ML22286A242
| ML22286A242 | |
| Person / Time | |
|---|---|
| Site: | Hermes File:Kairos Power icon.png |
| Issue date: | 10/13/2022 |
| From: | Kairos Power |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22286A240 | List: |
| References | |
| KP-NRC-2210-008 | |
| Download: ML22286A242 (3) | |
Text
PostulatedEventAnalysisMethodology NonProprietary DocNumber Rev EffectiveDate KPTR018NP 1
September2022
©2022KairosPowerLLC
29of98 duringthetransient;peakvesselandcorebarreltemperaturesarekeyfigureofmerittoensurethe reactorvesselperformsitssafetyfunction.
Thefiguresofmeritusedforsystemscodeanalysis(KPSAM)areasurrogatefordemonstratingthat consequencesareboundedbyMHAdoses,orformaintainingacoolablegeometry.However,ifdoseis thefigureofmeritforanevent(i.e.,adoseanalysisisperformedfortheevent),thenthosesurrogate figuresofmeritfordosedonotneedtomeetacceptancecriteria,becausethedoseacceptancecriterion isbeingexplicitlyevaluated.Likewise,whenafigureofmerithasbeenanalyzedseparatelyforbounding conditions(e.g.,astructuralanalysisofthevesselisperformedseparatelyfromthesystemsanalysis) thenthatfigureofmeritdoesnotneedtobeanalyzedinthesystemscodetomeetanacceptance criterion.
Thefiguresofmeritderivedforeachpostulatedeventandtheassociatedacceptancecriteriaare providedinTable32.Theapplicableevent(s)arethosethatareexpectedtoprovidethelimitingcase foragivenfigureofmerit.
3.4.2.1 PeakTRISOTemperatureTime Thereleasepathwayforfuelisdiffusionalreleaseasafunctionoftemperature.Duringapostulated event,peakTRISOtemperatureisboundedbytemperaturetimecurvederivedfromtheassumedMHA fueltemperaturetimecurvetolimitdiffusionofradionuclidestolessthantheamountduringtheMHA.
BoundingtemperaturetimecurvederivedfromtheassumedMHAtemperaturetimecurvecanbe basedonintegratedeffectsondose.
3.4.2.2 TRISOFailureProbability BasedonTRISOfuelqualificationeffortsasdescribedin(Reference26),itisexpectedthatduringa postulatedevent,incrementalfailureofTRISOfuelislimitedtoanegligiblelevelifthepeaktemperature isbelow1600°C.FailureprobabilityofTRISOfuelcanincreaseduetooverpressureintheTRISO particles,whichisafunctiontemperature.ThefailureprobabilityofTRISOfuelisevaluatedusingthe methodologydescribedinSection4.2.
3.4.2.3 PeakFlibecovergasinterfacialtemperatures RadionuclidereleasefromFlibeisthroughevaporation.Duringapostulatedevent,peakFlibecovergas interfacialtemperatureisboundedbytemperaturetimecurvederivedfromtheassumedMHAFlibe covergasinterfacialtemperaturetimecurvetolimitevaporationmasstransferofradionuclidestoless thantheamountduringtheMHA.BoundingtemperaturetimecurvederivedfromtheassumedMHA temperaturetimecurvecanbebasedonintegratedeffectsondose.
3.4.2.4 Peakvesselandcorebarreltemperature Topreventvesselfailureandmaintainlongtermcoolingduringapostulatedevent,thepeakvesseland corebarreltemperaturesmustbelessthanboth(a)amaximumallowabletemperaturederivedtolimit excessivecreepdeformationanddamageaccumulationand(b)750°C.Themaximumallowable temperatureiscalculatedsothatthecreepstraininducedbyprimarymembranestresseswithinthe vesselandthecorebarreldoesnotexceed1%attheendofreactorlife.Itsderivationreliesonthe followingassumptions:
AllregionsofthevesselandcorebarrelincontactwithFlibeareexposedtotemperatureslower thanorequalto650°Cforthehotoperatingtimeofthevesselandtemperatureslowerthanor
PostulatedEventAnalysisMethodology NonProprietary DocNumber Rev EffectiveDate KPTR018NP 1
September2022
©2022KairosPowerLLC
30of98 equaltothevesselandcorebarrelpeaktemperaturesforamaximumdurationof360hours(15 days).
Themaximumprimarystressesundergonebythevesselandcorebarrelcanbeboundedbya maximumstressvaluederivedasdescribedintheevaluationmodelforstructuralintegrity.
3.4.2.5 Minimumreactorvesselinnersurfacetemperature ToensurethattheFlibetemperaturewithinthevesselremainsabovetheFlibefreezingtemperature duringthemissiontimeoftheDHRSforatleast72hours,alowerlimitonthereactorvesselinner surfacetemperatureisconservativelysettotheFlibefreezingtemperature.
3.4.2.6 Airbornereleasefractionofspilled/splashedFlibe Duringasaltspillevent,aerosolscanbegeneratedthroughjetbreakup,andspillingandsplashing.The airbornereleasefractionsduetoaerosolizationmustbelimitedsothatthedoseconsequencesofthe saltspilleventsareboundedbytheMHA.
3.4.2.7 VolatileproductsfromFlibechemicalreactions Flibecouldbeexposedtoairduringasaltspillevent.ThekeyreleasepathwayofradionuclidefromFlibe isthroughevaporation,whichisafunctionofvaporpressureoftheradionuclidespecies.WhenFlibeis exposedtoair,theFlibeairchemicalreactiondoesnotresultinexcessivereactivevaporizationwhich wouldformradionuclidechemicalspeciesthathaveahighervaporpressurethanthosealreadyexistsin Flibecirculatingactivity.ItisexpectedthatafewspecificRNchemicalspecieswillhaveahighervapor pressureafterreactingwithairthanthoseinthecirculatingactivity.However,thosespeciesare expectedtobepresentatverylowconcentrationsandtheresultingdifferenceinevaporationratewill beofminimalsignificance.Forexample,CsFdissolvedinFlibedoesnotreactwithairtoformahighly volatilecesiumhydroxide.Assuch,Flibeairreactiondoesnotresultinsignificantadditionalreleaseof radionuclidesfromFlibethroughevaporation.
ThereactorcellfloorisassumedtobedesignedtoprecludeFlibeconcretereaction.WhenFlibeis spilled,ithasthepotentialtocomeincontactwithstainlesssteelandinsulationmaterial.Flibe interactionswithstainlesssteelandinsulationdonotresultinformationofradionuclidechemical speciesthathaveahighervaporpressurethanthosealreadyexistsinFlibecirculatingactivity.
Therefore,FlibestainlesssteelandFlibeinsulationreactionsintheHermesdesignbasisdonotresultin additionalreleaseofradionuclidesfromFlibethroughevaporation.
Duringasaltspillevent,Flibeisnotexposedtowater,andthereforenoFlibewaterreactionneedtobe considered.However,ifacommoncausefailure(e.g.,seismic)causesawatercontainingSSCandFlibe containingSSCtofailconcurrently,theamountofwaterthatFlibecouldbeexposedtoisassumedtobe limitedtoanupperboundlimitbydesign.Wheninteractingwiththisupperboundamountofwater, Fliberedoxpotentialisstillmaintainedwithintheboundsofsaltchemistryconditionsdefinedforthe evaporationmodel;therefore,doesnotresultinadditionalreleaseofradionuclidesfromFlibethrough evaporation.
3.4.2.8 Masslossofstructuralgraphiteandpebblecarbonmatrix PebblesandstructuralgraphitenotsubmergedinFlibecanoxidizewhenexposedtoair.Ifthemassloss ofthepebblecarbonmatrixdoesnotextendtothefueledzone,tritiumreleaseistheonlyadditional MARreleasepathwaytobeconsideredwhenfuelpebbleoxidizes.Tritiumispuffreleasedfromoxidized pebblecarbonmatrixandoxidizedstructuralgraphite.IntheMHAanalysis,theassumedtemperature
PostulatedEventAnalysisMethodology NonProprietary DocNumber Rev EffectiveDate KPTR018NP 1
September2022
©2022KairosPowerLLC
56of98 Table32:DerivedFiguresofMeritandAcceptanceCriteriaforPostulatedEvents FigureofMerit AcceptanceCriterion ApplicableEvents PeakTRISOtemperaturetime Generallyboundedbytemperature timecurvesderivedfromthe assumedMHAfueltemperature timecurve SaltSpills,Reactivity Insertion,IncreaseinHeat Removal,LossofForced Circulation,PHSSbreak, Seismic TRISOfailureprobability NegligibleTRISOfuelfailure probability SaltSpills,Reactivity Insertion,IncreaseinHeat Removal,LossofForced Circulation,PHSSbreak PeakFlibecovergasinterfacial temperature Generallyboundedbytemperature timecurvesderivedfromthe assumedMHAFlibecovergas interfacialtemperaturetimecurve
SaltSpills,Reactivity Insertion,IncreaseinHeat Removal,LossofForced Circulation,PHSSbreak Peakvesselandcorebarrel temperatures Boundedbyboththemaximum allowabletemperaturederivedto limitexcessivecreepdeformation anddamageaccumulationandby 750°C(highestvesseldesign temperature)
SaltSpills,Reactivity Insertion,IncreaseinHeat Removal,LossofForced Circulation,PHSSbreak Minimumreactorvesselinner surfacetemperature AboveFlibemeltingtemperature LossofForcedCirculation (overcooling)
Airbornereleasefractionof spilled/splashedFlibe Belowairbornereleasefraction limitderivedtoboundtotalreleases ofthepostulatedeventtolessthan theMHA SaltSpills,Seismic Volatileproductformationfrom Flibeairreaction Negligibleamountofadditional volatileproductsformed SaltSpills,PHSSbreak Volatileproductformation fromFlibechemicalreactionwith water,concrete,and/or constructionmaterials(e.g.,
insulation,steel)
Negligibleamountofadditional volatileproductsformed SaltSpill Masslossofpebblecarbon matrixduetooxidation Masslossdoesnotextendintothe fueledzone SaltSpills,PHSSbreak Masslossofstructuralgraphite duetooxidation BoundedbytheMHArelease SaltSpills,PHSSbreak Peakstructuralgraphite temperaturetime Generallyboundedbytemperature timecurvesderivedfromthe assumedMHAstructuralgraphite temperaturetimecurve
SaltSpills,Reactivity Insertion,IncreaseinHeat Removal,LossofForced Circulation,PHSSbreak