Developmentofathermal-hydraulicanalysiscodeforannularfuelassembliesOriginalResearchArticle

Athermal-hydraulicanalysiscodewhichiscapableofmodelingbothinternallyandexternallycooledannularfuelpinswasdeveloped.Thecoolantflowdistributionintheannularfuel-basedassembliesisadjustedbyapressuredropmodelallowingforconditionssuchasnon-equalvelocityandnon-saturatedphases.Theheattransferfractionisdeterminedbytheratioofcross-sectionalareasdistinguishedbytheradiusatwhichthefirstderivativeofthetemperaturewithintheannularfuelequalszero.ThecodepredictionshavebeencomparedwithcalculationsfromKoreaAtomicEnergyResearchInstitute(KAERI)andMIT.TheheattransferfractiondifferencebetweenthecodeandRELAPwasabout3.9%,andtheDeparturefromNucleateBoilingRatio(DNBR)predictionofthecodeagreedwellwiththeMIT’sresultintheregionbelow3m.Fortheapplicationofthecode,thermal-hydraulicsofthorium-basedfuelassembliesloadedwithannularseedpinswerecomparedwiththoseoftheexistingthorium-basedassemblies.Thepressuredropintheassemblygenerallyincreasedinthecaseofannularfuelduetothelargerwettedperimeter.Intheinnersubchannelsoftheseedpins,massfluxeswerehighduetothegridformlossesintheoutersubchannels.About43%oftheheatgeneratedfromtheseedpinflowedintotheinnersubchannelandtherestintotheoutersubchannel.TheminimumDNBRs(MDNBRs)oftheannularfuel-basedassemblieswerehigherthanthoseoftheexistingones.Becauseinterchannelmixingcannotoccurintheinnersubchannels,temperaturesandenthalpieswerehigherintheinnersubchannels.