ProbabilisticassessmentofthermalfatigueinnuclearcomponentsOriginalResearchArticle

Aprobabilisticframeworkissetuptoassessthefatiguelifeofcomponentsofnuclearpowerplants.Itintendstoincorporateallkindsofuncertainties,suchasthoseappearinginthespecimenfatiguestrength(number-of-cycles-to-failureofspecimens),designmarginfactors(takingintoaccountthesize,surfacefinishandenvironmentaleffects),mechanicalmodel(precisely,theuncertaintyonthemodelinputparameters)andthethermalloading.Thispaperpresentstheglobalmethodologyanddetailsthestatisticaltreatmentofthefatiguespecimentestdata.AfirstanalyticalexampleshowsthatthereliabilityofastructuresubmittedtoaperiodicstresscycleSchangessignificantlywithrespecttothevalueofS,althoughthecodified(deterministic)designcriterionisequallyfulfilled.Amorecomprehensiveexampleinvolvingamechanicalmodelofapipesubmittedtoadeterministicinnertemperatureloadingisfinallyanalysed.Theuseofthefirst-orderreliabilitymethod(FORM)allowstocomputetheprobabilityoffailureasafunctionoftheforeseenlifetimeandtoranktheinputrandomvariablesaccordingtotheirimportanceinresponsesensitivity.