ML23086C025

Enclosure 1: NRC Ntr License Renewal Audit Questions

ML23086C025
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Site:	Vallecitos Nuclear Center
Issue date:	03/24/2023
From:	GE-Hitachi Nuclear Energy Americas
To:	Office of Nuclear Reactor Regulation
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Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION001 1

GEHmodifiedTS3.7.4,table33,StackReleaseActionLevelsinrevision5ofthetechnicalspecificationsand indicatedindiscussionthatthiswouldbeexplainedinEnclosure1,tosubmittalof2/23/23(ML23054A321).The reasonforthechangeisexplainedbutthealarmsetpointsarenotexplainedsuchthatitcanbeunderstoodwhere theycamefromoriftheywillsupporttheweeklyreleaselimit.

Theauditteamrequiresabetterunderstandingofthealarmsetpoints.PleasecleanupverbiageinTable33.

PossiblyremovetheexplanationofeffluentcalcsfromtheTSandrefertoexplanationinSAR11.2.5.

TheVNCstaffhasreviewedsections11.2.4and11.2.5oftheSARandagreeswiththeNRCauditteamthatitis confusing.Attemptstoexplainitascurrentlywrittenarealsoconfusing.Therefore,thefollowingchangeshavebeen madetotheSARandthebasisforTechnicalSpecification3.7.4hasbeenupdatedtoalignwiththecorrespondtothe SAR.

Sections11.2.4and11.2.5oftheSARhavebeenrewrittenasfollows:

11.2.4RadioactiveGaseousWasteManagement ReleaseofroutinegaseouseffluentsisdominatedbyAr41,whichisgeneratedbyneutronactivationofAr40 inair.AirborneradioactivewasteexitingthroughtheNTRstackismonitoredasradioactiveeffluentandis wellwithintheTechnicalSpecificationand10CFR20requirements.Monitoringandalarmsassociatedwith theNTRstackhavebeendiscussedinthisChapters7andSection3.5ofthisSAR.

Thereactorcellandstackventilationsystemwereoriginallyrequiredtomitigateananalyzedfueled experimentfailureofatypethathasnotbeenperformedattheNTRformorethan30years.Nevertheless, thereactorcellwillcontainanyradioactivereleasewhileitisexhaustedthroughtheventilationsystemand outthestack.

11.2.5StackReleaseActionLevels TheStackReleaseActionLevelsaredefinedasthereleaseratesforeachradionuclidegroup(noblegas,I131, betaparticulate,oralphaparticulate)atwhichactionshouldbetakentoreducethereleaserate.Ongoing operationbelowtheseStackReleaseActionLevelsensuresdosestomembersofthepublicduetoairborne releaseareatorbelowthe10CFR20.1101(d)limitof10mremperyear.Themethodforestablishingthe StackReleaseActionLevelsisdescribedbelow.

TheVNCisamultilicensedsitethatperformsprocessesnotassociatedwiththeNTR.Theseprocessestake placeinotherbuildingsapartfromBuilding105thatalsoemitradionuclidesfromstacks.Thisisrelevantfor tworeasons.

First,contributionsfromallstackstositeboundaryexposuremustbeaccountedforinestablishingthestack actionlevelsforeachstack.Thisisconservativelyandsimplydonebyassumingeachstackproduceshalfof thedoseatthesiteboundaryandapplyinganotherstackreductionfactorof2.

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION001 2

Second,whileallsitestackactionlevelsdiscussedinthissectionaretrackedbythesiteseffluentprogram, onlygasesandparticulatesareincludedinTechnicalSpecification3.7.4.ThisisbecausetherealtimeNTR effluentmonitorsareonlycapableofdetectinggaseousandparticulate(,)releases,makingthesetheonly StackReleaseActionLevelsthatareactionablebytheNTRoperators.Alphaparticulateandhalogen(I131) releasesareevaluatedviasamplescollectedandcountedonaweeklybasisandaremonitoredaccordingto thesiteseffluentcontrolprogram.

11.2.5.1 BasisforStackReleaseActionLevels TheStackReleaseActionLevels(weeklytotalorspecificconcentrations)fornoblegasreleasesfromtheNTR stackensurethattheactivityreleasedwillnotexceedanannualaverageconcentrationofAr41atthesite boundaryof10%oftheannualeffluentconcentrationlimit(ECL)in10CFR20,AppendixB,Table2Column 1.Ar41hasbeenshowntobethepredominantnoblegasinthestackeffluent(Climent,1969).Fission producednoblegasesareaminorfractionunlessfuelmaterialisexposedtotheeffluentair.Ar41is producedbytheneutronirradiationoftheairpassingthroughthereactor.

TheStackReleaseActionLevelsforallotherisotopegroupsensurereleasesfromeachstack(includingNTR)at theVNCwillnotyieldanannualaverageconcentrationatthesiteboundaryof20%ofthe10CFR20effluent concentrationlimitfortherestrictive,credibleisotopesofeachoftheisotopegroups:I131,unidentifiedbeta radionuclide,andNp237.

Oncereducedbyafactorof2toaccountforotherstacks,theStackReleaseActionLevelsensurethatany singlestackreleasewillnotexceedanannualaverageconcentrationthatiseffectively5%oftheECLforAr41 and10%oftheECLforothercredibleisotopes.

11.2.5.2 ComputingStackReleaseActionLevels ToderivetheStackReleaseActionLevel,aboundingreleaseconcentrationrate(µCi/sec)mustbedetermined thatwillnotexceedtheeffectiveECL(5%forgasand10%forother).Todothis,theeffectivesiteboundary ECLisdividedbytheatmosphericdispersion(/Q)factor(sec/ml)todeterminetheallowablereleaserate

(µCi/sec)atthestack(pointofrelease).Theallowablereleaserateisthenadjustedtoaweeklyreleaserate

(µCi/week),whichhasbeendeterminedtobeanactionabletimeperiodinwhichoperatoractionscanbe takentoensurethestackreleasedoesntchallengetheeffectiveECL.Theallowablereleaserateisthen adjustedfortheaveragesitebuildingventilationflowrate(1800ft3/min)todeterminethespecific concentrationStackReleaseActionLevel.Fornoblegas(Ar41)andbeta/gammaparticulates,thespecific concentrationStackReleaseActionLevelsareappliedinTechnicalSpecification3.7.4astheAlarmSetpoints fortheeffluentmonitorsandarethenfurtheradjustedtoprovideweeklyreleaseStackReleaseActionLevels basedona30hroperationalweekaccountingforthefactthattheseconcentrationsaremonitoredinreal time.

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION001 3

Table 11-4 STACK RELEASE ACTION LEVELS Stack Nominal

FlowRate, cfm NobleGas Ci/wk

µCi/cc Halogen mCi/wk

µCi/cc Alpha

µCi/wk

µCi/cc Beta

µCi/wk

µCi/cc 105,NTR 1.80E+03 9

• 9.5E05 3.48E+02 6.8E07 1.74E+01 3.4E11 1.74+E03 1.9E08

• Accesstothereactorcellwhenthereactorisnotoperatingisprocedurallycontrolledby observationofCAM(seeTable113)activityreadings.

11.2.5.3 Assumptions Stackflowratesfluctuate.Forexample,theNTRflowdependsonthepositionofthecelldoor.Theflowinall filteredsystemsvariesasthedustloadingonfiltersincreasesandascontainmentsystemsarechanged.The 1,800cfmaveragestackflowrateforBuilding105isusedforlimitingconcentrationsandcalculating measuredreleases.

TheapplicableeffluentconcentrationlimitvaluesfromAppendixB,Table2,Column1of 10CFR20aregivenbelow:

ReleaseCategory Limiting Isotope 10CFR20Effluent ConcentrationLimit,

µCi/ml NobleGas*

Ar41 1.00E08 Halogen I131 2.00E10 AlphaParticulate Np237 1.00E14**

BetaGammaParticulate 1.00E12 Thedilutiondispersion(/Q)factorandreductionfactortoaccountforreleasesfrom otherstacksonsitearegivenbelow:

StackLocation

/Q,sec/ml Otherstackreduction factor Building105,NTR 3.48E11 2

• TheNTRnoblegasinventoryavailabletotheboundaryhasbeenfoundtobeprimarily Ar41,whichisanactivationproductofair.Fissionproductswouldbeofconcernin theeventoffuelfailure,anabnormalcondition.

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION001 4

• • Thereareseveralisotopeswithmorerestrictivelimits,buttheycanbeshowntobe insignificantfractionsofthetypicalmixofalphaemittersfoundatVNC.

• • • Unidentifiedisotopes,whereseveralnatural,transuranic,andotherrareelementsare knowntobeabsent.Thesearemainlyalphaemitterswhichwouldbeaccountedforinthe alphaanalysis.

TheannualaveragedilutiondispersionfactorfortheNTR,andtheotherstacksatVNC,wascalculatedfrom validhourlyrecordsofmeasuredmeteorologicalconditionsforatwoyearperiodin1976and1977.The sectoraverage/Qfactorswereconservativelycomputercalculatedforeachof16sectors(22.5degrees each)using:

Scaleddistancesfromasitelayoutmaptodeterminethedistancesfromthereactortothecenterof thesectoratthesiteboundary.

Abuildingcrosssectionof281squaremeters,forwakeeffects.

Agroundlevelreleaseelevation.

Nocredittakenforplumedepletion.

Thesinglemaximumcalculatedannualaverage/Qvalueof3.48E11sec/mlwasselectedfromthe16sector averagevalues.Thisvalue,whichhappenstooccurintheeastsoutheastsectorat622metersfromthestack, isusedtodeterminetheNTRstackreleaselimits.

TheECLreleaserate,i.e.,thecontinuousreleaseratewhichwouldproduceanannualaverageboundary concentrationequivalenttotheECL,wouldbecalculatedbydivisionoftheECLbythe/Qvalue.TheAction Levelratesarecalculatedas5%oftheECLreleaseratesfornoblegas(10%oftheECLreleaserate,anda reductionfactorof2forreleasesfromotherstacks).TheActionLevelReleaseRatesarecalculatedas10%of theECLreleaseratesforotherisotopegroups(20%oftheECLreleaserateandareductionfactorof2for otherstacks).

IsotopeGroup ActionLevelRelease RatesµCi/sec NobleGas 1.44E+01 Halogen 5.75E01 Alpha 2.87E05 Beta 2.87E03 Theseconservativereleaseratelimitsareconvertedandpresentedasactionlevelsbasedoncumulative weeklyreleasesinTable114Table114andtheTechnicalSpecificationweeklyreleaseratelimitsofTable33 inChapter14,TechnicalSpecifications.

AnormalmaximumoperatingtimefortheNTRtypicallywouldnotexceed30hoursinaweek.Therefore,this partialoperatingtimeisusedtocalculatetheoperatingstackeffluentconcentrationlimits.

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION001 5

TechnicalSpecification3.7.4Basisisrewrittenasfollows:

Thebasisstatementhasbeenchangedtoread:

ThestackreleaseactionlevelsarebasedontheannualaveragedilutionfactorfromtheNTRstacktotheSITEboundary.

Anominalstackflowrateof1800ft3/minand30hoursperweekNTRoperationtimeareassumed.Thisinformation, alongwithotherconservativeassumptions,ensuresthateffluentconcentrationsatthesiteboundarywillnotexceed thoselistedin10CFR20,AppendixB,Table2,Column1,norwillthedosefromairemissionsexceedthe10mrem/yr constraintfrom10CFR20.1101(d).AdetaileddescriptionoftheweeklyreleaseandalarmsetpointscanbefoundinSAR sections11.2.4and11.2.5.

TechnicalSpecification3.7.4table33hasbeenupdatedasfollows:

Table33 STACK RELEASE ACTION LEVELS

GaseousActivity (Ar41)

ParticulateActivity (Beta)

Weeklyrelease

9Ci/wk

1.7E+03µCi/wk

Alarmsetpoint

9.5E05µCi/cc

1.9E08µCi/cc Due to slight variations in assumptions used in calculation, some values in Table 11-4 have been changed. The spread sheet below is provided to demonstrate corrections made to some values. The real time operating limits are used in Technical Specification 3.7.4 as the Alarm Setpoint Stack Release Action Levels for the effluent monitor. The calculated weekly stack limits are adjusted for a 30-hr week and results for Ar-41 and

+ particles are used in Technical Specification 3.7.4 as weekly release Stack Release Action Levels. Weekly stack limits for halogens (I-131) and alpha particulate (Np-237) are tracked according to site procedure VSS 7.2, Radioactive Effluent Control.

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION001 6

Limiting Isotope in Each Category

10CFR20, Appendix B, Table 2, Column 1 ECL Dose Rate Reduction Factors Reduction Factor for Other Stacks NTR Design Basis Dilution Factor NTR Action Level Release Rate Nominal NTR Stack Flow Rate NTR Stack Action Level Concentration a How monitored?

RealTime Operation Limit b Weekly Stack Limit

(µCi/mL)

(sec/mL)

(µCi/sec)

(cc/s)

(µCi/cc)

(µCi/cc)

(µCi/week)

Ar-41 1.0E-08 10%

50%

3.48E-11 1.44E+01 849505 1.69E-05 RealTime 9.5E-05 8.69E+06 I-131 2.0E-10 20%

50%

3.48E-11 5.75E-01 849505 6.77E-07 Weekly Charcoal on Gamma N/A c 3.48E+05 Np-237

(

particles) 1.00E-14 20%

50%

3.48E-11 2.87E-05 849505 3.38E-11 Weekly particulate on Tennelec N/A c 1.74E+01

+

particles 1.0E-12 20%

50%

3.48E-11 2.87E-03 849505 3.38E-09 RealTime and Weekly Particulate on Tennelec 1.89E-08 1.74E+03

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION002 7

TS3.8.11and3.8.12inrevision5oftheNTRTechnicalSpecificationsseektoboundexperimentsforfissionable materials.TS3.8.11isgoodaswritten;however,incombinationtheydontprecludeexperimentsonnon encapsulatedplutoniumorotherwisecomprehensivelyexplaintheboundingforsuchfueledexperiments.Also,the,tosubmittalof2/23/23(ML23054A321)wasnotupdatedtoreflecttheadditionof3.8.12.Itdoesseem thattheseTSscouldbecombinedandrewordedtoclearlydefinetheboundingforfueledexperiments.

TechSpecs3.8.11and3.8.12havebeencombinedandrewordedtoalignwithboundingassumptionsmadeforthenew proposeddesignbasisaccidentinSAR13.6.4.

3.8.11 FISSILEMATERIALEXPERIMENTALLIMITATIONS ExperimentscontainingfissilematerialSHALLbeencapsulatedandlimitedtoaU235inventoryof50mg.

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION003 8

TheNUREG1537,app14.1,3.3(8)SecondaryandPrimaryCoolantRadioactivityLimits,recommendsaTSforperforming samplingforradiologicalconstituentsintheprimarycoolant.TheNTRhasnosuchTS.Theauditteamrequeststhe additionofsuchaTSoranexplanationastowhyoneisnotneeded.

NUREG1537,App14.1,3.3(8)recommendsaTSrequiring(forexample)quarterlyisotopicanalysisandweeklysampling forgrossactivitytrendingoranoutputfissionproductmonitororotherprimarycoolantcontinuousradiation monitor.ThegivenintendedpurposeofthisTSistodetectdeteriorationofcomponentsintheprimarycoolantloop, suchasacontrolelement,andleakageintothesecondarycoolantloop.BecausetheNTRprimaryoperatesat atmosphericpressureandhasminimalflowthroughthetankcore,deteriorationofthecontrolelementsisnota significantconcernandsincetheNTRsecondaryoperatesatabout30psi(higherthantheprimary),aprimaryto secondaryleakisnotafeasibleevent.MoreimportanttotheongoingoperationoftheNTRismonitoringforfuel degradation,whichiscontinuouslyandeffectivelydonebythestackmonitors.

ThisquestionwaslargelyaddressedinthedocketedresponsetoSARauditQuestion023(ADAMSML21265A247, ML21265A248,ML21265A249,ML21265A250).Asperthatresponse:

Stackparticulateandgaseousactivitieswouldprovidethefirstindicationofescapingfissionproducts.Stackalarm actionlevelsareveryclosetothenormaloperatingactivitylevelsStackactivitythatexceedsthealarmlevellimits wouldpromptanimmediatereactorshutdownaccordingtoprocedureSOP8.3,AbnormalOperation,toevaluatethe cause,whichwouldincludedrawingaprimarysampleforanalysis.

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

BecausetheNTRprimaryis,bydesign,continuouslyventedtotheatmosphereinthereactorcell,theairinthereactor cellisessentiallyanextensionoftheprimarysystemforanygaseousandvolatileconstituentsinthecoolant.Sincethe reactorcellatmosphereiscontinuallyexhaustedthroughthestack,thestackgasmonitorisextremelyreflectiveof changesinnoble(orfissionproduct)gassesinthecoolant.Thisrendersanadditionaltechspecforcoolantsample analysisunactionableandvaluelesssinceTSRev5,3.7.4wouldplacethereactorinshutdownmodelongbeforea markedincreaseincoolantgrossactivitywouldbedetected-regardlessofthefrequencyofsampling.Theonlytrue valueofsamplingthen,isasconfirmatoryanalysisorasaninvestigatorytoolfollowingastackmonitoralarm(asnoted intheaboveQuestion023response.).Asidefromapprovedmaintenancerelatedwork,thereisnoscenariothatwould resultinamarkedacuteincreaseinthestackmonitorreadingsapartfromfuelfailure.

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION003 9

AsstatedintheSARchapter16.1,GEHdoesmonitorforchronicfueldegradationbyperiodicallysamplingforSr91and Sr92-incrementalincreasesofwhichwouldbelesslikelythannoblegasestoescapefromthecoolanttothereactor cellatmosphere,andthereforelesslikelydetectedbythestackmonitor.Internal2020GEreportDBR0052607(which wasmadeavailabletotheauditteamduringtheSARaudit)concludedthatabouthalfoftheoriginalfuelcladding thicknessremainsafterover60yearsofoperation.Nevertheless,thatreportconservativelyrecommendedthatSR 91/92samplingfrequencybeincreasedtoquarterlyortriannually(3timesperyear).Italsosuggestedthattighter conductivitylimitswouldservetolimitthepossibilityoffueldegradation.

BasedontherecommendationsofDBR0052607,samplingfrequencyhasbeenincreasedtotriannuallyandthecoolant conductivitylimitloweredfrom10µS/cmto5µS/cm(aswasalsosuggestedbytheNRCauditteam(seeTS3.3.3)).

Otherguidance:

ANSI15.1hasnospecificrequirementforatechspecrelatedtoradioisotopesinthecoolantandgenerallysaysthat specificationsaretobeassignedonlytothoseparametersandequipmentrequirementsdirectlyrelatedtoverifyingand preservingthesafeoperatingenvelope.Theabilitytodetectincrementalfuelfailureisnotasafeoperatingenvelope limitingissueanditisunclearatwhatlevelofincreaseinSr91/92anactionwouldbeestablishedorwhatthataction wouldbe.

Itisnotablethatpowerreactorsroutinelyoperatewithfailedfuelelementsandthattherequiredactionforexceedinga waterchemistryLCOlimitisgenerallytoincreasesamplingfrequencytomonitortheconditionuntilthereactorisforced toshutdownbyanotherLCO.ThisLCOismostlikelyoneassociatedwithcontainmentatmosphereorventilation exhaustradiationmonitorssincecoolantinsuchreactorsistypicallyathigherpressuresthanthecontainment atmosphereandfissionproductsinevitablyleak.InthecaseoftheNTR,gasesleakcontinuallyfromthecoolanttothe reactorcellbydesign.ThismakesthestackmonitortheultimatemethodfordetectingincrementalfuelfailureandLCO 3.7.4providestheultimateassurancethatthereactorisplacedinshutdownlongbeforeairborneradiationlevels becomeimpactfultostafformembersofthepublic.

Vallecitos NRCNTRLicenseRenewalAuditQuestions QUESTION004 10

TechnicalSpecification3.5.3.13(shownbelow)isinthecurrentlyapprovedTechnicalSpecificationsbuthasapparently beenremovedinrevision5;however,nojustificationhasbeenprovided.

TS3.5.3.13-Theradioactivematerialcontent,includingfissionproducts,ofanydoublyencapsulatedorvented experimenttobeutilizedintheexperimentalfacilitiesshallbelimitedsothatthematerialsatriskfromtheencapsulation orconfiningboundaryoftheexperimentcouldnotresultinadosetoanypersonoccupyinganunrestrictedarea continuouslyforaperiodof2hoursstartingatthetimeofreleaseinexcessof0.5remtothewholebodyor1.5remto thethyroidoradosetoanypersonoccupyingarestrictedareaduringthelengthoftimerequiredtoevacuatethe restrictedareainexcessof5remtothewholebodyor30remtothethyroid.

TS3.5.3.13isnecessarytoboundtheexistingSARChapter13experimentdesignbasisaccident(DBA)whichincludes variableexposureresultsbasedondouble/singleencapsulated,powder/solid,Pu239/U235.

ThenewproposedDBAinSAR13.6.4narrowlyspecifies50mgofpowderedU235inasinglecapsuleandconcludes2hr exposureattheSABtobe66mremand5minescapeexposuretobe470mrem.PerSAR13.6.2.1,Dose consequencesfordoublycladdedorpelletformsofU235</=50mgareboundedbytheresultsofthisanalysis.

Therefore,underthenewSAR,theconditionsthatwarrantedtheneedforthistechspeccannotexistbecausetheyare outsideanalysis.ThenewproposedTSensuresexperimentsstaywithinthenewanalysis.

NewTS3.8.11(RefertoQuestion002.)providesappropriateboundingforthisupdatedanalysis.