ML22237A326

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Kairos Power LLC, Changes to Preliminary Safety Analysis Report Chapters 3, 4, 5, 9 and 14
ML22237A326
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Issue date: 08/25/2022
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KPNRC2208010

ChangestoPSARChapters3,4,5,9and14 (NonProprietary)

PreliminarySafetyAnalysisReport

DesignofStructures,Systems,andComponents KairosPowerHermesReactor 37 Revision0 PrincipalDesignCriteria SARSection PDC26,Reactivitycontrolsystems 4.2.2 4.5 PDC28,Reactivitylimits 4.2.2,7.3 PDC29,Protectionagainstanticipatedoperationoccurrences 4.2.2,7.3,7.5 PDC30,Qualityofreactorcoolantboundary 4.3 PDC31,Fracturepreventionofreactorcoolantboundary 4.3 PDC32,Inspectionofreactorcoolantboundary 4.3 PDC33,Reactorcoolantinventorymaintenance 4.3,9.1.4,9.3 PDC34,Residualheatremoval 4.6,6.3 PDC35,Passiveresidualheatremoval 4.3,4.6,6.3 PDC36,Inspectionofpassiveresidualheatremovalsystem 6.3 PDC37,Testingofpassiveresidualheatremovalsystem 6.3 PDC44,Structuralandequipmentcooling 9.1.5,9.7 PDC45,Inspectionofstructuralandequipmentcoolingsystems 9.1.5,9.7 PDC46,Testingofstructuralandequipmentcoolingsystems 9.1.5,9.7 PDC60,Controlofreleasesofradioactivematerialstothe environment 5.1,9.1.3,9.2,11.2 PDC61,Fuelstorageandhandlingandradioactivitycontrol 9.3 PDC62,Preventionofcriticalityinfuelstorageandhandling 9.3 PDC63,Monitoringfuelandwastestorage 9.3,11.2 PDC64,Monitoringradioactivityreleases 9.1.2,9.1.3,9.2 PDC70,Reactorcoolantpuritycontrol 9.1.1 PDC71,Reactorcoolantheatingsystems 9.1.5 PDC73,Reactorcoolantsysteminterfaces 5.2

PreliminarySafetyAnalysisReport ReactorDescription KairosPowerHermesReactor

Revision0 430 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.Thecorebarrelincludescutoutfeatureswhichlimitthesiphoning ofreactorcoolantintheeventofabreakinthevesselcoldleg,andThecorebarrelhasaflangedtop whichisweldedtotheinnerwallofthevesselshell.Thebarreliskeptconcentrictotheshellbyradial tabswhichallowfordifferentialthermalexpansion.

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.

ConsistentwithPDC30,reactorvesselisfabricated,andtestedtoqualitystandards,andpreandin serviceinspections,aswellastestingwherepracticable,willbeusedtodetectandidentifythelocation ofcoolantleakage.

ConsistentwithPDC31,thereactorvesselhassufficientmargintowithstandstressesunderoperating, maintenance,testing,andpostulatedeventssuchthatthereactorcoolantboundarydoesnotdegrade duetotheeffectsofneutronembrittlement,corrosion,materialwear,fatigue,stressrupture,thermal loads,orfailureduetostressruptureandfracture.Thedesignshallaccountforresidual,steadystate, andtransientstressesandconsiderflawsize.

PreliminarySafetyAnalysisReport ReactorDescription KairosPowerHermesReactor

Revision0 431 ConsistentwithPDC32,thereactorvesselpermitsinspection,monitoring,orfunctionaltestingof importantareasandfeaturestoassessstructuralintegrityandleaktightnessofthesafetyrelated portionsofthereactorcoolantboundary.

ConsistentwithPDC33,thecorebarreldesignincludesantisiphonfeaturestolimitreactorcoolant inventorylossintheeventofbreaksinthePHTScoldleg.

ConsistentwithPDC35,thereactorvesselinternalswillassuresufficientcorecoolingduringpostulated eventsandremoveresidualheat.Thesafetyfunctionofthefluidicdiodeistoprovideaflowpathvia naturalcirculationtotransferheatfromthereactorcoreduringandfollowingpostulatedeventssuch thatfuelandreactorinternalstructuredamagethatcouldinterferewithcontinuedeffectivecore coolingisprevented.

ConsistentwithPDC74,thedesignofthereactorvesselandreflectorblocksshallbesuchthattheir integrityandgeometryaremaintainedduringpostulatedeventstopermitsufficientinsertionofthe controlandshutdownelementsprovidingforreactorshutdown.

4.3.3 SystemEvaluation The316HSSstructuresofthereactorvesselsystemarefabricatedandtestedinaccordancewith Reference1standards.The316HSSvesselinternalsalsosatisfythechemistryrestrictionsoftheASME SectionIIIcodeinDivision5,ArticleHGB2000.PertheASMEstandard,ER1682weldmetalwillbe usedinfabricationofthe316Hstructures.Commensuratewiththesafetyrelatedfunctionofthe reflectorblockinensuringacceptabledesignlimitsandmaintainingthereactorcoolantflowpath, qualityrelatedcontrolswillbeplacedontheETU10graphite.KPFHRspecificationsandprocurement documentsincorporateandreferencetheapplicableguidanceandASMEstandards.Thequality assuranceprogramisdescribedinSection12.9.ThesecontrolsdemonstrateconformancewithPDC1.

Thereactorvesselsystemmakesupaportionofthereactorcoolantboundary.Thereactorvesseland graphitereflectorblocksarethereforedesignedtomaintaingeometryduringasafeshutdown earthquaketoensurethevesselintegrity,insertionofnegativereactivityviatheRCSS,andtomaintain theflowpath.Thereactorvesselandvesselinternalswillhavedynamicbehaviorsduringadesignbasis earthquake.Theseincludefluidstructureinteractionwithinthevessel,oscillatoryresponseof componentsmountedtothereactortophead,i.e.,headmountedoscillators,andrelativemovementof graphitereflectorblockswithrespecttooneanotherwithinthecoolant.Thesedynamicbehaviorsare accountedforinthedesignofthereactoranditsinternals,toensurecontinuedfunctionalityduringand afteradesignbasisearthquake.Modelsareusedtounderstandfluidmigrationtendenciesconsidering thepebblebed,reflectorblocks,corebarrel,andotherreactorvesselinternalfeatures.Theinsights gainedfromtheanalysisofthesemodelsareusedtodesignthereactortopreventdamagetothevessel duringadesignbasisearthquake.Thereactorvessel,vesselinternals,andvesselattachmentssuchas theRCSSareclassifiedasSDC3perASCE4319SeismicDesignCriteriaforStructures,Systems,and ComponentsinNuclearFacilities(Reference2).Thereactorvesselwillalsobeprotectedfromthe failureofnearbynonsafetyrelatedSSCsduringadesignbasisearthquakebyseismicallymounting, physicallyseparating,orusingabarriertoprecludeadverseinteraction,andfromfailureofattached nonsafetyrelatedSSCs,suchasattachedpiping(e.g.,bydesignforpreferentialfailureofthenonsafety componentisawaythatdoesnotimpactthevessel).ThesefeaturesdemonstratecompliancewithPDC 2.

Thereactorvesselcanaccommodateinternalandexternalstaticanddynamicloads.Thethermal expansionofthereactorvesselshellandbottomheadissupportedbythereactorvesselsupportsystem (RVSS)(seeSection4.7)duringreactorstartup,normaloperation,andpostulatedevents.Mechanical loadingsfromstaticweight,seismicload,andforcesfromthepebblebed,coolant,andcore

PreliminarySafetyAnalysisReport ReactorDescription KairosPowerHermesReactor

Revision0 433 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.

AntisiphoncutoutsareabovethePHTScoldlegwithcoolantonbothsidesofthecorebarrelduring normaloperation.Intheeventofacoldlegbreak,reactorcoolantlevelisexpectedtodecreaseand the covergas moves intothedowncomertobreakthesiphonthusprecludingcoolantfrombeing siphoned belowthefluidicdiodeflowpathwayelevation.ThesedesignfeaturesdemonstrateconformancetoPDC 33.

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 453 4.6 THERMALHYDRAULICDESIGN 4.6.1 Description Thethermalhydraulicdesignofthereactorisacombinationofdesignfeaturesthatenableeffective heattransportfromthefuelpebbletothereactorcoolantandeventuallytotheheatrejectionsystem ofthereactor,consideringtheeffectsofbypassflowandflownonuniformity.Thedesignfeaturesthat playakeyroleinthethermalhydraulicdesignofthereactorsystemincludethefuelpebble(seeSection 4.2.1),reactorcoolant(seeSection5.1),reactorvesselandreactorvesselinternalstructures(see Section4.3),theprimaryheattransportsystem(PHTS)(seeSection5.1),andtheprimaryheatrejection system(PHRS)(seeSection5.2).Thermalhydrauliccomputercodesandevaluationmodelsare discussedinSection4and5ofReference1,andSection4ofReference2.

4.6.1.1 CoreGeometry Thecoregeometryismaintainedinpartbythereactorvesselinternalsincludingthereflectorblocks whichkeepthepebblesinageneralcylindricalcoreshape.Coolantinletchannelsinthegraphite reflectorblocksareemployedtolimitthecorepressuredrop.Theuseofpebblesinapackedbed configurationalsocreateslocalvelocityfieldsthatenhancepebbletocoolantheattransfer.Thereactor thermalhydraulicdesignusesthefollowingheattransfermechanismstoextractthefissionheat.

Pebbletocoolantconvectiveheattransfer

Pebbleradiativeheattransfer

Pebbletopebbleheattransferbypebblecontactconduction

Pebbletopebbleheattransferbyconductionthroughthereactorcoolant

Heattransfertothegraphitereflectorbymodesofconduction,convection,andradiation.

4.6.1.2 CoolantFlowPath Duringnormaloperation,reactorcoolantatapproximately550°Centersthereactorvesselfromtwo PHTScoldlegnozzlesandflowsthroughadowncomerformedbetweenthemetalliccorebarrelandthe reactorvesselshellasshowninFigure4.61.Thecoolantisdistributedalongthevesselbottomhead throughthereflectorsupportstructure,upthroughcoolantinletchannelsinthereflectorblocksandthe fuelingchuteandintothecorewithaportionofthecoolantbypassingthecoreviagapsbetweenthe reflectorblocks.Thecoolanttransfersheatfromfuelpebbleswhicharebuoyantinthecoolantand providescoolingtothereflectorblocksandthecontrolelementsviaengineeredbypassflow.Coolant travelsoutoftheactivecorethroughtheupperplenumviathecoolantoutletchannelsandexitsthe reactorvesselviathePHTSoutlet.Themaximumvesselexittemperatureis620°Canddependentonthe amountofcorrespondingbypassflowthroughthereflectorblocks.

DuringpostulatedeventswherethenormalheatremovalpaththroughthePHTSisnolongeravailable, includingwhenthePHTSisdrained,afluidicdiode(seeSection4.3),isusedtocreateanalternateflow path.Duringsuchevents,forcedflowfromtheprimarysaltpump(PSP)isalsonotavailable.Thefluidic diodethendirectsflowfromthehotwelltothedowncomerasshowninFigure4.61.Thisopensthe pathforcontinuousflowvianaturalcirculation.Duringnormaloperation,whilethePSPisinoperation, thefluidicdiodeminimizesreverseflow.

PreliminarySafetyAnalysisReport ReactorDescription KairosPowerHermesReactor

Revision0 455 4.6.4 TestingandInspection Reactorcoolanttemperatures,flow,andcorepowerwillbeperiodicallymonitoredduringoperationsto bewithinspecifiedlimits.Instrumentationwillalsobeperiodicallycalibrated.

4.6.5 References 1.

KairosPowerLLC,KPFHRCoreDesignandAnalysisMethodology,KPTR017P,Revision0.

2.

KairosPowerLLC,PostulatedEventMethodology,KPTR018P,Revision0.

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,andradionuclideconcentrationislimitedbytechnical specifications.ThetransportofradionuclidesthroughFlibeisbasedonthermodynamicdatathatwillbe justifiedintheapplicationforanOperatingLicense.Thesefeaturesdemonstrateconformancewiththe requirementsinPDC16.

ThePSPcasingdesignsetstheinletelevationoftheantisiphonsurfaceforthehotlegshouldaleak occurintheexternalportionofthePHTS.IntheeventofabreakintheexternalportionofthePHTShot legThisantisiphonfeaturelimitsthelossofreactorcoolantinventoryfrominsidethereactorvesselthe eventofaPHTSbreachorinbreachesofinventorymanagementsystempipingconnectedtothePHTS (seeSection9.1.4.),reactorcoolantlevelisexpectedtodecreaseandthe covergasmoves intothe pump welltobreakthesiphon.Thisprecludescoolantfrombeingsiphonedbelowtheelevationofthe PSPcasing.TheseantisiphonfeaturesdemonstratecompliancewithPDC33.

ThedesignofthePHTScontrolsthereleaseofradioactivematerialsingaseousandliquideffluentsin theeventthePHTSworkingfluidisinadvertentlyreleasedtotheatmospherevialeaksinthepiping system.ThePHTSSSCsthatarepartofthereactorcoolantboundaryaredesignedtotheASMEB31.3 Code(forthepiping)andSectionVIII(forthePHX)suchthatleaksareunlikely.Meansareprovidedfor detectingand,totheextentpractical,identifyingthelocationofthesourceofreactorcoolantleakagein thePHTSSSCs.ApostulatedeventinthePHTSwouldbeaPHXtubefailure.ThiseventwouldcauseFlibe

PreliminarySafetyAnalysisReport AuxiliarySystems KairosPowerHermesReactor 917 Revision0 interactions.TheIMSisdesignedtopreferentiallyfailinawaythatdoesnotimpacttheRVsystem.This satisfiesPDC2fortheIMS.

TheIMSisdesignedsuchthatsafetyrelatedsystemsinproximitytotheIMSareprotectedagainstthe dynamiceffectspotentiallycreatedbythefailureofIMSequipment.TheIMSisalowpressuresystem, asthereactorcoolantpressuresareboundedbythereactorcoolantstaticheadpressures,thus precludingpipewhip.ThissatisfiesPDC4fortheIMS.

TheIMSisdesignedtoprecludetheinadvertentdrainingoftheRVduringnormaloperationandduring RVfill/drainoperations.Duringnormaloperation,whenthereactorvesselisfueled,theRVfill/drain transferlineisequippedwithpassiveRVisolationfeaturessuchascaps,flanges,and/oratransferline disconnect,designedtoprecludeinadvertentreactorcoolantdrainingfromtheRVbysiphoning.Inthe eventofaleakintheRVfill/draintransferline,whileconnectedtothereactorvesselduringfueled operation,thereactorcoolantleakisdetectedbytheplantcontrolsystem,thePSPistripped,andthe RVcovergaspressureislimitedtoanupperboundthusprecludingtheejectionofreactorcoolant throughthetransferlinediptube.DuringRVfill/drainoperations,thereactorvesselisdefueled,andthe fill/drainlineisconnected,anisolationvalveisusedtointerruptthereactorcoolantflowandacover gasinletisusedtobreakthesiphoninthetransferlines.Thesedesignfeaturessatisfytherequirements ofPDC33.

TheRVcoolantlevelmanagementlineshortdiptubeandoverflowweirdesignsprecludeinadvertent reactorcoolantdrainingfromtheRVintotheRVlevelmanagementtank.Asleveldropsinresponsetoa breakinthereactorcoolantlevelmanagementline,covergaswouldfilltheshortdiptubeandwould breakthesiphon.Additionally,theoverflowweirisdesignedinawaythatprecludestheuncoveringof fuelduetothermalexpansionofthereactorcoolant.IntheeventofaleakintheRVlevelmanagement tankortransferline,thereactorcoolantleakisdetectedbytheplantcontrolsystem,andthepumpfor thereactorlevelmanagementistrippedtominimizetheoverflowofreactorcoolantfromtheRV throughtheoverflowweir.Asleveldropsinresponsetoabreakinthereactorcoolantlevel managementline,covergaswouldfilltheoverflowweirandwouldbreakthesiphon.Thisdesign configurationsatisfiestherequirementsofPDC33.

TheIMSencompassesaPHTSdrainline,equippedwithaPHTSdrainvalve,whichinterfaceswiththe PHTSfill/draintank.ThePHTSdesigncontainsanRVantisiphonfeature(seeSection5.1),thus precludinginadvertentreactorcoolantdrainfromtheRV,precludingtheIMSfromdrainingtheRV.

ThesedesignfeaturessatisfytherequirementsofPDC33.

ThemakeupinventoryfunctionofIMSisnotreliedontomitigatetheconsequencesofapostulated event.AsdescribedinSection4.3,thesafetyrelatedportionsofthereactorcoolantboundaryare limitedtothereactorvesselandafailureofthereactorvesselisprecludedbydesign.Therefore,the makeupfunctionalrequirementsofPDC33havebeenaddressedbydesign.

Thesystemisexpectedtohandlereactorcoolantwithfissionaswellasactivationproducts;therefore, thesystemwillbedesignedtominimizecontaminationandsupporteventualdecommissioning, consistentwiththerequirementsof10CFR20.1406.

9.1.4.4 TestingandInspection ThecomponentsoftheIMS,includingvalves,tanks,pumpsandothercomponents,arelocatedsuch thattheyareaccessibleforperiodicinspectionandtesting.

9.1.4.5 References 1.

AmericanSocietyofMechanicalEngineers,ProcessPiping,ASMEB31.3.2016.

PreliminarySafetyAnalysisReport AuxiliarySystems KairosPowerHermesReactor 929 Revision0 graphiteorareexpectedtocoolquicklysuchthatoxidation,ifany,wouldbeminimalandnotaffectthe acceptabilityofthepebbleforreuse.ThesedesignfeaturessatisfytherequirementsofPDC3forthe PHSS.FireprotectionsystemsarefurtherdiscussedinSection9.4.

ThepebblehandlingportionofthePHSSisprotectedfromtheeffectsofdischargingfluids.Thereareno pressurizedpipingsystemsinoraroundthePHSSthusprecludingthedesignfromhighenergyline considerations.Ahypotheticalwaterlinebreakintheareaofthestoragesystemdoesnotposea criticalityriskastheanalysessupportingthestoragesystemassumecompletesubmergenceandinternal floodingofthestoragecanistersinwater.ThePHSSisdesignedinconsiderationofthehighradiation environmentwhereequipmentwillbefunctioning.ThePHSSdesignalsoconsidersandaccountsforthe temperaturewithinthesystemtoprecludeoxidationofgraphitepebbles.ThestainlesssteelPHSS storagecanistersaredesignedtoaccommodatepressureduetotheaccumulationofradionuclidesand thermalloadsassociatedwiththeamountofspentfuelloadedineachcanisterduringnormaland postulatedeventconditions.Thecanistersarealsodesignedtoaccommodatethetensilestressexerted duringtransferandarecompatiblewithhandlingequipment.Theinteriorofthestainlesssteelcanisters isalsodesignedtoaccountforradiolysisproductsfromspentnuclearfuelandensurestheintegrityof thecanister,seal,andweldthusprecludingthepotentialreleaseofradionuclidesfromthecanister.

ThesedesignfeaturesdemonstratethatthePHSSsatisfiestheenvironmentalanddynamiceffectsin PDC4.

ThePHSSinterfaceswiththereactorvesselatthePEMandthepebbleinsertionline.Theelevationof thePEMrelativetothecoolantfreesurfaceissuchthatcoolantinventorylossfromthereactorvesselis limitedintheeventthePEMbreaks.Thepebbleinsertionlineisdesignedtolimitinventorylosstoan elevationnolowerthantheprimarysaltpumpelevation,intheeventofabreakintheinsertionline.

Thepebbleinsertionlineusesoverflowprotectioncutoutstodirectanycoolantintheinsertionline backdownintothereactorvessel. Cover gas fills the line to break the siphon.Thesedesignfeatures of thePHSSsatisfytherequirementsinPDC33.

PDC61requiresthatthesafetyrelatedportionsofthePHSSthatcontainradioactivitybedesignedto ensure(1)capabilitytopermitappropriateperiodicinspectionandtestingofcomponents,(2)suitable shieldingforradiationprotection,(3)appropriatecontainment,confinement,andfiltering,(4)residual heatremovalcapability,and(5)significantreductioninfuelstoragecoolingunderpostulatedevent conditionsisprecluded.ThedesignfeatureswhichaddressPDC61forthePHSSarediscussedbelow:

TheTRISOfuelparticleprovidesafunctionalcontainmentasdescribedinSection6.2.Radioactive materialandfissionproductsarecontainedwithintheparticleunlesstheTRISOlayersare compromisedordefective(seeSection4.2.1).Thefuelpebble,asdescribedinSection4.2.1,is designedtoprecludephysicaldamageorchangesingeometrytotheTRISOparticleduring anticipatedloadsfromnormaloperation,storage,shippingandhandling.Therefore,theTRISO particleiscreditedfortheconfinementofradioactivematerialsratherthanthePHSS.Thepebble canexperiencethermalandmechanicalloadswhilebeinghandled,inspected,operated,andstored; however,suchloadsdonotintroduceincrementalfailuresofTRISOparticles.Furthermore,thePHSS designprecludespebbledamagefromoverheatingandoxidation.Heatremovalmechanismswithin thesystem,suchasthermalradiationandconvectionvianaturalcirculation,aresufficientto removethedecayheatproducedbyindividualpebblesduringtheirtransitthroughthePHSS.Also, oxidationassociatedwithairormoistureingressintothePHSSisnegligibleforpebblesat temperaturesexperiencedinthesystem.Thesystemalsominimizespebblewear.ThelimitingPHSS malfunctionevent,whichisdiscussedinSection13.1.5,doesnotcausetemperatureexcursions, oxidation,ormechanicalstressesontheTRISOparticles.Therefore,containmentandconfinement ofradioactivityismaintainedbytheTRISOparticles.

PreliminarySafetyAnalysisReport

TechnicalSpecifications

KairosPowerHermesReactor 145 Revision0 Section SectionName LCOorCondition Basis Inletgassystempressureis maintainedwithinanupper boundlimit.

Theobjectiveistolimitthe quantityandpressureof spilledFlibeorcovergasto ensureapostulatedevent doesnotexceedlimits.

Argonpurityinthecovergasis maintainedwithinanupper boundlimit.

Theobjectiveistolimit radionuclidesintheFlibe belowsolubilitylimitswhere solutesoluteinteractionscan beneglected.

Thequantityofmaterialsatrisk inthegasspaceoftheprimary heattransportsystemandthe primaryheatrejectionsystemis maintainedwithinanupper boundlimit.

Theobjectiveistolimitthe quantityofmaterialsatrisk inthecovergastoensurea postulatedeventdoesnot exceedlimits.

Thequantityofairinthereactor coolantsystemduringsteady stateismaintainedwithinan upperboundlimit.

Theobjectiveistolimitthe airingresstothereactor coolantsystemtoprevent voidaccumulationand corrosion.

3.4 EngineeredSafety Features Decayheatremovalsystem operability Theobjectiveistospecifythe requirementtohavean operabledecayheatremoval systemtoensurethatthe safetylimitswillnotbe exceeded.

Reactorvesselintegrity Theobjectiveistospecifya designoperating temperaturelimittoensure thesafetylimitisnot exceededforpostulated events.

3.5 VentilationSystems N/A N/A 3.6 EmergencyPower N/A N/A Highlightedtextwasadded previously.Submitted2/18/22 (ML22049B556)

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