ML22062B686

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Enclosure 1: Kairos Power Response to NRC Question Q14
ML22062B686
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Issue date: 03/03/2022
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Office of Nuclear Reactor Regulation
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ML22062B684 List:
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KP‐NRC‐2203‐002
Download: ML22062B686 (19)
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Enclosure1

Kairos PowerResponsetoNRCQuestionQ14

(NonProprietary)

Question#2322Q14

QuestionNumber:2322Q14 PSARSection4.3statesTheantisiphonfeaturealsolimitsthelossofreactorcoolantinventory frominsidethereactorvesselincaseofa[primaryheattransportsystem(PHTS)]breach.Describe theantisiphonfeaturethatlimitsthelossofvesselinventoryintheeventofabreakinthePHTS.

Couldaleakinthepipingconnectedtothedefuelingchuteorthepebbleinsertionlineestablisha siphonandresultinalossofcoolantwithinthecore?

KairosPowerResponse:

Designfeaturesarefoundinfluidsystemsconnectedtothereactorvesseltolimitlossofcoolant inventoryintheeventofabreakintheprimaryheattransportsystem(PHTS),theinventory managementsystem(IMS)andthepebblehandlingandstoragesystem(PHSS).PSARSections5.1, 9.1.4,and9.3havebeenclarifiedasshownbelow.ConformingchangeshavebeenmadetoChapter 3and13.

Thecasingdesignoftheprimarysaltpump(PSP)setstheinletelevationoftheantisiphonsurface forthehotlegshouldaleakoccurintheexternalportionofthePHTS.Thisantisiphonfeaturelimits thelossofreactorcoolantinventoryfrominsidethereactorvesselintheeventofaPHTSbreakorin breachesintheIMSpipingconnectedtothePHTS.

TheIMSinterfaceswiththereactorvessel(RV)throughtheRVfill/draintransferlineandtheRV levelmanagementline.Duringnormaloperation,whenthereactorisfueled,theRVfill/drain transferlineisequippedwithpassiveRVisolationfeaturessuchascaps,flangesand/oratransfer linedisconnect,designedtoprecludeinadvertentreactorcoolantdrainingfromtheRVbysiphoning.

DuringRVfill/drainoperations,whenthereactorvesselisdefueled,andtheRVfill/draintransfer lineisconnected,anisolationvalveisusedtointerruptthereactorcoolantflowandacovergasinlet isusedtobreakthesiphoninthetransferlines.TheconfigurationoftheRVlevelmanagementlines shortdiptubeandoverflowweirprecludesinadvertentreactorcoolantdrainingfromtheRVby design.

ThePHSSinterfaceswiththereactorvesselatthePEMandthepebbleinsertionline.Theelevation ofthepebbleextractionmachine(PEM)relativetotheFlibefreesurfaceissuchthatcoolant inventorylossfromthereactorvesselintheeventofbreaksinthePEMwouldbelimited.The pebbleinsertionlineisdesignedwithoverflowprotectioncutoutstodirectanycoolantintheinsert linebackdownintothereactorvessel.Thepebbleinsertionlineisdesignedtolimitinventoryloss suchthatreactorcoolantlevelisnolowerthantheelevationoftheprimarysaltpumpintake,inthe eventofabreakintheinsertionline.

Inpreparationofthisresponse,KairosPowernotedthatSection9.1.4ofthePSARincorrectlycited PDC15asadesignbasis.Figure9.1.41alsoincorrectlyreferencedthePHXwhichwasremovedper LetterKPNRC2202002.Theattachedchangesmakethesecorrections.

References:

None

ImpactonLicensingDocument:

ThisresponseimpactsTables3.13,3.61,andSections4.3,5.1,9.1.4,9.3,and13.1oftheKairos PowerPreliminarySafetyAnalysisReport.Amarkupoftheaffectedsectionsisprovidedwiththis response.

Page1of1 PreliminarySafetyAnalysisReport DesignofStructures,Systems,andComponents

Table3.13:PrincipalDesignCriteria

PrincipalDesignCriteria SARSection PDC1,QualityStandardsandRecords 3.5,4.3,6.3,7.3,7.4,7.5

PDC2,Designbasesforprotectionagainstnaturalphenomena 3.5,4.2.2,4.3,4.7,5.1,6.3,7.3,7.4,7.5, 8.2,8.3,9.1.1,9.1.2,9.1.3,9.1.4, 9.1.5,9.2,9.3,9.4,9.7,9.8.2,9.8.4, 9.8.5,11.2 PDC3,FireProtection 6.3,7.3,7.5,9.3,9.4

PDC4,Environmentalanddynamiceffectsdesignbases 4.2.2,4.3,4.7,6.3,7.3,9.1.2,9.1.4,9.3, 9.7,9.8.29.8.4 PDC5,Sharingofstructures,systems,andcomponents 3.1

PDC10,ReactorDesign 4.2.1,4.3,4.5,4.6,5.1,6.3,7.3

PDC11,ReactorInherentProtection 4.5

PDC12,Suppressionofreactorpoweroscillations 4.5,4.6,5.1

PDC13,InstrumentationandControl 7.2,7.3,7.5,9.1.3

PDC14,ReactorCoolantBoundary 4.3

PDC15,Reactorcoolantsystemdesign 7.3,9.1.4

PDC16,Containmentdesign 4.2.1,5.1

PDC17,ElectricPowersystems 8.2,8.3

PDC18,Inspectionandtestingofelectricpowersystems 8.2,8.3

PDC19,Controlroom 7.4

PDC20,Protectionsystemfunctions 7.3

PDC21,Protectionsystemreliabilityandtestability 7.3,7.5

PDC22,ProtectionSystemIndependence 7.5

PDC23,Protectionsystemfailuremodes 4.2.2,7.3

PDC24,Separationofprotectionandcontrolsystems 7.5

PDC25,Protectionsystemrequirementsforreactivitycontrol 7.3 malfunctions

KairosPowerHermesReactor 36 Revision0 PreliminarySafetyAnalysisReport DesignofStructures,Systems,andComponents

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 5.1,9.1.4,9.3

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 5.1,5.2,9.1.3,9.2,11.2 environment 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

KairosPowerHermesReactor 37 Revision0

PreliminarySafetyAnalysisReport ReactorDescription

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 reflectorsupportstructureandisdistributedintothecorebythedesignofthereflectorblocks.Upon exitingthecore,thecoolantleavesthereactorvesselviatheprimarysaltpump(PSP)(seeSection5.1.1) whichdrawssuctiondirectlyfromapoolofreactorcoolantabovethecoreandinsidethevessel.An antisiphonfeatureisprovidedtolimitlossofvesselinventoryintheeventofabreakinthePHTS.

Designfeaturesareprovidedinfluidsystemsconnectedtothereactorvesseltolimitlossofcoolant inventoryintheeventofabreakinthosesystemsasdescribedinSections5.1,9.1.4,and9.3.

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 leavingthecoreflowsbackintothedowncomerannulusviafluidicdiodes.Theheatfromthecoreis transferredtothereactorvesselshellwhichtransferstheheattothedecayheatremovalsystem(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

KairosPowerHermesReactor Revision0428 PreliminarySafetyAnalysisReport ReactorDescription

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.

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,Revision1.

KairosPowerHermesReactor Revision0433 PreliminarySafetyAnalysisReport HeatTransportSystems

functionalcontainmentandenhancedsafety.Thecirculatingactivityofthereactorcoolantissampled (seeSection9.1.1)toremainwithinlimitsestablishedinthetechnicalspecifications.

5.1.1.2 PrimarySaltPump ThePSPisavariablespeed,cartridgestylepumplocatedonthereactorvesselheadthatcontrolssystem flowrateandpressureinthePHTSundernormaloperation.ThePSPcirculatesthereactorcoolant betweenthereactorcore,wheretheFlibeisheatedasitcontactswiththefuel,andthePHXwherethe heatistransferredtothePHRS.PHTSflowratesarevariedbasedonmaintainingaspecified temperaturechangeacrossthecoreasthermaloutputchangesandmaintainingpositivepressure differentialbetweentheprimaryandintermediatecoolantsinthePHX.ThedesignofthePSPoperates continuouslyatfullthermalpowerflowratesandtemperatures,aswellasatreducedpowerandflow rates.

Thecantileverpumpdesignextendstheshaftdownintothereactorcoolantwhilekeepingthebearings andsealsinalowertemperatureregionabovethecoolant.Thepumpflowdischargeshorizontally abovethereactorvesselheadandhasahighpointventthatisusedforvacuumfill.Thepumphasa positivepressureinertgasspacewithapurgegasflowwhichdischargesintotothereactorvesselcover gasspace.Thepumpmotorrotorisdirectlymountedontheshaftandoperatesinthecovergas environment,eliminatingtheneedforconventionalshaftsealsandprovidingahermeticboundaryfor covergas.TheinertgassystemisdescribedinSection9.1.2.

Thedesignofthepumpsuctioncontrolsandpreventsentrainmentofcovergasatnormalsubmergence levels.ResidualgasinthePHTSatstartupisremovedbydeentrainmentlocationsintheupper reflector.Thepumpcasingdesignsetstheinletelevationoftheantisiphonsurfaceforthehotleg shouldaleakoccurintheexternalportionofthePHTS,andforwhentheexternalPHTSpipingis drained.TheantisiphoningfunctionisdescribedinSection4.3.

5.1.1.3 PrimaryHeatExchanger ThePHXservesastheheattransferinterfaceandcoolantboundarybetweenthePHTSandPHRS.The PHXdoesnotperformanysafetyrelatedfunctions.ThereactorcoolantiscirculatedfromthePSPoutlet nozzlethroughtheprimarypipingbeforeitentersthePHX,wheretheheatistransferredfromthe reactorcoolanttointermediatecoolantonthecoolingside.ThereactorcoolantentersthePHXat approximately600650°CandleavesthePHXatapproximately550°Cduringnormal,steadystate operationatfullpower.Aftertransferringitsheat,thereactorcoolantleavestheoutletnozzleofthe PHXandisreturnedtotheinletnozzleofthereactorvessel.

ThePHXdesignandlocationassuresthatapositivepressuredifferentialismaintainedbetweenthe reactorcoolantandintermediatecoolantunderallnormaloperationandnormaltransientconditions, sothattubeleakageisfromthePHTStothePHRS.ThePHXislocatedatanintermediateelevation betweenthereactorvesselcoolantfreesurfaceandthePHRScoolantfreesurfacetoassurepositive pressuredifferentialduetohydrostaticheadundershutdownconditions.PHTSandPHRSpumpspeeds arecontrolledtomaintainpositivepressuredifferentialunderallnormaloperatingmodes.Apressure differentialmeasurementbetweenthePHXintermediatecoolantinletpressure(highestintermediate coolantpressure)andreactorcoolantoutletpressure(lowestreactorcoolantpressure)monitorsfor positivepressuredifferentialandinitiatestripsofthePHTSandPHRSpumpsifthedifferentialfalls belowapredeterminedlimit.

KairosPowerHermesReactor 52 Revision0 PreliminarySafetyAnalysisReport HeatTransportSystems

5.1.1.4 PrimaryLoopPiping Theprimarylooppipingconsistsoftheinterconnectingpipingandsmallcomponentsnotspecifically allocatedwithintheotherarchitecturalelements.Thisincludescrossconnectionpiping,valves,and interfaceswiththeinventorymanagementsystem.

Theprimarylooppipingdoesnotperformanysafetyrelatedfunctionsandisnotcreditedtomitigate theconsequencesofpostulatedevents.

ThePHTSpipingisdesignedtotheASMEB31.3Codeandaccommodatesthereactorcoolant temperature,pressure,andcorrosionproperties.ThesectionofpipingfromthePSPdischargetothe PHXinletsistermedthehotlegandthesectionofpipingfromthePHXoutletstothereactorvessel inletistermedthecoldleg.Anantisiphonfeatureisimplementedinthedesignthatcanbreakthe siphonfromthereactorvesselifaleakinthePHTSoccurs.ThisfeatureisdiscussedinSection4.3.

5.1.1.5 PrimaryLoopAuxiliaryHeating TheauxiliaryheatingfunctionprovidesnonnuclearheatingtothePHTSasneededforvarious operationsincludinginitialcoolantmelt,plantstartupandshutdown,andsupplementalheatingduring normaloperation.AuxiliaryheatingmaintainsthePHTSpipingandPHXabovethetraceheatingsetpoint temperature.Thesourceoftheheatdependsonthesubsystemorcomponentrequiringtheheat.For example,electricalheatingisusedinsomeareasoftheplantthatwouldbesusceptibletocoolant freezingwiththeuseofinsulationalone.Sufficientheatingisprovidedtomaintainreactorcoolant temperatureinexternalpipingandPHXabovefreezingthroughoutthefilling,operation,anddraining processes.

5.1.1.6 NormalShutdownCooling ThePHTSprovidesnormalshutdowncoolingfollowingplanttrips.Thetransitionfrompoweroperation tonormalshutdowncoolinginvolvesaprogramedrundownofthePSPandintermediatesaltpump speeds,tominimizethethermaltransientexperiencedbythereactorvesselandPHTS.Normal shutdowncoolingusesthePHRSastheheatsink.

5.1.2 DesignBasis ConsistentwithPDC2,thesafetyrelatedSSCslocatednearthePHTSareprotectedfromtheadverse effectsofpostulatedPHTSfailuresduringadesignbasisearthquake.

ConsistentwithPDC10,thedesignofthereactorcoolantsupportstheassurancethatspecified acceptablesystemradionuclidereleasedesignlimits(SARRDLs)arenotexceededduringanycondition ofnormaloperation,aswellasduringanyunplannedtransients.

ConsistentwithPDC12,thedesignofthereactorcoolant,inpart,ensuresthatpoweroscillations cannotresultinconditionsexceedingspecifiedacceptableSARRDLs.

ConsistentwithPDC16,thedesignofthereactorcoolant,inpart,providesameanstocontrolthe releaseofradioactivematerialstotheenvironmentduringpostulatedeventsaspartofthefunctional containmentdesign.

ConsistentwithPDC33,thedesignofthePHTSincludesantisiphonfeaturestomaintainreactorcoolant inventoryintheeventofbreaksinthesystem.

ConsistentwithPDC60,thedesignofthePHTSsupportsthecontrolofradioactivematerialsduring normalreactoroperation.

KairosPowerHermesReactor 53 Revision0 PreliminarySafetyAnalysisReport HeatTransportSystems

Consistentwith10CFR20.1406,thedesignofthePHTS,totheextentpracticable,minimizes contaminationofthefacilityandtheenvironment,andfacilitateeventualdecommissioning.

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.Thisantisiphonfeaturelimitsthelossofreactorcoolant inventoryfrominsidethereactorvesselintheeventofaPHTSbreachorinbreachesofinventory managementsystempipingconnectedtothePHTS(seeSection9.1.4.)Theseantisiphonfeatures demonstratecompliancewithPDC33.

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

KairosPowerHermesReactor 54 Revision0 PreliminarySafetyAnalysisReport AuxiliarySystems

9.1.4.1.2 RVFill/DrainTank TheRVfill/draintankprovidesameansoffillinganddrainingtheRVthroughatransferlineandadip tube.ThetransferintotheRVispumpdrivenandthetransferoutoftheRVisgravitydriven.TheRV fill/draintanktransferlineisequippedwithapassiveRVisolationsystemtopreventunintentional draining,whichisdiscussedinSection9.1.4.3.TheRVfill/draintankissizedtoholdtheRVcoolant inventory.

9.1.4.1.3 PHTSFill/DrainTank ThePHTSfill/draintankprovidesameansoffillinganddrainingthereactorcoolantfromthePHTS(see Section5.1),includingtheprimaryheatexchanger(PHX),throughatransferline.ThePHTSdrainis gravitydrivenandthefillispumpdrivenbetweenthePHTSfill/draintankandthePHTS.

ThePHTSfill/draintankissizedtoholdthePHTSandPHXreactorcoolantinventory.

9.1.4.1.4 SolidIMS Newandusedreactorcoolantisstoredintransfercanistersusedtotransportreactorcoolanttoand fromthesiteinsolidstateatambienttemperature.WithintheIMS,thereactorcoolantistransferred-inliquidform-throughtransferlines,drivenbyacovergaspressuredifferential.ThesolidIMSfunction istomeltnewreactorcoolantinthecanisterspriortoatransferintotheIMSortofreezetheused reactorcoolantinthecanistersfollowingatransferfromtheIMS.Theusedreactorcoolantpresentsa potentialhazardduetoradiologicalcontamination.

ThetransfercanistersareconstructedofstainlesssteelandaredesignedperASMEBPVC,SectionVIII.

Thetransfercanistersaredesignedandfabricatedtomeetthepressure,mechanicalloads,corrosion, andtemperaturerequirementsofthesystem.

9.1.4.2 DesignBases ConsistentwithPDC2,safetyrelatedSSCslocatedneartheIMSareprotectedfromtheadverseeffects ofIMSfailuresduringadesignbasisearthquake.

ConsistentwithPDC4,safetyrelatedSSCslocatedneartheIMSareprotectedfromtheadverseeffects ofIMSfailuresduringdynamicevents.

ConsistentwithPDC15,theIMSisdesignedtoensurethedesignconditionsofthereactorcoolant boundaryssafetyrelatedelementsaremaintainedduringnormalandaccidentconditions.

ConsistentwithPDC33,thedesignoftheIMSincludesdesignfeaturestolimitthesufficientreactor coolantinventoryisprovidedtoprotectagainstalossofreactorvesselcoolantinventoryinthesafety relatedportionsofthereactorcoolantboundaryeventofbreaksinthesystem.

Consistentwith10CFR20.1406,theIMSisdesigned,totheextentpracticable,tominimize contaminationofthefacilityandtheenvironment,andfacilitateeventualdecommissioning.

9.1.4.3 SystemEvaluation TheIMSdoesnotperformsafetyrelatedfunctionsandisnotcreditedforthemitigationofpostulated events.Thesystemisalsonotcreditedforperformingsafeshutdownfunctions.Thesystemisnot creditedtomaintaintheintegrityofthereactorcoolantpressureboundary.

PortionsoftheIMSmaybelocatedinproximitytoSSCswithsafetyrelatedfunctions.Thosesafety relatedSSCsareprotectedfromfailureoftheIMSduringadesignbasisearthquakebyeitherseismically

KairosPowerHermesReactor 916 Revision0 PreliminarySafetyAnalysisReport AuxiliarySystems

mountingtheapplicableIMScomponents,physicalseparation,orbarrierstoprecludeadverse interactions.TheIMSisdesignedtopreferentiallyfailinawaythatdoesnotimpacttheRVsystem.This satisfiesPDC2fortheIMS.

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

TheIMSisdesignedtoprecludetheinadvertentdrainingoftheRVduringnormaloperationandduring RVfill/drainoperations.Duringnormaloperation,whenthereactorvesselisfueled,theRVfill/drain transferlineisequippedwithapassiveRVisolationsystemfeaturessuchascaps,flangesand/ora transferlinedisconnect,designedtoprecludeinadvertentreactorcoolantdrainingfromtheRVby siphoning.IntheeventofaleakintheRVfill/draintransferline,whileconnectedtothereactorvessel duringfueledoperation,thereactorcoolantleakisdetectedbytheplantcontrolsystem,thePSPis tripped,andtheRVcovergaspressureislimitedtoanupperboundthusprecludingtheejectionof reactorcoolantthroughthetransferlinediptube.DuringRVfill/drainoperations,thereactorvesselis defueled,andthefill/drainlineisconnected,anisolationvalveisusedtointerruptthereactorcoolant flowandacovergasinletisusedtobreakthesiphoninthetransferlines.Thesedesignfeaturessatisfy therequirementsofPDC33.

TheRVcoolantlevelmanagementtanklineshortdiptubeandoverflowweirdesignspreclude inadvertentreactorcoolantdrainingfromtheRVintotheRVlevelmanagementtank.Additionally,the overflowlineweirisdesignedinawaythatprecludestheuncoveringoffuelduetothermalexpansion ofthereactorcoolant.IntheeventofaleakintheRVlevelmanagementtankortransferline,the reactorcoolantleakisdetectedbytheplantcontrolsystem,andthepumpforthereactorlevel managementistrippedtominimizetheoverflowofreactorcoolantfromtheRVthroughtheoverflow weir.ThisdesignconfigurationsatisfiestherequirementsofPDC33.

TheIMSencompassesaThePHTSdrainlineis,equippedwithaPHTSdrainvalvewhichinterfaceswith thePHTSfill/draintank.IntheeventofaleakinthePHTSfill/draintankordrainline,thereactorcoolant leakisdetectedbythecontrolsystem,thePSPistripped.WhileaPHTSleakcannotbeprecluded,Tthe PHTSdesigncontainsanRVantisiphonfeature(seeSection4.35.1),thusprecludinginadvertentreactor coolantdrainfromtheRV,.precludingtheIMSfromdrainingtheRV.Thesedesignfeaturessatisfythe requirementsofPDC3315.

ThesafetyrelatedportionsofthereactorcoolantboundaryarelimitedtotheRV(seeSection4.3).

FailuresofotherSSCscontainingreactorcoolant(e.g.,saltspill),donotresultinunacceptable consequencesasdescribedinChapter13.AfailureoftheRVisapreventedevent.Thus,Tthemakeup inventoryfunctionofIMSreactorcoolanttothereactorvesselisnotreliedontomitigatethe consequencesofapostulatedevent.AsdescribedinSection4.3,thesafetyrelatedportionsofthe reactorcoolantboundaryarelimitedtothereactorvesselandafailureofthereactorvesselisprecluded bydesign.Therefore,themakeupfunctionalrequirementsofPDC33havebeenaddressedbydesign.

Thesystemisexpectedtohandlereactorcoolantwithfissionaswellasactivationproducts;therefore, thesystemwillbedesignedtominimizecontaminationandsupporteventualdecommissioning, consistentwiththerequirementsof10CFR20.1406.

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

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Figure9.1.41:InventoryManagementSystem

Figure9.1.41:InventoryManagementSystem

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9.3 PEBBLEHANDLINGANDSTORAGESYSTEM ForfuelpebblesinthePHSStheTRISOfuelparticlesprovideafunctionalcontainmentsuchthat radionuclidesarecontainedwithintheparticle.Thepebblesaredesignedtopreventdamagetothe TRISOfuelparticlesduringnormaloperation,storage,shippingandhandlingthusthefuelparticleis creditedforconfiningradioactivematerialratherthanthepebblematrixmaterial,thehandling equipmentandthestoragesystem.Thefuelpebblescanexperiencethermalandmechanicalloadswhile beinghandled,inspected,operated,andstoredbutsuchloadsarewithinthedesignbasisofthefuel pebbledesign.

9.3.1 Description ThePHSSprovidesforhandlingandstoringfuelandotherpebbles.Thesystemencompassesreceiptand inspectionofnewfuelupondelivery,coreloading,sensing,inspectionandsortingduringdownstream circulation,reinsertion,coreunloading,andremovalandtransfertostorage.

MajorcomponentsandfeaturesofthePHSSincludethepebbleextractionmachine(PEM),debris removal,offheadconveyanceline,pebbleprocessing,pebbleinspection,pebbleinsertion,PHSSinert gasboundary,pebblestorage,andnewpebbleintroduction.Aprocessflowdiagramisprovidedin Figure9.31.

ThePHSSinterfaceswiththereactorvessel(Section4.3),IGS(Section9.1.2),spentfuelcoolingsystem (SFCS)(Section9.8.2),andtheCCWS(Section9.7.3)asshowninFigure9.32.

9.3.1.1 PebbleExtractionMachine ThePEMremovesbuoyantpebbleswhichaccumulateinthereactordefuelingchuteatthetopofthe reactorcoreandroutesthemtowardstheoffheadconveyance.ThePEMiscomprisedofasinglescrew shaftlocatedatthetopofthereactorvesselhead.Asthepebblestraversethescrew,theyareremoved fromthemoltenFlibeandmovedintotheinertgasspace.ThePEMalsoactsasapathwayfordebris removalfromthevesseltothedebrisremovalportionofthesystem.ComponentsinthePEMare cooledbythereactorthermalmanagementsystem(seeSection9.1.5)toprecludeoverheating.The elevationofthePEMrelativetothecoolantlimitscoolantleaksfromthereactorvesselintheeventof breaksinthePEM.

9.3.1.2 DebrisRemoval PebbleorgraphitedebrisremovalisaccomplishedbyextractingFlibeprimarycoolantupthePEMviaa pressuredifferential,transferringdebriscarryingFlibetoafilteringtankthroughadebrispipe,filtering debrisfromthecoolantinanoffheadtank,andreturningfilteredFlibebacktothevesselthroughthe PEM.

9.3.1.3 OffHeadConveyance AnoffheadconveyancelineroutespebblesfromthePEMtoabufferstoragepriortotheprocessing system,locatedoffthereactorheadasshowninFigure9.32.Theoffheadconveyancemechanismisa downwardangledchutewithadiameterthatislargerthanthepebbles.Theoffheadconveyanceline includesdesignfeaturesforremovingdebrisorjamsthatcouldimpedepebblemovement.Thisdesign minimizestheriskofpebblesanddebrisfromjammingtheline,suchthatageometricallysafe configurationismaintainedatalltimes.

9.3.1.4 PebbleProcessing PHSSpebbleprocessingdirectspebblestothecorrectinsertionchannelortoastoragecanisterfor spentfuel,basedonresultsfromtheinspectionsystemviaanautomatedmechanism.Arotatingwheel

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intheprocessingsystemmovespebblesfromtheoffheadconveyancetotheinspectionarea.After inspection,thepebblesaredirectedforreinsertionintothecore,ortopebblestorageforremovalfrom thecirculatingpebbleinventory,basedoninspectionresults.

9.3.1.5 PebbleInspection AnautomatedinspectionsystemprovidesinformationtotheprocessingportionofthePHSSfor determiningpebblehealth.Thisincludesinspectionofthephysicalconditionofthepebblefor unacceptablewearordamage,identifyingmoderatorandfuelpebbles,aswellasanevaluationofthe burnupofthefuelrelativetoamaximumburnuplimitusingtheburnupmeasurementsensor(BUMS).

Theburnupmeasurementisdonebymeansofagammaspectrometer.Furtherdetailspertainingto inspectionsforwearanddamagewillbeprovidedwiththeapplicationforanOperatingLicense.

9.3.1.6 PebbleInsertion Pebblesarereceivedfromtheprocessingsystemandplacedinabufferstorageuntilrequiredfor reinsertion.Thepebblebufferstorageissizedandorientatedtopreventacriticalconfiguration.

Individualpebblesarefedintothestepfeederinsertionmachinefromthispebblebufferstorageas showninFigure9.32.Thepebblesareinsertedintothetopofthereactorvesselhead,thenpushed throughtheinsertionlineandenterthereactorcoreviatheinvesselfuelingchuteatthebottomofthe core(seeSection4.3).Thereisasingleactiveinsertionlineintothevesselandisdesignedwithoverflow protectioncutoutstolimitcoolantlossfromthereactorvesselintheeventtheinsertionlinebreaks.

9.3.1.7 PHSSInertGasBoundary ThecomponentsofthePHSSaredesignedtomaintainaninertgasboundaryoutsideofthereactor vesselforpebblehandling.Thefunctionoftheinertgasenvironmentistopreventabsorptionof moistureandoxygenintopebblesforpebblehandlingduringnormaloperations.Theinertgasboundary withinthePHSS(seeFigure9.32)iscreatedbyamechanicalstructurethatenclosesthe aforementionedcomponentswithpenetrationsformotorshafts,storageoutlets,inspectionviewport, datachannels,electricalpower,andpebblesfromtheoffheadconveyancemechanismandfor insertion.Portionsoftheinertgasboundarythatareadjacenttopersonnelaccessareashavethe appropriateradiationshielding.

9.3.1.8 PebbleStorage Pebblestorageisprovidedforpebbledebris,damagedpebbles,spentfuel,andendoflifemoderator pebbles.Thestorageportionofthesystemiscomposedofastainlesssteelstoragecanisterand transporterdevice.Individualstoragecanistersaresizedtoholdapproximately1,9002,100pebbles.

Thedimensionsofthecanisterandquantityofpebblesaresizedtomaintainanoncriticalconfiguration.

Atransporterdeviceisusedtotransfercanisterstoeitherthespentfuelstorageareaduringnormal operationorthefullcoreoffloadareaintheeventofaperiodicmaintenancefullcoreoffloadoran emergentfullcoreoffload.

9.3.1.8.1 SpentFuelStorage Spentfuelisdischargedfromserviceinthecoreundernormaloperatingconditions,placedinsealed storagecanisters,andmovedtothespentfuelstorageareaasshowninFigure9.32.Theinitialstorage areaisacoolingpooldesignedtoholdspentfuelcanisterswhilethedecayheatofthepebblesdrops.

Thepoolisdesignedtolimitradiationexposuretopersonnel.Aftercoolinginpoolstorage,thecanisters aremovedtoaconcretestoragebaywithradiationshieldingandforcedaircooling.Thepoolisactively cooledbytheCCWSusinganinpoolheatexchanger.WaterisrecirculatedinthepoolbytheSFCSand makeupwaterisprovidedbythetreatedwatersystem(seeSection9.7.2).Thepoolandconcrete

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processisdoneviatwosequentialvalvestopreventintroductionofcontaminantstothePHSSinertgas boundaryornewpebbles.Theinterstitialspacebetweenthevalvesispurgedpriortoopeningofeither valvetolimittheingressofoxygen.

9.3.2 DesignBases ConsistentwithPDC2,thePHSSisdesignedtowithstandtheeffectsofnaturalphenomenawithout exceedingtheoffsitedoseconsequencesoftheMHA,compromisingdecayheatremoval,orcriticalityas aresultofasystemfailureorbreach.

ConsistentwithPDC3,thePHSSisdesignedandlocatedwithinthefacilitytominimizetheprobability anddoseconsequencesoffiresandexplosions.

ConsistentwithPDC4,thePHSSisdesignedtoaccommodateenvironmentalconditionsassociatedwith normaloperation,maintenance,testingandpostulatedevents.

ConsistentwithPDC33,thePHSSisdesignedtolimitthelossofreactorcoolantfromthereactorvessel duetopotentialbreaksinthesystem.

ConsistentwithPDC61,thePHSSisdesignedtopermitperiodicinspectionandtestingandissuitably shieldedforradiationprotection.ThePHSSdesignincludesappropriateconfinementandadequately accountsfordecayheatandareductioninfuelstoragecoolingunderpostulatedevents.

ConsistentwithPDC62,thePHSSisdesignedtopreventcriticality.

ConsistentwithPDC63,thePHSSisdesignedtodetectconditionsthatmayresultinexcessiveradiation levelsandinitiatesappropriatesafetyactions.

Consistentwith10CFR70.24(a)(1),thePHSSdesignincludesamonitoringsystemcapableofdetecting criticality.

Consistentwith10CFR20,thePHSSisdesignedtobeshieldedtosupportworkeroccupationaldose limitsandadheretoaradiationprotectionprogram.

Consistentwith10CFR20.1406,thePHSSisdesigned,totheextentpracticable,tominimize contaminationofthefacilityandtheenvironment,andfacilitateeventualdecommissioning.

9.3.3 SystemEvaluation Theconcretestructuresassociatedwiththestoragebay,pool,andsupportrestraintsinthepoolare designedasSDC3structurestoensurethegeometryofthestorageareaismaintainedtoprecludean inadvertentcriticalityduringadesignbasisearthquake.Thedesignofthesupportrestraintsandstorage bayalsoensuresadequatespacingismaintainedforaircoolingbetweeneachcanister.Duringa postulatedearthquake,thefuelparticlespreventradionucliderelease.Theparticlesaresupportedin theirsafetyfunctionduringapostulatedearthquakebythepoolandbythecanistertransporter,bothof whichprovidepassivecoolingandspacingtorestrictpebblemovementtherebypreventingrecriticality.

OtherportionsofthePHSSthatdonotperformasafetyfunctionaredesignedtobeeitherseismically mountedorphysicallyseparatedtoprecludeadverseinteractionswithothersafetyrelatedSSCsduring adesignbasisearthquake.ThesedesignfeaturessatisfytherequirementsofPDC2.

ThePHSSisdesignedtominimizetheprobabilityofafireorexplosionbylimitingtheaccumulationof potentiallycombustiblematerialsuchasgraphitedustanddebriswithinthesystem.Grindingofpebbles whichcontributetographitedustgenerationisprecludedbysystemdesign.Thesmallamountof graphitedustthatmightbegeneratedisdirectedthroughpebblemotiontothestoragecanistersfor removalfromthesystem.ThePHSSisnotlocatednearnorinterfaceswithpneumaticsystemswiththe

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potentialforairinleakage.Thesystemisfilledwithaninertgasoperatedataslightlypositivepressure tofurtherpreventairingressintheeventofaPHSSbreach.Locationswherepebblesarenotsubmerged incoolant,suchasthePEM,willeithernotexceedtemperaturesthatwouldinduceoxidationofthe 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.ThesedesignfeaturesofthePHSSsatisfytherequirementsinPDC33.

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

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volatileproductsandoxidizesportionsofthestructuralgraphiteabovethesurfaceoftheFlibeandthe carbonmatrixforpebblesintransitabovethesurfaceoftheFlibe.Radionuclidesfromthecoolant circulatingactivityinthebrokenpipearereleasedintothefacilityairwhenaerosolsaregeneratedfrom thecoolantthatexitsthepipe.AllthefloorsurfaceswhereFlibemaybespilledwillhavedesignfeatures suchassteellinerstopreventFlibeconcreteinteraction,asdescribedinSection3.5.ThespilledFlibe spreadsontopofthelinerandformsaFlibepool.RadionuclidesinthespilledFlibeisreleasedthrough evaporationuntilthetopsurfaceoftheFlibepoolissolidified.

Thelimitingsaltspillpostulatedeventboundsothersaltspillevents,including:

Spuriousdrainingandsmallerleaksfromtheprimaryheattransportsystem LeaksfromotherFlibecontainingsystemsandcomponents(e.g.,IMSfill/draintank,IMSpiping, chemistrycontrolsystempiping)

Leaksuptothehypotheticaldoubleendedguillotineprimarysaltpipingbreaksize MechanicalimpactorcollisioneventsinvolvingFlibeContainingSSCs(exceptthevessel)

LeaksfromtheprimaryheatrejectionsystemthatcontainsanonFlibecoolant,whichmaycontain nonzeroamountofFlibefromheatexchangerleaks Thesefollowingsectionsdescribekeyassumptionsassociatedwiththelimitingsaltspillevent.The quantitativevaluesassociatedwiththeseassumptions,aswellasthemethodsusedtoevaluatethe surrogatefiguresofmeritthatensuretheeventconsequencesareboundedbytheMHAareprovidedin Reference2.

13.1.3.1 InitialConditionsAssumptions NormaloperatingparametersareprovidedinSection4.1.Conservativeinitialvaluesareassumedfor eachoperatingparametertoensureaboundingresultforthefiguresofmeritthatdemonstratethe eventisboundedbytheMHA.

AhypotheticaldoubleendedguillotinebreakinthePHTShotlegpipingisassumedastheevent initiator.TheinitialFlibeconditionsarediscussedinSection5.1.

13.1.3.2 StructuresSystemsandComponentsMitigationAssumptions ThissectiondescribestheSSCsperformingafunctiontomitigatetheconsequencesoftheevent.

TheRPSiscreditedwithdetectingthebreakonlowreactorcoolantlevelandinitiatingareactortrip, PSPtrip,ISPtrip,andthePHSStrip.TheDHRSisoperatingwhenthereactorisaboveathresholdpower, asdiscussedinSection6.3,andremainsinanalwaysonmode.TheRPSinitiatesareactortriptoshut downthereactorandlimitstheadditionofheattothesystem.TheRPStripsthePSPlimittheamountof spilledFlibe.TheISPistrippedconcurrentlytoensureapositivepressuredifferentialbetweenthe primaryandintermediateloops.ThePHSStripstopspebbleextractionandinsertionfollowingthe reactortriptoprecludeanydamagetopebblesfromfaultsduringtheevent.TheDHRSremainsactiveto ensurethatanadequateamountofdecayheatisremovedfromthesystem.ThedesignbasesoftheRPS arediscussedinSection7.3.TheRPSdetectionandactuationcapabilitiesareautomaticanddonotrely onmanualoperatoractiontoperformthesefunctions.

TheRCSSiscreditedwithshuttingdownthereactoruponreceivingthereactortripsignal.The shutdownandcontrolelementsareassumedtohavesufficientworthtoshutdownthereactorand maintainlongtermshutdown.ThedesignbasesoftheRCSSshutdownfunctionareprovidedinSection 4.2.2.

TheantisiphondesignfeaturesofthereactorvesselPHTS(seeSection5.1)discussedinSection4.3are creditedwithlimitingtheamountofFlibeavailabletospilloutofthebreak.Thedesignfeaturesbelow

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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.ThePHTSreactorvesselis designedwithantisiphonfeaturesdiscussedinSection4.35.1.Thesefeaturesaredesignedtopassively breakthesiphonintheeventofabreak.ThePSPalsotripstoallowtheprimarysystemtodepressurize.

ThereliabilityoftheRPS,whichtripsthePSPandISPintheeventofasaltspill,isdiscussedinSection 7.3.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 SignificantIntermediateCoolantIngressIntoPHTS Thepostulatedeventsassumeapositivepressuredifferentialbetweentheprimaryandintermediate coolantsystems.EventswheresignificantquantitiesofintermediatecoolantenterthePHTSare excludedfromthedesignbasis.Chapter5discussesthedesignfeaturesofthePHTSandPHRSthat maintainapositivepressuredifferential.

13.1.10.6 DHRSReactorCavityFlooding TheDHRSisawaterbasedsystemthatremovesheatfromthereactorvesselshell.Eventswherethe waterfromtheDHRSleaksintothereactorcavityinquantitiessignificantenoughtowetthereactor

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