Three-dimensionalnumericalsimulationofflowandheattransportinhigh-temperaturenuclearreactorsOriginalResearchArticle

ThenextgenerationofHigh-TemperatureReactors,anannularnuclearcoreconsistingofacentralcolumnofgraphitespheres(orpebbles)andasurroundingannulusoffuelpebbles,maybeemployed.Duetothisgeometryaswellasduetothecomplexfeedingandshutdownmechanismsofsuchaconfiguration,three-dimensionalnuclearheatproduction,gasflowandheattransportmechanismshavetobeinvestigated.Tosimulatetheflowandheattransportwithinthecoreandthesurroundinggraphitereflector,anewcodesystembasedonthethree-dimensionalcomputationalfluiddynamicspackageCFX-4hasbeendeveloped.Asavalidationofthenewprogram,steadystateandtransientsimulationsofanexperimentinvolvingapebblebed(SANAtestrigattheJülichResearchCenter)areperformed.ExtensivefurthercodeverificationhasbeendonebycomparisonaxisymmetricsimulationswithknownresultsobtainedwiththewellestablishedthermalanalysiscodeTHERMIX,whichisformulatedintwo-dimensionalcylindricalcoordinates.Inordertodemonstratethefeasibilityandthecomputationaleffortofthree-dimensionalnonaxisymmetricsimulations,anassumedinfluenceofamisplacedpackageofheat-generatingfuelpebbleslocatedasymmetricallyinthecentralcolumnisinvestigated.Asignificantincreaseofthecomputedmaximumcoretemperatureafteraloss-of-forced-coolingincidentisfound.