ImportantviewpointsproposedforasafetyapproachofHTGRreactorsinEurope:FinalresultsoftheEC-fundedHTR-LprojectOriginalResearchArticle

TheinherentsafetyfeaturesofmodularHighTemperatureReactors(HTRs)makeeventsleadingtoseverecoredamagehighlyunlikelyandconstitutethemaindifferentiatingaspectscomparedtoLWRs.Furthermore,whileaknownandstableregulatoryenvironmenthaslongbeenestablishedforLightWaterReactors(LWRs),differentwaysofthinkingmayhelptodevelopamoreappropriatelicensingprocessforHTR-basedpowerplants. TheHTR-LprojectfundedbytheEuropeanCommissioninthe5thFrameworkProgrammewasdedicatedtothedefinitionofacommonandcoherentEuropeansafetyapproachandtheidentificationofthemainlicensingissuesforthelicensingframeworkofthemodularHTRs.Severaltopicsweredevelopedduringthecourseofthisproject. DuetothecharacteristicsoftheHTRdesign,ithasbeennecessarytodefinespecificdefence-in-depthrequirementswhichhavethenbeenevaluatedforimplementationinthesafetyapproach.Safety-relatedfunctionsappropriatefortheHTRdesignhavealsohadtobeidentifiedandlisted. Ononehand,thedifferentpossiblesolicitationsofthefuelparticlesconstitutedthestartingpointfortheidentificationoftheaccidentalconditions(bymeansoftheMasterLogicDiagramsmethodology);theseaccidentalconditionswereclassifiedandthemostappropriatemethodstoconsiderultralowprobabilitysevereaccidentswereexamined. Ontheotherhand,theelementsconstitutingthesourcetermand,inparticular,therequirementsfortheconfinementofradioactiveproductsandtheconditionsrequiredtopreventtheneedfora“conventional”containmentstructurehavebeendiscussed. Inthedefinitionofthesafetyapproach,attentionhasbeenpaidtotheneedtomaintainthepotentiallyinterestingeconomicperspectivesofHTRreactors.KeyissuestobeaddressedinthelicensingprocessoftheHTRshavealsobeenidentified.Aninnovativesystems,structuresandcomponentsclassificationmethodhasbeendevelopedandrulesthatwillgovernequipmentqualificationproposed.