ML22171A017
| ML22171A017 | |
| Person / Time | |
|---|---|
| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 06/20/2022 |
| From: | Kairos Power |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22171A015 | List: |
| References | |
| KP-NRC-2206-008 | |
| Download: ML22171A017 (8) | |
Text
PreliminarySafetyAnalysisReport
EngineeredSafetyFeatures
KairosPowerHermesReactor 64 Revision0 6.3 DECAYHEATREMOVALSYSTEM 6.3.1 Description Thedecayheatremovalsystem(DHRS)removesresidualdecayheatfromthereactorcoreduring normalandoffnormalconditions.TheDHRSiscreditedinChapter13fordecayheatremovalduring postulatedeventsthatassumetheprimaryheattransportsystemandprimaryheatrejectionsystemare unavailable,includingthemaximumhypotheticalaccident.TheportionsoftheDHRSthatmustfunction toperformthedecayheatremovalcreditedinChapter13aredesignatedassafetyrelatedandareall passive.TherearenoactivesafetyrelatedportionsoftheDHRS,andtheDHRSdoesnotrequire electricalpowertoperformsafetyfunctionsduringpostulatedevents.TheDHRSisanexvesselsystem thatcontinuouslyoperateswhenthereactorisoperatingaboveathresholdpowerbyremovingenergy fromthevesselwallviathermalradiationandconvectiveheattransfertowaterbasedthermosyphons.
Inventoryinthethermosyphonsisboiledoffandventsdirectlytotheatmosphereoutsideofthereactor building.
TheDHRSconsistsofannularthermosyphonthimblesinthereactorcavity,steamseparators,andwater storagetanks.Thesecomponentsarearrangedintofourindependentcoolingtrainswithinventory sufficienttosustainpassiveoperationoftheDHRSforatleast72hoursupto7daysfollowingasneeded tomitigateapostulatedeventwherenormalcoolingsystemsareunavailable.Eachtrainiscomposedof onewaterstoragetank,onesteamseparator,andsixthimbles.ThegeneralarrangementoftheDHRSis illustratedinFigure6.31.
TheoperationoftheDHRSisgovernedbytwooperationalmodes.Whenreactorpowerislessthana specifiedthresholdpower,parasiticlossesfromthereactorvesselduetoconvectivelossesfromair ingressandparasiticthermalradiationandconductionlossesthroughsolidstructuresaresufficientto maintainvesseltemperaturesbelowthedesignlimitduringapostulatedeventwhenthePHTSis unavailable.Whenthereactorpowerisabovethethresholdpower,supplementalcoolingbytheDHRS isrequired.Thisthresholdpowerdependsonthereactorpowerhistoryduetotheaccumulationof fissionproductsinthecoreasafunctionofpower.Thethresholdpowerisnominally10MWforafresh core.Assuch,theDHRSoperatingmodesaredefinedas:
LowDecayPowerOperation(Reactorpower<thresholdpower)
Thermosyphonthimblesinthereactorcavityaredryandisolatedfromtherestofthesystem.
Waterisheldinfourseparatewaterstoragetanks(oneforeachDHRStrain)locatedabovethe thimblesandoutsideofthereactorcavity.Decayheatremovalisachievedthroughparasitic cavitylosses.
HighDecayPowerOperation(Reactorpower>thresholdpower)
Thethimblesarefilledwithwaterandtheconnectedsteamseparatorcontainsafreesurface belowthethimbleoutletandabovethethimbleinlet.Theseparatoriscontinuouslyand passivelyreplenishedfromthewaterstoragetankaswaterinthethimblesisboiledoffand ventedtoatmosphereoutsidethereactorbuilding,therebyremovingheatfromthereactor vessel.
Theseoperatingstatesrequireatransitionperiod.Thetransitionperiodoccursatthethresholdpower, wheredecayheatloadsexceedtheremovalratebynaturalparasiticlosses.Theisolationvalvesonthe thimblefeedwaterlinesopen,whichallowswatertoflowfromthewaterstoragetanktothethimbles, asindicatedbyapositiveflowrate.Thepeakflowrateislimitedbyfrictionallossesduetothelinesizes andgravitationalheadassociatedwiththewaterstoragetanklocations.Thetemperatureofthe evaporatortubescontainedinthethimblesdecreasesfromstandbytemperature(550°C)duringlow decaypoweroperationtothenominalboiloffoperatingtemperature(100°C)astheevaporatoris
PreliminarySafetyAnalysisReport
EngineeredSafetyFeatures
KairosPowerHermesReactor 65 Revision0 wetted.Thetransientquenchingprocesstimeisdependentonthethimblefeedwaterflowrate.Steady stateconditionsoccuruponcompletionofthefillwithapseudostableliquidlevelintheseparators.
ThecontinuousoperationoftheDHRSdoesnotrequireacontrolactuationtotransitionfromnormal operationtopassiveheatremoval.However,eventmonitoringandthecapabilityforactiveactuation areprovided.TheprimaryinterfacingsystemsthroughwhichtheseoccuraredescribedinChapter7.
TheDHRSislocatedinthereactorbuilding,whichisdescribedinSection3.5andcontainsthereactor cavityandthereactorcell.TheDHRSthimblesandsteamseparatorsarelocatedwithinthereactor cavity,butdonothavedirectcontactwiththereactorvesselshell.Energyistransferredfromthevessel totheDHRSthroughthermalradiationandconvection.Thereactorauxiliaryheatingsystem(RAHS)is locatedinthefreespacebetweenthereactorvesselandthereactorcavityinsulation(seeSection 9.1.5),buttheoverallperformanceoftheRAHSdoesnotadverselyaffecttheDHRSremovalefficiency becauseitisdeactivatedwhiletheDHRSisactivelyremovingheat.Thewaterstoragetanksarelocated outsideofthereactorcavity,withinthereactorcell.Theprimarybiologicalshieldisaconcretestructure whichseparatesthereactorcavityfromthereactorcell.Thisprovidesdirectstructuralsupportforthe DHRSthimbleunitsandseparationandshieldingofthewaterstoragetanksfromthereactorcavity environments.Italsoprovidesthroughportsforthesteamreturnandthimblefeedwaterlines.The primarybiologicalshieldisdescribedinSection4.4.TheDHRSprimarymodeofheatremovalisventing steamproducedinthethimblestotheatmospherethroughthewaterstoragetanks.
TheprimarycomponentsoftheDHRSaredescribedinthefollowingsubsections.
6.3.1.1 WaterStorageTanks TheDHRScontainsfourwaterstoragetankswhichsupplycoolinginventorytotheDHRSthimbles.These tanksarelocatedoutsideofthereactorcavity,withinthereactorcell,atahigherelevationthanother DHRScomponents.Thislocationenablesgravitydrivenflowtothethimblesandsteamseparators.Each waterstoragetankiscoupledtoasetofsixthimblesthroughafeedwaterlineandsteamreturnline whichpassthroughtheprimarybiologicalshield.Theselinesaredistributedtoindividualthimbles throughthesteamseparatorlocatedintheupperreactorcavity.
AtleastthreestoragetanksmustbeavailablefortheDHRStoadequatelyperformitsfunctionduring postulatedeventconditions.Eachtankholdssufficientinventorysuchthatthethimblesconnectedtoit maybeoperatedcontinuouslyforatleast72hoursupto7daysasneededtomitigatepostulatedevents resultinginfollowingalossofthewaterstoragetankfeedwatersupplyduringapostulatedevent.In addition,tankwaterlevelismonitoredtoensureDHRSoperability.Eachstoragetankislocatedinan independentlocationsuchthatdamageatonelocationdoesnotprecludeoperationoftheentireDHRS whenrequiredfordecayheatremoval.Thislocationalsoprovidesadditionalassurancethatfailuresof thewaterstoragetankdonotresultinleakingintothereactorcell,andthatventedorleakedwaterand steamdonotmixwithFlibe.
ThekeywaterstoragetankparametersareprovidedinTable6.31.
6.3.1.2 SteamSeparators Thesteamseparatorsprovideaninterfacebetweenthewaterstoragetanksandtheindividualthimbles thatthetankssupply.Thesteamseparatorachievesthisfunctionbycontrollingthewaterlevelinsideits volumethroughtheuseofapassivefloatvalvelocatedonthethimblefeedwaterline.Thecontrolled freesurfaceintheseparatorislocatedabovethethimblefeedwaterportandbelowthesteamvent port.Thethroughputofwateristhereforeafunctionoftheboiloffrateinthethimbles.
PreliminarySafetyAnalysisReport
EngineeredSafetyFeatures
KairosPowerHermesReactor 68 Revision0 tornadoes,floods,andwindinducedmissileevents.TheDHRSdesignrequirementsforseismicand othernaturalhazardsdemonstrateconformancewiththerequirementsinPDC2.
TheDHRSisdesignedandlocatedtominimizetheprobabilityandeffectoffiresandexplosionsbythe useoflowcombustiblematerialsandphysicalseparation.Thesedesignfeatures,inconjunctionwiththe fireprotectionplandescribedinSection9.4,provideassurancethattheDHRSdemonstrate conformancewiththerequirementsinPDC3.
TheDHRSisdesignedwithmaterialsthatwillwithstandtheradiationenvironmentofthereactorcavity andenvironmentaltemperaturesupto800°CtoensuretheDHRSiscapableofperformingitssafety functionunderconditionsassociatedwithnormaloperation,maintenance,testing,andpostulated events.TheDHRSisdesignedagainstequipmentfailuresthatcouldresultfromFlibespills.Pipewhip andothersimilardynamicfailuresareavoidedbythelowpressuredesignoftheDHRSandtheuseof restraints.EachcomponentoftheDHRSisdesignedsuchthatfailureofonecomponentdoesnot cascadeandcausefailuresofnearbysafetysystems,includingotherDHRScomponents.Thesedesign considerationsdemonstrateconformancewiththerequirementsinPDC4.
Naturalcirculationinthereactorcoretransfersdecayheatfromthefueltothereactorvesselshellwhen normalcoolingisnotavailable,asdescribedinSection4.6.3.Thermalhydrauliccalculations demonstratethattheDHRSiscapableofpassivelyremovingasufficientamountofdecayheatfromthe reactorvesselwithoutrelianceonelectricpowerforatleast72hoursupto7daysfollowingasneeded tomitigatepostulatedevents,suchthatthereactorvesseltemperatureremainsbelowitsdesignlimitof 816°Candisdecreasingbytheendofthe72hourperiod.Inaddition,fueltemperaturesremainbelow theirdesignlimits.TheDHRSisdesignedwithsufficientredundancy,leakdetectioncapability,and isolationtoensurethesafetyfunctioncanbeperformedassumingasinglefailure.Thesystemincludes fourindependentloopsandmaintainstheabilitytoperformitsfunctionwiththelossofasingleloop.
Isolationofthefourwaterstoragetanksfromoneanotherensuresthatdamageatonetanklocation doesnotresultinatotallossofDHRSinventory.Thethimbles,separators,andthimblefeedwaterand steamreturnpipingareallcontainedwithintheleakbarrier.Theleakbarrierprovidesleakdetection capabilityandensuresthatafailureoftheprimaryDHRSpressureboundarydoesnotpreventthe systemfromperformingitsheatremovalfunction.TheseDHRSdesignfeatures,alongwiththenatural circulationcharacteristicsofthereactorcore,demonstrateconformancewiththerequirementsinPDC 34andPDC35.
TheDHRSdesignincludesthecapabilityforonlinemonitoringofleakstomonitorforsystemintegrity andtoensurethatDHRSinventoryremainssufficienttoperformthesafetyrelatedheatremoval function.Thewaterlevelinthestoragetanksisalsocapableofbeingmonitoredtoensurethatsufficient inventoryispresentattheonsetofapostulatedeventtoprovidesufficientcoolingcapacity.TheDHRS isalsosufficientlyaccessibletoperforminspectionsforsystemintegrity.ThesefeaturessatisfyPDC36.
Whenthereactorisabovethresholdpower,theDHRSisanalwaysonoperatingconditionwhich providesanongoingdemonstrationofsystemavailability.Thetransitionfromnormaltopostulated eventoperationcanalsobefunctionallytested.Thesefeaturesdemonstrateconformancewiththe requirementsinPDC37.
6.3.4 TestingandInspection ThedetailsoftheinspectionandtestingprogramforDHRStosatisfytheapplicableportionsofASME SectionXI,Division1and2,RulesforInserviceInspectionofNuclearPowerPlantComponents (Reference2)willbedescribedintheapplicationforanOperatingLicense.
PreliminarySafetyAnalysisReport
EngineeredSafetyFeatures
KairosPowerHermesReactor 610 Revision0 Table6.31:WaterStorageTankParameters Parameter Value Material StainlessSteel DesignPressure[psig]
30 DesignTemperature[°F]
274 MinimumVolumepertank[gal]
17382900 Numberperreactor 4
PreliminarySafetyAnalysisReport
ElectricPowerSystems
KairosPowerHermesReactor 81 Revision0 CHAPTER8 ELECTRICPOWERSYSTEMS 8.1
SUMMARY
DESCRIPTION Thepurposeoftheelectricalsystemistoprovidepowertoplantequipmentforoperation.Theelectrical systemconsistsofthenonClass1Enormalpowersystem(discussedinSection8.2)andthebackup powersystem(discussedinSection8.3).Duringnormaloperations,thelocalutilitysuppliesACelectrical powertothenormalpowersystem.Ifthenormalpowersourcefails,thebackuppowersystemsupplies plantpower.Thebackuppowersystemutilizesbackupgeneratorsanduninterruptiblepowersupplies (UPS)toachievethisfunction.
OwingtothepassivedesignofHermes,safetyrelatedstructures,systems,andcomponents(SSCs)do notrequireelectricpowertoperformsafetyrelatedfunctionsforaminimumof72hoursfollowinga designbasispostulatedevent.Therefore,ACpowerfromoffsiteorbackuppowersourcesisnot requiredtomitigateadesignbasispostulatedevent.Asimplifieddiagramofthemajorelectricalsystem componentsisprovidedinFigure8.11.
PreliminarySafetyAnalysisReport
ElectricalPowerSystems
KairosPowerHermesReactor 83 Revision0 8.2 NORMALPOWERSYSTEM 8.2.1 Description Thenormalpowersystemissuppliedbyanoffsitepowersourcefromthelocalutility.Thelocalutility providesamediumvoltagefeeder.Fromthepointofconnection,anappropriatestepdowntransformer reducesthevoltagetothenominalbusvoltageof480V,whichisdistributedtoplantloadsasdepicted inFigure8.11.Alossofvoltageordegradedvoltageconditiononthenormalpowersystemdoesnot adverselyaffecttheperformanceofsafetyrelatedfunctions.
8.2.1.1 ACElectricalPower ACpowerisdistributedtotheplantelectricalloadsduringstartupandshutdown,normaloperation,and offnormalconditions.TheACelectricalpowercomponentsincludethefollowing:
Asingleincomingfeederfromtheutilitytothenormalpowersystemwithnominalfeedervoltageof 4.16kV, A4.16kV/480Vstepdowntransformer,and ThelowvoltageACelectricalpowerdistributionwithnominalbusvoltagesof480Vand120V.
SelectedloadsaresuppliedwithcontinualACelectricalpowerviauninterruptiblepowersupplies(UPS).
EachUPSprovidesahighlyreliablepowersupplyduringnormaloperationsandisautomatically configuredtoprovidebackuppowerduringalossofnormalelectricalpowerevent.Thebackupfunction oftheUPSisdescribedinSection8.3.1.2.
8.2.1.2 DCElectricalPower DCelectricalpowersupplyislimitedtoinstrumentationandcontrolfunctionsthatrequire24VDC electricalpowerforoperation.Thecabinetsassociatedwiththesefunctionsareequippedwith120VAC to24VDCpowersupplies,asshowninFigure8.11.ACelectricalpowerissuppliedtothesecabinetsvia UPStoensurecontinuous,failuretolerantDCpowerduringnormaloperationandforaspecified minimummaximumdutycyclefollowingatotallossofACelectricalpower.
8.2.2 DesignBases Thenormalpowersystemdoesnotperformanysafetyrelatedfunctionsandisnotcreditedforthe mitigationofpostulatedevents.Thesystemisalsonotcreditedwithperformingsafeshutdown functions.
8.2.3 SystemEvaluation ThenormalpowersystemisprovidedtopermitfunctioningofplantSSCsthatrequireelectricalpower.
Thepassivedesignfeatures,basedonfundamentalphysicsprinciples,donotrelyonelectricalpowerfor safetyrelatedSSCstoperformtheirsafetyfunctionsduringpostulatedevents.Thesefeatures demonstrateconformancewiththerequirementinPDC17.
Asdiscussedabove,thenormalpowersystemisnotreliedonforsafetyrelatedSSCstoperformtheir safetyfunctionsforaminimumof72hoursfollowingpostulatedevents.Therefore,therearenosafety relatedportionsofthenormalpowersystem,andnotestsorinspectionsarerequiredtodemonstrate conformancewiththerequirementinPDC18.
Thedesignofthenormalpowersystemissuchthatmalfunctionofthesystemwillnotcausereactor damageorpreventsafereactorshutdown.Thenormalpowersystemensuresthatadequate independenceismaintainedbetweenthenonsafetyrelatedequipmentandcircuitsofthenormal powersystemandClass1Einstrumentationandcontrol(I&C)equipmentandcircuits(seeSection8.3.3).
PreliminarySafetyAnalysisReport
ElectricalPowerSystems
KairosPowerHermesReactor 85 Revision0 8.3 BACKUPPOWERSYSTEM 8.3.1 Description Thepurposeofthebackuppowersystem(BPS)istoprovideACelectricalpowertotheessentialfacility loadswhenthenormalACpowersupplyisnotavailable.Thesystemincludesbackupgeneratorsand uninterruptiblepowersupplies(UPS),aswellaselectricalequipmentandcircuitsusedtointerconnect thebackupgeneratorstothelowvoltageACelectricalpowerdistribution.Inaddition,thefacilityis equippedwithapluginconnectionforusewithaportable480VACgeneratortoprovidepowerto essentialloadsintheeventthebackupgeneratorsareunavailable.
8.3.1.1 BackupGenerators Thebackupgeneratorsautomaticallystartintheeventofalossofoffsitepowerandprovidebackup electricalpowertotheessentialfacilityloads.Therewillbeatleastoneredundantgeneratorbydesign (n1contingency),whichensuresthatsufficientbackuppowerwillbesuppliedintheeventofasingle generatorfailure.Thebackupgeneratorsarelocatedonanenclosedskidinstallationoutsidethereactor buildingandincludeconventionalcomponentssuchas:
Enginestarter Combustionairintakeandengineexhaust Enginecooling Enginelubricatingoil Enginefuel(includingfuelstorageandtransfer)
Generatorexcitation,protectiverelaying,andassociatedinstrumentationandcontrols Thebackupgeneratorsareprovidedwithcontrolstofacilitatemanualstartupandshutdown,either locallyorfromatransferswitchinthemaincontrolroom(MCR)(seeSection7.4),andtoprovidefor monitoringandcontrolduringbackupgeneratoroperation.
Thebackupgeneratorswitchgearisconnectedtoadistributionswitchgearwhichprovidespowerto 480Vmotorcontrolcenters(MCCs)anddistributionpanels.Onalossofnormalpower,thebackup generatorsstartupandtheautomatictransferswitch(ATS)transferspowersupplyfromthenormal utilityfeedtothebackupgeneratorfeed.Aloadsheddingschemeisemployedtoensurethatonly essentialloadsaresuppliedwithbackuppower.Alistofthespecificessentialloadsthatreceivebackup powerwillbeprovidedintheapplicationforanOperatingLicense.
8.3.1.2 UninterruptiblePowerSupplies SelectedloadsaresuppliedwithcontinuousACelectricalpowerviauninterruptiblepowersupplies(UPS),
asdepictedinFigure8.11.EachUPSprovidesahighlyreliablepowersupplyduringnormaloperations andisautomaticallyconfiguredtoprovidebackuppowerduringalossofnormalelectricalpowerevent.
TheUPSaresizedtoprovidesufficientpowertothoseselectedloadstomaintainfunctionalityduring backupgeneratorstartup,andfortheirrespectivespecifiedminimummaximumdutiesasdescribedin Section8.3.3.
8.3.2 DesignBases TheBPSdoesnotperformanysafetyrelatedfunctionsandisnotcreditedforthemitigationof postulatedevents.Thesystemisalsonotcreditedwithperformingsafeshutdownfunctions.
8.3.3 SystemEvaluation Thenormalandbackuppowersystemsaredesignedtopreventinterferencewithsafetyrelated functions.Ifthebackupgeneratorsfailduringalossofnormalpowerevent,theUPSsupplyingthe
PreliminarySafetyAnalysisReport
ElectricalPowerSystems
KairosPowerHermesReactor 86 Revision0 reactorprotectionsystem(RPS)blockloads(asshowninFigure8.11)willfailbydesigntoensure properfailsafefunctions.ThisUPSissizedtoprovideshorttermbackuppowertotheRPSblockloads, andtolosepoweronfailureofthebackupgenerators.Thefailsafefunctionsaredescribedinfurther detailinthefollowingparagraphsandinSection7.3.
ToensurefailtosafetyintheeventofacompletelossofACelectricalpower,thereactivitycontroland shutdownsystem(RCSS)isequippedwithasafetyrelatedclutchthatrequires24VDCtoremainclosed.
Onalossofpower,therelayopens,andthecontrolelementsdropintothereactorbygravity.
ToensurefailtosafetyintheeventofacompletelossofACelectricalpower,theprimarysaltpump (PSP)andintermediatesaltpump(ISP)powersuppliesareequippedwithrelaysrequiring24VDCto remainclosed.Onalossofpower,therelaysopentopreventinadvertentpumprestartonpower restoration.Amanualresetisrequiredtorestartthepumps.
Onactivationofthedecayheatremovalsystem(DHRS),thereactorprotectionsystemwillremove24 VDCfromtheactivationcircuitrelaytopreventinadvertentshutdownoftheDHRSbyoperatorerror.
EquipmentformonitoringreactorstatuswillbesuppliedbyUPSuntilthenormalpowersupplyor backupgeneratorsarerestored.
TheBPSisprovidedtopermitfunctioningofSSCsfollowingalossofnormalpower.Thepassivedesign featuresoftheHermesreactor,basedonfundamentalphysicsprinciples,donotrelyonACorDC electricalpowerforsafetyrelatedSSCstoperformtheirsafetyfunctionsduringpostulatedevents.Safe shutdownofthereactordoesnotrelyonACelectricalpowerfromtheBPS.Thesefeaturesdemonstrate conformancewiththerequirementsinPDC17.
Asdiscussedabove,theBPSisnotreliedonforsafetyrelatedSSCstoperformtheirsafetyfunctionsfor aminimumof72hoursfollowingpostulatedevents.Therefore,therearenosafetyrelatedportionsof theBPS,andnotestsorinspectionsarerequiredtodemonstrateconformancewiththerequirementin PDC18.
Thebackuppowersystemisnotsafetyrelated,butportionsofthesystemmaycrosstheisolationmoat discussedinSection3.5.SSCsthatcrossabaseisolationmoatmayexperiencedifferential displacementsasaresultofseismicevents.Thebackuppowersystemisdesignedsothatpostulated failuresofSSCsinthesystemfromdifferentialdisplacementsdonotprecludeasafetyrelatedSSCfrom performingitssafetyfunction.Designfeaturesaddressingdifferentialdisplacementarediscussedin Section3.5.ThesefeaturesdemonstrateconformancewiththerequirementinPDC2.
ThebackuppowersystemisdesignedinaccordancewithNFPA70,NationalElectricalCode (Reference8.31).
8.3.4 TestingandInspection TheBPSdoesnotperformanysafetyfunctions.Periodicinspectionandtestingareperformedonthe BPSforoperationalpurposes.
8.3.5 References
- 1. NationalFireProtectionAssociation,NFPA70,NationalElectricalCode.2020.