ML23027A211

GE-Hitachi Nuclear Energy Americas, LLC, NRC Ntr License Renewal Audit Questions Set 1 Rev 2

ML23027A211
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Site:	Vallecitos Nuclear Center
Issue date:	01/27/2023
From:	GE-Hitachi Nuclear Energy Americas
To:	Office of Nuclear Reactor Regulation
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Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION003 1

-GENTRLicenseRenewalQuestionsandResponses FSARsection4.4.2statethatthecoolanttemperaturecoefficientiscalculatedbasedonoveralltemperaturechanges anddescribesdeterminationofthevoidcoefficientbyextrapolatingthetemperaturecoefficientdata.FSARfigure1319 showsthatsomevoidfractionisexpectedforsteadystateoperationatallnonzeropowerlevels.

a. Providetheexperimentaldataandcalculationsofthecoolanttemperatureandvoidcoefficientsof reactivity.

b. Basedonthediscussioninthissameparagraph,theNTCstaffinterpretsthatthecoolanttemperature coefficientincludeseffectsofbothwaterdensitychangeandvoidbuildup,antthatthevoidcoefficientof 5.7¢/%voidisonlyapplicableover124°F.

i.

IstheNRCstaffinterpretationcorrect?Ifnot,explaintheeffectsincludedinthecoolant temperaturecoefficient.

ii.

ExplainoverwhatrangesthereactivitycoefficientslistedinTable42areapplicable.

a.

Accordingtohistoricaldocumentsfrom1959to1964,valuesfortemperaturecoefficientwerepainstakingly derivedbyexperimentationandmeasurementandrequiredsomemodificationtotheplantthatincludedinstallationof a10Kwheaterandtheadditionandremovalofaluminumdiskspacerstoadjustfuelrodlength.Whilenotprovidedin tabularform,thedatawasplottedasafigureinaninternal1964document(NUSA114)producedbytheGENuclear SafetyAnalysisGroup(seeattachment).Thisresultingrelationshipprovidesforthecoolanttemperaturecoefficientthat isusedeventoday.

b.

i.Yes.TheNTRcoolanttemperaturecoefficientofreactivity,whichisdescribedonpage420ofNEDE32740P, Rev.3,istheresultofdensitychangesonly,soareconvertedtoavoidcoefficient(inthatthisisalsoanetdensity change),andthusyieldsavoidcoefficientof5.7/%voidabovethetemperaturecoefficientturningpointof124°F.It isonlyapplicableabovetheturningpoint,wherethesignofthecoefficientwillbenegative.

ii.TheCoefficientsofReactivitylistedinTable42areapplicableforthefollowingranges:

Temperaturecoefficientin:

ApplicableTemperatureRange Watercoolant Takenasapplicablebetween60°Fand~200°F.Supporting datatakenwereintherange~65°Fto~150°F(internal memoSager,March15,1965.

Innergraphite Calculatedasaverageover:74°Fto236°F Outergraphite Calculatedasaverageover:74°Fto236°F Averagevoidcoefficient 124°Fto~200°F Dopplercoefficient Alltemperatures

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION003 2

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION003 3

Therelationshipforthecoolanttemperaturecoefficientofreactivityisconvertedtoaneffectivevoidcoefficientof reactivityfortemperaturesabovetheturnoverpoint(124°F)wherebulkcoolantvoidingmaybepossible.Whilethe detailsofthisconversionfirstperformedinthe1960sarenotavailable,thevalueof5.7/%voidmaybedemonstrated tobeconservativebythefollowinganalysis.

Thecoolanttemperaturereactivitycoefficient,whichwaspreviouslydeterminedbyNTRreactivitymeasurements(prior to1965),isgivenbytheexpression:

5.7 10124 Usingpropertiesofwaterat1atmtodeveloparelationshipforthechangeinvoids(i.e.,netdensity)withachangein temperature,thiscanbeexpressedas:

5.7 10124

Voidsarecalculatedrelativeto124°Fdensitybyusingtherelationship:

%124 124 100 Thetablebelowprovidesdataofdensityvs.temperatureat1atmforwater,alongwiththecalculatedeffectivevoid fraction(inpercent),aswellastheratiooftheincrementaldifferencesintemperatureandvoid,ordT/dV.

T(°F) Density(g/cc)

V(%)

dT/dV(°F/%)

124 0.98754 0.00

125 0.98729 0.03 39.502

130 0.98597 0.16 37.407

135 0.9846 0.30 36.042

140 0.98319 0.44 35.019

145 0.98173 0.59 33.820

150 0.98023 0.74 32.918

155 0.97868 0.90 31.856

160 0.9771 1.06 31.251

165 0.97547 1.22 30.293

170 0.9738 1.39 29.925

180 0.9704 1.74 29.045

190 0.9668 2.10 27.432

200 0.963 2.48 25.988 Avg

32.35

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION003 4

Usingthatrelationship,theequivalentvoidsat200°Fis~2.5%.

Toapplythisrelationshipandhaveitrepresentareasonablevoidcoefficientacrosstheentiretemperaturerange,the averagetemperatureinthisrangeischosen.Sotheaboveequationsareappliedusingthetemperaturecoefficientof reactivityat155°F,andtheaverageofthevariationintemperaturewitheffectivevoids.Thisresultsinanevaluationof avoidcoefficientof:

5.7 10124

5.7 10155 12432.35 5.7 ¢/%

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION004 5

Insection4.4.3,theFSARstatesthatmanualpoisonsheetsshallberestrainedinamannerwhichwillpreventmovement bymorethan1/2inchrelativetothereactorcore.

b. Howmuchmovementisexpectedoncethepoisonsheetshavebeenlatchedinplace?

c. Isthismovementintheradialorazimuthaldirection?

d. Discusstheeffectonthereactivityworthofthe1/2inchofmovementofthesepoisonsheets.

a. Movementofthemanualpoisonsheets(MPS)isapproximately1mmoncelockedinplace(Figure2).This latchingmechanismwasinstalledbyCA117in11/1977.Thereare6availableMPSslots,ofwhichonly3were updatedwiththelockingmechanism.Theother3arepadlockedtopreventusageofthoseslots.

b. TheMPSareconfiguredradiallyaroundthecore(Figure1),andonlymoveparalleltotheaxisofthehorizontally configuredcore(Figure2&3).

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION004 6

TheMPScannotmoveradially(increase/decreasedistance)awayfromthecore(Figure1),norazimuthal (tiltinginanyofthe3planes)inrelationtothecore,norevencircularly(360degreetypemotion)aroundthe axisofthecore(Figure3).NorcantheMPSitselfrotateonitsownaxis(Figure3).Figure3showstheshapeof theslotthattheycanslideintowhichisaTshapethatpreventsrotations.ThewideportionoftheMPSis parallelwiththeaxisofthecore(Figure1),andthereforeonlyallowsmovementalongthatplanethesame typeofmovementthattheControlandSafetyRodsengagein.Thelockingmechanismpreventsmovement (Figure2),in(towardthecore)orout.

c. The1/2inchrelativemovementwasenteredintotheprevious(1997)SARtoboundconditionsforthe0.76$

potentialexcessreactivitylimitanalysis.AsstatedinSAR4.2.2andasexplainedinbabove,theMPS movementislimitedtoapproximately1mminaparallelplanewiththecoreaxis.

IfweassumetheMPSmovementcouldmovetheanalysisboundinglimitof1/2,andnotingthattheonly directionofmovementavailabletotheMPSisthesametypeofmovementastheRods,itwouldhaveasimilar affectforthat1/2inchofmovementasdoestheRodmovement.Thedifferencewilldependonthesizeofthat MPS.Wehaveseveralvariationsofpoisonthickness,currentlyinstalledisa1/16thickness.Fullthicknessis 2.75ofcadmiumandthethicknessrangeisfull,half,etc.,downto1/16thickness.Theanalysisboundinglimit of1/2mayhavebeenforafullthicknessMPS,whichwillnotbeinsertedatthistimeduetocoreage.

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION006 7

FSARSection4.4.4,statesthatdifferencesbetweenthecoremodelpredictedcontrolrodworthsandnetreactivity gainsfromMPSchangesandtheNTRmeasureddataarewithintheoverallmodeluncertainty.

a. Doesthisapplytosafetyrodworths?

b. Whatisconsideredincalculationoftheoverallmodeluncertainty?

6.a.Thisappliestocoremodelpredictionsofsafetyrodworth(s)sincethecoremodelanddepletionanalysisfuel isotopicresultswerevalidatedtosimulateNTRoperationandcalculatereactivityworthpredictionsforreactor componentsandcoreconfigurationchanges.ItisnotedthatNTRmeasurementsofsafetyrodworthswerenotavailable fromcurrentoperationtouseforcomparisontocoremodelpredictedsafetyrodworths.Therefore,thecoremodel predictionswerecomparedwiththehistoricalSARChapter4safetyrodworthvalues,andwerefoundtosupportthe historicalvalues.

6.b.TheoverallmodeluncertaintyisacombinationoftheuncertaintyassociatedwiththeMCNP6code,depletion analysisfuelisotopics,asmodeledNTRconfiguration,andchangesincontrolrodpositionsfromthedifferentpast operationstatepointsandcoreconfigurationsmodeled.

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION023 8

FSARsection16.1statesthatthefuelcladdingthicknessis50%ofitsoriginalvalue.Discussanddescribethelimiting thicknesswhereafuelrodwouldneedtobereplaced.

Inadditiontocorrosion,somefuelagingmechanismsconsideredfortheNTRaluminumcladUAlxfuelincludethe following:

Fatigue Creep Ductility Frettingwear Fissionproductleaching TheNTRfuelisofanonstandarddesignthatisdescribedinsection4.2.1ofthesubmittedSAR.Thefuelbearingmeatis auranium/aluminum(UAlx)compositehotrolledbetweentwolayersofaluminumintoaphysicallybonded,cladmeat strip.Thealuminumfuelcladdingisnotastructuralmember;therefore,agingmechanismsthataffectitsmechanical statesuchasfatigue,creep,andductilityhavelimitedimportancetotheresidualcladdingthickness.Rather,the aluminumcladdingsprimarypurposeistoprovideaphysicalbarrierthatpreventsdirectcontactbetweenthecoolant andtheUAlxfuelwhichinturnprovidesabarrierforunrestrictedreleaseoffuelandfissionproductstothecoolant.

Thecladdingcanservethisphysicalbarrierpurposewithonlyaminimalresidualthickness,forexamplewithaslittleas 0.001inchresidualthickness,whichisabout5%oftheoriginalcladdingthickness.Agingmechanismssuchasfretting wearandfissionproductleachingcouldbedelayedtosomeextentbyathickerresidualcladdingthickness,butthese agingmechanisms,ifactive,wouldstillbepossiblewhetherthethicknessisasfabricatedorreducedbycorrosionto 0.001inch.Since25%oftheoriginalcladdingthicknessisestimatedtoremainafter37moreyearsofoperation,the claddingisdeemedadequateoverthenextlicensingperiodtoserveitsprimarypurposeasaphysicalbarrieragainst unrestrictedfuelandfissionproductrelease.

Claddingbreachduetocorrosionrelatedcladmetalthinning,shoulditoccur,isexpectedtobealeakbeforebreak conditionwherebyseriousbreachwouldbereadilydetectedandappropriateactionstaken.Claddingbreach,leadingto escapeoffissionproductsandfueltothecoolant,ismonitoredthroughcontinuousmonitoringofstackparticulateand gaseousactivities,andperiodicsamplingoftheprimarycoolantforStrontium91and92activity.

Stackparticulateandgaseousactivitieswouldprovidethefirstindicationofescapingfissionproducts.Stackalarm actionlevelsareveryclosetothenormaloperatingactivitylevels.Seetablebelow.Stackactivitythatexceedsthealarm levellimitswouldpromptanimmediatereactorshutdownaccordingtoprocedureSOP8.3,AbnormalOperation,to evaluatethecause,whichwouldincludedrawingaprimarysampleforanalysis.

GaseousActivity(µCi/cc)

ParticulateActivity(µCi/cc)

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION023 9

NormalOperations 4.0E05 3.0E09 AlarmLevel 9.5E05 2.1E08

Periodicstrontium91and92activitymonitoringoftheprimarycoolantprovidesanindicationofalessseriousbreach conditionthanthatwhichwouldbedetectedbycontinuousmonitoringofthestackalarms.Strontium91and92are measuredinaccordancewithNTRplannedmaintenanceprocedureSOP12.15,PrimaryChemistry.Startingin2021, samplesaredrawnandanalyzed3timesperyear,whileinpastyears,anannualsamplewastaken.Therearenoaction levelsonprimarysampleactivityresults;however,strontium91and92trendsaremonitoredtolookfor unexpected/unfavorabletrendsovertime.Actionstakenbasedonunfavorablestrontium91and92trendswouldbe dependentonthenatureandseverityofthetrend,butwouldincludeactionsuptoandincludingsuspendingreactor operationtoevaluatetheconditionandtoidentifyappropriatecorrectiveactions.

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION026 10

TS1.2.15definesPotentialExcessReactivityasThatexcessreactivitywhichcanbeaddedbytheremote manipulationofcontrolrodsplusthemaximumcrediblereactivityadditionfromprimarycoolanttemperaturechange plusthereactivityworthofallinstalledexperiments.

a. Provideanexamplecalculationtoshowhowpotentialexcessreactivityiscalculatedinorderto meetTS4.1.3.1.

b. Describehowchangesingraphitetemperaturefactorintotheexcessreactivitycalculationandthe changeingraphitetemperaturethatisexpectedduringnormaloperation.

c. Couldreactivitybeaddedbyothermeansofcontrolrodmovementexceedthataddedbyremote manipulation?

a.First,recordcurrentcoolanttemperatureatT/C7.Let'sassumeit's80degrees.Next,recordyesterday'sactualexcess reactivityfromrods.Let'sassumeitwas21.5cents.Now,usingtoday'sT/C7temp,yesterday'sT/C7temp,andthe associatedtableofreactivitytotemperature,determinechangeinreactivityfromtemperature.Subtracttoday's temperaturereactivityfromyesterday'stemperaturereactivity.Assumingyesterdaywas78degrees,thiscomesoutto 6.05.5=0.5cents.Undernormaloperatingconditions,wedonotchangeMPSsheetsoranyotherreactor configurations,soourpredictedexcessinrodswilljustbe21.5(yesterday'sactual)+0.5(differencefromtemperature change)=22cents.

Nowweadd6.5centsfortheexperimentworth(thisiscoveredinSOP66,butinshort,thisisduetopinholeand sourcelogpositioning),andadd5.5cents(temperaturereactivityfor80degrees)=34cents.Thisisourpredictedtotal excessreactivity.

Attachedforvisualreferencearetworeactivitycalculationsfromdayswhenunusualtestingwastakingplace.Inthe first,datedJuly172020,ExperimentWorthislistedas0duetoremovalofthepinholeandsourcelog.Inthesecond, datedJuly202020,MPSpislistedas+17duetochangingwhichMPSwasinserted.

b.Changesingraphitetemperaturearenotactivelyfactoredintoexcessreactivitycalculations.However,itispassively included,inthatprimarycoolanttemperatureisbeingmaintainedbytheheatfromthegraphite.

Withslightseasonalvariability,graphitetemperatureisgenerally7080degreesatstartup.Overthecourseof34hours ofoperationatfullpower,graphitetemperaturewillstabilizearound120Fat6"and140Fat18".

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION026 11

c.Rodscannotbemanuallyrepositionedtoaddreactivity.Forsafetyrods,theshutdownpositionoftherodfollower andmagnetphysicallyblocktherodfrombeingwithdrawn.

Forcontrolrods,there'snoelectromagnetblockingrodwithdrawal,butthemotorthatdrivestherodfollowerwilldrive therodbackinthemomentthe"RodIn"limitswitchisnolongermadeup.Evenifthiswerenotthecase,themotor cannotbemanualhandcranked.

Vallecitos NRCNTRLicenseRenewalAuditQuestionsSet1Rev2 QUESTION026 12