Thermal-hydraulicperformanceofprimarysystemofRBMKincaseofaccidentsOriginalResearchArticle

WithintheframeworkofanEuropeanCommissionsponsoredactivity,anoverallassessmentofthedeterministicsafetytechnologyofthe‘post-Chernobylmodernized’RBMKhasbeencompleted.Theaccidentanalysis,limitedtotheareaofdesignbasisaccident,constitutedthekeysubjectforthestudy;therefore,thenotoriousChernobylunit4eventwasoutsidethescopeoftheinvestigation. ThepresentpaperdealswiththeevaluationoftheaccidentperformanceoftheprimarysystemoftheRBMK.Ignalina-2andSmolensk-3nuclearpowerplants(NPP)areconsidered.Thedocumentedactivityincludesfourmainparts:(a)descriptionofkeyfeaturesoftheprimarysystemforthetwoNPP;(b)identificationandcharacterizationofrelevantaccidentscenariospartofthe(DBA)area;(c)keyfeaturesandqualificationlevelofadoptedcomputationtoolsprimarilyincludingcodesandinputdecks;(d)resultsfromtheanalysisofselectedaccidentscenarios. InthefirstpartofthepaperthelayoutcomplexityoftheRBMKsystems,includingtheemergencycorecoolingandrelatedlogicsispointedouttogetherwithmaindifferencesbetweenSmolensk-3andIgnalina-2units. Accidentscenariossuitablefortheanalysis,secondpartofthepaper,arederivedfromrecentlyissuedInternationalAtomicEnergyAgency(IAEA)reports,fromtheavailableSafetyAnalysisReports(SAR)ofexistingRBMKNPPandfromthelistofboundingaccidentsderivedfromthealreadymentionedECProject. ThefeaturesofKorsarandRelap5thermal-hydraulicsystemcodesdevelopedinRussiaandUS,respectively,areoutlinedinthethirdpartofthepaper,givingemphasistothequalificationlevelintherangeofparametersofinteresttoRBMKsystems.TheadoptednodalisationsresemblingIgnalina-2andSmolensk-3NPParealsodescribedincludingthedemonstrationofthequalificationlevel. Theresults,fourthpartofthepaper,basicallyshowtheoverallRBMKsystemrobustnesswithintheDBAarea,whenthenominaloperatingconditionsconstitutethestartingconditionsfortheaccidentscenarios.However,parallelchannelinstabilitiesmaytriggerdry-outphenomenaandconsequentrodsurfacetemperatureexcursionincaseofspecialaccidenttypes.