ML22300A212
| ML22300A212 | |
| Person / Time | |
|---|---|
| Site: | Vallecitos Nuclear Center, Vallecitos |
| Issue date: | 10/07/2022 |
| From: | Heckman D GE-Hitachi Nuclear Energy Americas |
| To: | Office of Nuclear Material Safety and Safeguards, Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML22300A209 | List: |
| References | |
| M2200143 | |
| Download: ML22300A212 (1) | |
Text
Eva l u at i o nofVallecitosNuclearCenterNTREf f l u e n tAbnormal RadiologicalConditionsEmergencyActionLevelThresholds
PROBLEMSTATEMENT TheVallecitosNuclearCenter(VNC)ReactorFacilitiesRadiologicalEmergencyPlan(REP),Revision1 (June2021)containstheEmergencyActionLevels(EALs)applicabletothereactorsatVNC,includingthe NuclearTestReactor(NTR).Section5.1oftheREPincludesabnormalradiologicalConditionsthatwould resultinanunusualeventoralertdeclaration.Foranunusualevent,RU3states:
Radiologicaleffluentlevel(µCi/cc)meetanyofthefollowingforgreaterthan60minutes:
2.4E5NTRNobleGasStackMonitor 2.4E5NTRParticulateStackMonitor 2.4E1fromanyreactorfacilityeffluentNobleGassample 4.7E3fromanyreactoreffluentHalogensample 2.4E7fromanyreactorfacilityeffluentParticulatesample 2.4E5fromanyreactorfacilityeffluentParticulatesample
Foranalert,RA3states:
Radiologicaleffluentlevel(µCi/cc)meetanyofthefollowingforgreaterthan60minutes:
1.2E4NTRNobleGasStackMonitor 1.2E4NTRParticulateStackMonitor 1.2E0fromanyreactorfacilityeffluentNobleGassample 2.4E2fromanyreactoreffluentHalogensample 1.2E6fromanyreactorfacilityeffluentParticulatesample 1.2E4fromanyreactorfacilityeffluentParticulatesample
TheEALthresholdsnotwithstanding,theNTRNobleGasStackMonitorreadsapproximately2.7E5to 3.3E5µCi/ccduringnormaloperations,whichexceedstheRU3limitforthemonitor.ProcedureNTR SOP5.2currentlysetstheoperationalalarmsetpointat9.5E5µCi/ccbasedonthestackreleaseaction levelinSARTable61ofLicenseAmendment25datedJune29,2022.Thisisapproximately4timesthe RU3EALthreshold(butbelowtheRA3EALthreshold).
BACKGROUND TheEALthresholdsforRU3andRA3werecalculatedbasedonthe10CFR20,AppendixB,Table2values fortheapplicableradionuclides.Theassumedradionuclidesareasfollows:
Table1CurrentREPEALThresholdBasis
Monitor/Sample Radionuclide NobleGas Unlisted,nonAlphaandnonspontaneousfission, greaterthan2hourhalflife ParticulateStackMonitor Unlisted,nonAlphaandnonspontaneousfission, greaterthan2hourhalflife NobleGasSample Ar41 HalogenSample I131 AlphaParticulateSample Np237
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BetaParticulateSample Unlisted,nonAlphaandnonspontaneousfission, greaterthan2hourhalflife
TheEALthresholdsweredeterminedastheactivityconcentrationthat,ifreleasedfromtheNTRstack withtheassumedX/Qdispersioncoefficient(3.48E11s/cc),andwithamodifierformultiplestack releases,wouldresultinafraction(either10%or20%)ofthe10CFR20,AppendixB,Table2effluent concentrationsformembersofthepublic.
Forthenoblegasmonitor,theunlisted,nonalpha,>2hourhalflifeeffluentconcentrationlimitof1E 12µCi/ccwasassumed.
ThebasisfortheRU3EALthresholdsforRU3andRA3iscontainedintheREP,Att.3:
Figure1RU3andRA3ThresholdSetpoints(fromREPAtt.3)
Page2of7 Eva l u at i o nofVa l l e c i t o sNuclearCenterNTREf f l u e n tAbnormal RadiologicalConditionsEmergencyActionLevelThresholds
Thesiteboundaryreleaseconcentrations(above)aredeterminedbyadjustingthe10CFR20Effluent concentrationlimit(whichcorrespond)to50mrem/yr,toaconcentrationof4mR/hr(fortheunusual eventdeclaration)or20mR/hr(forthealertdeclaration)TheNTRStackReleaseRate(inµCi/s)isthat concentrationadjustedbytheassumed/Q(3.48E11sec/cc).TheNTRStackReleaseconcentration thenaccountsfortheNTRstackreleaserate(nominal1800cfm).
SYSTEMCONFIGURATION EffluentsfromtheNTRarereleasedviatheNTRstack.Thenoblegassampleisdrawnfromthestackat arateof1cfm.Thesampleispulledthroughaparticulatefilter,thenacharcoalfilter,andfinallyinto thenoblegas(Kanne)detector(Seefigurebelow).Assuch,thesamplemeasuredbythenoblegas monitorshouldonlycontainradioactivenoblegases,astheparticulatesandhalogenshavebeen strippedout.TheNTRstackexhaustispoweredbya3000cfmmotor,whichnominallyoperatesat1800 cfm.
Figure2NTRVentilationSystem(fromSARFigure63)
EVALUATION ThebasisforthenoblegasmonitorEALthresholdisthattheapplicable10CFR20effluentconcentration isbasedontheUnlisted,nonalpharadionuclideswith>2hourhalflife.Thatvalue,however,assumes thattheunlisted,orunknownradionuclidesmayincludeparticulates.However,basedonthesystem configurationnoparticulatesnorhalogensarepresent.Theeffluentconcentrationlimitsfor particulatesandhalogensaregenerallymuchlowerthanthosefornoblegases.Alowereffluent concentrationlimitwillresultinacorrespondinglylowerEALthreshold.
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Foranaccident(oroperating)scenario,theradionuclidesthatwillbeseenbythenoblegasmonitorwill beradioactivenoblegases.Undernormaloperations,thatispredominantlyAr41.Underaccident scenarios,theradionuclideswillbethevariousisotopesoffissionnoblegases,namelyKryptonand Xenon.The10CFR20AppendixB,Table2EffluentConcentrationsforpertinentradionuclidesareas follows:
Table210CFR20AppendixB,Table2EffluentConcentrations
Nuclide 10CFR20AppendixB Table2Effluent ConcentrationLimit (uCi/cc)
Unlisted 1.00E15 alpha Unlisted>2 1.00E12 hour Unlisted<2 1.00E09 hour Kr88 9.00E09 Ar41 1.00E08 Kr74 1.00E08 Xe121 1.00E08 Kr77 2.00E08 Kr87 2.00E08 Xe138 2.00E08 Xe123 3.00E08 Kr76 4.00E08 Xe120 4.00E08 Xe135m 4.00E08 Xe127 6.00E08 Kr79 7.00E08 Xe125 7.00E08 Xe135 7.00E08 Kr85m 1.00E07 Xe122 3.00E07 Xe133 5.00E07 Xe133m 6.00E07 Kr85 7.00E07 Xe129m 9.00E07 Xe131m 2.00E06 Kr81 3.00E06 Kr83m 5.00E05
Asshownabove,thesmallestandmostconservativeeffluentconcentrationthatwouldbeseenbythe noblegasmonitoris9E09µCi/ccforKr88.
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However,theeffluentconcentrationlimits(ECL)in10CFR20AppendixB,Table2donothaveconsistent dosebasis.PerReg.Guide4.20,radionuclideswithastochasticbasedAnnualLimitofIntake(ALI)have anECLbasedona50mrem/yrdosebasis.Forpurposesofthisevaluation,thatisanyparticulateor halogenradionuclide.Conversely,forradionuclideswithasubmersionbasedALI(i.e.,noblegases)the ECLisbasedona100mrem/yrdosebasis.Asaresult,thenoblegasmonitorEALthresholdsmustbe calculatedassumingthatthe10CFR20ECLresultsina100mrem/yrdoserate.
TheREPAtt.3calculationsforthenoblegasmonitorEALthresholdsforRU3andRA3shouldbe1.07E 01µCi/ccand5.34E01µCi/cc.respectively.
CONCLUSIONANDRECOMMENDATION TheRU3EALthresholdforthenoblegasmonitorascontainedintheVallecitosRadiologicalEmergency Planisincorrectandoverlyconservative,becauseitisbasedonanoverlyconservative10CFR20 effluentconcentrationvalue.Themostconservative,butreasonable,effluentconcentrationvaluefora radionuclidethatwillbedetectedbythenoblegasmonitorunderaccidentconditionsisKr88.
ConservativelyassumingallfissiongassesreleasedduringanaccidentareKr88,theRU3andRA3EAL thresholdforthenoblegasmonitorshouldberevisedto2.13E01µCi/ccand1.07E+00µCi/cc.
WhilethischangeresultsinanonconservativeadjustmentinbothEALs,theexistingbasiscurrently yieldsacalculatedRU3levelof2.4E5µCi/cc.ThisisnotdiscerniblefromnormalAr41effluentreleases whichrangefrom2.7E5µCi/ccto3.3E5µCi/cc.Further,itisbelowtheeffluentalarmsetpointforthe NTRstackmonitorof9.5E5µCi/ccand,asaresult,providesnopromptfortheoperatorstosuspect theymaybeenteringintoanEAL.Thischangedoesnotconstituteareductionineffectiveness.Itdoes resultinanoverallimprovementtotheemergencyplanningfunctionofclassifyingemergenciesby providingadiscernibleyetconservativeRU3setpoint.Thischangedoesnotreducethecapabilityto performanyemergencyfunctionintheeventofaradiologicalemergencyasper10CFR50.54(q)(1)(iv).
ArevisedREPAppendix3EALTechnicalBasesisshownbelow:
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Appendix3-EALTechnicalBasesforEffluentReleases
Method:10CFR20effluentconcentrationlimits,representativeofa50mrem/yrdose,areadjustedto anequivalentconcentrationlimitfortheEALsiteboundarythresholdvalueinmr/hr.Thesiteboundary EALconcentrationlimitisbackcalculatedtoaneffluentstackreleaserateusingthelimitingSARX/Q dispersionfactorandstackflowrate.
NobleGas*Kr88 9.00E09 7.01E10 2.02E+011.07E01 NobleGas**Ar41 1.00E08 7.01E06 2.02E+05 2.37E01 Halogen**I131 2.00E10 1.40E07 4.03E+03 4.74E03 AlphaParticulate**Np237 1.00E14 7.01E12 2.02E01 2.37E07 BetaGammaParticulate** 1.00E12 7.01E10 2.02E+01 2.37E05
NobleGas*Kr88 9.00E09 3.51E09 1.01E+025.34E01 NobleGas**Ar41 1.00E08 3.51E05 1.01E+06 1.19E+00 Halogen**I131 2.00E10 7.01E07 2.02E+04 2.37E02 AlphaParticulate**Np237 1.00E14 3.51E11 1.01E00 1.19E06 BetaGammaParticulate** 1.00E12 3.51E09 1.01E+02 1.19E04
CalculationsConstants 10CFR20EffluentConcentrationDoseBasis-Stochastic(mrem/yr): 50 10CFR20EffluentConcentrationDoseBasisStochastic(mrem/hr): 5.70E03 10CFR20EffluentConcentrationDoseBasis-Submersion,noblegas(mrem/yr): 100 10CFR20EffluentConcentrationDoseBasis-Submersion,noblegas(mrem/hr): 1.14E02 EALRU3Limt(mR/hr): 4 EALRU3Limt(mR/hr): 20 LimitingX/Q*(sec/cc): 3.48E11 NTRBldg105StackFlowRate*(cfm): 1800 ConversionFactor(cc/secpercfm): 471.95 NTRBldg105StackFlowRate(cc/sec): 8.50E+05
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- 10CFR20effluentconcentrationlimitforKr88,themostconservativevalueforfissionnoblegases.
- BasedonNTRSARSection6.4fornormaloperations
CompletedBy: 10/6/2022 DuaneM.DeMoreCHP,VNCRSO Date
ReviewedBy: 10/7/2022 DaveHeckman Date
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