Abstract :
DoesanHTRneedacontainment–pressureresistant–orisitpossible–licensable–tohaveonlyaso-calledconfinement.
Theanswerdependsonboththeresultsofthesafetyanalysisoftheaccidentsconsideredinthedesignandtheacceptancebythelicensingauthoritiesandthepublicofasafetyapproachonlybasedonseverecoredamageexclusion.
ThesafetyapproachtobedevelopedformodularHTRsmustdescribetheapplicationofthedefenceindepthprincipleforsuchreactors.Whatevertherequirementsonthelastconfinementbarriercouldbe,aconvincingdemonstrationoftheexclusionofanyseverecoredamageisneeded,relyingonexhaustiveandboundingconsiderationsofseverecoredamageinitiatorsandtheuseofnon-questionablearguments.
ThepaperpresentsthecontainmentissuesforHTRsbasedonGermanexperiencebackgroundandconsiderationsformodernmodularHTRsafetyapproachincludingbeyonddesignsituations.
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FortheGermanHTRs(designedinthe80s),itcouldbeshowninthelicensingproceduresinGermanythattherewasnoneedforapressureretainingandgastightcontainmenttoencloseradioactivenuclidesreleasedfromthenuclearheatsource.Instead,theconfinementenvelopeactedinconjunctionwithotherbarrierstominimizethereleaseofradioactivenuclidesandtheradiologicalimpactontheenvironment.
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Theconfinementenvelopeconsistedofthereactorbuilding,asub-atmosphericpressuresystem,abuildingpressurereliefsystem,anHVACsystemsisolationandafiltrationsystem.
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Duringamajordepressurizationaccident,unfilteredreleasesweredischargedtotheenvironment.TheanalysesresultsshowthattheenvironmentalimpactwasfarbelowthedoselimitsaccordingtotheGermanRadiologicalProtectionOrdinance,evenwhentheeffectoffilterswasnottakenintoaccount.
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Thedemonstrationstronglyreliedontheassumptionsmadeforthesourcetermdefinition,e.g.thefuelparticlesfailurerates(underirradiationandduringaccidentalconditions),thediffusiondata,thedustdataandthedeposition/lift-offmechanisms.
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FormodernmodularHTRs,thelastconfinementbarrierperformanceswillhavetobedeterminedinaccordancewiththesetofaccidentstobeconsideredinthedesignincludinginternalandexternalhazardsandthelimitstargetedforthepublicandtheenvironmentprotection.
FurthermorethepaperpresentsananalysisofeffectsofadeliberatecrashofalargecommercialairlineronaformerGermanHTRdesign.
