RegulatoryguidesareissuedtodescribeandmakeavailabletothepublicsuchinformationasmethodsacceptabletotheNRCstaffforimplementingspecificpartsoftheNRC’sregulations,techniquesusedbythestaffinevaluatingspecificproblemsorpostulatedaccidents,anddataneededbytheNRCstaffinitsreviewofapplicationsforpermitsandlicenses.Regulatoryguidesarenotsubstitutesforregulations,andcompliancewiththemisnotrequired.MethodsandsolutionsdifferentfromthosesetoutintheguideswillbeacceptableiftheyprovideabasisforthefindingsrequisitetotheissuanceorcontinuanceofapermitorlicensebytheCommission.Thisguidewasissuedafterconsiderationofcommentsreceivedfromthepublic.Commentsandsuggestionsforimprovementsintheseguidesareencouragedatalltimes,andguideswillberevised,asappropriate,toaccommodatecommentsandtoreflectnewinformationorexperience.WrittencommentsmaybesubmittedtotheRulesandDirectivesBranch,ADM,U.S.NuclearRegulatoryCommission,Washington,DC20555-0001.Regulatoryguidesareissuedintenbroaddivisions:1,PowerReactors;2,ResearchandTestReactors;3,FuelsandMaterialsFacilities;4,EnvironmentalandSiting;5,MaterialsandPlantProtection;6,Products;7,Transportation;8,OccupationalHealth;9,AntitrustandFinancialReview;and10,General.Singlecopiesofregulatoryguides(whichmaybereproduced)maybeobtainedfreeofchargebywritingtheDistributionServicesSection,U.S.NuclearRegulatoryCommission,Washington,DC20555-0001,orbyfaxto(301)415-2289,orbyemailtoDISTRIBUTION@NRC.GOV.ElectroniccopiesofthisguideandotherrecentlyissuedguidesareavailableatNRC’shomepageat(NRC)andthenuclearindustryhaverecognizedthatprobabilisticriskassessment(PRA)hasevolvedtobemoreusefulinsupplementingtraditionalengineeringapproachesinreactorregulation.AfterthepublicationofitsPolicyStatementontheuseofPRAinnuclearregulatoryactivities,theCommissiondirectedtheNRCstafftodeveloparegulatoryframeworkthatincorporatedriskinsights.ThatframeworkwasarticulatedinaNovember27,1995,papertotheCommission(SECY-95-280).Thisregulatoryguide,whichaddressesinserviceinspection(ISI)ofpiping,withitscompanionStandardReviewPlan,Section3.9.8ofNUREG-0800(SRPChapter3.9.8),andotherregulatorydocuments(RegulatoryGuides1.174,1.175,1.176,and1.177;SRPChapters3.9.7,16.1,and19),implement,inpart,theCommission'sPolicyStatementandthestaff'sframeworkforincorporatingriskinsightsintotheregulationofnuclearpowerplants.InSeptember1998,theCommissionpublishedaversionofthisregulatoryguidefortrialuse.Asstatedtherein,thatregulatoryguideissuedfortrialusedidnotestablishanyfinalstaffpositionsforpurposesoftheBackfitRule,10CFR50.109,andanychangestotheregulatoryguidepriortostaffadoptioninfinalformwouldnotbeconsideredtobebackfitsasdefinedin10CFR50.109(a)(1).Thiswasintendedtoensurethatthelessonslearnedfromthesubsequentregulatoryreviewofindustrymethodologiesandthepilotplantapplicationscouldbeadequatelyaddressedinthisdocumentandthattheguidanceissufficienttoenhanceregulatorystabilityinthereview,approval,andimplementationofproposedRI-ISIprograms.1.178-2TheNRCstaffhasapprovedtwomethodsdescribinghowrisk-informedISIprogramscanbedevelopedandimplemented.Onemethodology(EPRITR-112657)wasdevelopedbytheElectricPowerResearchInstitute(EPRI).Theothermethodology(WCAP-14572)wasdevelopedbytheWestinghouseOwnersGroup(WOG).RegulatoryGuide1.178(fortrialuse)wasusedtosupportthereviewandapprovalofthetwoindustry-developedmethodologies.Basedontheexperienceduringthereviewandapprovaloftheindustrymethodologiesandthereviewandapprovalofnumerousplant-specificreliefrequestsforinserviceinspectionprograms,theNRCstaffisnowissuingthisupdatedversionofthisregulatoryguide.Whiletherehasbeenasubstantialefforttoprovideanopportunityforstakeholdersinthismethodologytointereactwiththestaffinthedevelopmentofthisguide’srevisions,therevisedguidewasnotissuedindraftforminthemannerthathasnormallybeenusedforregulatoryguides.Rather,amorelimitedstakeholder’sreviewwasutilized,includingapublicmeetingnoticedontheNRCwebsite.Priortothepublicmeeting,thedraftofthisguidewasplacedinADAMSwithapublicnoticeidentifyingtheADAMSaccessionnumber.Thisapproachwasconsideredadequatesincetherevisionsaregenerallyeditorialinnatureandintendedtoeitherupdatecertaininformationortoclarifylanguagewithoutsubstantialchangestothemethodologyitself.Inaddition,sincethisguidewasfirstissuedin1998,ithasbeensuccessfullyusedbytheindustryandstaffinprocessingnumerousrequestsbylicenseestomakerisk-informedchangestoinserviceinspectionprograms.Untiltherisk-informedinserviceinspection(RI-ISI)processisapprovedforgenericuse,theNRCstaffanticipatesthatlicenseeswillrequestchangestotheirISIprogramsbyrequestingNRCapprovalofalternativeinspectionprogramsthatmeetthecriteriaof10CFR50.55a(a)(3)(i)inSection50.55a,CodesandStandards,of10CFRPart50,DomesticLicensingofPr