ML22236A595
| ML22236A595 | |
| Person / Time | |
|---|---|
| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 08/24/2022 |
| From: | Kairos Power |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22236A593 | List: |
| References | |
| KP-NRC-2208-009 | |
| Download: ML22236A595 (4) | |
Text
PreliminarySafetyAnalysisReport
EngineeredSafetyFeatures
KairosPowerHermesReactor 65 Revision0 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 maybeoperatedcontinuouslyforatleast72hoursfollowingalossofthewaterstoragetankfeedwater supplyduringapostulatedevent.Inaddition,tankwaterlevelismonitoredtoensureDHRSoperability.
Eachstoragetankislocatedinanindependentlocationsuchthatdamageatonelocationdoesnot precludeoperationoftheentireDHRSwhenrequiredfordecayheatremoval.Thislocationalso providesadditionalassurancethatfailuresofthewaterstoragetankdonotresultinleakingintothe reactorcell,andthatventedorleakedwaterandsteamdonotmixwithFlibe.
ThekeywaterstoragetankparametersareprovidedinTable6.31.
6.3.1.2 SteamSeparators Thesteamseparatorsprovideaninterfacebetweenthewaterstoragetanksandtheindividualthimbles thatthetankssupply.Thesteamseparatorachievesthisfunctionbycontrollingthewaterlevelinsideits volumethroughtheuseofapassivefloatvalvelocatedonthethimblefeedwaterline.Thecontrolled freesurfaceintheseparatorislocatedabovethethimblefeedwaterportandbelowthesteamvent port.Thethroughputofwateristhereforeafunctionoftheboiloffrateinthethimbles.Figure6.32 providesanotionaldiagramoftheDHRSseparatorandfloatvalve.
Thefloatvalveconsistsofafreehollowfloatwhichblocksthefeedwaterlinewhenwaterlevelexceeds athresholdvalueandallowsforcontinuousflowatallotherfloatpositions.Therearenoindependent movingmechanicalpartsbeyondthefloatitself.Thevalveisdesignedwithsufficientreliabilityto supportthesafetycaseandprovideapassivelycontrolledflowoffeedwatertothethimbles.Thevalve
PreliminarySafetyAnalysisReport
EngineeredSafetyFeatures
KairosPowerHermesReactor 66 Revision0 isfailopenbydesignwithsufficientredundancytoensurereliableoperationupondemand.Failopen performancefloodstheseparatorvolumeuponfailureanddoesnotaffectthenetheatremoval performanceofthethimbles.
Theseparatorsarecontainedwithintheleakbarrier(describedinSection6.3.1.4);therefore,failuresof theseparatorpressureboundarydonotprecludetheheatremovalfunctionoftheDHRS.Thewater ejectedfromtheseparatorduetoafailureofthepressureboundaryiscapturedinthemonitoredleak barrier.Thisinitiatesshutdownofthereactorifithasnotalreadyoccurred.Theleakbarrierisapressure boundary,whichensuresthatwaterdoesnotleakdirectlyintothereactorcavityorcell.
ThekeysteamseparatorparametersareprovidedinTable6.32.
6.3.1.3 Thimbles TheDHRSthimblesareannularthermosyphonslocatedcircumferentiallyaroundtheoutsideofthe reactorvessel.Thethimblesremoveheatfromthereactorvesselthroughcontinuousboiloffofthe thimblefeedwatersupply.Athimbleconsistsofacentrallylocatedguidetubecontainedwithinan evaporatortube.Theentireunitisfullyenclosedwithinanouterthimblecasing,whichispartofthe leakbarrier(seeFigure6.33).Heatfromthereactorvesselisincidentupontheleakbarrier,whichre irradiatestotheevaporatortube.Fluidisfedfromthesteamseparatortotheguidetubeandbackup theevaporatortubethroughbuoyancydrivenflow.Thedensitydifferentialassociatedwiththisflowis developedintheevaporatorregion,whereheatisabsorbedinthefluidviaconvectiveheattransfer, causingnucleationandflowboiling.Thetwophasemixtureisejectedintothesteamseparator,which returnsliquidtothestaticlevelandallowssteamtoflowfreelyoutthesteamreturnline.Thefluidre circulationandsteamproductionrateinthethimbleisafunctionofthereactorvesselsurface temperature,resultinginavariableflowratethataccommodatesthereactorvesselconditions.
Thethimblesaresupportedbytheweldjointtothesteamseparatorsandareseismicallyrestrained.The thimblesarelocatedinthefreegasspacebetweenthevesselshellsurfaceandtheinsulationliningthe primarybiologicalshield.Thedistributionofthimblesissuchthatfailureofallsixthimblesfromasingle traindoesnotcausethereactorvesseltoexceeditstemperaturelimits.
Thethimblesincludeanoutercasing,whichfunctionsaspartoftheleakbarriersystemasdescribedin Section6.3.1.4.Individualthimblesmaybeeitherpluggedorreplacedduringmaintenanceperiods.Each trainofDHRSincludesoneredundantthimble,suchthatthelossofasinglethimblewillnotinhibit operationofthetrain.
ThekeythimbleparametersareprovidedinTable6.33.
6.3.1.4 LeakBarrier Componentsinthereactorcavityaredesignedtopreventwaterleaksandflooding.Forthisreason, DHRScomponentslocatedinsidethereactorcavityaredualwalled.Thisincludesthethimbles, separators,andthimblefeedwaterandsteamreturnpiping.Theoutercasingofthethimblesservesasa dualwall.Thecontinuousandconnecteddualwallmaybepressurizedforperiodicleakcheckingofthe gasregionduringnormaloperation.Thisconfirmsintegrityofthewaterpressureboundaryandtheleak barrier.Inaddition,continuousleakdetectionoftheinternalwaterpressureboundaryispossibleby monitoringforarelativeriseinhumidityinthegasspaceandadropintheexternalsurface temperature,whichwouldindicatetheformationofaleak.Therefore,thissystemprovidesareliable mechanismforpreventionoffloodingintothereactorcavity.Thissecondarybarrieralsoprovides protectionfortheDHRSfromexternalhazardsassociatedwithFlibecoolantleakingfromthePHTSin theeventofafailure.
PreliminarySafetyAnalysisReport
EngineeredSafetyFeatures
KairosPowerHermesReactor 615 Revision0 Figure6.32:NotionalDiagramoftheDHRSSeparatorandFloatValve
PreliminarySafetyAnalysisReport
EngineeredSafetyFeatures
KairosPowerHermesReactor 616 Revision0 Figure6.33:AnnularThimbleGeometry