UncertaintiesofcreepmodelinstressanalysisandlifepredictionofgraphitecomponentOriginalResearchArticle

Theirradiation-inducedcreepisakeyfactorinstressanalysisandlifepredictionofnucleargraphiteinhightemperaturegas-cooledreactors(HTRs).Numerouscreepmodelshavebeenestablishedandgoodagreementshavebeenobservedwithuni-axialcreepexperiments.However,theeffectofcreepstrainratiohasnotbeenfullyaddressed,andtheprimarycreepstrainisconsideredinsomecaseslessimportantincomparisonwiththesecondaryone.Theseuncertaintiesincreepmodelmightresultinlargediscrepanciesintheevaluationofstressesandservicelivesofgraphitecomponents.Inthispaper,thevariationofcreepstrainratioandtheimpactoftheprimarycreepstrainarestudiednumericallyandthecorrespondingdiscrepanciesinstressesandlifepredictionofgraphitecomponentsinHTRsarediscussed.TwoimplicitformulationsoftheincrementalfiniteelementsolutionfortheparametervariationsofcreepmodelsarepresentedandintegratedintoafiniteelementcodedevelopedbyINET.Thenumericalresultsshowthatbothincreaseofthecreepstrainratioandabsenceoftheprimarycreepstrainwillleadtoanincreaseofstresslevelsanddecreaseofservicelifedramatically,suggestingthatuncertaintiesofcreepmodelshavetobetakenintoaccountinthedesignofgraphitecomponentsinHTRs.