Initialversionofanintegratedthermalhydraulicsandneutronkinetics3DcodeX3DOriginalResearchArticle

Atheoreticalconceptforthedescriptionof3Dnuclearkinetics,heatconductionandthethermal-hydraulicsingleandtwo-phaseflowphenomenaina3Dlightwaterreactorcoresimulatedbyparallelchannelsispresented.Theheatgenerationwithineachfuelelementisdescribedbya3Dcorekineticscodeemployingatwo-groupdiffusiontheorymodel.Finitedifferencesareusedtoapproximatethediffusionequationsforfastandthermalneutronfluxes.Theresultingalgebraicequationsaresolvedbyaniterativeprocedure.TheheattransportoutofafuelelementisdeterminedfromafinitedifferenceversionoftheFourierheatconductionequationappliedintheradialdirectiononly.Animplicitsolutionforthetemperatureineachradialcellisfoundusingatri-diagonalalgorithm.Theheattransferrateintothecoolantchanneliscalculatedfromthecladandcoolanttemperatures.Thethermal-hydraulicpartofthecodeisbasedonthegenerallyapplicableandself-contained‘coolantchannelmodule’(CCM)developedbyHoeld[Hoeld,A.,2004a,Atheoreticalconceptforathermal-hydraulic3Dparallelchannelcoremodel.PHYSOR2004,April25–29,Chicago,USA;Hoeld,A.,2004b,Areseparate-phasethermal-hydraulicmodelsbetterthanmixture-fluidapproaches.Itdepends.Rathernot.InternationalConferenceon‘NuclearEngineeringforNewEurope2004’.September6–9,Portoroz,Slov;Hoeld,A.,2005,Athermal-hydraulicdrift-fluxbasedmixture-fluidmodelforthedescriptionofsingle-andtwo-phaseflowalongageneralcoolantchannel.NURETH-11,October2–6,Avignon,France],whichoffersanewapproachforthesimulationofsteadystateandtransientbehaviourofsingle-ortwo-phaseflowwithinageneralcoolantchannel.TheconceptisdemonstratedintheexperimentalcodeX3D,concentratinginafirststageonthesteadystatebehaviourofahypotheticalBWRorPWRcorewhichconsistsofacentralchannelandfourquadrants.Initialresultsarepresentedtodemonstratetheviabilityoftheproposedconcept.Thiscodethereforetestsadifferenttheoreticalapproachofhowtodeterminetheessential3Dthermal-hydraulicmassflowdistributionintoparallelchannelsbymaintainingequalpressuredecreasetermsoverallchannels.