PassivecoolingofthePBMRspentandusedfueltanksOriginalResearchArticle

Thepebblebedmodularreactor(PBMR)isanewgenerationhightemperaturegas-cooledreactor,makinguseofsphericalfuelelements.Thespentfuelandpartiallyburntfuel(calledusedfuel)isstoredinlargestoragetanks.Thispaperpresentsthecoolingdesignofthestoragetanks,withspecialemphasisonitspassivecoolingability. Forcorrosionprotection,thetanksarecooledwithaclosedloopactivesystem,however,passivecoolingisseenastheultimatecoolingmodeforthestoragetanks.Iftheactivecoolingfails,theflowautomaticallybypassestheactivesystemandpassivecoolingtakesover.Theactivecoolingisthusnotsafety-related;ratheritspurposeisforinvestmentprotection. Thestoragetankdesignwithitslongitudinalinternalcoolingpipeshasagoodpassivecoolingability.Thelayoutofthetankconcretecubicleensuresthatcoolingaircanflowonlyinthedesireddirection.Computationalfluiddynamics(CFD)analyseshavebeendoneforvariousheatloadscenariosinsidethetank.Passivecoolingexistsfortankswithalowspentfuelfilllevelwithheatloadbelow25kWuptoatankcontainingafullPBMRcore(usedfuel)withheatloadof640kW.Forallscenarios,themaximumfueltemperatureisbelow400°C. AmethodwasdevelopedtocalculatethepassivecoolingcharacteristicsofthetankatafractionofthetimeittakesCFDbyusingthepipenetworksimulationsoftwareFlownex.ThemethodwasalsousedtoanalyzetransientpassivecoolingeventsandshowedflowphenomenonsimilartowhatCFDanalyseshavepredicted. Asmall-scaletwo-dimensionalrepresentationofthestoragetankandcubiclelayouthasbeenbuilt.Thisexperimentdemonstratesthepassivecoolingabilityofthetank.ItalsoprovedtheflowcharacteristicsthatwerepredictedbytheCFDandFlownexanalyses. Ithasbeenshownthroughdiversetechniquesthatthefuelinsidethetankscanbecooledpassively.Therearestillafewaspectswhichneedtobeexploredinmoredetail,butoverallitcanbesaidthatpassivecoolingofthePBMRspentandusedfuelinbulkstoragetanksisviable.