LOCAfrequencyevaluationusingexpertelicitationOriginalResearchArticle

Thedouble-ended-guillotinebreak(DEGB)criterionofthelargestprimarypipingsystemintheplant,whichgenerallyprovidesthelimitingconditionfortheemergencycorecoolingsystemrequirements,iswidelyrecognizedasanextremelyunlikelyevent.Asaresult,USNuclearRegulatoryCommission(NRC)staffarecurrentlyconsideringarisk-informedrevisionofthedesign-basisbreaksizerequirementsforcommercialnuclearpowerplants.Insupportofthiseffort,loss-of-coolantaccident(LOCA)frequencyestimateshavebeendevelopedusinganexpertelicitationprocessbyconsolidatingservicehistorydataandinsightsfromprobabilisticfracturemechanics(PFM)studieswithknowledgeofplantdesign,operation,andmaterialperformance.BaselineLOCAfrequencyestimatesforthe5thpercentile,median,meanand95thpercentileweredeterminedfromeachpanelistʹselicitationresponses.Groupestimatesweredeterminedbyaggregatingtheindividualestimatesusingthegeometricmeanoftheindividualestimatesforeachfrequencyparameter.Groupvariabilitywasestimatedbycalculating95%confidenceboundsforeachofthegroupfrequencyparameters(i.e.,median,mean,and5thand95thpercentiles).Anumberofsensitivityanalyseswereconductedtoexaminetheeffectsonthequantitativeresultsfromvaryingtheassumptions,structureandtechniquesofthebaselineanalysisprocedure.