Studyofflowinstabilitiesindouble-channelnaturalcirculationboilingsystemsOriginalResearchArticle

Naturalcirculationboilingsystemsconsistingofparallelchannelscanundergodifferenttypesofoscillations(in-phaseorout-of-phase)dependingonthegeometricparametersandoperatingconditions.Disturbancesinonechannelaffecttheflowinotherchannels,whichtriggersthermal–hydraulicoscillations.Inthepresentwork,themodesofoscillationunderdifferentoperatingconditionsandchannel-to-channelinteractionduringpowerfluctuationsandon-powerrefuelinginadouble-channelnaturalcirculationboilingsystemareinvestigated.ThesystemismodeledusingalumpedparametermathematicalmodelandRELAP5/MOD3.4.Parametricstudiesarecarriedoutforanequal-powerdouble-channelsystem,atdifferentoperatingconditions,withboththemodels,andtheresultsarecompared.Instabilities,non-linearoscillations,andeffectsofrecirculationloopdynamicsandgeometricparametersonthemodeofoscillations,arestudiedusingthelumpedmodel.Thetwochannelsoscillateout-of-phaseinType-Iregion,butinType-IIregion,boththemodesofoscillationareobservedunderdifferentconditions.Channel-to-channelinteractionandon-powerrefuelingstudiesarecarriedoutusingtheRELAPmodel.Athighpowers,disturbancesinonechannelsignificantlyaffectthestabilityoftheotherchannel.Duringon-powerrefueling,anear-stagnationconditionorlow-velocityreverseflowcanoccur,thepossibilityofreverseflowbeinghigheratlowerpressures.