedInserviceInspectionProgramPlanSouthTexasProject Units1and2.