ML19318D216

Enclosure Model SLR New and Significant Assessment Approach for SAMA August 2019

ML19318D216
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Issue date:	08/31/2019
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nei.org NEI1704,[Rev1]

©2017NuclearEnergyInstitute

MODELSLRNEWANDSIGNIFICANTASSESSMENT APPROACHFORSAMA

PreparedbytheNuclearEnergyInstitute Revision1 August2019 TheNuclearEnergyInstituteisthenuclearenergyindustryspolicyorganization.

Thisdocumentandadditionalinformationaboutnuclearenergyareavailableatnei.org 1201FStreet,NWWashington,DC20004

August2019 NEI1704,[Rev.1]

nei.org ExecutiveSummary

The purpose of this document is to provide a model approach for assessing the significance of new informationofwhichtheapplicantforrenewalofanuclearpowerreactoroperatinglicenseorextension ofacombinedlicenseisawarethatrelatestoeither(1)thesevereaccidentmitigationdesignalternatives (SAMDA)analysisorsevereaccidentmitigationalternatives(SAMA)analysisdocumentedintheNRCs finalenvironmentalstatement(FES,FSEIS,orEA)thatsupportedissuancepursuantto10CFRPart50(or Part54)ofthereactorsinitial(orrenewed)operatinglicenseor(2)theSAMDAanalysisdocumentedin theNRCsfinalenvironmentalstatement(FES,FSEIS,orEA)thatsupportedissuancepursuantto10CFR Part52ofthereactorscombinedlicenseandthedesigncertificationincorporatedthereinbyreference, ifany.

Themodelapproachprovidedinthisdocumentisatieredapproachthatemploysacoarsescreening processinStage1andprogressestoadetailedscreeningprocessinStage3.Applicantsthatareableto demonstrateintheStage1screeningprocessthatthereisnopotentiallysignificantnewinformationare notrequiredtoperformtheStage2orStage3evaluations.Newinformationwillbedeemedpotentially significanttotheextentitresultsintheidentificationinStage1ofanunimplementedSAMAthatreduces themaximumbenefit(MB)by50%ormore.

ThefirststageofthemodelapproachusesPRAriskinsightsand/orriskmodelquantificationstoestimate thepercentreductioninMBassociatedwith(1)anyunimplemented"FinalPlantSpecificSAMAs",and(2) thoseSAMAsidentifiedaspotentiallycostbeneficialforotherindustryplantsthathavebeendetermined tobeapplicabletobutnotalreadyimplementedattheanalyzedplant(referredtohereinasApplicable IndustrySAMAs).IntheeventthatoneormoreunimplementedFinalPlantSpecificSAMAsorApplicable IndustrySAMAsareshowninStage1toreducetheMBby50percentormore,theapplicantmustdevelop anupdatedavertedcostriskestimateforimplementingthoseSAMAs.SuchdevelopmentistheStage2 assessment.

IntheeventthattheresultsoftheStage2assessmentsupporttheStage1conclusionthatoneormore SAMAsreducetheMBby50%ormore,thosepotentiallysignificantSAMAsmustbefurtherassessedin Stage3.

TheStage3assessmentconsistsofperformingacostbenefitanalysisforthepotentiallysignificant SAMAsidentifiedinStage2.IfanypotentiallysignificantSAMAisfoundinStage3tobealsopotentially costbeneficial,thenthefindingindicatestheexistenceofnewandsignificantinformation.Hence, becausenewandsignificantinformationexists,theapplicantmustsupplementthepreviousSAMA analysis.

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nei.org Acknowledgements NEIappreciatestheconsiderableeffortofDonMacLeod(JensenHughes)indevelopingthetechnical aspectsofthisdocument.Inaddition,NEIthanksNancyRanek(ExelonGeneration)forherleadershipof theLicenseRenewalEnvironmentalTaskForceduringthedocumentsdevelopmentandthefollowing TaskForceparticipantsfortheirreviewandcommentsonmultipledrafts.WerecognizetheNEImember organizationswithwhichtheyareaffiliatedaswellformakingtheirparticipationpossible:

MichaelGallagher,ExelonGeneration TonyBanks,Dominion WilliamWebster,Dominion DavidLewis,PillsburyWinthropShawPittman DeborahLuchsinger,EnerconServices WilliamMaher,FloridaPower&LightCompany RickyBuckley,Entergy LisaMatis,TetraTech,Inc.

JeffGabor,JensenHughes MichelleOlsofsky,PacificGas&ElectricCompany MikeFranklin,DukeEnergy DaleFulton,SouthernCompany

Revision DescriptionofChanges Date Modified Responsible Person 0

InitialIssuance June2017 JerudHanson 1

ClarificationofthedefinitionofSAMAstobeanalyzedin firststageofthemodelapproachandclarificationofthe processesthatmaybeusedtoestimateStage1risk reduction.

August 2019 ChrisEarls

Notice NeitherNEI,noranyofitsemployees,members,supportingorganizations,contractors,orconsultants makeanywarranty,expressedorimplied,orassumeanylegalresponsibilityfortheaccuracyor completenessof,orassumeanyliabilityfordamagesresultingfrom,useofanyinformationapparatus, methods,orprocessdisclosedinthisreportorthatsuchmaynotinfringeprivatelyownedrights.

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TABLE OF CONTENTS 1

OVERVIEW...................................................................................................... 1 2

DEFINITION OF NEW AND SIGNIFICANT........................................................ 3 2.1 DefinitionofNewInformation.................................................................... 3 2.2 SignificantInformation.............................................................................. 4 2.2.1 ThresholdforPotentialSignificance................................................................ 5 3

ASSESSMENT PROCESS.................................................................................... 8 3.1 DataCollection........................................................................................... 9 3.2 Stage1Assessment................................................................................... 12 3.2.1 PrescreeningIndustrySAMAs..................................................................... 12 3.2.2 EvaluationofRiskReduction....................................................................... 12 3.3 Stage2Assessment................................................................................... 14 3.3.1 Stage2AvertedCostRiskAssessment........................................................... 14 3.4 Stage3CostBenefitAssessment.................................................................. 15 3.5 DocumentationoftheNewandSignificantInformationReviewforSAMA............ 15 3.5.1 ApplicantsEnvironmentalReport................................................................ 15 3.5.2 SupportingDocumentation........................................................................ 16 4

CONCLUSIONS.............................................................................................. 18 5

REFERENCES................................................................................................. 19

List of Figures Figure 1 - FV as a Function of Failure Probability........................................................................ 6 Figure 2 - RAW as a Function of Failure Probability..................................................................... 7 Figure 3 - SAMA New & Significant Assessment Flowchart....................................................... 9

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nei.org ii ListofAcronyms,AbbreviationsandInitialisms

ANS AmericanNuclearSociety ASME AmericanSocietyofMechanicalEngineers BWR Boilingwaterreactor CDF Coredamagefrequency CFR CodeofFederalRegulations e.g.

Forexample EA Environmentalassessment EIS Environmentalimpactstatement ER Environmentalreport FES Finalenvironmentalstatement FLEX Diverse and flexible coping capability to implement lessons learned from the FukushimaDaiichinuclearplantaccident FR FederalRegister FSEIS Finalsupplementalenvironmentalimpactstatement FV FussellVesely i.e.

Thatis IPE IndividualPlantExamination IPEEE IndividualPlantExaminationofExternalEvents LERF Largeearlyreleasefrequency MACCS MELCORAccidentConsequencesCodeSystem MB MaximumBenefit MSIV Mainsteamisolationvalve NRC U.S.NuclearRegulatoryCommission PRA ProbabilisticRiskAssessment PWR Pressurizedwaterreactor RAI Requestforadditionalinformation RAW RiskAchievementWorth RRW Riskreductionworth SAMA Severeaccidentmitigationalternatives SAMDA Severeaccidentmitigationdesignalternatives SGTR Steamgeneratortuberupture SLR Secondlicenserenewal SSC Structure,system,orcomponent

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1 OVERVIEW

Thepurposeoftheevaluationofsevereaccidentmitigationalternatives(SAMAs)istoidentifydesign alternatives,proceduralmodifications,ortrainingactivitiesthatarecostbeneficialandfurtherreducethe risks of severe accidents [1]. The analysis of SAMAs includes the identification and evaluation of alternatives thatreducetheriskfrom asevereaccidentbypreventingsubstantial coredamage (i.e.,

preventingasevereaccident)orbylimitingreleasesfromcontainmentintheeventthatsubstantialcore damage occurs (i.e., mitigating the impacts of a severe accident) [2]. In accordance with 10 CFR 51.53(c)(3)(ii)(L)andTableB1ofAppendixBto10CFRPart51,SubpartA,licenserenewalEnvironmental Reports(ERs)mustprovideaconsiderationofalternativestomitigatesevereaccidentsiftheNRCstaff hasnotpreviouslyconsideredsuchalternatives1fortheapplicantsplantinanenvironmentalimpact statement(EIS)orrelatedsupplementorinanenvironmentalassessment(EA).

AlicenserenewalapplicantforaplantthathasalreadyhadaSAMAanalysisconsideredbytheNRCas partofanEIS,supplementtoanEIS,orEA,doesnotneedtoprovideanotherSAMAanalysisinthelicense renewalER.InformingitsbasisfordeterminingwhichplantsneededtosubmitSAMAanalysesatlicense renewal,theCommissionnotedthatalllicenseeshadundergone,orwereintheprocessofundergoing, moredetailedsitespecificsevereaccidentmitigationanalysesthroughprocessesseparatefromlicense renewal,specificallytheContainmentPerformanceImprovement,IndividualPlantExamination(IPE),and IndividualPlantExaminationofExternalEvents(IPEEE)programs(61FR28467,28481;June30,1996).In lightofthesestudies,theCommissionstatedthatitdidnotexpectfutureSAMAanalysestouncover majorplantdesignchangesormodificationsthatwillprovetobecostbeneficial(61FR28467,28481; June 30, 1996). The NRCs experience in completed license renewal proceedings has confirmed this prediction.2 Nevertheless,theapplicantsERmustcontainanynewandsignificantinformationofwhichtheapplicant isaware(10CFR51.53(c)(iv))andtheNRCStaffmustconsiderwhethersuchinformationaffectsprior 1

Someplants(e.g.,LimerickGeneratingStation)performedanalysesofsevereaccidentmitigationdesign alternatives as components of initial plant licensing environmental reviews. Hence, the NRC considered such analysesintheEISsregardinginitialplantlicensesforthoseplants.Also,forplantsseekingsecondlicenserenewals (i.e.,60to80yearsofoperation),theNRCwillhavepreviouslyconsideredSAMAanalysesforthemintheirfirst licenserenewal(i.e.,40to60yearsofoperation)EISs.

2 AsstatedinAppendixEofNUREG1437,Revision1atE45[13].

CAUTION The purpose of this document is to provide a model approach for assessing the significance of new informationofwhichtheapplicantforrenewalofanuclearpowerreactoroperatinglicenseorextensionof acombinedlicenseisawarethatrelatestoeither(1)thesevereaccidentmitigationdesignalternatives (SAMDA)analysisorsevereaccidentmitigationalternatives(SAMA)analysisdocumentedintheNRCsfinal environmentalstatement(FES,FSEIS,orEA)thatsupportedissuancepursuantto10CFRPart50(orPart 54)ofthereactorsinitial(orrenewed)operatinglicenseor(2)theSAMDAanalysisdocumentedinthe NRCsfinalenvironmentalstatement(FES,FSEIS,orEA)thatsupportedissuancepursuantto10CFRPart52 ofthereactorscombinedlicenseandthedesigncertificationincorporatedthereinbyreference,ifany.

OnlyafterpriorconsultationwiththeNRCStaff,shouldthismodelapproachbeappliedinanyother context.

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genericenvironmentaldeterminations,reflectedintheCategory1issuesinTableB1.See61FR28467to 28468.Althoughtheissueofsevereaccidents(Issue66inTableB1)isclassifiedasaCategory2issue,it readsasfollows:

The probabilityweighted consequences of atmospheric releases, fallout onto open bodiesofwater,releasestogroundwater,andsocietalandeconomicimpactsfromsevere accidentsaresmallforallplants.However,alternativestomitigatesevereaccidentsmust beconsideredforallplantsthathavenotconsideredsuchalternatives.

Theexceptionin10CFR51.53(c)(3)(ii)(L)operatestoconvertthisCategory2issueintothefunctional equivalentofaCategory1issueforplantstowhichitapplies(ExelonGenerationCompany,LLC(Limerick GeneratingStation,Units1and2),CLI1219,76NRC377,386,October23,2012).Hence,theERina licenserenewalapplicationforanuclearplantthatqualifiesfortheexceptionmustidentifynewand significantinformationofwhichtheapplicantisawarethatrelatestothepreviousevaluationoftheissue.

TosupporttheSecondLicenseRenewal(SLR)effortsfornuclearpowerplants,theapproachpresentedin thisdocumentprovidesamodelstructurefordefining,identifying,evaluating,anddocumentingwhether newinformationissignificantwithrespecttoaSAMAanalysispreviouslyconsideredbytheNRC.

However, this document does not provide guidance on the process to be used by license renewal applicantsforevaluatingthesignificanceofnewinformationrelatedtotheNRCsotherconclusionin TableB1,Issue66.Thatis,theconclusionthat[t]heprobabilityweightedconsequencesofatmospheric releases,falloutontoopenbodiesofwater,releasestogroundwater,andsocietalandeconomicimpacts from severe accidents are small for all plants. Hence, license renewal applicants are cautioned to separatelyexplorenewandsignificantinformationthatrelatestothisnonSAMAanalysisconclusion.

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2 DEFINITION OF NEW AND SIGNIFICANT Inordertoprovideanassessmentofwhethernewandsignificantinformationexistswithrespecttoa priorSAMAanalysis,itisfirstnecessarytodefinetheterm.AsdiscussedbytheNRCinsection5.3.9of NUREG1437,Supplement49[8],Newinformationissignificantifitprovidesaseriouslydifferentpicture oftheimpactsoftheFederalactionunderconsideration.Thus,formitigationalternativessuchasSAMAs, newinformationissignificantifitindicatesthatamitigationalternativewouldsubstantiallyreducean impactoftheFederalactionontheenvironment.Consequently,withrespecttoSAMAs,newinformation maybesignificantifitindicatedagivencostbeneficialSAMAwouldsubstantiallyreducetheimpactsofa severeaccidentortheprobabilityorconsequences(risk)ofasevereaccidentoccurring.3Theimplication ofthisstatementisthatsignificanceisnotsolelyrelatedtowhetherornotaSAMAiscostbeneficial, butdependsalsoonaSAMAspotentialtosignificantlyreducerisktothepublic.

Atthetimeofthiswriting,theNRChasnotprovidedaquantitativemethodologyforinterpretingthe above definition of new and significant information. Accordingly, for the purposes of this model approach,thetermnewandsignificanthasbeenbrokendownintoitsconstituentpartstoaidinthe developmentofafunctionaldefinition.

There are various inputs to the SAMA analysis that could be affected by new information (e.g.,

populationchanges,riskmodelupdates,etc.),butinthecontextofaSAMAanalysis,thedetermination of whether new information is alsosignificant is ultimately made in relation to averted costrisk values,whichisaprimaryoutputmetricofaSAMAanalysis.TheavertedcostriskofaSAMAcandidateis ameasureofthechangeinrisk,expressedindollars,associatedwithimplementationoftheSAMA,and itisconsideredtobeanappropriatemeansofcharacterizingthepotentialimpactsofplantoperationon thepublicandenvironment.Thedefinitionofnewandsignificantthatisdevelopedbelowisdesigned toincludeinputsthatcanbereflectedintermsofanavertedcostrisk.

2.1 DefinitionofNewInformation NewinformationpertainstodatausedinaSAMAanalysisthathaschangedorbecomeavailablesince thetimetheprecedingSAMAanalysiswasperformed.

TherearesomeinputstotheSAMAanalysisthatareexpectedtochange,ortopotentiallychange,forall plants.Theseinputsinclude:

Updated Level 3 Model consequence results, which may be impacted by multiple inputs, including,butnotlimitedto,thefollowing:

Projectedpopulationwithina50mileradiusoftheplant Regionaleconomicdata(e.g.,valuefarmwealth,valueofnonfarmwealth Coreinventory(e.g.,duetopoweruprate)

Releasecategorysourcetermcharacteristics Eventresponsecostdata Emergency response costs (e.g., per diem food and housing expenses, per capita relocationexpenses) 3 Informationisnewandsignificantifitissufficienttoshowthatthefederalactionwillaffectthequality ofthehumanenvironmenteitherinasignificantmannerortoasignificantextentnotalreadyconsideredinanEIS.

SeeMarshv.OregonNaturalResourcesCouncil,490U.S.360,374(1989).Tobesignificant,suchinformationmust paintadramaticallydifferentpictureofimpactscomparedtothosepreviouslyevaluated.Massachusettsv.NRC, 708F.3d63,6869(1stCir.2013).

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GeneralLevel3methodologyguidanceandgenericinputs NUREG/BR0058[10]costbenefitmethodologyupdates Inaddition,otherchangesthatcouldbeconsideredtobenewinformationaredependentonplant activitiesorsitespecificchanges.Thesetypesofchangesinclude:

Theidentificationofanewhazard(e.g.,afaultthatwasnotpreviouslyanalyzedintheseismic analysis)

Anupdatedplantriskmodel(e.g.,afireprobabilisticriskassessment[PRA]thatreplacestheIPEEE analysis)

Theimpactsofplantchangesthatareincludedintheplantriskmodelswillbereflected inthemodelresultsanddonotneedtobeassessedseparately.

Nonmodeledmodifications/changestotheplant Modificationsdeterminedtohavenoriskimpactneednotbeincluded(e.g.,replacement ofthecondenservacuumpumps)4 ForriskmodelupdatesperformedtoreflectthelatestPRAmodelstateofthepractice,itisnotedthatthe actual physical plant risk may not have

changed, but because the best estimate assessment/understandingoftheriskhaschanged,itisconsideredtobenewinformation.

AtthedirectionoftheCommission[12],theNRCStaffaskedtheapplicantinarequestforadditional information(RAI)[7]whythesetofpotentiallycostbeneficialSAMAsthatwereidentifiedforplants similarindesigntoLimerickaftertheperformanceofLimericks1989SevereAccidentMitigationDesign Alternatives(SAMDA)analysiswerenotnewandsignificantinformation.Thiseventwassitespecific; however,becauseasimilarrequestcouldbemadeofanySLRapplicant,itmaybeadvisableforapplicants toconsiderwhetherpotentiallycostbeneficialSAMAsidentifiedinU.S.licenserenewalapplicationsafter submittaloftheSAMAanalysisfortheanalyzedplantcouldbenewinformation.

BWRsshouldassessSAMAsfromotherBWRsandPWRsshouldassessSAMAsfromotherPWRs.

IfthereisabasisforexcludingthisbodyofSAMAsfromthepoolofnewinformationtobeevaluated forsignificance,therationaleshouldbedocumented.

2.2 SignificantInformation InSection5.3.9oftheGenericEnvironmentalImpactStatementforLicenseRenewalofNuclearPlants RegardingLimerickGeneratingStation,NUREG1437,Supplement49[8],theNRCexplainedthatwith respecttoSAMAs,newinformationmaybesignificantifitindicatedthatagivencostbeneficialSAMA wouldsubstantiallyreducetheimpactsofasevereaccidentortheprobabilityorconsequences(risk)of severeaccidentoccurring.Thus,tobesignificant,newinformationmustresultinidentificationofaSAMA that(1)iscostbeneficialand(2)substantiallyreducesrisk.

Toapplythisframework,itisnecessarytoprovideaquantitativethresholdforsubstantialriskreduction fromaSAMA.SuchathresholdwaspreviouslydevelopedtosupporttheLimerickGeneratingStation LicenseRenewalApplication,whichhasbeenreviewedandacceptedbytheNRC.Basedonthesuccessful applicationofthethreshold usedintheLimerickLicenseRenewalproceeding todeterminewhether potentiallycostbeneficialSAMAsaresignificant,thesamedefinitionisproposedherein.Theremainder ofthissectiondescribesthatthreshold.

4 UnlesstheyimpactaspecificinputtoSAMA(e.g.,anewlowpressureturbineinthepowerconversion systemthatresultsinagreaternetelectricaloutput).

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2.2.1 ThresholdforPotentialSignificance PRAstandardsandotherrelevantindustryguidancedocumentscanbereviewedtoidentifythethresholds for what may be considered significant in risk evaluations to help develop a basis for the terms definition.ResultsofsuchareviewwerereportedtotheNRCinReference7andarereproducedbelow.

Therewereafewnotabledocumentsthatprovidenumericalcriteriathatmaybeappliedtodetermine thethresholdforpotentialsignificance.ThefirstoneistheAmericanSocietyofMechanicalEngineers (ASME)/AmericanNuclearSociety(ANS)PRAStandard[4],whichincludesthefollowingdefinitionof asignificantbasicevent:

Significantbasicevent:abasiceventthatcontributessignificantlytothecomputedrisksforaspecific hazard group. For internal events, this includes any basic event that has an FV [FussellVesely]

importance5greaterthan0.005oraRAW[RiskAchievementWorth]6importancegreaterthan2.

SimilarnumericalcriteriaalsoappearinNUMARC9301[5],whichincludesthefollowingguidance:

AnSSCwouldprobablybeconsideredrisksignificantifitsRiskReductionWorthexceeds0.5percent oftheoverallCoreDamageFrequency(RiskReductionWorth>1.005).

[]

An SSC [structure, system or component] would probably be considered risk significant if its Risk AchievementWorthshowsatleastadoublingoftheoverallCoreDamageFrequencyandshouldbe providedtotheexpertpanelasaninputinriskdetermination.

Finally,NEI0004[6]providesdetailedguidanceoncategorizingstructures,systemsandcomponentsfor licenseesthatchoosetoadopt10CFR§50.69,RiskInformedCategorizationandTreatmentofStructures, SystemsandComponentsforNuclearPowerReactors.InthediscussionofusingriskanalysesforSSC categorization,thefollowingguidanceisprovided:

TheriskimportanceprocessusestwostandardPRAimportancemeasures,riskachievementworth (RAW)andFussellVesely(FV),asscreeningtoolstoidentifycandidatesafetysignificantSSCs.The criteria chosen for safety significance using these importance measures are based on previously acceptedvaluesforsimilarapplications.

[]

Theimportancemeasurecriteriausedtoidentifycandidatesafetysignificanceare:

SumofFVforallbasiceventsmodelingtheSSCofinterest,includingcommoncauseevents>0.005 MaximumofcomponentbasiceventRAWvalues>2 Insummary,anFVvalue>0.005andaRAWvalue>2arewellestablishedindicatorsofPRAsignificance.

Thiscanbeextendedtoapplytonotjustinternaleventscoredamagefrequency(CDF)andlargeearly releasefrequency(LERF),buttoexternaleventsCDFandLERF,andotherintegratedkeyoutputfigures ofmerit.Inthecontextoflicenserenewal,theacceptedkeyoutputfigureofmeritfordecisionmakingis potentialavertedcostrisk.

5Foraspecifiedbasicevent,FussellVeselyimportanceisthefractionalcontributiontothetotalofaselected figureofmeritforallaccidentsequencescontainingthatbasicevent.

6Foraspecifiedbasicevent,riskachievementworthimportancereflectstheincreaseinaselectedfigureofmerit whenanSSCisassumedtobeunabletoperformitsfunctionduetotesting,maintenance,orfailure.Itistheratio orintervalofthefigureofmerit,evaluatedwiththeSSCsbasiceventprobabilitysettoone,tothebasecasefigure ofmerit.

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Whenavertedcostrisksareanalyzed,theFVimportancemeasureisfoundtobehighlydependentonthe assumedreliabilityofthesystemonceitisinstalled.ThisisillustratedinFigure1whichshowsanexample ofhowtheFVvaluechangeswithassumedfailureprobabilityvaluesgivenacasewherea50%reduction inthemeasuredparameterisestimatedassumingperfectreliability.Inthisexample,a0.005FVvalue wouldbeobtainedwhenthefailureprobabilityis~0.005.Thisfailureprobabilityrepresentsasystemor componentthatis99.5%reliable,whichisfairlyrepresentativeofmanycomponentsmodeledintypical PRAanalyses.

Ontheotherhand,asthereliabilityofthesystemincreases(i.e.,asthelikelihoodofsystemfailure decreases), the RAW importance measure would asymptotically approach a RAW of 2 if 50% of the measuredparametercanbeaverted.ThisisillustratedinFigure2,whichshowsanexampleofhowthe RAWchangeswithassumedfailureprobabilityvalueswhena50%reductioninthemeasuredparameter isestimatedassumingperfectreliability.Therefore,acorrelationtoaRAW>2astheacceptancethreshold forsignificanceisestablished,anda50%reductioninaplantsMaximumBenefit(MB)(asdefinedin Section4.5ofReference9)ischosenforthesignificancethreshold(i.e.,a50%reductionintheMBisa monetarymeasureofreducingtheplantsriskby50%).

Inotherwords,thethresholdthathasbeendescribedherewouldbeequivalenttoahighlyreliablesystem leadingtodoublingthecostriskwhenitistakenoutofserviceformaintenance.Thiscorrelatestoawell establishedthresholdfordeterminingrisksignificanceinthePRAapplicationsdiscussedabove.Basedon thischaracterizationofsignificance,achangethatwouldreduceaplantsMBbyafactorofatleast2 wouldbeconsideredpotentiallysignificantpendingthedeterminationofwhetheritisalsopotentially costbeneficial.Forthisapproach,therefore,plantchangesthatwouldreducetheMBbyafactorof2are characterizedaspotentiallysignificantSAMAswiththefinaldeterminationofsignificancedependent ontheresultsofacostbenefitanalysis.

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 1.00E05 1.00E04 1.00E03 1.00E02 1.00E01 1.00E+00 FVValue FailureProbability BetterReliability Figure 1 - FV as a Function of Failure Probability

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In order to apply this threshold in the context of determining whether new information might be significant,however,itisnecessarytoidentifythemodelthatwillbeusedtomeasuretheMBreduction, whichforthisapplicationisconsideredtobethemodelthatreflectsthemostuptodateunderstanding ofplantrisk(i.e.,thecurrentmodelofrecord).Theimplicationofusingthecurrentmodelofrecordwith thisdefinitionofsignificantisthatthecostbenefitinformationfromtheoriginalSAMAevaluationis supersededbythatwhichwouldbederivedbythecurrentmodel.BecausetheMBandavertedcostrisk calculationsaredirectlycorrelatedtoplantrisk,theassessmentofsignificancecanbeperformedusing onlytheLevel1andLevel2PRAmodels(i.e.,itmaynotbenecessarytoupdatetheLevel3modelorother partsofthecostbenefitanalysis).IfitcanbeshownthataparticularSAMAwouldnotreducetheCDFor anyoftheimportantLevel2releasecategoryfrequenciesinthemodelofrecordbymorethanafactorof two,thenthatparticularSAMAcouldnotreducetheMBbyafactorofmorethantwo.Therefore,that SAMAwouldnotbeconsideredpotentiallysignificantandwouldnotbeevaluatedfurtherinassessingthe significanceofnewinformation.

ThisisconsistentwiththefollowingstatementfromNUREG1437,Supplement49[8],whichindicatesthe assessmentofnewinformationcanbeframedintermsoftheimpactofSAMAimplementation:new informationmaybesignificantifitindicatedagivencostbeneficialSAMAwouldsubstantiallyreduce the impacts of a severe accident or the probability or consequences (risk) of a severe accident occurring. If there are no potentially significant SAMAs, no new information would be deemed significant.

0.00 0.50 1.00 1.50 2.00 2.50 1.00E05 1.00E04 1.00E03 1.00E02 1.00E01 1.00E+00 FailureProbability BetterReliability RAWValue Figure 2 - RAW as a Function of Failure Probability

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3 ASSESSMENT PROCESS Thissectiondescribesamultistageassessmentprocesstodeterminewhetherornotthereisanynew andsignificantinformationrelevanttoapreviousSAMAanalysis.Ifnewandsignificantinformation hasbeendeterminedtoexist,anupdatedSAMAassessmentasdescribedinNEI0501orasupplement totheSAMAanalysiswouldfollow.

Thefirststageoftheprocess(seeSection3.1)usesPRAriskinsightsand/orriskmodelquantificationsto estimatethepercentMBreductionassociatedwith(1)anyunimplementedFinalPlantSpecificSAMAs (seeSection3.1,Stage1AssessmentNewInformationElements),and(2)thoseSAMAsidentifiedas potentiallycostbeneficialforotherindustryplantsthathavebeendeterminedtobeapplicabletobutnot already implemented at the analyzed plant (referred to herein as Applicable Industry SAMAs; see subsection3.2.1).IfitcanbedemonstratedthatnoneoftheSAMAsbeingevaluatedcanreducetheMB by50percentormore7,thentheapplicantmaydocumenttheconclusionthatthereisnonewand significantinformationrelevanttothepreviousSAMAanalysis.

IntheeventthatoneormoreunimplementedFinalPlantSpecificSAMAsorApplicableIndustrySAMAs areshowntoreducetheMBby50percentormore,theapplicantmustdevelopanupdatedavertedcost riskestimateforimplementingthoseSAMAs.SuchdevelopmentistheStage2assessment(seeSection 3.2).TwooptionsareprovidedforperformingtheStage2assessment:

Option1:Performasimplified(conservative)Level3modelupdatetosupporttheupdateofthe avertedcostriskcalculations.

Option2:PerformafullLevel3modelupdatetosupporttheupdateoftheavertedcostrisk calculations.

ThedesirabilityofusingOption1willvarybyplantdependingontheavailabilityofinformation.

IntheeventthatrefinementstotheavertedcostriskcalculationsrelatedtotheStage2assessment demonstratethattheMBreductionislessthan50%forallSAMAs,thentheapplicantmaydocumentthe conclusionthatthereisnonewandsignificantinformationrelevanttothepreviousSAMAanalysis.

IftheresultsoftheStage2assessmentindicatethatoneormoreSAMAsreducetheMBby50%ormore, thentheimpactofnewinformationonthoseSAMAsmustbefurtherassessedtodeterminewhetheritis significant. New information will be deemed potentially significant to the extent it results in the identificationofanunimplementedSAMAthatreducestheMBby50%ormore.

The final determination of significance will be made in the Stage 3 assessment, which consists of performingacostbenefitanalysisforunimplementedSAMAsthatreducetheMBby50%ormore(i.e.,

potentiallysignificantSAMAs).IfsuchSAMAsarefoundtobepotentiallycostbeneficial,thenthey indicatetheexistenceofnewandsignificantinformationrelevanttothepreviousSAMAanalysis.

Figure3providesaflowchartofthe3stageassessmentprocess.

7ASAMAthatreducestheMBby50%ormoreisnotconsideredtobenewandsignificantifitwasalso determinedinthepreviousSAMAanalysistoreducetheMBby50percentormore(i.e.,inthe40to60yearER).

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Figure 3 SLR Assessment Flowchart Unscreened SAMAs Yes Document the conclusion that there is no new and significant information relevant to the SAMA analysis.

No Collect Information Pre-screen SAMAs Are there any unscreened SAMAs that could reduce the MB by 50%?

Stage 1 Update averted cost-risk assessment for potentially significant SAMAs.

Option 2 Perform full Level 3 update to support averted cost-risk calculations Option 1 Perform simplified Level 3 update to support averted cost-risk calculations Updated averted cost-risk >50% for any SAMA?

Updated averted cost-risk >50% for any SAMA?

Stage 2 Perform Cost Benefit Analysis:

The identification of potentially cost beneficial, potentially significant SAMAs implies the existence of new and significant information.

Stage 3 No No Yes Potentially Significant SAMAs Yes Yes Potentially Significant SAMAs 3.1 DataCollection An initial step of the assessment process is to identify the new information relevant to the SAMA analysisandtocollect/developthoseelementsofinformationthatwillbeusedtosupporttheassessment.

TheinformationelementsthatarerelevanttoeachoftheNEIassessmentstagesshowninFigure3are provided below. Each applicant should collect, develop, and document the information elements correspondingtothestage(s)oftheanalysisperformedforthesite.Forthosestagesofanalysisthatare notrequiredtobeperformed,thecorrespondinginformationelementsshouldbedocumentedasnew informationrelevanttotheSAMAanalysis,butdeterminednottobepotentiallysignificantbasedonthe analysisprocess.Itisnotnecessarytodevelopthedetailsoftheseinformationelements.Forexample,if aplantisabletodemonstratethatnoneoftheSAMAsevaluatedintheStage1assessmentarepotentially significant,thentheStage2inputs,suchastheprojectedpopulationwithina50mileradiusoftheplant, shouldbelistedasnewinformation,butnoworktoestimatetheactual50milepopulationisrequired.

Theabilitytoclassifynewinformationpertainingtoassessmentstagesthatarenotrequiredtobe performed as not significant is possible because, as discussed in Section 2.0, information that is significantinthecontextofaSAMAanalysisisinformationtheimpliesacostbeneficialSAMAexiststhat wouldsubstantiallyreduceplantrisk.Section2.2.1,definesasubstantialorsignificantreductionin riskasa50%reductionintheMB;therefore,iftheStage1assessmentdemonstratesthatnoSAMAscan reducetheMBby50%ormore,thennewinformationelementsthatimpactthecostbenefitanalysis cannotalterthisconclusion.Changesintheestimatesoftheconsequencesofanaccidentmayimpact Figure 3 - SAMA New & Significant Assessment Flowchart

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nei.org 10 whetherornotSAMAsarecostbeneficial,butifallStage1SAMAshavebeenshowntoreducetheMBby lessthan50percent,thenreclassificationofaSAMAascostbeneficialalonewouldnotprovidea seriouslydifferentpictureoftheimpactsoftheFederalaction(i.e.,licenserenewal)andtheinformation wouldnotbeclassifiedassignificant.

Thefollowingaretheinformationelementsthatshouldbecollectedandidentifiedasnewinformation foreachoftheassessmentstages:

Stage1AssessmentNewInformationElements PRAmodels(Level1and2)

Use the latest risk models that are available for Internal Events (including internal flooding)andforeachoftheexternaleventscontributorsidentifiedforevaluationinNEI 0501[9].

ForthoseplantsthathavenotmaintainedafullLevel2model,itwillbenecessaryto eitherupdatetheLevel2modelordevelopaprocessbywhichtherelevantrelease categoryfrequenciescanbeestimatedforeachSAMAconsideredtoensurethefull spectrumofplantriskcanbeaccountedforintheStage1assessment.Regardingthe degreeofgranularityrequiredifafullLevel2modelhasnotbeenmaintained,the followingprocessesarepossiblealternatives.

1. Groupingofreleasecategoryresultsintohighlevelcategories(e.g.,Large/Early, Moderate/Late) is adequate for the Stage 1 assessment. That is, it is not necessarytoexplicitlyquantifysubgroupssuchasLarge/Early01,Large/Early02, etc.,evenifthe40to60yearSAMAanalysisdidso.

2. Atechnicalbasiscanbeprovidedtosupporttheuseofareducedsetofrelease categoriesfortheStage1assessment.Forexample,ifinformationisavailable thatdemonstratesasubsetofreleasecategoriesarenotsignificantcontributors torisk,itwouldbepossibletoprecludethemfromexplicitquantificationformost conditions(seeSection3.2.2).

NotethatRAIson40to60yearSAMAanalyseshaveoftenrequestedtheassessmentof newinformationnotintheplantriskmodels;therefore,applicantsshouldbeprepared to extrapolate the impact of forthcoming model revisions and/or updated modeling techniquesintotheresultsoftheevaluation.

Thesetypesofissueswillvarybyplant,andtheymaybeinfluencedbycurrentindustry issues.

Plantchangesnotyetincorporatedintoplantriskmodels UnimplementedFinalPlantSpecificSAMAs TheseareunimplementedSAMAswhosestatuswasdeterminedthroughacostbenefit analysiscomparingplantspecificavertedcostrisktoprojectedimplementationcost.

SAMAsthatweredispositionedusingotherevaluationcriteriainthe40to60year SAMAanalysiswouldnotbeFinalPlantSpecificSAMAs.Forexample,neitherSAMAs thatweredeterminedtobenotpotentiallycostbeneficialbecausetheircostsof implementationexceededtheMBnorSAMAsthatweredeterminedtobenot applicabletotheplantareFinalPlantSpecificSAMAs.Hence,theydonotneedtobe evaluatedagain.

SourcesforidentifyingFinalPlantSpecificSAMAsare:

August2019 NEI1704,[Rev.1]

nei.org 11 The40to60yearSAMAanalysis,whichistypicallyanappendixtotheEnvironmental Reportinthe40to60yearLicenseRenewalApplication(oritsequivalentifsevere accidentmitigationalternativeswereconsideredduringinitialplantlicensing).

ResponsestoRAIsissuedonthe40to60yearSAMAanalysis(oritsequivalentif severeaccidentmitigationalternativeswereconsideredduringinitialplantlicensing).

The Generic Environmental Impact Statement (NUREG1437) Supplement for the analyzedplant.

PotentiallycostbeneficialSAMAsidentifiedinSAMAanalysesforothersimilarplantssubmitted afterthatoftheanalyzedplant.

IncludethoseSAMAsofthesamegeneralplanttype(i.e.,BWRorPWR)8, ThepotentiallycostbeneficialSAMAsareidentifiedintheplantspecificSupplementsof theGenericEnvironmentalImpactStatement(NUREG1437).

Stage2AssessmentNewInformationElements Plantsourcetermradiologicalreleaseinformation Coreinventory(e.g.,poweruprate)

Releasecategorysourcetermcharacteristics(e.g.,releasefraction,releasestarttime, releaseduration)

Evacuationpreparednessplans(e.g.,evacuationtiming,evacuationspeed)

Siteregionaldata Projectedpopulationwithina50mileradiusoftheplant Regionaleconomicdata(e.g.,valueoffarmwealth,valueofnonfarmwealth)

Eventresponsecostdata Emergency response costs (e.g., per diem food and housing expenses, per capita relocationexpenses)

Decontaminationcosts GeneralLevel3methodologyguidanceandgenericinputs Costbenefitmethodology ThedraftversionofNUREG/BR0058[10]containsthecurrentguidancefordeveloping theMaximumBenefit(alsousedtoperformthecostbenefitanalysisforaStage3 analysis).Thefinalizedversionofthedocument,whenavailable,wouldbethebasisfor aStage2analysis.

NUREG1530,Revision1[15]providesthebasisforthedollarperpersonremcost,which hasbeenupdatedsincethereleaseofNEI0501andisreferencedinNUREG/BR0058as thesourceforthisvalue.

IncludesinformationpreviouslycontainedinNUREG/BR0184[3]

Stage3AssessmentNewInformationElements ImplementationcostsforthoseSAMAsnotscreenedinStage2 8 CommissionOrderCLI1307indicatesthatSAMAsidentifiedforMarkIIBWRscouldbeusedforanyBWR.This assertionisusedasthebasisfornotlimitingthescopeofpotentiallycostbeneficialSAMAstobeconsideredto onlythoseassociatedwithaparticularplantsubtype.Acoarsescreeningstepisperformedlatertoeliminate thoseSAMAcandidatesthatarenotapplicabletothedesignoftheanalyzedplant.

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nei.org 12

Theanalystshouldreviewplantspecificconditionstoidentify,document,anddevelop,asnecessary,any other inputs to the SAMA analysis that have changed since the 40to60year SAMA analysis was completed.

3.2 Stage1Assessment TheStage1AssessmentincludessubtasksforprescreeningindustrySAMAcandidatesandforestimating theriskreductionoftheunscreenedSAMAcandidates,whicharedescribedinfurtherdetailbelow.

3.2.1 PrescreeningIndustrySAMAs WhilethismodelapproachadvisesincludingthepotentiallycostbeneficialSAMAsfromindustryplantsof thesamegeneraltypeinthebodyofSAMAstobeconsidered,itisnotexpectedthatariskreduction assessment would be necessary for each of those SAMAs. Before the risk reduction estimates are developed, the SAMA candidates should be prescreened to identify 1)those SAMAs that are not applicabletothedesignoftheanalyzedplant,2)thoseSAMAsthathavealreadybeenimplementedat theanalyzedplant,and3)thoseSAMAsthatarealreadyaddressedbyafunctionallyequivalentSAMAor thatmaybecombinedwithorsubsumedbyamorecomprehensiveSAMA.ThisstepissimilartothePhase 1screeningprocessinNEI0501withtheexceptionsthatSAMAsarenoteliminatedduetoexcessive implementationcost(becauseanupdatedMBisnotdevelopedfortheStage1analysis)andSAMAswith verylowbenefitsarenotexemptedfromanexplicitriskreductionassessment.

Theprescreeningcriteria,whichhavebeenadoptedfromNEI0501andslightlymodified,areprovided below:

NotApplicable:IfaSAMAcandidatedoesnotapplytotheplantdesign,itmaybeexcludedfrom furtherreview.Forexample,installationofaccumulatorsforturbinedrivenfeedwaterpumpflow controlvalveswouldnotbefurtheranalyzedforaplantwithmotoroperatedturbinedriven feedwaterpumpflowcontrolvalves.

AlreadyImplemented:IfaSAMAcandidatehasalreadybeenimplementedattheplant,orits benefit achieved by other means, it may be excluded from further review. For example, installationofmotorgeneratorsettripbreakersinthecontrolroomtoreducethefrequencyof coredamageduetoanATWSwouldnotbefurtheranalyzedforaplantwithacontrolroom actuateddiversescramsystem.

Combined:IfaSAMAcandidateissimilarinnatureandcanbecombinedwithanotherSAMA candidatetodevelopamorecomprehensiveorplantspecificSAMAcandidate,onlythecombined SAMAcandidateisretained.Forexample,additionofanindependentreactorcoolantpumpseal injectionsystemanduseofanexistinghydrotestpumpforreactorcoolantpumpsealinjection providesimilarriskreductionbenefits.Ifthelowercostalternativeisnotcostbeneficial,the highercost alternative also will not be costbeneficial. Therefore, the highercost alternative wouldnotbefurtheranalyzed.

ForeachoftheSAMAsthatareprescreenedusingtheabovecriteria,documentthecriterionusedto eliminatetheSAMAfromfurtherconsideration.TheremainingSAMAcandidatesarereferredtoherein asApplicableIndustrySAMAs.

3.2.2 EvaluationofRiskReduction FortheunimplementedFinalPlantSpecificSAMAsandApplicableIndustrySAMAs,estimatethepercent bywhichtheMBwouldbereducediftheSAMAwereimplemented.Therearedifferentmethodsthat maybeusedtoaccomplishthisgoal,butwhichevermethodisused,theriskinsightsmustbecorrelated totheultimatemetric,whichistheavertedcostrisk.Forexample,itiscriticalthatanassessmentofa

August2019 NEI1704,[Rev.1]

nei.org 13 SAMAimpactingSteamGeneratorTubeRuptureaccountsforthereductionintheLevel2bypassrelease categoryfrequencyinadditiontotheCDFbecauseamajorityoftheavertedcostriskmaybeassociated withthebypassfrequency.

WithouttheinsightsofanupdatedLevel3modelandMBcalculation,itisdifficulttocorrelatespecific changestotheCDFandLevel2releasecategoriestoacurrentavertedcostrisk;therefore,inthisstage oftheanalysis,theapproachistoboundtheimpactbydemonstratingthatSAMAimplementationwould notreducetheCDForanyoftheLevel2releasecategoryfrequenciesby50percentormore.Ifthiscan bedemonstrated,itcanbeinferredthattheSAMAsavertedcostriskwouldnotbemorethan50percent oftheMB.ThisisbecausetheavertedcostriskisdirectlytiedtothechangesinCDFandtheLevel2 releasecategoryfrequencies.NotethatasanalternativetocalculatingthepercentreductionineachLevel 2releasecategoryfrequencysubgroup,suchasLarge/Early01,Large/Early02,etc.,itwouldbesufficient togroupreleasecategoryresultsintohighlevelcategories(e.g.,Large/Early,Moderate/Late),evenif the40to60yearSAMAanalysisreportedvaluesforthesubgroups.Anotheralternative,ifatechnical basisisprovidedthatdemonstratestheoverallriskreductionfortheplantcanbeadequatelyquantified usingasubsetofLevel2releasecategories,wouldbetoperformthedemonstrationforthatsubsetofthe Level2releasecategories.Forexample,ifthereisinformationtoshowthat(i)99%ofaplantsriskis representedbytheHighEarly,HighIntermediate,andModerateIntermediatereleasecategoriesand(ii) thesameplantsnineotherreleasecategoriesrepresentlessthan1percentofthatplantsrisk,there wouldbenoneedtoquantifythereductionsinthefrequenciesofthenineotherreleasecategoriesfor theStage1analysis.

TheimpactofSAMAimplementationontheCDFandtheLevel2releasecategoryfrequenciescanbe estimatedusingimportancemeasuresforeventsthatcapturetheimpactoftheSAMA.Forexample,the impactofimplementingaSAMAtoinstallabypassswitchforthelowlevelMSIVisolationlogicinaBWR maybedirectlycorrelatedtotheoperatoractionforperformingtheMSIVlowlevelisolationlogicbypass.

Ifthisistrue,theimportancelistsfortheCDFandeachofthereleasecategoriescouldbereviewedto identifytheRRWvalues(orFVvalues)forthatoperatoraction,andthepercentreductioninCDFand releasecategoryfrequenciescouldthenbeestimatedfromthisinformation.Morespecifically,ifthe operatoractiontobypasstheMSIVlowlevelisolationlogiccorrelatestoRiskReductionWorth(RRW)9 valuesof1.05orlessforCDFandeachoftheanalyzedLevel2releasecategories,theavertedcostrisk wouldbelimitedtoabout5percentoftheMBandtheSAMAcouldnotbepotentiallysignificant.

If correlating the impact of SAMA implementation to basic event importance measures is not straightforward,theSAMAcanbemodeledinthePRAtoobtainestimatesofCDFandreleasecategory frequencyreductions.

ApotentialdifficultyisascenarioinwhichimplementationofaSAMAreducessomefrequenciesbymore than50percentwhileitdoesnotimpactothersatall.Intheseborderlinecases,itmaybepossibleto justifythattheSAMAsavertedcostriskwouldstillbelessthan50percentoftheMBiftherelease categorywiththereductionthatisgreaterthan50percentisalowconsequencereleasecategory.For example,ifaSAMAhasalargeimpactonSGTRscenariosinwhichsteamgeneratormakeupisavailable (i.e., the releases are scrubbed), a discussion could be provided that includes both qualitative and quantitativeinsightsaboutwhythereductioninthatreleasecategoryfrequencywouldnotalsoreduce theMBbymorethan50percent.

9 Foraspecifiedbasicevent,riskreductionworthimportancereflectsthedecreaseinaselectedfigureofmerit whenanSSCisassumedtobeperfectlyreliable.Itistheratioorintervalofthefigureofmerit,evaluatedwiththe SSCsbasiceventprobabilitysettozero,tothebasecasefigureofmerit.

August2019 NEI1704,[Rev.1]

nei.org 14 IfoneormoreSAMAsarefoundtoreducetheMBbyatleast50percent,thentheSAMAsareconsidered tobepotentiallysignificantandaStage2assessmentisrequired.

WhiletheapproachdescribedaboveisadequateformostSAMAs,analternatequantificationprocessis requiredforanySAMAsthatreducetheconsequencesofaccidentswithoutreducingtheCDForrelease categoryfrequencies.AnexampleofsuchaSAMAistheinstallationofanexteriorcontainmentspray systemthatwoulddelugethecontainmentbreakpointafteracontainmentfailureinordertoprovidea scrubbing function for materials released through the break. For these types of SAMAs, it would be necessarytodevelopaplantspecificbasisfortheMBreductionthatwouldresultfromimplementation oftheSAMA.TheapproachtakenmayincludetheuseofinsightsfromtheLevel2analysistoidentifythe frequenciesofrelevantcontainmentfailuremodes,andinformationfromtheavailableLevel3analysis (updatedtoaccountforconditionsrelevanttoSLR)todeterminetherelativeimportanceoftheaccident scenarios that would be mitigated. If a clear basis cannot be developed that would characterize the reductionintheMBresultingfromimplementationoftheSAMA,thenaStage2evaluationoftheSAMA wouldbenecessary.

AssessmentConsiderations:

Asidentifiedabove,RiskReductionWorthvaluesforCDFandallreleasecategoriescanbeused toapproximatethepercentreductionintheMBforaSAMA.Ifthisprocessisused,however,care shouldbetakentoensurethatalloftheeventsimpactedbytheSAMAareconsideredinthe assessmentandthatthecombinedimpactsofmultipleeventsareappropriatelyaccountedfor (e.g., do the events impact some of the same cutsets, or are the events always in separate cutsets).

Account for the impact of unimplemented plant changes on the SAMA averted costrisk assessments.Insomecases,ageneralassessmentmaybeappropriate(e.g.,noimpactonplant risk)whileinothersitmaybenecessarytoconsidersuchanimpactexplicitlyforeachSAMA.

If the PRA model has been updated since the performance of the 40to60year SAMA, it is possiblethattheriskprofilehaschangedsubstantiallyeveniftheoverallCDFandreleasecategory frequencieshavenot.Forthisreason,donotuseriskreductionassessmentsfromthe40to60 yearSAMAanalysisdirectlyifthePRAmodelhaschanged.

3.3 Stage2Assessment IftheStage1analysiscannotdefinitivelydeterminethatalloftheunimplementedFinalPlantSpecificand ApplicableIndustrySAMAshaveavertedcostriskvaluesthatarelessthan50%oftheMB,itwillbe necessarytoperformamoredetailedavertedcostriskcalculationforthepotentiallysignificantSAMAs.

ThisrequiresanupdateoftheLevel3consequencemodelandrecalculationoftheavertedcostriskfor eachpotentiallysignificantSAMAusingthelatestplantriskmodels.

3.3.1 Stage2AvertedCostRiskAssessment Oncethenewinformationhasbeencollected/developedfortheStage2assessment(Section3.1),the following principal steps should be performed to assess the averted costrisk for the potentially significantSAMAs:

1. UpdatetheLevel3consequenceanalysis:

a. Option 1 - Simplified Level 3 Update: In general, the scope of new information that will potentiallyimpacttheLevel3modelisbroad,whichmakesitdifficulttoestimatehowthe Level 3 results (DoseRisk, Offsite Economic CostRisk) will be changed without directly integratingthenewinformationintotheLevel3model.Forexample,theforthcomingversion

August2019 NEI1704,[Rev.1]

nei.org 15 oftheMACCScodeandassociatedguidanceisanticipatedtoincludechangestotheinternal economiccostmodelsrelatedtopopulationrelocation,whichwillhavereleasecategory specificimpacts(i.e.,theoffsiteeconomicresultswillscaledifferentlyfordifferentplants).If theapplicantcandevelopastrategytoestimatetheimpactofthenewinformationonthe previous Level 3 results (e.g., using insights from previous Level 3 model sensitivity case results)anddefendthequalityofthestrategy,itmaybeusedtojustifyOption1;otherwise, Option2shouldbeused.Issuestoconsiderinclude,butarenotlimitedto,thefollowing:

i. Changesto50milepopulation ii. Changestoagriculturalandlandbasedeconomicdataforthe50mileradiusarea iii. Changestocoreinventory(e.g.,duetopoweruprate) iv. Changestoevacuationtimes

v. ChangestoMACCScode

b. Option2-FullLevel3Update:UsetheLevel1and2InternalEventsPRAoutputandsite specific meteorology, demographic, land use, and emergency response data as inputs to update the Level 3 consequence analysis performed using the latest available MELCOR Accident Consequences Code System version (as was done for the 40to60year SAMA analysis).

2. BaselineRiskMonetization-UseNRCregulatoryanalysistechniques[10]tocalculatethemonetary valueofthesevereaccidentrisk.Thatvaluerepresentstheupdatedmaximumavertedcostrisk(MB).

3. Evaluate the potentially significant SAMAs in a manner consistent with the NEI 0501 [9]

methodology.

Calculatetheavertedcostrisk.

IntheeventthatthisavertedcostriskcalculationdemonstratesthattheSAMAdoesnot reducetheupdated MBby50percentormore, theSAMA maybeclassifiedasnot significant.

This reclassification could occur when the detailed averted costrisk calculations removetheconservatismsoftheStage1assessmentsforborderlineSAMAs.

SAMAswithavertedcostriskvaluesthatareequaltoorgreaterthan50percentofthe MBremainpotentiallysignificant.

3.4 Stage3CostBenefitAssessment ForthoseSAMAsclassifiedaspotentiallysignificantintheStage2assessment,determinewhetherthey arepotentiallycostbeneficialinaccordancewiththeprocessdescribedinSections7and8ofNEI0501.

Ifthenewinformationconsideredinthisassessmentdoesnotresultinidentificationofanypotentially significantSAMAsthatarealsopotentiallycostbeneficial,thenewinformationisnotsignificant.The identificationofapotentiallysignificantSAMAthatisalsopotentiallycostbeneficialisanindicationthat newandsignificantinformationexistsrelevanttothepreviousSAMAanalysis.

3.5 DocumentationoftheNewandSignificantInformationReviewforSAMA 3.5.1 ApplicantsEnvironmentalReport ConsistentwithguidanceinNRCRegulatoryGuide4.2,Supplement1,Revision1[16],theSLRERshould briefly describe the processes that were used for identifying new information and determining its

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nei.org 16 significance.Ifadeterminationismadethatnonewandsignificantinformationexists,thentheSLRER shouldstatethisdetermination.

Alternatively, if a determination is made that one or more potentially significant SAMAs are also potentially cost beneficial, then the SLR ER should describe those SAMAs and state that new and significant information has been identified. The ER should also indicate whether the new and significantSAMAsareagingrelatedanddescribesupplementaryactionstobetakenrelativetotheir discovery,ifany.

Furtherdocumentationofthenewandsignificantinformationreviewthatshouldbemaintainedislisted inSection3.5.2,below.SuchdocumentationshouldbeavailabletotheNRCeitherintheSLRER(atthe SLRapplicant'sdiscretion),orinsupplementalinformationforreviewviaEdocumentreadingroom,audit, andRAIs.

3.5.2 SupportingDocumentation Descriptionofdatareview Descriptionofcurrentriskmodels(atalevelofdetailconsistentwithwhatwasexpectedforthe 40to60yearLicenseRenewalApplication)

Level1 Level2 Level3(ifapplicable)

IfonlyaStage1analysisisrequired,noLevel3modeldiscussionisneeded10.

Ifaborderline,potentiallysignificantSAMAisassessedusingaStage2averted costriskcalculationanddeterminednottobesignificant,indicatetheSAMAwas assessedaccordingtothemodelapproachanddeterminednottobesignificant.

MaintaintheLevel3modelinaseparatedocumenttosupportanyauditrelated activities.

IfoneormoreSAMAshasbeendeterminedtobepotentiallysignificant,describe theupdatedLevel3model.

Descriptionofchangestotheriskmodelssincethe40to60yearLicenseRenewalApplication ListofPRArevisions Qualitativedescriptionsofthemostsignificantchangesforeachrevision Includeadiscussionofthechangesmadeattheplantthathavereducedrisk.

TheprescreeningcriterionusedtoexcludeanyoftheStage1SAMAcandidatesfromfurther consideration,includingifapplicable,therationaleforexcludingpotentiallycostbeneficialSAMAs identified in U.S. license renewal applications after submittal of the SAMA analysis for the analyzedplant(i.e.,industrySAMAs).

PercentriskreductionforthenonscreenedStage1SAMAs MBcalculation(ifapplicable)

Stage 2 averted costrisk calculation and results for the potentially significant SAMAs (if applicable) 10AsdocumentedinSection3.1,newinformationelementsassociatedwiththosestagesoftheassessment processthatwerenotrequiredtobeperformedinaplantsanalysisshouldbeidentifiedanddocumentedas newinformation,buttheydonotneedtobefurtherdeveloped.

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nei.org 17 Modelingdescription(PRAmodelchanges,assumptions,etc.)

CDF, release category frequencies, and averted costrisk values for potentially significantSAMAs ImplementationcostsforthepotentiallysignificantSAMAspassedtotheStage3assessment(if applicable)

NetvaluesforthepotentiallysignificantSAMAspassedtotheStage3assessment(ifapplicable)

Conclusions Identify SAMAs, if any, determined in the Stage 1 assessment to be potentially potentiallysignificant(i.e.,theSAMAsdeterminedtoreducetheMBby50percentor more).

IdentifySAMAs,ifany,thatareconsideredtobepotentiallysignificantaftertheStage 2assessment AlsoidentifySAMAsthatweredeterminedtobepotentiallysignificantinStage1, butweredemonstratedtobenotpotentiallysignificantinStage2.

IdentifyassignificantanypotentiallysignificantSAMAsdeterminedinStage3tobe alsopotentiallycostbeneficial.

IndicatewhethernewandsignificantSAMAsareagingrelated.

Describesupplementaryactions,ifany,tobetakenrelativetodiscoveryofnewand significantSAMAs.

IdentifyanynewandsignificantSAMAsthatwerenotpotentiallycostbeneficialin the40to60yearSAMAanalysis.

IdentifyhowanynewandsignificantSAMAsthatwerenotpotentiallycostbeneficial in the 40to60year SAMA analysis will be further assessed. The discussion should include:

Anexplanationoftheprocessbywhichtheywillbefurtherconsidered/evaluatedby theplant.

Anassessmentofwhethertheyareagingrelated.

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nei.org 18 4

CONCLUSIONS Thisdocumentprovidesamodelapproachforassessingwhethernewandsignificantinformationexists atthelicenserenewalstagewithrespecttoapriorSAMA(orSAMDA)analysisandevaluatinganysuch information,whichisatopicthatmustbeconsideredinasuccessfulSLRapplication.Theintentisto describethehighlevelstepsthatarerequiredtoperformtheanalysisandtoleavethedetailsofhoweach ofthestepsshouldbeperformedtotheindividualanalyststoensurethatanyplantspecificissuesare properlyaddressed.Identifyingandprescribingaprocesstoaddressthesetypesofplantspecificissuesis beyondthescopeofthisdocumentanditisincumbentontheanalysttoidentifyandevaluatesuchissues aspartofpreparingtheSLRapplication.

Additionally,licenserenewalapplicantsarecautionedthatforanuclearplantforwhichIssue66inTable B1ofAppendixBto10CFRPart51,SubpartAisafunctionalequivalentCategory1issue,theapplicant should also investigate nonSAMArelated new and significant information relevant to the NRCs conclusionforthisissuethat[t]heprobabilityweightedconsequencesofatmosphericreleases,fallout ontoopenbodiesofwater,releasestogroundwater,andsocietalandeconomicimpactsfromsevere accidentsaresmallforallplants.

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