Full-scalemodellingoftheMNSRreactortosimulatenormaloperation,transientsandreactivityinsertionaccidentsundernaturalcirculationconditionsusingthethermalhydrauliccodeATHLETOriginalResearchArticle

Afull-scaleATHLETsystemmodelfortheSyrianminiatureneutronsourcereactor(MNSR)hasbeendeveloped.Themodelrepresentsallreactorcomponentsofprimaryandsecondaryloopswiththecorrespondingneutronicsandthermalhydrauliccharacteristics.UndertheMNSRoperationconditionsofnaturalcirculation,normaloperation,stepreactivitytransientsandreactivityinsertionaccidentshavebeensimulated.TheanalysesindicatethecapabilityofATHLETtosimulateMNSRdynamicandthermalhydraulicbehaviourandparticularlytocalculatethecorecoolantvelocityofprevailingnaturalcirculationinpresenceofthestrongnegativereactivityfeedbackofcoolanttemperature.Thepredictedtimedistributionofreactorpower,coreinletandoutletcoolanttemperaturefollowcloselythemeasureddataforthequasisteadyandtransientstates.However,sensitivityanalysesindicatetheinfluenceofpressureformlosscoefficientsatcoreinletandoutletontheresults.Theanalysisofreactivityaccidentsrepresentedbytheinsertionoflargereactivity,demonstratesthehighinherentsafetyfeaturesofMNSR.Evenincaseofinsertionoftotalavailablecoldexcessreactivitywithoutscram,thehighnegativereactivityfeedbackofmoderatortemperaturelimitspowerexcursionandavoidsconsequentlytheescalationofcladtemperaturetothelevelofonsetofsub-cooledvoidformation.Thecalculatedpeakpowerinthiscaseagreeswellwiththedatareportedinthesafetyanalysisreport.TheATHLETcodehadnotpreviouslybeenassessedundertheseconditions.TheresultsofthiscomprehensiveanalysisensuretheabilityofthecodetotestsomeconceptualdesignmodificationsofMNSRʹscoolingsystemaimingtheimprovementofcorecoolingconditionstoincreasethemaximumcontinuousreactoroperationtimeallowingmoreeffectiveuseofMNSRforirradiationpurposes.