FractureassessmentofabrittleRPVundercoldloadingOriginalResearchArticle

TheoldestSwedishreactorisaboilingwaterreactor(BWR)withavesselmadeofA302GradeBwithratherhighCuandNicontent.TheseelementshaveintensifiedtheirradiationembrittlementinthebeltlineregionsothatRTNDTofcertainweldsmayexceed100°Cattheend-of-lifecondition.Apreliminarystudyofthefractureriskforthebeltlineregionshowedthatthelimitingloadingcasewouldbethecoldover-pressurizationofthereactor.Theobjectiveofthisstudywastodevelopareliablemethodologyforfractureassessmentoftheagedreactorvesselundercoldloadingscenarios.ThetestprogramcoveredexperimentsonstandardSEN(B)specimensandcladbeamsunderuniaxialandbiaxialloading.Thetestmaterialwasareactorvesselsteelpreparedwithaspecialheattreatmenttosimulatefracturetoughnesspropertiesoftheagedreactor.Nosignificanteffectsofshallowcrackandbiaxialloadingwereobservedoncleavagefracturetoughnessindifferentcladspecimens.WhiletheASMEKIcreferencecurvewasshowntobeoverlyconservative,theMasterCurvemethodologysatisfactorilypredictedtheexperimentaloutcomesofthetestprogram.TheMasterCurvemethodologyindicatedthata20-mmdeepsurfacecrackwasacceptableinthebeltlineregionunderacoldover-pressurizationscenario.ThisvaluewasthreetimesgreaterthanwhatamethodologybasedontheASMEKIcreferencecurveyielded.