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1ForthefulltextoftheGeneralDesignCriteriaandothersectionsoftheregulationscitedinthisguide,see10CFRPart50,“DomesticLicensingofProductionandUtilizationFacilities.”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.ManyregulatoryguidesarealsoavailableontheinternetatNRC’shomepageat(DraftwasDG-1045)SETPOINTSFORSAFETY-RELATEDINSTRUMENTATIONA.INTRODUCTIONCriterion13,InstrumentationandControl,1ofAppendixA,GeneralDesignCriteriaforNuclearPowerPlants,to10CFRPart50,DomesticLicensingofProductionandUtilizationFacilities,requires,amongotherthings,thatinstrumentationbeprovidedtomonitorvariablesandsystemsandthatcontrolsbeprovidedtomaintainthesevariablesandsystemswithinprescribedoperatingranges.Criterion20,ProtectionSystemFunctions,ofAppendixAto10CFRPart50requires,amongotherthings,thattheprotectionsystembedesignedtoinitiateoperationofappropriatesystemstoensurethatspecifiedacceptablefueldesignlimitsarenotexceeded.Paragraph(c)(1)(ii)(A)of§50.36,TechnicalSpecifications,of10CFRPart50requires,inpart,that,wherealimitingsafetysystemsettingisspecifiedforavariableonwhichasafetylimithasbeenplaced,thesettingbesochosenthatautomaticprotectiveactionwillcorrecttheabnormalsituationbeforeasafetylimitisexceeded.Italsorequires,amongotherthings,thatthelicenseenotifytheNRCifthelicenseedeterminesthatanautomaticsafetysystemdoesnot2CopiesmaybeobtainedfromtheInstrumentSocietyofAmerica,67AlexanderDrive,ResearchTrianglePark,NC20779.2functionasrequired.Thelicenseeisrequiredtothenreviewthematterandrecordtheresultsofthereview.ThisguidedescribesamethodacceptabletotheNRCstaffforcomplyingwiththeNRC'sregulationsforensuringthatsetpointsforsafety-relatedinstrumentationareinitiallywithinandremainwithinthetechnicalspecificationlimits.TheguideisbeingrevisedtoendorsePartlofISA-S67.04-1994,“SetpointsforNuclearSafety-RelatedInstrumentation.”2Thisstandardprovidesabasisforestablishingsetpointsfornuclearinstrumentationforsafetysystemsandaddressesknowncontributingerrorsinthechannel.Theinformationcollectionscontainedinthisregulatoryguidearecoveredbytherequirementsin10CFRPart50,whichwereapprovedbytheOfficeofManagementandBudget,approvalnumber3150-0011.TheNRCmaynotconductorsponsor,andapersonisnotrequiredtorespondto,acollectionofinformationunlessitdisplaysacurrentlyvalidOMBcontrolnumber.B.DISCUSSIONInstrumentsetpointuncertaintyallowancesandsetpointdiscrepancieshaveledtoanumberofoperationalproblems.Operatingexperienceindicatesthatsetpointsforsafety-relatedinstrumentationmayallowplantstooperateoutsidethelimitingconditionsofoperationspecifiedintheirtechnicalspecifications.Licenseeshavediscoveredconflictsbetweenexistingsetpointsandengineeringcalculations.Thecausesforthesesetpointdiscrepancieswereproblemswithindustrypracticesthatledtoerrorsincalibrationproceduresandalackofunderstandingoftherelationshipofthesetpointtotheallowablevalue.Additionalproblemsnotedincludedvaryingsetpointmethodologiesforengineeringcalculations,alackofaconsistentdefinitionofallowablevaluebetweendifferentsetpointmethodologies,andimproperunderstandingoftherelationshipoftheallowablevaluetoearliersetpointterminology,procedures,andoperabilitycriteria.Furtherproblemswerenotedwhenprocedures(thesetpointprocess)(1)failedtoprovideanadequatemarginbetweentheinstrumentas-leftcriteriaandthevalues(tripsetpointorallowablevalues)requiredperthetechnicalspecifications,(2)didnotalwaysreflectcurrentdesigncriteria,and(3)didnotensurethatrevisedinstrumentloopswereverifiedtotheoriginaldesignrequirementsorthatinstrumentmodificationswereevaluatedfortheireffectonsetpo