ConceptualdesignmodificationsofthecoolingsystemofMNSRreactortoincreaseitsmaximumcontinuousoperationtimeOriginalResearchArticle

ToincreasethemaximumdailyoperationtimeofMiniatureNeutronSourceReactor(MNSR)reactorseveralconceptualthermalhydraulicdesignmodificationshavebeeninvestigatedaimingattheimprovementofreactorcoolingconditionstolimittheincreaseofaveragecoretemperature.Forthispurposeanintegratedfull-scalethermalhydraulic-neutronicsmodelusingtheadvancedcodeATHLEThasbeendeveloped,testedandverified.Theselecteddesignmodificationsrelyuponintroducingauxiliarycoolingsystemsoperatinginfourdifferentmodestocoolpoolwaterorreactorwaterusingheatexchangerlocatedeitherinsideoroutsideofreactorpool.Thesimulationresultsshowthattheincreaseofcontinuousreactoroperationtimevariesbetween1and8additionaloperationhours.Theoptimalresultsareachievedforthesecondandthefourthoptionsthatuseexternalheatexchanger.Thesecondoptionenablestheextendingofcontinuousoperationtimeupto10handthefourthupto15h,bothatnominalreactorpowerandundertheassumptionofinitialexcessreactivitycorrespondingtothefreshreactorcore.Theanalysisincludedtheevaluationofxenonpoisoningeffectontheincreaseofoperationtime.Ithasbeenshownthatitsremarkableeffectstartsafterthefirst3operationhoursandincreasescontinuouslyafterthat.Forthebestcoolingoptions,wheretheaveragecoretemperatureisbeingfixedatcertainvalueresultingincompleteeliminationofreactivityfeedbackofcoolingtemperature,xenoneffectbecomestheexclusivelimitingeffectduringthelateroperationphase.TheanalysisdiscussalsogeneralaspectsoftechnicalrealizationforthedifferentcoolingoptionsinrelationwiththespecificfeaturesofMNSRandthepreliminaryengineeringsafetymeasuresandoperationalradiologicalprotectionthathavetobetaken.TheperformedanalysisandtheachievedresultsduringthisworkwouldmakevaluablecontributionforupdatingtheSafetyAnalysisReport(SAR)ofMNSR.