ML22243A250

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Enclosure 2: Response to NRC Request for Additional Information 339
ML22243A250
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Site: Hermes File:Kairos Power icon.png
Issue date: 08/31/2022
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Kairos Power
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Office of Nuclear Reactor Regulation
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KP-NRC-2208-014
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KPNRC2208014

ResponsetoNRCRequestforAdditionalInformation339 (NonProprietary)

Page1of5 NRCRequestforAdditionalInformation RAIPackage339,Question399

Section50.34ofTitle10oftheCodeofFederalRegulations(10CFR50.34),"Contentsofapplications; technicalinformation,"providesrequirementsforinformationtobeprovidedinaConstruction Permit(CP).10CFR50.34(a)(4)statesthataCPshallcontainapreliminaryanalysisandevaluationof systems,structures,andcomponents(SSCs)providedformitigationoftheconsequencesofaccidents todeterminemarginsofsafetyduringnormaloperationsandtransientconditionsduringthelifeof thefacility.

Section3.1.1,"DesignCriteria,"oftheKairosPower(KP)HermesPreliminarySafetyAnalysisReport (PSAR)referencesdocumentKPTR003NPA,"PrincipalDesignCriteria[PDC]fortheKairosPower FluorideSaltCooled,HighTemperatureReactor,"Revision1,toprovidetheprincipaldesigncriteria fortheHermestestreactor.KPFHRPDC32,"Inspectionofthereactorcoolantboundary,"describes requirementstoinspectportionsofthereactorcoolantboundary.ThebasisforthisPDCstatesthat "thepotentialforflowblockages/restrictionfromfailedinternals(suchasgraphitereflectorblocks) isaddressedaspartofcompliancewithPDC35,36,and37,includinginspectionsifappropriate."This indicatesthattherequirementsofPDCs35,36,and37areapplicabletovesselinternalsaswellas othercomponentsintheresidualheatremovalsystem.PDC36statesthat"[t]hepassiveresidual heatremovalsystemshallbedesignedtopermitappropriateperiodicinspectionofimportant componentstoensureintegrityandcapabilityofthesystem."

HermesPSAR,Section4.3,"ReactorVesselSystem,"describesSSCswhichareneededtomaintainthe passiveresidualheatremovalpath.Thispathwayisessentialtoensureadequatecoolingduring postulatedeventswheretheprimaryheattransportandprimaryheatrejectionsystemsarenot available.Assuch,itisvitalthatadequatemeasuresbeavailabletoassurethatthenatural circulationflowpathwillbeavailableifcalleduponinapostulatedevent.Section4.3.3,"System Evaluation,"ofthePSARdescribeshowthecomponentsinthereactorvesselsystemmeetspecific PDCs.However,itdoesnotdescribehowcertaincomponentsmeetPDC36.Basedoninformation discussedduringtheGeneralAudit,thestaffunderstandsthatthevesselheadwillhavefour inspectionportsandthatKairoshasproposedtoconfirmthecapabilityoftheflowpathduring operationbymonitoringtemperatureandflow.Thestaffhasthefollowingquestions:

1. Provideadetaildrawingofthenaturalflowpathintheregionsabovethecore.
2. Itappearsthatapotentialfailureofgraphitereflectorblocks(e.g.,debris,geometrychanges, etc.)couldcauseflowblockagesorrestrictionsofthenaturalcirculationflowpath.Where cantheflowpathbeinspectedversuswherewoulditneedtobeverifiedwithflowand temperaturemonitoring?Canallofthenaturalcirculationflowpaththatisntpartofforced circulationflowpathbeinspected?
3. Willflowandtemperaturemonitoringbeusedtoverifythefunctionalityoftherelatively stagnantnaturalcirculationflowpathduringnormal(pumped)operation?Willflowand temperaturemonitoringidentifythecauseofanoffnormalconditionandthelocationof potentialissueswithSSCs?Ifso,pleasedescribehowthesewillbeaccomplished.
4. ProvidethenumberoffluidicdiodesintheHermesdesign.Inthecaseoffailureofoneor morefluidicdiodes,howmanyareneededforadequatepassiveheatremoval?

Page2of5 KairosPowerResponse NRCQuestion399,Item1

Provideadetaildrawingofthenaturalflowpathintheregionsabovethecore.

Figure1(providedwiththisresponse)showsthenaturalcirculationflowpathinthegraphite structuresabovethecore.

NRCQuestion399,Item2

Itappearsthatapotentialfailureofgraphitereflectorblocks(e.g.,debris,geometrychanges,etc.)

couldcauseflowblockagesorrestrictionsofthenaturalcirculationflowpath.Wherecantheflow pathbeinspectedversuswherewoulditneedtobeverifiedwithflowandtemperaturemonitoring?

Canallofthenaturalcirculationflowpaththatisntpartofforcedcirculationflowpathbe inspected?

Thephysicalgeometryofthereactorcoolantnaturalcirculationflowpathwithinthereactorvessel consistsofthefollowing:thedowncomer,thevesselbottomplenumformedbythereflector supportstructure,graphitereflectorblocks,andthefluidicdiodes.Thedowncomer,reflector supportstructure,graphitereflector,andfluidicdiodearedesignedtomaintaintheirstructural integrityduringpostulatedeventstomaintainanaturalcirculationpathandcoolablecoregeometry tosupportremovalofdecayheat.Functionalcapabilityofthedowncomerandgraphitereflectoris assuredbydesignbecausethereactorvesselinternalsarequalifiedinaccordancewithReference1 andReference2.Thevesselandinternalsarealsodesignedtoperformtheirfunctionduringseismic eventsperReference3.

Thedowncomer,asdescribedinSection4.3.1.2.2,isanannularcoolantflowpathwaybetweenthe vesselandthecorebarrel.Flowfromthedowncomermovesthroughthereflectorsupportstructure andintothereflectorblockcoolantinletchannels.Thegraphitereflectorblockstructuresare machinedtoformaphysicalgeometryforreactorcoolanttopassthroughasdescribedinSection 4.3.1.2.1ofthePreliminarySafetyAnalysisReport(PSAR).Thephysicalgeometrycreatedwithinthe graphitestructuresthatformthereactorcoolantnaturalcirculationflowpathincludesthecore, coolantchannels,annularhotwell,anddiodepathway.Thisnaturalcirculationflowpathisclarified inFigure1,aswellastheattachedchangestoPSARSection4.3.1.2.1,Section4.3.3,Figure4.31and Figure4.61.

Duringnormal(pumped)operation,asmallamountofflowbypassesthepebblebedthroughthe graphitereflectorstructures,diodepathway,andfluidicdiode.Changesinbypassflowthroughthe fluidicdiodeduringnormaloperationareinferredbytemperaturemonitoring.Thetemperature monitoringacrossthefluidicdiodeprovidesassurancethatflowisnotstagnantinthisportionofthe naturalcirculationflowpath.

Failuresofinternalgraphitecomponents,includingfuelpebbles,arenotlikelyduringnormalplant operationorpostulatedevents.Thepebblehandlingandstoragesystem(PHSS),describedin Section9.3.1.5ofthePSAR,isdesignedtoinspectpebblestopreventdamagedpebblesfrom enteringthereactor.ThePHSSisalsodesignedtoremovebuoyantdebrisandfilterdebriscarrying coolantasdescribedinSection9.3.1.2ofthePSAR.Asstatedabove,thegraphitereflectorsare qualifiedinaccordancewithReference1,thereforegrossstructuraldamagetothereflectorblocksis precludedbydesign.FuelpebblesarequalifiedinaccordancewithReference4,thereforegross

Page3of5 failureofpebblesthatwillresultinlargedebris,isprecludedbydesign.Theonlygraphitedebris presentinthesystemwouldbearesultofnormalwear(e.g.,graphitedust).

Mostofthenaturalcirculationflowpathisthesameasthenormalflowpathandsignificantflow obstructionswouldbenoticeableduringnormal(pumped)operations.Portionsofthepathwaythat areuniquetonaturalcirculationincludethefluidicdiodepathwayandfluidicdiode.Thefluidic diodemaybevisuallyinspectedusinginspectionportsonthereactorvesselhead.Althoughthe diodepathwaycannotbevisuallyinspected,reactorcoolanttemperatureismonitored.Reactor coolanttemperaturemonitoringprovidesanindicationofflowthroughtheflowpathwayduring normaloperationandprovidesassurancethatthenaturalcirculationflowpathwayisavailable.

Directflowmonitoringcapabilityisnotincludedinthedesigntoassesstheconditionofthenatural circulationflowpath.PSARSection4.3.1,4.3.2,Section4.3.3,Table4.31,Figure4.31,andFigure 4.32havebeenupdatedtoreflectthecapabilityforfluidicdiodepathwaymonitoringandfluidic diodeinspections.

NRCQuestion399,Item3

Willflowandtemperaturemonitoringbeusedtoverifythefunctionalityoftherelativelystagnant naturalcirculationflowpathduringnormal(pumped)operation?Willflowandtemperature monitoringidentifythecauseofanoffnormalconditionandthelocationofpotentialissueswith SSCs?Ifso,pleasedescribehowthesewillbeaccomplished.

Muchofthenaturalcirculationflowpathisthesameasthenormalcirculationflowpathandflowis notconsideredrelativelystagnant.AsdiscussedintheresponsetoItem2,thebypassflowthrough thefluidicdiodepathway,fluidicdiode,andgraphitestructuresprovidesassurancethatflowisnot stagnantinthenaturalcirculationflowpath.Althoughflowmonitoringwillnotbeusedtoverify functionalityofthenaturalcirculationflowpathduringnormal(pumped)operation,temperature monitoringisusedtoconfirmflowisoccurringintheseareasanddemonstratesthefunctional capabilityofthenaturalcirculationflowpathduringnormal(pumped)operationasdescribedinthe responsetoItem2.

Temperaturemonitoringwillnotidentifythepotentialcausesofanoffnormalcondition.However, temperaturemonitoringcanbeusedtoidentifythelocationofpotentialissuesbydetecting unexpectedchangesinplantparametersascomparedtoexpectedvalues.

NRCQuestion399,Item4

ProvidethenumberoffluidicdiodesintheHermesdesign.Inthecaseoffailureofoneormorefluidic diodes,howmanyareneededforadequatepassiveheatremoval?

TheHermesdesignincludesfourfluidicdiodes.Preliminaryanalyseshavebeenperformedandshow thattheHermesdesigncontainsadequateheatremovalwithatleast25%reductionintotaldiode flowpatharea,whichwouldindicatethatthefailureofonediodewouldstillallowadequateflowfor heatremovalwithmargin.Section4.3.1.2.1ofthePSARhasbeenupdatedtoreflectthenumberof fluidicdiodesintheHermesdesignasshownintheattachedmarkup.

References:

1. KairosPowerLLC,GraphiteMaterialQualificationfortheKairosPowerFluorideSaltCooled HighTemperatureReactor,KPTR014P,Revision3.

Page4of5

2. KairosPowerLLC,MetallicMaterialsQualificationfortheKairosPowerFluorideSaltCooled HighTemperatureReactor,KPTR013P,Revision3
3. ASCE4319,SeismicDesignCriteriaforStructures,Systems,andComponentsinNuclear Facilities.
4. KairosPowerLLC,FuelQualificationMethodologyfortheKairosPowerFluorideSaltCooled HighTemperatureReactor(KPFHR),KPTR011P,Revision2 ImpactonLicensingDocument:

ThisresponseimpactsSections4.3.1,4.3.1.1.1,4.3.1.2.1,4.3.2,4.3.3,4.3.5,4.6.1.2,4.6.3,Table4.3 1,Figure4.31,Figure4.32,andFigure4.61oftheKairosPowerPreliminarySafetyAnalysisReport.

Amarkupoftheaffectedsectionsisprovidedwiththisresponse.

Page5of5

Figure1

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 9.1.4 PDC34,Residualheatremoval 4.3,4.6,6.3 PDC35,Passiveresidualheatremoval 4.3,4.6,6.3 PDC36,Inspectionofpassiveresidualheatremovalsystem 4.3,6.3 PDC37,Testingofpassiveresidualheatremovalsystem 4.3,6.3 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 428 4.3 REACTORVESSELSYSTEM 4.3.1 Description Thissectionprovidesanoverviewofthereactorvesselsystem(seeFigure4.31)whichincludesthe reactorvesselandthereactorvesselinternals.Thereactorvesselformsamajorelementofthereactor coolantboundaryandtheinertgasboundary.Thereactorvesselandvesselinternalsdefinetheflow pathforreactorcoolantandfuelintothecore.Thereactorvesselsystemcontainsthereactorcoreand providesforcirculationofreactorcoolantandpebblesaswellasinsertionofthereactivitycontroland shutdownelementsthroughthereactorcore.

Thereactorvesselsystemprovidesaflowpathforreactorcoolanttotransferheatfromthereactorcore totheprimaryheattransportsystem(PHTS)duringnormaloperations.Thereactorcoolantentersthe reactorvesselthroughtwosideinletnozzlesandflowsdownwardthroughadowncomerannulus formedbetweenthemetalliccorebarrelandthereactorvesselshell.Coolantflowmovesthroughthe vesselbottomplenumformedbythereflectorsupportstructureandisdistributedintothecorebythe designofthereflectorblocks.Uponexitingthecore,thecoolantleavesthereactorvesselviathe primarysaltpump(PSP)(seeSection5.1.1)whichdrawssuctiondirectlyfromapoolofreactorcoolant abovethecoreandinsidethevessel.Anantisiphonfeatureisprovidedtolimitlossofvesselinventory intheeventofabreakinthePHTS.

Thereactorvesselsystemalsoprovidesaflowpathforpebblestoallowonlinerefuelinganddefueling ofthereactorcorebythepebblehandlingandstoragesystem(PHSS)(Section9.3)duringnormal operation.ThePHSSinsertspebblesintothereactorvesselanddeliversthemtothefuelingchutebelow thereactorcorebythepebbleinsertionline(Section9.3.1).Thebuoyantpebblesfloatupward,and pebblesinsertedviatheinsertionlinewilljointhepackedpebblebedinthereactorcore.Upon circulatingthroughthecore,thepebblesaccumulateinthedefuelingchuteatthetopofthereactor core.Thepebbleextractionmachine(PEM)(Section9.3.1)atthetopofthereactorcoreremoves pebblesfromthereactorvessel(seeFigure4.32.)

DuringpostulatedeventswhenthePHTSandtheprimaryheatrejectionsystem(PHRS)arenot available,thereactorvesselprovidesanalternativeflowpathasdiscussedinSection4.6.1toallow naturalcirculationofthereactorcoolanttoremoveheatfromthereactorcore.Thereactorcoolant leavingthecoreflowsintothehotwell,fluidicdiodepathway,fluidicdiode,throughacorebarrel penetrationandbackintothedowncomerannulusasshowninFigure4.31viafluidicdiodes.Theheat fromthecoreistransferredtothereactorvesselshellwhichtransferstheheattothedecayheat removalsystem(DHRS)(Section6.3).

Thereactorvesselsysteminterfaceswithfuel(Section4.2.1),primaryheattransportsystem(PHTS)

(Section5.1),reactivitycontrolandshutdownsystem(RCSS)(Section4.2.2),reactorvesselsupport system(RVSS)(Section4.7),decayheatremovalsystem(DHRS)(Section6.3),pebblehandlingand storagesystem(PHSS)(Section9.3),reactorthermalmanagementsystem(RTMS)(Section9.1.5),inert gassystem(IGS)(Section9.1.2),inventorymanagementsystem(IMS)(Section9.1.4),and instrumentationandcontrols(Chapter7).

4.3.1.1 ReactorVessel Thereactorvesselisaverticalcylinderdesignwithflattopandbottomheads.Thevesselhousesthe reactorvesselinternals.Thereactorvesselshellandbottomheadprovideamajorelementofthe reactorcoolantboundary.Thevesselisconstructedof316Hstainlesssteel(SS)withER1682weld metalandisdesignedandfabricatedperASMEBPVCSectionIII,Division5(Reference1).Itcontainsthe inventoryofreactorcoolantsuchthatthereactorcoreiscoveredbythecoolantduringnormal

PreliminarySafetyAnalysisReport

ReactorDescription

KairosPowerHermesReactor

Revision0 429 operationandpostulatedevent.Therearenopenetrationsorattachmentstothevesselbelowthe 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.

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.Thebottomreflectorblocksare machinedwithcoolantinletchannelsfordistributionofcoolantinletflowintothecore.Thetop reflectorblocksaremachinedwithcoolantoutletchannelstodirectthecoolantexitingfromthecore intotheupperplenum,whichincludesthehotwell,andthePSPpumpwell,fromwhichthePSPdraws suction.Thetopreflectorblocksalsoformapebbledefuelingchute,asshowninFigure4.31,todirect thepebblesfromthecoretothepebbleextractionmachine(PEM),allowingonlinedefuelingofthe

PreliminarySafetyAnalysisReport

ReactorDescription

KairosPowerHermesReactor

Revision0 430 reactor(seeSection9.3).Thereflectorblocksalsoprovidemachinedchannelsforinsertionand withdrawalofthereactivitycontrolandshutdownelementsdescribedinSection4.2.2.

Thereflectorblocksformanupperplenumandahotwellandpathwaystoeachoffourfluidicdiodes.,

whichThefluidicdiodesisaarestainlesssteelpassivedevicesthatconnectstheupperplenumhotwell viathepathwaytothetopofthedowncomerviaapenetrationinthecorebarrelasshowninFigure4.3 1.Thediodeintroducesahigherflowresistanceinonedirection,whilehavingalowerflowresistancein theotherdirection.Thedioderestrictsflowfromthehigherpressuredowncomerintotheupper plenumhotwellduringnormalplantoperatingconditionswithforced(pumped)circulation.During naturalcirculation,tTheflowpassesinthelowresistancedirectionofthediodefromtheupper plenumhotwelltothetopofthedowncomerdrivenbynaturalcirculation.Nozzlesonthereactorvessel headanddiodeinspectionchannelsintheupperreflectorblockstructureareusedtoperformremote visualinspectionsofthefluidicdiodes.

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.

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

ConsistentwithPDC31,thereactorvesselhassufficientmargintowithstandstressesunderoperating, maintenance,testing,andpostulatedeventssuchthatthereactorcoolantboundarydoesnotdegrade

PreliminarySafetyAnalysisReport

ReactorDescription

KairosPowerHermesReactor

Revision0 431 duetotheeffectsofneutronembrittlement,corrosion,materialwear,fatigue,stressrupture,thermal loads,orfailureduetostressruptureandfracture.Thedesignshallaccountforresidual,steadystate, andtransientstressesandconsiderflawsize.

ConsistentwithPDC32,thereactorvesselpermitsinspection,monitoring,orfunctionaltestingof importantareasandfeaturestoassessstructuralintegrityandleaktightnessofthesafetyrelated portionsofthereactorcoolantboundary.

ConsistentwithPDC34,theflowpathestablishedbythereactorvesselinternalsisdesignedtosupport theremovalofdecayheatduringnormaloperationandpostulatedevents,suchthatSARRDLsandthe designconditionsofthesafetyrelatedelementsofthereactorcoolantboundaryarenotexceeded.

ConsistentwithPDC35,thereactorvesselinternalsaredesignedtomaintainstructuralintegritytowill assuresufficientcorecoolingduringpostulatedeventsandtosupportremovaloferesidualdecayheat.

Thesafetyfunctionofthefluidicdiode,reflectorblocks,anddowncomeristoprovidemaintainaflow pathviathatsupportsnaturalcirculationtoandtransferheatfromthereactorcoreduringand followingpostulatedeventssuchthattopreventfuelandreactorinternalstructuredamagethatcould interferewithcontinuedeffectivecorecoolingisprevented.

ConsistentwithPDC36andPDC37thefluidicdiodesaredesignedtopermitperiodicmonitoringand inspectiontoprovideassurancethattheintegrityofthenaturalcirculationflowpathfordecayheat removalismaintained.Thedesignofthedecayheatremovalnaturalcirculationflowpathprovidedby thedowncomer,graphitereflector,hotwell,diodepathwayandfluidicdiode,isalsocapableofbeing periodicallyconfirmedtoprovideassurancethattheintegrityofthenaturalcirculationflowpathfor decayheatremovalismaintained.

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

PreliminarySafetyAnalysisReport

ReactorDescription

KairosPowerHermesReactor

Revision0 433 testing.TheRVSSreactorvesselbottomheadinterfaceisdesignedtoallowaccessforweldinspections.

Thereactorvesseltopheadsupportsinserviceinspectionofattachmentsandpenetrations.

Thereactorvesselshellandbottomheadmaintainacoolantpathwayforcoolingthereactorcoreand ensuresubmergenceoffuelpebblesinthecore.Thereactorvesselisfabricated,erected,andtestedin accordancewithReference1asaClassAcomponenttoaccountforthermalandphysicalstressesduring normaloperationandpostulatedevents.Thevesselisfabricatedfrom316HSSbasemetalandER1682 weldmetalusingagastungstenarcweldingprocess.Reference1providesforweldmentstressrupture 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.

Thereactorvesselinternalssupportdecayheatremovalduringnormaloperationsbyestablishingthe physicalgeometryforthecoolantflowpath.Duringnormaloperations,thereactorvesselinternal structuresactinconjunctionwithforcedflowinthePHTStoensurethetransferandrejectionofheat fromthecoreviathecoolantflowpath.Whenpassivedecayheatremovalisrequiredinresponseto postulatedevents,thephysicalgeometryandstructureofthereactorvesselinternalsprovidesa pathwayforcontinuousnaturalcirculationofcoolantviaflowthroughthefluidicdiodes.Thesefeatures demonstrateconformancetoPDC34.

Thedowncomer,graphitereflector,hotwell,fluidicdiodepathwayandfFluidicdiodesareusedto establishaflowpathforcontinuousnaturalcirculationofcoolantinthecoreduringpostulatedevents toremoveresidualdecayheatfromthereactorcoretothevesselwall.Duringandfollowinga postulatedevent,thehotcoolantfromthecoreflowsfromtheupperplenumhotwellthroughthediode pathway,thelowflowresistancedirectionofthefluidicdiode,tothecoolerdowncomervianatural circulation.,therebycoolingTthecoreistherebycooledpassively.Continuouscoolantflowthroughthe reactorcorepreventspotentialdamagetothevesselinternalsduetooverheatingtherebyensuringthe coolablegeometryofthecoreismaintained.Theantisiphonfeaturesalsolimitsthelossofreactor coolantinventoryfrominsidethereactorvesselintheeventofaPHTSbreach.Thesefeatures

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Revision0 434 demonstratecompliancewithPDC35.AdditionalfunctionsperformedbytheDHRStosupportpassive decayheatremovalaredescribedinSection6.3.

Thedowncomer,graphitereflectorblocks,andfluidicdiodesarepassivecomponentsdesignedto maintainstructuralintegrityduringpostulatedeventstomaintainanaturalcirculationpathanda coolablecoregeometryforremovalofdecayheat.Thereactorvesselinternalsarequalifiedin accordancewithReference3andReference4andaredesignedtoperformtheirfunctionduringseismic eventsasnotedabove.Basedonthedesignandqualification,therearenocrediblefailuremechanisms withinthedesignbasisofthecorebarrelandthegraphitestructuresthatresultinalossofstructural integrity.Therefore,degradationofthenaturalcirculationflowpathrequiredtosupportdecayheat removalisnotexpectedduringnormalorpostulatedeventsandsuchfailureswouldbebeyondthe designbasis.However,graphitedustisexpectedtobepresentinsmallquantitiesinthesystemand couldbepostulatedtoaccumulateinportionsofthereactorcoolantpathway.Thefunctionalcapability ofthenormalflowpathcanbeperiodicallyconfirmedduringoperationbymonitoringtemperature changestotheexitfromthereactorvessel.Similarly,theportionsofthereactorcoolantflowpaththat areuniquetonaturalcirculation(diodepathwayandfluidicdiode)arecapableofbeingconfirmed duringnormaloperationsviatemperaturechangesacrossthediodeandacrossthepathway.

Additionally,thefluidicdiodesaredesignedtopermitperiodicremoteinspectionsviapenetrationson thevesseltopheadtoensurethepathwayremainsunobstructed.Thesefeaturesandcapabilities demonstrateconformancetoPDC36andPDC37.AdditionalfunctionsperformedbytheDHRSto supportpassivedecayheatremovalaredescribedinSection6.3.

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.

4.3.4 TestingandInspection Thereactorvesselandinternalswillbeincludedinaninserviceinspectionprogramwhichwillbe submittedatthetimeoftheOperatingLicenseApplication.

4.3.5 References

1. ASMEBoiler&PressureVesselCode,SectionIII,Division5(2019)
2. ASCE4319,SeismicDesignCriteriaforStructures,Systems,andComponentsinNuclearFacilities.
3. KairosPower,LLC,MetallicMaterialsQualificationfortheKairosPowerFluorideSaltCooledHigh TemperatureReactor,KPTR013P,Revision31.
4. KairosPower,LLC,GraphiteMaterialQualificationfortheKairosPowerFluorideSaltCooledHigh TemperatureReactor,KPTR014P,Revision31.

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Revision0 435 Table4.31:ReactorVesselTopHeadPenetrations NameofPenetration NumberofPenetrations System PebbleExtractionMachine(PEM) 1 PHSS PebbleInsertion 2

PHSS ReactivityShutdownElement 3

RCSS ReactivityControlElement 4

RCSS PrimarySaltPump(PSP) 1 PHTS CoolantFill/DrainLine 2

IMS InertGasLine 2

IGS MaterialSurveillanceSystem 1

MSS NeutronSource 1

RSS SourceRangeNeutronDetector 3

RSS ReserveInstrumentation 3

I&C ReactorCoolantLevelSensor 4

I&C ReactorCoolantThermocouple 3

I&C GraphiteThermocouple 2

I&C FluidicDiodeInspectionNozzle 4

I&C

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Revision0 438 Figure4.32:ReactorVesselTopHeadDesign

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Revision0 455 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).

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 reactorvesselshellasshowninthenormal,pumpedflowpathwayonFigure4.61,part(a).Thecoolant isdistributedalongthevesselbottomheadthroughthereflectorsupportstructure,upthroughcoolant inletchannelsinthereflectorblocksandthefuelingchuteandintothecorewithaportionofthe coolantbypassingthecoreviagapsbetweenthereflectorblocks,thefluidicdiodepathwayandthe fluidicdiode.Thecoolanttransfersheatfromfuelpebbleswhicharebuoyantinthecoolantand providescoolingtothereflectorblocksandthecontrolelementsviaengineeredbypassflow.Coolant travelsoutoftheactivecorethroughtheupperplenumviathecoolantoutletchannelsandexitsthe reactorvesselviathePHTSoutlet.Themaximumvesselexitnominalcoreoutlettemperatureis620°C anddependentontheamountofcorrespondingbypassflowthroughthereflectorblocks.

DuringpostulatedeventswherethenormalheatremovalpaththroughthePHTSisnolongeravailable, includingwhenthePHTSisdrained,afluidicdiode(seeSection4.3),isusedtocreateanalternate, naturalcirculationflowpath.Duringsuchevents,forcedflowfromtheprimarysaltpump(PSP)isalso notavailable.Thefluidicdiodethendirectsflowfromthehotwellandtothedowncomerdiodepathway throughthecorebarrelandintothedowncomerasshowninthenaturalcirculationflowpathwayon Figure4.61,part(b).Thisopensthepathforcontinuousflowvianaturalcirculation.Duringnormal operation,whilethePSPisinoperation,thefluidicdiodeminimizesreverseflow.

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Revision0 456 4.6.2 DesignBasis ConsistentwithPDC10,thethermalhydraulicdesignprovidesadequatetransferofheatfromthefuel tothecoolanttoensurethatthespecifiedacceptablesystemradionuclidereleasedesignlimits (SARRDLs)willnotbeexceededduringnormaloperationandunplannedtransients.

ConsistentwithPDC12,thethermalhydraulicdesignofthereactorsystemensuresthatpower oscillationsthatcanresultinconditionsexceedingSARRDLsarenotpossibleorcanbereliablyand readilydetectedandsuppressed.

ConsistentwithPDC34,thethermalhydraulicdesignremovesresidualheatduringnormaloperation andanticipatedtransients,suchthatSARRDLsandthedesignconditionsofthesafetyrelatedelements ofthereactorcoolantboundaryarenotexceeded.

ConsistentwithPDC35,thereactortransfersheatfromthereactorcoreduringanticipatedtransients suchthatfuelandreactorinternalstructuredamagethatcouldinterferewithcontinuedeffectivecore coolingisprevented.

4.6.3 SystemEvaluation Thereactorcoreandheatremovalsystemsassociatedwiththethermalhydraulicdesignofthereactor systemhaveappropriatemargintoensurethatSARRDLsarenotexceededduringanycondition.The heightofthecore(e.g.,heightofthedowncomer)andtheaxialdecayheatprofile(e.g.,the temperaturedifferencebetweenthehotlegandthecoldleg)ensurethereissufficientdrivingforceto enablenaturalcirculationintheeventofalossofforcedcirculation.Pressurelossesarealsominimized bydesigntoensurethatheatistransferredfromthecoolantinthedowncomerbelowthefluidicdiode tothevesselshellduringalossofforcedcirculationevent.Duetobuoyancyforces,hotfluidcomingout fromthefluidicdiodepathintothedowncomerwillflowdownwardasaplume,whichenhancesheat removalfromthevesselshellabovetheelevationofthefluidicdiode.Asummaryofpertinentthermal hydraulicparametersisprovidedinTable4.61.Thesefeaturesandanalysesdemonstrateconformance toPDC10withrespecttothermalhydraulicdesign.

Thethermalhydraulicdesignofthereactorsysteminherentlyprohibitsinstabilityphenomenathat couldexceedSARRDLs.Thereactoriskeptatatmosphericpressure;thecoolantinthecoredoesnot experiencetwophaseflowandhasahighthermalinertiamakingthereactorrestrictivetocorewide thermalhydraulicinstabilityevents.ThisdemonstratescompliancewithPDC12withrespecttothe thermalhydraulicdesign.Theresultsofanalysessupportingtheinherentstabilityofthereactorwillbe providedwiththeapplicationforanOperatingLicense.

Thethermalhydraulicdesignofthereactorsystemprovidesresidualheatremovalduringnormal operations,includingstartupandshutdown.Duringnormaloperations,thethermalhydraulicdesignof thereactorinconjunctionwithforcedflowinthePHTSandPHRSensuresthetransferandrejectionof heatfromthecoreviathecoolantflowpathasdescribedinSection4.6.1.2.Therelationshipbetween powerandflowofthethermalhydraulicsystemaswellasthethermalinertiaofthecoolantensures thatheattransfercanbeachievedataratethatmaintainsthedesignconditionsofthecore.These featuresdemonstrateconformancetoPDC34withrespecttothermalhydraulicdesign.

Thethermalhydraulicdesignofthereactorsupportspassiveresidualheatremovalfollowingpostulated events.Thedesignofthereactorhotwell,downcomer,reflectorblocksandthefluidicdiodeprovidea pathforcontinuousflowtoensuredecayheatistransferredvianaturalcirculationfromthecoretothe reactorvesselshell,asdescribedinSection4.6.1.2.Thesefeatures,inpart,demonstratecompliance withPDC35.ResidualheatisremovedfromthevesselwallbytheDHRSasdescribedinSection6.3.

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