ML22095A282
| ML22095A282 | |
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| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 04/05/2022 |
| From: | Kairos Power |
| To: | Office of Nuclear Reactor Regulation |
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| KP-NRC-2204-002 | |
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Text
Enclosure 1 Changes to the PSAR (Non-Proprietary)
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 41 CHAPTER4 REACTORDESCRIPTION 4.1
SUMMARY
DESCRIPTION Thereactorisdesignedwithafunctionalcapabilitytoachievearatedthermalpowerofupto35MWth atamaximumreactorcoolantoutlettemperatureof620650°C.Thenormalreactorinlettemperatureis 550°C.Thereactordesignemploysahightemperaturegraphitematrixcoatedtristructuralisotropic (TRISO)particlefuelandachemicallystable,lowpressuremoltenfluoridesaltcoolant(Flibe).TRISOfuel andFlibeconstitutethefunctionalcontainmentwhichisreliedonasameansofretainingfission productsandpreventingradionuclidereleasetotheenvironmentduringnormaloperationsand postulatedevents.
Thischapterprovidesadescriptionofthereactorwhichincludes:
ReactorCore(Section4.2)
ReactorFuel(Section4.2.1)
ReactivityControlandShutdownSystem(Section4.2.2)
NeutronStartupSource(Section4.2.3)
ReactorVesselandtheReactorVesselInternals(Section4.3)
BiologicalShield(Section4.4)
NuclearDesign(Section4.5)
ThermalHydraulicDesign(Section4.6)
ReactorVesselSupportSystem(Section4.7)
ThereactorgeneratesheatbythecontrolledfissionofmaterialcontainedwithintheTRISOfuel.The reactortransfersheattothereactorcoolantandprovidesforcirculationofreactorcoolantthroughthe reactorcore.Controlelementsareprovidedtocontrolthereactivityofthecore.Aseparateand independentsetofshutdownelementsprovidesforsafeshutdownofthereactorduringoffnormal conditions.Aneutronsourceisprovidedduringinitialprecriticaloperationstoassistwithinitialstartup ofthereactorcore.Theonlinerefuelingcapabilityofthereactorcompensatesforchangesinreactivity duetodepletionoffuelandaccumulationoffissionproducts.Thedesignofthereactorvesseland internalsensuresthatacoolablegeometryismaintainedforthereactorcoreunderallnormal operationsandpostulatedevents.Thereactordesignincludesprovisionsforonlinemonitoringto supportcontrolandprotectionfunctions,aswellasthecapabilityforinserviceinspection, maintenance,andreplacementactivities.Shieldingisincludedtolimitradiationdosestoworkersand equipment.
Table4.11providesasummaryofkeyparametersforthereactor.
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 42 Table4.11:ReactorParameters Parameter Value ThermalPower(MWth) 35 ReactorCoolantOutletTemperature(°C) 65020 ReactorCoolantInletTemperature(°C) 550 ReactorVesselOperatingPressure(bar)
<2 ReactorCoolantType Flibe FuelType TRISOparticle;UCOkernel FuelMatrix Pebble EquilibriumFuelEnrichment(wt%)
<19.75 ReflectorType ETU10Graphite ControlMaterial B4C NeutronSpectrum Thermal
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 441 ThemethodologyfordeterminingshutdownmarginisdescribedintheKPFHRCoreDesignand AnalysisMethodologytechnicalreport(Reference1).
Hotshutdownisdefinedasthestatewherereactorissubcriticalatatemperatureof550°C.The shutdownmarginisdefinedforthemostlimitingcoreatthereactorcoolantfreezingtemperature.The shutdownmargindesigncriterionisthatkeffectivemustbelessthan0.99.
4.5.1.5 NuclearTransientParameters Thekeykineticparametersthatareusedintransientanalysisare:
Promptneutronlifetime Delayedneutronfractiongroupsandtheirdecayconstants Inaddition,corepowerdistributionandreactivitycoefficientsarealsoprovidedasinitialcondition inputstothetransientanalysis.Themethodologyforcalculatingthesecoefficientsisprovidedin Reference1.
4.5.1.6 AnalyticalMethods ThecoredesignmethodsarecomprisedoftheSerpent2,StarCCM+,KPACS,andKPATHcomputer codes.TheSerpent2codeisamultipurpose,threedimensionalcontinuousenergyMonteCarlo particle(neutronsandgammas)transportcode.STARCCM+isadiscreteelementmodelofpebbleflow throughthecoreandisthethermalhydraulicenginewiththeporousmediaapproximation.STARCCM+
isacomputationalfluiddynamicssimulationsoftwarethatusesdiscreteelementmodelingandporous mediaapproximationcapabilitiesforthermalhydrauliccharacterizationofpebblebedflowand temperature.KPACSisafuelcycleanalysiscode.KPATHisusedforcouplingSerpent2andStarCCM+.
Themethodforvalidationandverificationofthesecodesincludingthemethodfordetermining uncertaintyfactorsisdescribedinReference1.
4.5.2 DesignBases Thedesignbasesrelatedtonucleardesignareasfollows:
ConsistentwithPDC10,thereactorcorehasappropriatemargintoassurethatthespecifiedacceptable systemradionuclidereleasedesignlimits(SARRDLs)arenotexceeded.SARRDLsaredescribedinSection 6.2.
ConsistentwithPDC11,thereactorcoreisdesignedsothatinthepoweroperatingrangetheneteffect ofpromptinherentnuclearfeedbacktendstocompensateforrapidincreaseinreactivity.
ConsistentwithPDC12,thereactorcoreassuresthatpoweroscillationswhichcanresultinconditions exceedingSARRDLsarenotpossibleorcanbereliablyandreadilydetectedandsuppressed.
ConsistentwithPDC26,thenucleardesignanalysisisperformedtoconfirmthatthereactorcontroland shutdownsystem(RCSS)provideameansfor(1)insertingnegativereactivitysuchthatSARRDLs,are notexceededandsafeshutdowncanbeachievedduringnormaloperation;(2)reliablycontrolling reactivitychangesduringnormaloperation;(3)insertingnegativereactivityofasufficientamountto coolthecoreandmaintainsafeshutdownfollowinganaccident;and(4)holdingthereactorshutdown duringfuelloading,inspection,andrepair.
4.5.3 NuclearDesignEvaluation Thissectionprovidesanevaluationofthenucleardesignanddescribeshowthenucleardesignbasesin Section4.5.2aremet.Inaddition,thissectionalsodiscussesnucleardesignanalysesthatareprovided asinputtootherpartsofthedesign.
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 445 Table4.51:ComparisonofKPFHRTestReactorwithLightWaterReactor NuclearParameter KPFHRReactor SmallLightWaterReactor PowerLevel(MWth) 35 200 ReactorInlet/Outlet Temperature(°C) 550/65020 258/310 PowerDensity(MWth/m3) 17.5 58.9 CoreVolume(m3) 2 3.4 NumberofReactivityControl Elements 7
16 ShutdownMarginatEquilibrium (pcm) 4997 2696 DischargeBurnup(%FIMA) 6 4.3 Enrichment(%U235)
<20
<5
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).
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.Themaximumnominalcorevesselexitoutlettemperatureis620°C anddependentontheamountofcorrespondingbypassflowthroughthereflectorblocks.
DuringpostulatedeventswherethenormalheatremovalpaththroughthePHTSisnolongeravailable, includingwhenthePHTSisdrained,afluidicdiode(seeSection4.3),isusedtocreateanalternateflow path.Duringsuchevents,forcedflowfromtheprimarysaltpump(PSP)isalsonotavailable.Thefluidic diodethendirectsflowfromthehotwelltothedowncomerasshowninFigure4.61.Thisopensthe pathforcontinuousflowvianaturalcirculation.Duringnormaloperation,whilethePSPisinoperation, thefluidicdiodeminimizesreverseflow.
4.6.2 DesignBasis ConsistentwithPDC10,thethermalhydraulicdesignprovidesadequatetransferofheatfromthefuel tothecoolanttoensurethatthespecifiedacceptablesystemradionuclidereleasedesignlimits (SARRDLs)willnotbeexceededduringnormaloperationandunplannedtransients.
PreliminarySafetyAnalysisReport
ReactorDescription
KairosPowerHermesReactor
Revision0 455 Table4.61:SummaryofThermalHydraulicParameters Parameter NominalValue CorePower(MWth) 35 ReactorInletTemperature(°C) 550 MaximumCoreExitOutletTemperature(°C) 6206501 MaximumCoreReactorMassFlowRate(kg/s) 2101 MaximumCorePressureDropatMaximumFlowRate(kPa) 2121 CoreVolume(m3) 2.0 CorePackingFraction(%)
60 TotalPebbles(FuelandModerator) 36,000 PowerDensity(MW/m3) 17.5 Notes:
- 1. Valuedoesnotaccountforbypassflow
PreliminarySafetyAnalysisReport
InstrumentationandControls
KairosPowerHermesReactor 76 Revision0 TheRCScontrolsreactivityfornormaloperationsandnormalshutdownusingreactorcontrolelements andreactorshutdownelementsinthereactivitycontrolandshutdownsystem(RCSS)(seeSection4.2).
TheRCSiscapableofincrementallychangingthepositionofreactorcontrolelementsandofreleasing thecontrolandshutdownelements.TheRCSisonlycapableofwithdrawingelementsoneatatimeand theRCSincludesalimitontherateatwhichacontrolelementcanbewithdrawn,asalsodiscussedin Section4.2.2.Inthiswaythedesignprecludes,withmargin,thepotentialforpromptcriticalityand rapidreactivityinsertions.TheRCSinputsincludecorereactoraveragecoolantoutlettemperaturesand reactorinlettemperaturesensorsandsourceandpowerrangeneutrondetectors.TheRCSalsoprovides areactormonitoringfunctiontomonitorplantcomponentsthatareassociatedwithreactorfunctions.
TheRCSusessourceandpowerrangesensorsthatarelocatedoutsidethereactorvesselforreactor control.
TheRCScontrolspebbleinsertionandextraction,invesselpebblehandling,andexvesselpebble handlinginthepebblehandlingandstoragesystem(PHSS)(seeSection9.3).TheRCSiscapableof countinglinearizedpebblesexternaltothevessel,controllingtherateofpebbleinsertionandremoval fromthevessel,andcontrollingpebbledistributionwithinthePHSS.
TheRCScontrolsthereactorthermalmanagementsystem(RTMS)(seeSection9.1.5)tomonitorthe temperatureoftheprimarysystemtomaintainitwithinthenormaloperatingenvelopeandto implementplannedtransients.TheRCScontrolsexternalheatingelementsintheRTMStoprevent overcooling.
7.2.1.2 ReactorCoolantAuxiliaryControlSystem TheRCACScontrolsandmonitorssystemsandcomponentsthatsupportnormaloperationinthecore.
Thesystemsupportsthefollowingcapabilitiesinthecore:
Chemistrycontrolintheprimarysystem Inventorymanagementsystemcontrol Inertgassystemcontrolintheprimaryloops Tritiummanagementsystemmonitoringandcontrol TheRCACScontrolsthechemistrycontrolsystem(seeSection9.1.1)tomonitorreactorcoolant chemistry.Themonitoringsystemsprovideinformationtofacilitatemaintainingcoolantpurityand circulatingactivitywithinspecificationsforthesystem.
TheRCACSreceivesinputfromtheinventorymanagementsystem(seeSection9.1.4)whichmonitors primarycoolantlevelduringnormaloperations.Thesystemalsoprovidescontrolforchangestoprimary inventoryduringplannedprimaryfillinganddrainingoperations.
TheRCACSalsocontrolstheinertgassystem(seeSection9.1.2).Duringnormaloperation,thesystem providescontrolsignaltomaintaincovergaspressureandflow,monitorsventinggasforimpurities abovespecifiedlimitsinthegasspaceoftheprimarysystem.Duringstartup,thesystemmonitorsand controlsinertgasflowandtemperaturetosupportinitialheatingoftheprimarysystem.
TheRCACSreceivesinputfromthetritiummanagementsystem(seeSection9.1.3)andprovidescontrol signaltoremovetritiumfromthecovergasintheprimarysystem.
7.2.1.3 PrimaryHeatTransportControlSystem ThePHTCScontrolsandmonitorssystemsandcomponentsthatsupportnormaloperationofthe primaryheattransportsystem(PHTS).Thesystemsupportsthefollowingcapabilities:
ControloftheflowratethroughthePHTS
PreliminarySafetyAnalysisReport
InstrumentationandControls
KairosPowerHermesReactor 710 Revision0 Table7.21:PlantControlVariables ControlVariables(Inputs)
PrimaryLoop PSPspeed Controlroddriveposition Loopandvesseltemperatures Inertgaspressure IntermediateLoop ISPspeed Valvepositions Looptemperatures ControlledVariables(Outputs)
PrimaryLoop Neutronflux(selfpoweredneutron detectorsandioncambers)
Coreinlettemperature CoreReactoroutlettemperature CoolantCoremassflowrate IntermediateLoop IntermediateLoopflowrate IHXinlet/outlettemperature HeatRejectionRadiatorInlet/outlet temperature ConstrainedVariables(Outputs)
PrimaryLoop Excessreactivitymargin ReactoriInlettemperature
PreliminarySafetyAnalysisReport
InstrumentationandControls
KairosPowerHermesReactor 715 Revision0 Thewatertankisolationvalvesalsofailopenuponlossofpower.Thedecayheatremovalportionofthe RPScanreceivetheactuationsignalfromeitheranautomaticormanualsource.
ThedecayheatremovalportionoftheRPSusescoretemperatureandneutrondetectorsasinputs throughhardwired,analog,safetyrelatedsignalwirewaysthatareterminatedatlocalcabinets.Section 7.5providesadditionalinformationaboutthesensorsthatprovideinputtotheRPS.
ThedecayheatremovalportionoftheRPSalsoincludesamanualactuationcapabilityfromthemain controlroomandtheremoteonsiteshutdownpanel.Section7.4includesadiscussionofthehuman interfacewiththedecayheatremovalportionoftheRPS.
Table7.32providesalistofinterlocksimplementedforRPSsystems.Beforesufficientfissionproducts andsubsequentdecayheatisproducedinthecore,forexampleduringstartup,DHRShasnosafety function.Duringthisperiod,thedecayheatremovalportionoftheRPSincludesamanualinhibitionof theDHRSthatisavailabletoplantoperatorstoallowforadditionalthermalmanagementcapabilities.
Oncedecayheatisproducedatasufficientrateinthecore,theRPSblocksthemanualinhibition capabilityutilizingsafetyrelatedactuations.Aftershutdown,oncefissionproductdecayheat productionhasdroppedtolevelsnotrequiringDHRS,theRPSremovestheblockonthemanual inhibitioncapability.TheparameterstheRPSusestodetermineifthemanualinhibitionistobe permittedorblockedareneutrondetectors(sourceandpowerrange)andreactorcorevessel temperature.
7.3.2 DesignBases ConsistentwithPDC1,theRPSisdesignedusingrelevantindustrycodesandstandardsandthe QualityAssuranceprogram.
ConsistentwithPDC2,theRPSisdesignedtowithstandandbeabletoperformduringnatural phenomenaevents.
ConsistentwithPDC3,theRPSisdesignedandlocatedtominimize,consistentwithothersafety requirements,theprobabilityandeffectoffiresandexplosions.
ConsistentwithPDC4,theRPSisdesignedfortheenvironmentalconditionsassociatedwithnormal operation,maintenance,testing,andpostulatedevents.
ConsistentwithPDC10and20,theRPSprovidesreactortripanddecayheatremovalactuationthat ensureradionuclidereleasedesignlimitsarenotexceededduringnormaloperation.
TheRPSimplementsPDC13inthatthesystemincludessensorsthatmonitorcoretemperature, vessellevel,andpowerlevel.Thesensorsmonitorvariablesandsystemsovertheiranticipated rangesfornormaloperationandforpostulatedeventconditions.
ConsistentwithPDC15,theRPSprovidesreactortripanddecayheatremovalactuationtoensure thatthedesignconditionsofthereactorcoolantboundaryarenotexceededduringnormal operation.
ConsistentwithPDC20,theRPSprovidesautomaticreactortripanddecayheatremovalactuation toensureradionuclidereleasedesignlimitsarenotexceededasaresultofpostulatedevents.The RPSisalsodesignedtoidentifypostulatedeventconditionsandinitiatepassiveinsertionof reactivityshutdownelementsandpassivedecayheatremoval.
ConsistentwithPDC21,theRPSisdesignedwithsufficientredundancyandindependencetoassure thannosinglefailureresultsinlossofitsprotectionfunction.IndividualcomponentsoftheRPSmay beremovedfromservicefortestingwithoutlossofrequiredminimumredundancy.TheRPSis designedtopermitperiodictesting.
ConsistentwithPDC22,theeffectsofnaturalphenomena,andofnormaloperating,maintenance, testing,andpostulatedeventconditions,donotresultinlossoftheprotectionfunctionfortheRPS.
PreliminarySafetyAnalysisReport
InstrumentationandControls
KairosPowerHermesReactor 716 Revision0 TheRPSisdesignedwithsufficientfunctionalandcomponentdiversitytopreventthelossof functionfortheRPS.
Uponlossofelectricalpowerordetectionofadverseenvironmentalconditions,theRPSfailstoa safestate,consistentwithPDC23.
TheRPSsystemfunctionallyindependentfromthecontrolsystems,consistentwithPDC24.
ConsistentwithPDC25,theRPSisdesignedtoensurethatradionuclidereleasedesignlimitsarenot exceededuponreactortripactuation,includingintheeventofasinglefailureofthereactivity controlsystem.
ConsistentwithPDC28,theRPSsetpointsaredesignedtolimitthepotentialamountandrateof reactivitytoensuresufficientprotectionfrompostulatedeventsinvolvingreactivitytransients.The limitsaresetsuchthatreactivityeventscannotresultindamagetothereactorcoolantboundary greaterthanlimitedlocalyielding,andcannotsufficientlydisturbthecore,itssupportstructures,or otherreactorvesselinternalstoimpairsignificantlythecapabilitytocoolthecore.
TheRPSisdesignedtoberedundantanddiversetoassurethereisahighprobabilityof accomplishingitssafetyrelatedfunctionsinpostulatedevents,consistentwithPDC29.
Consistentwith10CFR50.55(i),RPSisdesigned,fabricated,erected,constructed,tested,and inspectedtoqualitystandardscommensuratewiththesafetyfunctiontobeperformed.
Consistentwith10CFR50.55a(h)(3),theRPSisdesignedinaccordancewithIEEEStd6032018 (Reference1).TheRPSimplementsthe2018editionofIEEEStd603asanalternativecodetoIEEE Std6031991(Reference2)andthecorrectionsheetdatedJanuary30,1995.
7.3.3 SystemEvaluation TheRPSprovidesautomaticreactortrip(1)ifplantparametersexceedthenormaloperationenvelope (PDC20),(2)intheeventofstationblackout,and(3)manuallyusingsignalfromthemaincontrolroom orremoteonsiteshutdownpanel.TheRPSalsoensuresthattheDHRSisrunningwhenthereactortrips.
TheRPSisconsistentwith10CFR50.55a(h)(3)andNUREG1537,GuidelinesforPreparingand ReviewingApplicationsfortheLicensingofNonPowerReactors,bymeetingIEEE6032018.Table7.31 providesalistoftheconsensusstandardstowhichtheRPSisdesigned.
Chapter13describesthepostulatedeventstowhichtheRPSisdesignedtorespond.TheRPSusesthe samesetofoperatingparametersinthetripandactuationlogicforallmodesofreactoroperation.The setpointsareestablishedtoensurethatthedesignconditionsofthereactorcoolantboundaryarenot exceededduringoperationwithinthedesignbasis.ThisisconsistentwithPDC25becausemaintaining thereactorcoolantboundarywithindesignbasisboundswillensurethatradionuclidereleasedesign limitsarenotexceeded.Thesetpointsareestablishedandcalibratedusingthemethoddescribedin Section7.1.2.
Consistentwith10CFR50.55a(h)(3),reactortripsimplementedbytheRPSmeetIEEE6032018, Section4.Theprimaryplanttripsignalisbasedonaveragecoretemperaturemeasurements.In addition,theplantwillalsohaveatripsignalforhighfluxratebasedoninputfromtheneutrondetector sensorsandatripofthereactorupondetectionofabreakinthePHSSextractionline.Whenthe temperatureorfluxrateareoutsidethenormaloperatingrangeorwhenaPHSSextractionlinebreakis detected,theprimaryplanttripdeenergizestheRSStripdevice,theDHRSlooptripdevice,andthePCS inhibitortripdevice.Redundanttripdevicesareprovidedforeachsignalpathway.SeeFigure7.31fora schematicoftheRPStriplogic.Tripsetpointsareestablishedandcalibratedusingthemethods describedinSection7.1.2.ThePCSinhibitortripdevicefunctionallyisolatestheRPSfromthePCS.This includestrippingthePSP,discussedinSection7.2.1.3.TheRPSalsoprovidesalarmsignalstothemain controlroom,whichwillbedescribedintheOperatingLicenseapplication.