ProgressonPWRlowerheadfailurepredictivemodelsOriginalResearchArticle

Agoodunderstandingofthemechanicalbehaviourofthereactorpressurevessel(RPV)lowerheadisnecessarybothforsevereaccidentassessmentandforthedefinitionofappropriateaccidentmitigationstrategies.Indeed,awell-characterizedfailureofthelowerheadleadstoabetterevaluationofthequantityandkineticswithwhichcorematerialcanescapeintothecontainment.Thesearetheinitialconditionsforseveralex-vesseleventssuchasdirectheatingofthecontainmentormoltencore–concreteinteraction. Inthiscontext,theobjectivesofthejointon-goingworkoftheWP10-2groupofSARNETare:(1)improvementofpredictabilityofthetime,modeandlocationofRPVfailure;(2)developmentofadequatemodelswiththeultimateaimofbeingincludedintointegralcodes;(3)interpretation/analysisofexperimentswithmodels/codescombinedwithsensitivitystudies;and(4)betterunderstandingofthebreachopeningprocessinordertobettercharacterizethecoriumreleaseintothecontainment. Differentapproachesareconsidered:asimplifiedbutwellpredictingmodelrecentlyimplementedinthesevereaccidentAstecandIcare-Catharecodes,andviscoplasticitymodelsimplementedintheCast3m,AnsysandCode_Asterfiniteelementcodes.Severalfailurecriteriaareconsidered:stresscriterion,straincriterionanddamageevaluation(coupledwayorpost-evaluation). Inthispaper,theOLHF-1experimenthasbeenusedtoassessthemodels,toperformsensitivitystudiesandtoevaluatefailurecriteriathatcouldbeappliedinthecaseofreactors.Allthepartnersperformed2Daxisymmetricanalyses,allowingtheevaluationoftime,modeandlocationofvesselfailure.Nevertheless,CEAconductedfurther3Dcalculationsinordertostudycrackpropagationandthecorrespondingresultswillbepresentedseparatelyattheendofthepaper.Thenumericalformulationofthedifferentmodelsusedisgivenandacomparisonofexperimentalandnumericalresultsispresented.Thepaperalsoshowstheprogressmadewiththeobjectiveofdefiningfailurecriteriathatcanbeusedforreactorvesselapplications.