AnalyticalstudyoneliminationofsevererecriticalitiesinlargescaleLMFBRSwithenhancementoffueldischargeOriginalResearchArticle

Thepossibilityofsevererecriticalitycouldbeexcludedifthemoltencorematerialsaredischargedfromreactorcoreintheearlystageofcoredisruptiveaccident(CDA).Basedonthisidea,severaldesignmeasuresforfuturecommercialliquidmetal-cooledfastbreederreactors(LMFBRs)havebeenproposedtoenhancethemoltenfueldischargefromcoreinordertopreventformationofthecore-widemoltenpoolwithhighmobility.Onepromisingconceptinthesedesigncandidatesismodified-FAIDUS(FuelsubassemblywithInnerDUctStructure).Theeventprogressioninunprotectedlossofflow(ULOF)accidentinasodium-cooledlargescaleFBRwithmodified-FAIDUSwasanalyzedtoassesstheeffectualperformanceofmodified-FAIDUSinpreventingsevererecriticalityusingtheSAS4AandSIMMER-IIIcodes.Twoparametriccaseswereperformedcoveringtheuncertaintyofductwallfailuremechanism,onewithstablefuelcrustandanotherwithunstablecrustcondition.Thecalculationshowedthatthefinalamountofdischargedfuelfromcoreinbothcaseswasmorethan20%ofinitialcoreinventory.Thedegradedcoreafterfueldischargeiscomposedofthemixtureofsolidifiedfuel,swollenfuelchunksandmoltensteel,ofwhichlowmobilitypreventsmassivefuelmotion.Thereactorpowerloweredtodecayheatlevelandthereactivityloweredaround−20$,thus,thepossibilityofsevererecriticalitywaseliminated.