Abstract :
Amethodologicalandstructuredproceduretoaddresstheuncertaintiesrelatedtopassivesafetyfunctionsispresented.Thematteristreatedwithreferencetoapassivesystemdesignedfordecayheatremovalofadvancedlightwaterreactors,relyingonnaturalcirculationandprovidedwithaheatexchangerimmersedinacoolingpool,actingasheatsink,andconnectedtothepressurevesselviasteamandcondensatemainlines.Twohazardidentificationusedqualitativemethods,asfailuremodeandeffectanalysis(FMEA)andhazardandoperabilitystudy(HAZOP),areutilizedandtherelativeresultscomparedinordertoassessthemainsourcesofphysicalfailure.Theidentificationofthesourcesofuncertaintiesrelatedtopassivesystemperformance,intermsofparameterswhichdrivethefailuremechanisms,follows.Finallytheuncertaintiesareevaluatedbothfortheirassessmentinprobabilistictermsandforthedeterminationofmostcontributorstothesystemthermal-hydraulicresponse.
