ML22243A249
| ML22243A249 | |
| Person / Time | |
|---|---|
| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 08/31/2022 |
| From: | Kairos Power |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22243A247 | List: |
| References | |
| KP-NRC-2208-014 | |
| Download: ML22243A249 (5) | |
Text
KPNRC2208014 ResponsetoNRCRequestforAdditionalInformation348 (NonProprietary)
Page1of4 NRCRequestforAdditionalInformation RAIPackage348,Question408
Section50.34ofTitle10oftheCodeofFederalRegulations(10CFR50.34),"Contentsofapplications; technicalinformation,"providesrequirementsforinformationtobeprovidedinaConstruction Permit(CP).10CFR50.34(a)(4)statesthataCPshallcontainapreliminaryanalysisandevaluationof structures,systems,andcomponents(SSCs)todeterminemarginsofsafetyduringnormaloperations andtransientconditionsandtheadequacyofSSCsprovidedforpreventionandmitigationofthe consequencesofaccidents.
AsgivenintheKairostopicalreportonprincipaldesigncriteriafortheKPFHR,criterion29,whichis referencedintheHermesPreliminarySafetyAnalysisReport(PSAR),states,"Theprotectionand reactivitycontrolsystemsshallbedesignedtoassureanextremelyhighprobabilityofaccomplishing theirsafetyfunctionsintheeventofanticipatedoperationaloccurrences."FortheHermestest reactor"anticipatedoperationaloccurrencesisreplacedbypostulatedevents"perPSARSection3.1.
NUREG1537,Part2,Section4.2.2,"ControlRods,"statesthatthestaffshoulddeterminethat reasonableassuranceexiststhatthescramfeaturesdesignedforthisreactorwillperformas necessarytoensurefuelintegrityandtoprotectthehealthandsafetyofthepublic.
PreliminarySafetyAnalysisReportSection13.1.10.1,"RecriticalityandUnprotectedEvents"states, "Unprotectedevents,oreventswherereactorshutdownisnotachievable,areexcludedfromthe designbasis."Inaddition,Section13.1.10.1states,"TheRCSS[reactivitycontrolandshutdown system]isdesignedwithsufficientindependence,diversity,andredundancyfromdetectionand actuationtoelementinsertiontoensurereactorshutdownwhennecessary."Toreachareasonable assurancefindingthattheRCSShassufficientreliabilitytoprecludeunprotectedevents,thestaffis requestingadditionalinformationregardingthefollowing:
- 1. Pleasedescribeanyinstrumentationandcontroldesignfeatureswhichprovidedefenseindepth orreducetheprobabilityofacommoncausefailuretoprecludeanunprotectedevent.
- 2. WhatmechanicaltestingoftheRCSSsystemwillbeperformedtoensureelementinsertion, includingtheinsertionoftheshutdownelementsintothepebblebedandcontrolelementsinto thegraphitereflector?
- 3. Ifcontrolandshutdownelements(beyondtheassumedhighestworthstuckelement)failto insert,partiallyinsert,orsufferneutronabsorberloss(e.g.,throughthelossofelementcladding integrity),areothermeansofreactivitycontrolavailabletomitigatepostulatedevents?Ifother meansarenotavailable,pleasedescribehowthereissufficientdiversityorreliabilitytojustify excludingunprotectedeventsfromthedesignbasis.
Page2of4 KairosPowerResponse NRCQuestion408,Item1
Pleasedescribeanyinstrumentationandcontroldesignfeatureswhichprovidedefenseindepthor reducetheprobabilityofacommoncausefailuretoprecludeanunprotectedevent.
KairosPowerhassubmittedchangestothePSARandanalyticalmethodstodescribehowthedesign conformedtoPDC26(ML22243A138,ML22242A168).Thechangecreditsrelianceontheshutdown elementsasdesignedwithsufficientworthtoshutdownthereactorinresponsetopostulated events.Additionally,PSARSection13.1.10.1clarifiedthemeaningofanunprotectedeventasa scenarioinwhichthesafetyrelatedreactorshutdownsystemwouldnotbeavailabletomitigatea postulatedevent.Inordertoprecludethisscenariofromoccurringinthedesignbasis,theshutdown portionoftheRCSS,thereactorshutdownsystem(RSS),isdesignedwithsafetyrelatedtreatment, asdescribedin4.2.2toensurethatthereactorwillshutdownduringapostulatedevent.
Thereactorprotectionsystem(RPS)isthespecificinstrumentationandcontrolsystemcreditedfor initiatingtheshutdownfunctionwhichisperformedbytheRSS.TheportionoftheRPSthatinitiates theRSSisthereactortripsystem(RTS).TheRSSautomaticallyinitiatestheinsertionoftheshutdown elements.
Duringnormaloperation,theRTScontinuouslysendsasignaltokeeptheshutdownelements withdrawnfromthereactorcore.Ifpowerislost,thecontinuoussignalsenttotheRCSSbytheRTS isinterrupted,andboththecontrolelementsandshutdownelementsareinsertedintothereactor (althoughonlytheshutdownelementinsertioniscreditedforsatisfyingPDC26forpostulated events).Shutdownelementpositionsarealsomonitoredusingtwoconcurrentindependentand diversemethodswhichallowforrealtimefunctionalitychecksasdescribedinPSARSection4.2.2.1.
AsdescribedinPSARSection7.3.1,theRPSincludesthefollowingsafetyrelatedtreatmentsto precludeanunprotectedevent:
Separatechannelsofsensorelectronicsandinputdevices Redundantandseparategroupsofsignalconditioning Redundantandseparategroupsoftripdetermination SafetyrelatedcomponentstoprovideelectricalisolationfromthenonsafetyrelatedDC powersystempowersupply Multiplereactortripdevices RPSisolationhardware Twodivisionsofreactortripsystem(RTS)votingandactuationequipment Thesafetyrelatedtreatmentsincludeindependenceandredundancytoensurethatthereisno portionoftheRPS(fromthedetectionofanoffnormaleventtotheautomaticinitiationofthe shutdownfunctionofRSS)thatissubjecttoasinglefailure.
TheRPSdesignalsoincludesdiversedesignfeaturestoprecludecommoncausefailures.TheField ProgrammableGateArray(FPGA)portionoftheRPScouldbepostulatedtoexperienceasoftware logicbasedcommoncausefailure.Inordertoprecludesuchanunlikelyfailure,theRPSrequiresat leasttwodifferentFGPAarchitectures(e.g.,onetimeprogrammableorflashbased,andstatic
Page3of4 randomaccessmemory).Additionally,alossofpowertotheRPScouldrepresentapostulated commoncausefailure.However,asdescribedabove,thedesignissuchthatalossofpowerwill resultinshutdownelementinsertion.
Additionally(althoughnotcreditedforshutdownofthereactorduringapostulatedevent),theRPS willinitiatetheinsertionofthecontrolelementsconcurrentwithinsertionofshutdownelements, providingadditionalshutdownworth.RCSScontrolandshutdownelementwithdrawalfromthecore isinhibitedbyinterlocksafteralossofpower(whichrequireamanualreset)topreventinadvertent positivereactivityinsertionwhenpowerreturnsasdescribedinPSARSection7.3.1.
NRCQuestion408,Item2
WhatmechanicalqualificationtestingoftheRCSSsystemwillbeperformedtoensureelement insertion,includingtheinsertionoftheshutdownelementsintothepebblebedandcontrolelements intothegraphitereflector?
TheresultsofthemechanicaltestingoftheRCSSthatprovideassuranceitisqualifiedtooperatein normalandpostulatedeventenvironmentalconditionswillbeavailablewiththeapplicationforan OperatingLicense.ThePSARincludescommitmentstotestsafetyrelatedstructures,systems,and componentstoensurethesuccessfulperformanceofsafetyfunctions.AsdescribedinPSARSection 4.2.2.3,thesafetyrelatedportionofRCSSwillmeetPDC4,whichrequiresthatthecontrolelements accommodatedynamiceffectsandbecompatiblewiththeenvironmentalconditionsduringnormal plantoperationaswellasduringpostulatedevents.AsdescribedinPSARChapter12,AppendixB, Section2.3.3,theadequacyofthedesignwillbeverifiedusingmethodsincludingtheperformance ofqualificationtests.QualificationtestingforthesafetyrelatedportionoftheRCSSwillbedefined inaformaltestplanthatincludesappropriateacceptancecriteriaanddemonstratesthesystem reliabilityandadequacyofperformanceunderconditionsthatsimulatethemostadversedesign basisconditions.
TheshutdownelementsanddrivemechanismswillalsomeetASMESectionIII,Division5loadsdue tooperationalstepping,reactortrip,stuckelement,fatigue,andshippingandhandling.Asstatedin apreviouslysubmittedchangetoPSARSection4.2.2.3(ML22062B679),theshutdownelementsare qualificationtestedoutofpilepriortooperationandaconservativewearlimitisestablishedto ensurethatwearduringelementmovementisacceptable.
Thereactorvesselheadpenetrations,inwhichthesafetyrelatedreactorshutdownelementsinsert throughtheuppergraphitereflectoranddirectlyintothepebblebed,meetReference1 requirements.Theshutdownelementsthemselvesarealsoqualifiedtoinsertunderseismic conditions.Thegraphitereflectorblocksaredesignedtomaintaintheirstructuralintegrity,as describedinPSARSection4.3,andarequalifiedinaccordancewithReference2.
Testingisperformedtoconfirmtheinsertiontimeofindividualshutdownelementsiswithinthe insertiontimeassumedwithinthepostulatedeventanalysis.Testingisalsoperformedtoconfirm thattheinsertiontimeofallshutdownelementsconcurrentlyinsertingiswithintheinsertiontime assumedinthepostulatedeventanalyses.AsstatedinSection4.2.2.3ofthePSAR,theinsertion capabilityoftheshutdownelementswillalsobedemonstratedaspartofstartuptestingby performinginsertiontimetesting.Aninsertiontestofeachshutdownelementwillbeforthe expecteddeflectionoftheinsertionpath.Aninsertiontestdeflectstheshutdownelementupper
Page4of4 reflectorguidestructuresconsistentwiththemaximummisalignment.Theshutdownelement insertiontimeismeasuredandcomparedtotheinsertiontimetestingperformedwithnodeflection oftheupperreflectorguidestructures.Thesetestsprovideassurancethattheupperreflectorblocks maintaintheshutdownelementinsertionpathways.
NRCQuestion408,Item3 Ifcontrolandshutdownelements(beyondtheassumedhighestworthstuckelement)failtoinsert, partiallyinsert,orsufferneutronabsorberloss(e.g.,throughthelossofelementcladdingintegrity),
areothermeansofreactivitycontrolavailabletomitigatepostulatedevents?Ifothermeansarenot available,pleasedescribehowthereissufficientdiversityorreliabilitytojustifyexcluding unprotectedeventsfromthedesignbasis.
AlthoughthereareothermeansofreactivitycontrolinadditiontotheRSS,thosemeansarenot creditedtoperformtheshutdownsafetyfunction.Thefailureoftheshutdownelementstoinsertin responsetoapostulatedeventisbeyondthedesignbasis.Manyexistingsystemsprovideassurance thattheRSShassufficientdiversityandreliabilitytoshutdownthereactorinresponsetoa postulatedevent:thesafetyrelateddesignfeaturesoftheRPSandRSSdescribedintheresponseto Item1above,thetestingdescribedinresponsetoItem2above,andtheperiodictestingand inspectionsdiscussedinPSARSection4.2.2.4.ConsistentwiththeNRCguidanceinNUREG1537,the performanceoftheRSSisevaluatedinapostulatedeventassumingthehighestworthshutdown elementdoesnotinsert.
ThecontrolportionoftheRCSSisnotcreditedforshutdownworthinthemitigationofpostulated events.However,asdescribedintheresponsetoItem1above,theRPSinitiatesaninsertionofthe controlelementsconcurrentwiththeshutdownelements.Thissystemprovidesanadditionalnon crediteddiverseandreliablemeansofreactivitycontrol.Thefourreactivitycontrolelementsinsert intotheupperandsidereflector,neartheperipheryofthecore.Section4.2.2.1ofthePSARalso statesthatthecontrolelementsareanassemblyofsegmentedannularcylinderswhichdiffersfrom thecruciformshapedshutdownelements.
References:
- 1. ASCE4319,SeismicDesignCriteriaforStructures,Systems,andComponentsinNuclear Facilities.
- 2. KairosPowerLLC,GraphiteMaterialQualificationfortheKairosPowerFluorideSaltCooled HighTemperatureReactor,KPTR014P,Revision3.
ImpactonLicensingDocument:
ThisresponsedoesnotimpacttheKairosPowerconstructionpermitapplication.However,a previouslysubmittedchangetotheKairosPowerPreliminarySafetyAnalysisReport(ML22243A138, ML22242A168)maderelevantchanges.