FailurestrainsandproposedlimitstrainsforanreactorpressurevesselundersevereaccidentconditionsOriginalResearchArticle

Thelocalfailurestrainsofessentialdesignelementsofareactorvesselareinvestigated.Thesizeinfluenceofthestructureisofspecialinterest.Typicalsevereaccidentconditionsincludingelevatedtemperaturesanddynamicloadsareconsidered. Themainpartofworkconsistsoftestfamilieswithspecimensunderuniaxialandbiaxialload.Withinonetestfamilythespecimengeometryandtheloadconditionsaresimilar,butthesizeisvarieduptoreactordimensions.Specialattentionisgiventogeometrieswithaholeoranotchcausingnon-uniformstressandstraindistributionstypicalforthereactorvessel.Akeyproblemistodeterminethelocalfailurestrain.Heresuitablemethodshadtobedevelopedincludingtheso-called“vanishinggapmethod”,andthe“forgingdiemethod”.Theyarebasedonpost-testgeometricalmeasurementsofthefracturesurfacesandreconstructionsoftherelatedstrainfieldsusingfiniteelementmodels. Theresultsindicatethatstressesversusdimensionlessdeformationsareapproximatelysizeindependentuptofailureforspecimensofsimilargeometryundersimilarloadconditions.Localfailurestrainscouldbedetermined.Thevaluesareratherhighandsizedependent.Statisticalevaluationallowtheproposaloflimitstrainswhicharealsosizedependent.Iftheselimitstrainsarenotexceeded,thestructureswillnotfracture.