ML22251A400
| ML22251A400 | |
| Person / Time | |
|---|---|
| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 09/01/2022 |
| From: | Kairos Power |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22252A149 | List: |
| References | |
| KP‐NRC‐2209‐001 | |
| Download: ML22251A400 (15) | |
Text
KPNRC2209001
ResponsetoNRCRequestforAdditionalInformation350
(NonProprietary)
Page 1 of 5 NRCRequestforAdditionalInformation RAIPackage350,Question410 Section50.34ofTitle10oftheCodeofFederalRegulations(10CFR50.34),"Contentsofapplications; technicalinformation,"providesrequirementsforinformationtobeprovidedinaConstruction Permit(CP).10CFR50.34(a)(4)statesthataCPshallcontainapreliminaryanalysisandevaluationof SSCsprovidedformitigationoftheconsequencesofaccidentstodeterminemarginsofsafetyduring normaloperationsandtransientconditionsduringthelifeofthefacility.
Section3.1.1,"DesignCriteria,"oftheKairosPower(KP)HermesPreliminarySafetyAnalysisReport (PSAR)referencesdocumentKPTR003NPA,"PrincipalDesignCriteria[PDC]fortheKairosPower FluorideSaltCooled,HighTemperatureReactor,"Revision1,toprovidethePDCfortheHermestest reactor.KPFHRPDC14,"Reactorcoolantboundary,"statesthatsafetysignificantelementsofthe reactorcoolantboundaryshallhaveanextremelylowprobabilityofabnormalleakage,rapidly propagatingfailure,andgrossrupture.KPFHRPDC31,"Fracturepreventionofthereactorcoolant boundary,"statesthatthereactorcoolantboundaryshallbedesignedtoconsiderservice degradationofmaterialpropertiesincludingeffectsofcontaminants.KPFHRPDC35,"Passive residualheatremoval,"statesthatasystemshallbeprovidedtoremoveresidualheatduringand afterpostulatedaccidents.KPFHRPDC74,"Reactorvesselandreactorsystemstructuraldesign basis,"statesthatthevesselandreactorsystemshallbedesignedtoensureintegrityismaintained duringpostulatedaccidentstoensurethegeometryforpassiveheatremovalandallowforinsertion ofreactivitycontrolelements.
Section4.3ofthePSAR,"ReactorVesselSystem,"describesthecomponentsthatformthenatural circulationflowpathneededtoprovideresidualheatremovalduringandfollowingpostulated events.Theseincludeportionsofthegraphitereflectoraswellasmetalliccomponentssuchasthe corebarrel,reactorvessel,andfluidicdiode.ThissectionofthePSARdescribeshowthese componentsareneededtomeetPDCs14,31,35,and74.
Section5.1.3ofthePSAR,"SystemEvaluation,"statesthat"significant"airingressintotheprimary heattransportsystem(PHTS)isexcludedbydesignbasis.Inaneventwithpostulatedairingressinto thePHTS,thecomponentsthatcomprisethenaturalcirculationflowpathwillneedtoperformtheir safetyfunctions(i.e.,maintainthenaturalcirculationflowpath)tomeetthePDClistedabove.The staffnotesthatairingressintothePHTScancauseoxidationofthegraphitereflectoraswellas corrosionofmetalliccomponentsintheprimarysystem,andsuchdegradationcouldpotentially challengenaturalcirculationflow.Inordertoevaluateeffectsofairingress,thestaffneedsto understandtheamountofairingressthatwillbeallowedandhowthelimitationofingresswillbe achieved.
Therefore,theNRCstaffrequeststhefollowinginformation:
- 1. Definewhatconstitutes"significant"airingressintothePHTSandthebasisfordetermining whatis"significant."
- 2. Describehowcomponentintegrityisensuredifthedurationofanairingresseventislonger thanthedurationcoveredbythematerialsqualificationtesting.
- 3. Inaneventsuchasasaltspillorheatradiatortuberupture,howisfurtherairingress preventedafteraheatrejectionblowertrip?
Page 2 of 5 KairosPowerResponse NRCQuestion410,Item1 Definewhatconstitutes"significant"airingressintothePHTSandthebasisfordeterminingwhatis "significant."
ThediscussioninPreliminarySafetyAnalysisReport(PSAR)Section5.1.3isreferringtolimitingthe amountofairingressthatisforcedintotheFlibe,notlimitingtheamountofairingresstothe reactorsystemasawhole.AscitedinPSARSection5.1.3,thedesignevaluationoflimitingsignificant airingressdemonstratescompliancewithPrincipalDesignCriteria(PDC)33andPDC70.PDC33and PDC70arefocusedondetailsoftheFlibe,notthegasspaceabovethefreesurfaceofFlibe.This distinctionisimportanttorecognizefortheresponsesprovidedtothisRAI.TheresponsetoItem2 belowincludestheconsiderationofoxidationeffectsfornonFlibewettedgraphiteabovethefree surfaceofFlibe.
AsdescribedinPSARSection5.1.3,significantairingressintothePrimaryHeatTransportSystem (PHTS)referstotwoscenarios:
Significantairbeingentrainedinthecoolantduringnormaloperation(tomeetPDC33)
Forcedairingressoccurringduringpostulatedsystemleakageevents(tomeetPDC70)
Ifairisentrainedinthecoolantduringnormaloperation,operationalcontrolsareexpectedto monitorthequantityofairwithinthePHTStopreventaccumulatingsignificantquantitieswitha technicalspecification,asdiscussedinPSARSection13.1.10.5.Thelimitforsignificantairingress willpreventvoidaccumulationandlimitthetotalcorrosionofFlibewettedcomponents,as describedinPSARTable14.11.Consistentwith10CFR50.34(a)(5),thePSARidentifiesthevariable expectedtobesubjecttotechnicalspecificationcontrol,andPSARSection14.1commitsto providingtheparameterlimitswiththeapplicationforanOperatingLicenseApplication,consistent with10CFR50.34(b)(6)(vi).
Forthescenarioswheresignificantforcedairingressispreventedduringpostulatedeventsinvolving abreachorbreakinthePHTS,significantreferstoamountsofairthatcouldbeforcedintothe Flibebythedrivingforcesassociatedwiththeheatrejectionblowerortheprimarysaltpump.As describedinPSARSection7.3.1,therearesafetyrelatedtripsontheheatrejectionblowerand primarysaltpump,whichremovethemechanismsthatcouldforceairintotheFlibeduringasystem leakageeventtopreventsignificantforcedairingress.
PSARSections5.1.3,and13.1.10.5havebeenupdatedtoclarifythatforcedairingressintothePHTS isprecludedbydesign.
NRCQuestion410,Item2
Describehowcomponentintegrityisensuredifthedurationofanairingresseventislongerthanthe durationcoveredbythematerialsqualificationtesting.
Bymaintainingthequantityofairwithinthetechnicalspecificationlimitduringnormaloperation andremovingthemechanismstoforceairintotheFlibedescribedinItem1ofthisRAI,the structuralintegrityofmetallicandgraphitecomponentsthatremainFlibewettedisensuredto remainwithinconditionsboundedbythematerialsqualificationtestingprograms(References1and 2)forairingresseventsuptosevendays.Themetallicmaterialsqualificationtopicalreportincludes
((
))
Page 3 of 5 (Reference1).Thegraphitematerialqualificationtopicalreportdescribestheassessmentplanfor theeffectsofaircontaminationinFlibeonET10graphite(Reference2).
Duringnormaloperation,theargoninthegasspacewillbemonitoredforpotentialairingressas describedintheKairosPowerresponsetoRCI02(ML22231B230).
ThegraphitereflectorblocksthatarelocatedabovethefreesurfaceoftheFlibearesubjectto potentialoxidationeffectsduringapostulatedairingressevent.Sincetheshutdownelementsinsert atthebeginningoftheevent,thisexposedgraphitestructureisnotcreditedafterinsertionto performalongtermstructuralintegritysafetyfunctionwhenoxidationcouldbegintoaffectthe structuralintegrity.Additionally,ifsignificantoxidationweretoresultinalossofstructuralintegrity oftheexposedgraphite,thereisalayerofsubmerged(Flibewetted)graphitethatmitigatesdebris fromtheexposedgraphitefromenteringthenaturalcirculationflowpath.
AsshowninFigure1,thesecondaryholddownstructureisinstalledwithintheupperlayersofthe graphitereflectorandextendsbelowtheminimumFlibelevelforaPHTSbreakevent.Ifsignificant oxidationweretoresultinalossofstructuralintegrityofthegraphiteabovetheminimumFlibe level,thesecondaryholddownstructurewilltransferloadsfromthesubmergedgraphitetothetop head,keepingtheremainingreflectorstructureinplaceandsubmergedinFlibe.Theeffectsofnon forcedairingressontheintegrityofcomponentsbelowthesurfaceofFlibewillbeboundedbythe materialsqualificationtestingprogramsforatleastsevendaysfollowingtheinitiationoftheevent.
Beyondsevendays,defenseindepthfeaturesinclude:implementingrepairsondamagedSSCs, replenishingargonsupply,orremovaloffuelfromthevessel.Thisensuresthatthegeometryofthe coreandthenaturalcirculationflowpathsaremaintained.PSARSection4.3hasbeenupdatedto removethestatementthereactorvesselisdesignedtoprecludeairingressandtoreflectthe secondaryholddownstructuredesigndetailsdescribedabove.PSARSection13.1.10.5hasbeen updatedtodescribedefenseindepthfeaturesofthedesignavailableaftertheinitialsevenday periodofapostulatedairingressevent.Amarkupofchangestothegraphitequalificationtopical reportprovidingadditionaldetailsoftheoftheassessmentofairingressontheintegrityof componentsbelowthesurfaceofFlibeisbeingprovidedwiththisresponse.Arevisiontothe graphitequalificationtopicalreportwillbesubmittedbyseparateletter.
NRCQuestion410,Item3
Inaneventsuchasasaltspillorheatradiatortuberupture,howisfurtherairingresspreventedafter aheatrejectionblowertrip?
AsdescribedinItem1,safetyrelatedtripsontheheatrejectionblowerandprimarysaltpump removethemechanismsthatcouldforceairintotheFlibeduringasystemleakageevent.The HermesdesigndoesnotcreditanymeansoflimitingfurthernonforcedairingressintothePHTSin theeventofasaltspillorradiatortuberupture.SeeresponsetoItem2fordiscussionoftheimpacts ofnonforcedairingressonvesselinternals.
Page 4 of 5
References:
- 1. KairosPowerLLC,MetallicMaterialsQualificationfortheKairosPowerFluorideSalt CooledHighTemperatureReactor,KPTR013P,Revision3.
- 2. KairosPowerLLC,GraphiteMaterialQualificationfortheKairosPowerFluorideSalt CooledHighTemperatureReactor,KPTR014P,Revision3.
ImpactonLicensingDocument:
ThisresponseimpactsSections4.3,5.1.3,and13.1.10.5oftheKairosPowerPreliminarySafety AnalysisReportandSection5.3ofGraphiteMaterialsQualificationfortheKairosPowerFluoride SaltCooledHighTemperatureReactor.Markupsoftheaffectedsectionsareprovidedwiththis response.
Page 5 of 5 Figure1
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 429 coolantlevel.Thedesignofthereactorvesselallowsforonlinemonitoring,inserviceinspection,and maintenance.
4.3.1.1.1 VesselTopHead Thereactorvesseltophead(seeFigure4.32)isaflat316HSSdiscboltedandflangedtothevessel shell.Thisinterfaceisdesignedforleaktightnessbutisnotcreditedasbeingleaktightinsafety analyses.Thevesseltopheadcontrolstheradialandcircumferentialpositionsofthereflectorblocksto ensureastablecoreconfigurationforallconditions(e.g.,reactortripandcoremotion).Thetophead containspenetrations,asshowninFigure4.32andTable4.31,intoandoutofthevesselandprovides fortheattachmentofsupportingequipmentandcomponents(e.g.,reactivitycontrolelements,pebble handlingandstoragesystemcomponents,materialsamplingport,neutrondetectors,thermocouples, etc.).Thetopheadsupportsthevesselmaterialsurveillancesystem(MSS)whichprovidesaremote meanstoinsertandremovematerialandfueltestspecimensintoandfromthereactortosupport testing.Aholddownstructuresubassemblyisweldedunderneaththevesseltophead.Thisstructure contactswiththetopsurfaceofthegraphitereflectorandprovidesstructuralsupportagainstupward loadsduringnormaloperationandmostpostulatedevents.Asecondaryholddownstructureisinstalled throughtheuppergraphitelayers,extendingfromthereflectortopintosubmergedgraphitelayersto transferupwardloadsfromsubmergedgraphitetothevesseltopheadduringpostulatedairingress events.Thesecondaryholddownstructureextendstobelowtheminimumreactorvesselcoolantlevel thatcouldresultfrompostulatedsaltspillevents.
4.3.1.1.2 VesselShell Thereactorvesselisa316HSScylindricalshellthat,alongwiththevesselbottomhead,servestoform thesafetyrelatedreactorcoolantboundarywithinthereactorvessel.Itcontainsandmaintainsthe inventoryofreactorcoolantinsidethevessel.Theshellprovidesthegeometryforcoolantinletand vesselsurfacefortheDHRSwhichtransfersheatfromthereactorvesselduringpostulatedevents.The insideoftheshelluses316HSStabstomaintainthecorebarrelinacylindricalgeometryandhasa weldedconnectionatthetopofthecorebarrel.
4.3.1.1.3 VesselBottomHead Thereactorvesselbottomheadisaflat316HSSdiscthatisweldedtothevesselshell.Itcontainsand maintainstheinventoryofthereactorcoolantinsidethevessel,supportsthevesselinternals,maintains thereactorcoolantboundaryandprovidesflowgeometryforlowpressurereactorcoolantinlettothe core.Hydrostatic,seismicandgravityloadsonthevesselandvesselinternalsaretransferredtothe bottomheadandaretransferredtotheRVSS.
4.3.1.2 ReactorVesselInternals Thereactorvesselinternalstructuresincludethegraphitereflectorblocks,corebarrelandreflector supportstructure.Thevesselinternalstructuresdefinetheflowpathsofthefuelandreactorcoolant, provideaheatsink,apathwayforinstrumentationinsertion,controlandshutdownelementinsertion, aswellasprovideneutronshieldingandmoderationsurroundingthecore.Thedesignofthestructures supportinspectionandmaintenanceactivitiesaswellasmonitoringofthereactorvesselsystem.
4.3.1.2.1 ReflectorBlocks ThereflectorblocksareconstructedofgradeETU10graphite.Thereflectorblocksprovideaheatsink forthecoreandarerestrainedensuringalignmentofthepenetrationstoinsertandwithdrawcontrol elements.Thereflectorblocksarebuoyantinthereactorcoolant.Thetopsurfaceofthereflectorblocks contactsthevesseltopheadholddownstructuresubassemblywhichprovidesstructuralsupport
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 430 againstupwardloadsduringnormaloperationandmostpostulatedevents.Asecondaryholddown structureisinstalledthroughtheupperreflectorlayerstotransferupwardloadsfromsubmerged graphitetothevesseltopheadduringpostulatedairingressevents.Thebottomreflectorblocksare machinedwithcoolantinletchannelsfordistributionofcoolantinletflowintothecore.Thetop reflectorblocksaremachinedwithcoolantoutletchannelstodirectthecoolantexitingfromthecore intotheupperplenum,fromwhichthePSPdrawssuction.Thetopreflectorblocksalsoformapebble defuelingchute,asshowninFigure4.31,todirectthepebblesfromthecoretothepebbleextraction machine(PEM),allowingonlinedefuelingofthereactor(seeSection9.3).Thereflectorblocksalso providemachinedchannelsforinsertionandwithdrawalofthereactivitycontrolandshutdown elementsdescribedinSection4.2.2.
Thereflectorblocksformanupperplenumandafluidicdiode,whichisastainlesssteelpassivedevice thatconnectstheupperplenumtothetopofthedowncomerasshowninFigure4.31.Thediode introducesahigherflowresistanceinonedirection,whilehavingalowerflowresistanceintheother direction.Thedioderestrictsflowfromthehigherpressuredowncomerintotheupperplenumduring conditionswithforcedcirculation.Theflowpassesinthelowresistancedirectionofthediodefromthe upperplenumtothetopofthedowncomerdrivenbynaturalcirculation.
Thegraphitereflectorblocksreflectneutronsbackintothecore,increasingthefuelutilizationwhile protectingthereactorvesselfromfluencebasedformsofdegradation.Furtherdiscussionofthe reflectorsneutroniccharacteristicsaredetailedinSection4.5.
4.3.1.2.2 CoreBarrel The316HSScorebarrelcreatesanannularspacebetweenitselfandthereactorvesselanddefinesthe downcomerflowpathforthecoolant.Thecorebarrelhasaflangedtopwhichisweldedtotheinner wallofthevesselshell.Thebarreliskeptconcentrictotheshellbyradialtabswhichallowfor differentialthermalexpansion.
4.3.1.2.3 ReflectorSupportStructure The316HSSreflectorsupportstructure,asshowninFigure4.31,definestheflowpathfromthe downcomerannulusintothecoreaswellasprovidessupporttothegraphitereflectorblocks.The reflectorsupportstructureensuresastablecoreconfigurationforallconditions(e.g.,reactortripand coremotion)bycontrollingtheradialandcircumferentialpositionsofthereflectorblocks.
4.3.2 DesignBasis ConsistentwithPDC1,thesafetyrelatedportionsofthereactorvesselandreactorvesselinternalsare fabricatedandtestedinaccordancewithgenerallyrecognizedcodesandstandards.
ConsistentwithPDC2,thereactorvesselandreactorvesselinternalsperformtheirsafetyfunctionsin theeventofasafeshutdownearthquakeandothernaturalphenomenahazards.
ConsistentwithPDC4,thereactorvesselandreactorvesselinternalsaccommodatetheenvironmental conditionsassociatedwithnormaloperation,maintenance,testing,andpostulatedevents.
ConsistentwithPDC10,thereactorvesselandinternalsmaintainageometryandcoolantflowpathto ensurethatthespecifiedacceptablesystemradionuclidereleasedesignlimits(SARRDLs)willnotbe exceededduringnormaloperationincludingpostulatedevents.
ConsistentwithPDC14,thereactorvesselisfabricatedandtestedtohaveanextremelylowprobability ofabnormalleakageorsuddenfailureofthereactorcoolantboundarybygrossrupture.
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 433 factorsuptoatemperatureof650°CforER1682weldmetalwith316Hbasemetal.Testingprovides stressrupturefactorsupto816°Cforweldmaterialwith316Hbasemetal(Reference3).Theplant controlsystemwilldetectleakagefromthereactorvesselandcatchbasinsareusedtodetectleaksin nearbycoolantcarryingsystems.ThesefeaturesdemonstratecompliancewithPDC30.
Reactorvesselstressrupturefactorsaredeterminedupto816°Ctoencompasstransientconditions.
Thestressrupturefactorsaredeterminedbyacreeprupturetestonthevesselbasematerialwithweld metalunderthegastungstenarcweldingprocess.Thevesselprecludesmaterialcreep,fatigue,thermal, mechanical,andhydraulicstresses.Theleaktightdesignofthereactorvesselheadminimizesairingress intothecovergasandprecludescorrosionoftheinternals.Thehightemperature,highcarbongrade 316HSSofthecorebarrelandreflectorsupportstructurehavehighcreepstrengthandareresistantto radiationdamage,corrosionmechanisms,thermalaging,yielding,andexcessiveneutronabsorption.
Vesselfluencecalculations,asdescribedinSection4.5,confirmadequatemarginrelativetotheeffects ofirradiation.Thefastneutronfluencereceivedbythereactorvesselfromthereactorcoreandpebble insertionandextractionlinesisattenuatedbythecorebarrel,thereflector,andthereactorcoolant.
Coolantpuritydesignlimitsarealsoestablishedinconsiderationoftheeffectsofchemicalattackand foulingofthereactorvessel.ThesefeaturesdemonstrateconformancewithPDC31.
TheMSSutilizescouponsandcomponentmonitoringtoconfirmthatirradiationaffectedcorrosionis nonexistentormanageable.The316HSSreactorvesselandER1682weldmaterial,asapartofthe reactorcoolantboundary,willbeinspectedforstructuralintegrityandleaktightness.Asdetailedin Reference3,fracturetoughnessissufficientlyhighin316HSSunderreactoroperatingconditionsthat additionaltensileorfracturetoughnessmonitoringandtestingprogramsareunnecessary.These featuresdemonstrateconformancetoPDC32.
Fluidicdiodesareusedtoestablishaflowpathforcontinuousnaturalcirculationofcoolantinthecore duringpostulatedeventstoremoveresidualheatfromthereactorcoretothevesselwall.Duringand followingapostulatedevent,thehotcoolantfromthecoreflowsfromtheupperplenumthroughthe lowflowresistancedirectionofthefluidicdiodetothecoolerdowncomervianaturalcirculation, therebycoolingthecorepassively.Continuouscoolantflowthroughthereactorcorepreventspotential damagetothevesselinternalsduetooverheatingtherebyensuringthecoolablegeometryofthecoreis maintained.Theantisiphonfeaturealsolimitsthelossofreactorcoolantinventoryfrominsidethe reactorvesselintheeventofaPHTSbreach.ThesefeaturesdemonstratecompliancewithPDC35.
Thereactorvesselreflectorblockspermitinsertionofthereactivitycontrolandshutdownelements.The ETU10gradegraphiteofthereflectorblocksiscompatiblewiththereactorcoolantchemistryandwill notdegradeduetomechanicalwear,thermalstressesandirradiationimpactsduringthereflectorblock lifetime.ThegraphitereflectormaterialisqualifiedasdescribedintheKairosPowertopicalreport GraphiteMaterialQualificationfortheKairosPowerFluorideSaltCooledHighTemperatureReactor, KPTR014(Reference4).Toprecludedamagetothereflectorduetoentrainedmoistureinthegraphite, thereflectorblocksarebaked(i.e.,heateduniformly)priortocomingintocontactwithcoolantand thereactorvesselisdesigntoprecludeairingress.Thereflectors,whichactasaheatsinkinthecore, arespacedtoaccommodatethermalexpansionandhydraulicforcesduringnormaloperationand postulatedevents.Thegapsbetweenthegraphiteblocksalsoallowforcoolanttoprovidecoolingtothe reflectorblocks.Thereactorvesselpermitstheinsertionofthereactivitycontrolandshutdown elementsaswell.ThevesselisclassifiedasSDC3perASCE4319andwillmaintainitsgeometryto ensuretheRCSSelementscanbeinsertedduringpostulatedeventsincludingadesignbasisearthquake.
ThesefeaturesdemonstratecompliancewithPDC74.
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 439 Figure4.33:TheReactorVesselSystemSecondaryHoldDownStructure
PreliminarySafetyAnalysisReport
HeatTransportSystems
KairosPowerHermesReactor 54 Revision0 5.1.3 SystemEvaluation ThedesignofthenonsafetyrelatedPHTSissuchthatafailureofcomponentsofthePHTSdoesnot affecttheperformanceofsafetyrelatedSSCsduetoadesignbasisearthquake.Inadditiontoprotective barriers,thePHTSpipeconnectionstothereactorvesselnozzleshavesufficientlysmallwallthickness, suchthatifloadedbeyondelasticlimits,inelasticresponseoccursinthePHTSpipingwhichisnonsafety related.Thesefeatures,alongwiththeseismicdesigndescribedinSection3.5,demonstrate conformancewiththerequirementsinPDC2forthePHTS.
WhilethePHTSisaclosedsystem,thereareconceivablescenariosthatmayresultinthereleaseof radioactiveeffluents.Thefueldesignlocatesthefuelparticlesneartheperipheryofthefuelpebble, enhancingtheabilityofthefueltotransferheattothecoolant.Thethermalhydraulicanalysisofthe core(seeSection4.6)ensuresthatadequatecoolantflowismaintainedtoensurethatSARRDLs,as discussedinSection6.2,arenotexceeded.Thesefeaturesdemonstrateconformancewiththe requirementsinPDC10.
Thedesignofthereactorcoolant,inpart,ensuresthatpoweroscillationscannotresultinconditions exceedingSARRDLs.ThereactoriskeptnearambientpressureandthereactorcoolantinthePHTSdoes notexperiencetwophaseflow.Thecoolanthasahighthermalinertiamakingthereactorresilientto thermalhydraulicinstabilityevents.Thesefeatures,inpart,demonstrateconformancewiththe requirementsinPDC12.
ThefunctionalcontainmentisdescribedinSection6.2.Thedesignreliesprimarilyonthemultiple barrierswithintheTRISOfuelparticlestoensurethattheradiologicaldoseattheexclusionarea boundaryasaconsequenceofpostulatedeventsmeetsregulatorylimits.However,thereactorcoolant alsoservesasadistinctphysicalbarrierforfuelsubmergedinFlibebyprovidingretentionoffission productsthatescapethefuel.Thedesignofthereactorcoolantcompositionprovides,inpart,ameans tocontroltheaccidentalreleaseofradioactivematerialsduringnormalreactoroperationand postulatedevents(PDC60),andsupports,inpart,demonstrationofthefunctionalcontainmentaspects.
ThedesignaspectsofthereactorcoolantarediscussedinReference5.1.51.TheFlibealsoaccumulates radionuclidesfromfissionproducts,andtransmutationproductsfromtheFlibeandFlibeimpurities.The retentionpropertiesoftheFlibearecreditedinthesafetyanalysisasabarriertoreleaseof radionuclidesaccumulatedinthecoolant,andradionuclidecon
specifications.ThetransportofradionuclidesthroughFlibeisb
justifiedintheapplicationforanOperatingLicense.Thesefeat
requirementsinPDC16.
SignificantforcedairingressintothePHTSisexcludedbydesignbasis.Airingresscouldaffectthe inventoryofreactorcoolantinthereactorvesselaswellasaffectthepurityofthereactorcoolant.
Designfeaturesoftheheatrejectionsubsystemandthereactortripsystemwilllimitthequantitiesof airingressduringsystemleakageeventsbytrippingtheheatrejectionblowersandtrippingthePSP.
ThesedesignfeaturessatisfyPDC33andPDC70.TheeffectsofnonforcedairingressintothePHTSon safetyrelatedHermescomponentsareboundedbytheresultsofmaterialsqualificationprogramsas describedinSection4.3.
ThedesignofthePHTScontrolsthereleaseofradioactivematerialsingaseousandliquideffluentsin theeventthePHTSworkingfluidisinadvertentlyreleasedtotheatmospherevialeaksinthepiping system.ThePHTSSSCsthatarepartofthereactorcoolantboundaryaredesignedtotheASMEB31.3 Code(forthepiping)andSectionVIII(forthePHX)suchthatleaksareunlikely.Meansareprovidedfor detectingand,totheextentpractical,identifyingthelocationofthesourceofreactorcoolantleakagein thePHTSSSCs.ApostulatedeventinthePHTSwouldbeaPHXtubefailure.ThiseventwouldcauseFlibe Highlightedtextwaspreviously changed.Submitted21822 (ML22049B556)
PreliminarySafetyAnalysisReport
AccidentAnalysis
KairosPowerHermesReactor 1315 Revision0 ensurethereisnorecriticalityaftertheRCSShasinitiatedshutdown,asdescribedinSection4.5.
Additionally,thegraphitereflectorblocksaredesignedtomaintainstructuralintegrityandensure misalignmentsdonotpreventtheinsertionpathoftheshutdownelements,asdiscussedinSection4.3.
13.1.10.2 DegradedHeatRemovalorUncooledEvents Inpostulatedeventswherethenormalheatrejectionisnotavailable,naturalcirculationinthereactor vesselandtheheatremovalfunctionoftheDHRSarereliedupontoremoveheatfromthereactorcore.
Degradedheatremovaloruncooledeventsareexcludedfromthedesignbasis.Theinitiationofnatural circulationiscompletelypassive,andthedesignfeatures,includingthestructuralintegrityofthereactor vesselinternals,thatensureacontinuednaturalcirculationflowpatharediscussedinSection4.6.The DHRSisalignedandoperatingwhenthereactorpowerisaboveathresholdpowerandremainsinthis stateasdescribedinSection6.3,precludingtheneedforanactuationtooccurfortheDHRStoremove heatduringapostulatedevent.TheDHRSdesignincludessufficientredundancytoperformitssafety functionassumingthelossofasingletrain,asdiscussedinSection6.3.
13.1.10.3 FlibeSpillBeyondMaximumVolumeAssumedinPostulatedSaltSpills Inthesaltspillpostulatedeventcategory,anupperboundvolumeofFlibeisassumedtospilloutofthe PHTSontothefloor.AvolumeofFlibespillingoutofthesystembeyondtheamountassumedinthe boundingsaltspilleventisexcludedfromthedesignbasis.Thereareseveraldesignfeaturesensuring theamountofFlibeavailabletospillislimitedtoanupperboundvalue.Thereactorvesselisdesigned withantisiphonfeaturesdiscussedinSection4.3.Thesefeaturesaredesignedtopassivelybreakthe siphonintheeventofabreak.ThePSPalsotripstoallowtheprimarysystemtodepressurize.The reliabilityoftheRPS,whichtripsthePSPandISPintheeventofasaltspill,isdiscussedinSection7.3.
Thereactorvesselshellalsomaintainsintegrityinpostulatedeventstoensurethefuelinthecore remainscoveredwithFlibe.Thereactorvesselshelldesignfeaturesthatpreventleakagearediscussed inSection4.3.
13.1.10.4 InServiceTRISOFailureRatesandBurnupsAboveAssumptionsinPostulatedEvents Theinservicefuelfailureratesandtheburnupofpebblesassumedinthepostulatedeventsarebased onthefuelqualificationspecificationsinSection4.2.1.InserviceTRISOfailureratesabovetherate assumedinpostulatedeventsareexcludedfromthedesignbasis.Theinsertionofpebbleswitha burnuphigherthanthefuelqualificationenvelopeisexcludedfromthedesignbasis.Asdescribedin Section7.3,theRPSincludesafunctiontostopthepebbleinsertionandextractionfunctionstoensure pebblesarenotdamagedinfaultsoccurringafteraneventinitiation.Thefuelqualificationprogram includestesting,inspection,andsurveillancetoensurethefueloperatingenvelopeiswithinthefuel qualificationenvelope.InspectionandsurveillanceofthefuelinserviceisperformedinthePHSSas discussedinSection9.3.
13.1.10.5 SignificantIntermediateCoolantAirIngressIntoPHTS EventswheresignificantquantitiesofairareentrainedinthePHTScoolantduringnormaloperationare excludedfromthedesignbasis.Operationalcontrolsareexpectedtomonitorthequantityofairwithin thePHTStopreventaccumulatingsignificantquantities.Chapter14discussestheexpectedcoolant systemstechnicalspecificationsthatmonitorsignificantairingress.
EventswheresignificantquantitiesofforcedairenterthePHTSfollowingpostulatedHRRtubebreak eventsarealsoexcludedfromthedesignbasis.Chapter5discussesthedesignfeaturesoftheHRRthat Highlightedtextwaspreviously changed.Submitted21822 (ML22049B556)
PreliminarySafetyAnalysisReport
AccidentAnalysis
KairosPowerHermesReactor 1316 Revision0 limitsthequantitiesofforcedairingressduringsaltspilltransients.Thepostulatedeventsassumea positivepressuredifferentialbetweentheprimaryandintermediatecoolantsystems.Eventswhere significantquantitiesofintermediatecoolantenterthePHTSareexcludedfromthedesignbasis.
Chapter5discussesthedesignfeaturesofthePHTSandPHRSthatmaintainapositivepressure differential.
Theeffectsofnonforcedairingressonreactorvesselandvesselinternalcomponentswillremain boundedbythematerialsqualificationtestingprogramsforatleastsevendaysduringairingressevents asdescribedinSection4.3.Beyondsevendays,defenseindepthstrategiesinclude:implementing repairsondamagedSSCs,replenishingtheargonsupply,andremovaloffuelfromthevessel(fuelcore offloadcapabilitydiscussedinSection9.3.1.8.3).
13.1.10.6 DHRSReactorCavityFlooding TheDHRSisawaterbasedsystemthatremovesheatfromthereactorvesselshell.Eventswherethe waterfromtheDHRSleaksintothereactorcavityinquantitiessignificantenoughtowetthereactor vesselareexcludedfromthedesignbasis.Leakprevention,includingdoublewalledcomponentsand leakdetection,fortheDHRSisdescribedinSection6.3.
13.1.10.7 InsertionofExcessReactivityBeyondRateAssumedinPostulatedEvents Theinsertionofexcessreactivitypostulatedeventcategoryincludesalimitingreactivityinsertionrate basedonthemaximumcontrolelementdrivewithdrawalrate.Multiplecontrolelementsmoving simultaneouslyisexcludedfromthedesignbasis.Controlelementmovementislimitedtooneelement atatime,asdescribedinSection7.2.Acontrolelementwithdrawingfasterthanthelimitisexcluded fromthedesignbasis.Themaximumdrivewithdrawalspeedislimitedbythedrivehardware,as describedinSection4.2.2.Arapidcontrolelementejectionisexcludedfromthedesignbasisbecause thereactoroperatesatlowpressures.
Theinsertionofreactivityduetoanovercoolingeventisalsoboundedbythelimitingreactivityinsertion rate.CorecoolingduetopumpoverspeedfromthePSP,ISP,orPHRSblowerarelimitedtoamaximum limitwithintheprogrammednormaloperatingrangediscussedinSection7.2.
13.1.10.8 CriticalityOccurrenceExternaltoReactorCore PebblesoutsideofthereactorcorearecontainedinthePHSS.ThePHSSincludespebblesintransit duringhandling,instorage,andinatransportconfiguration.ThePHSSisdesignedtoprecludecriticality assumingpostulatedeventconditionsusingdesignfeaturesthatmaintainanoncriticalgeometryof pebblesineachoftheseareas.ThedesignfeaturesofPHSSpreventingcriticalityaredescribedin Section9.3.
13.1.10.9 ExcessiveRadionuclideReleasefromFlibe ThepostulatedeventsassumeareleaseofradionuclidesfromthefreesurfacesofFlibe.Theassumed releaseofradionuclidesfromFlibecouldbeaffectedbythecharacteristicsofthecovergassuchasa higherpressureaffectingthecovergasfloworthepurityofthecovergasaffectingtheradionuclides availableforrelease.Thecovergasismaintainedbytheinertgassystem,describedinSection9.1.2.
13.1.10.10 InternalorExternalEventsInterferingwithSSCs SSCsthatperformsafetyfunctionsarelocatedinaportionofthereactorbuildingdesignedtopreclude damagefrombothinternalandexternalhazardsthatcouldinterferewiththosefunctions.Additionally, SSCscontainingFlibeareprotectedfrominternalfloodstoprecludethepotentialforFlibe-water interactions.Thefailureofsafetyfunctionsduetointernalorexternalhazardsisexcludedfromthe Highlightedtextwaspreviously changed.Submitted21822 (ML22049B556)