Regulatory Guide 1.105
| ML993560062 | |
| Person / Time | |
|---|---|
| Issue date: | 12/31/1999 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Aggarwal S K (301)415-6005 | |
| References | |
| RG-1.105, Rev. 3 | |
| Download: ML993560062 (7) | |
1ForthefulltextoftheGeneralDesignCriteriaandothersectionsoftheregulationscitedinthisguide,see10CFRPart50,"DomesticLicensingofProductionandUtilizationFacilities."RegulatoryguidesareissuedtodescribeandmakeavailabletothepublicsuchinformationasmethodsacceptabletotheNRCstaffforimplementingspecificpartsoftheNRC'sregulations,techniquesusedbythestaffinevaluatingspecificproblemsorpostulatedaccidents,anddataneededbytheNRCstaffinitsreviewofapplicationsforpermitsandlicenses.Regulatoryguidesarenotsubstitutesforregulations,andcompliancewiththemisnotrequired.MethodsandsolutionsdifferentfromthosesetoutintheguideswillbeacceptableiftheyprovideabasisforthefindingsrequisitetotheissuanceorcontinuanceofapermitorlicensebytheCommission.Thisguidewasissuedafterconsiderationofcommentsreceivedfromthepublic.Commentsandsuggestionsforimprovementsintheseguidesareencour agedatalltimes,andguideswillberevised,asappropriate,toaccommodatecommentsandtoreflectnewinformationorexperience.Writtencommentsmayb esubmittedtotheRulesandDirectivesBranch,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,Ge neral.Singlecopiesofregulatoryguides(whichmaybereproduced)maybeobtainedfreeofchargebywritingtheDistributionServicesSection,U.S.Nuclea rRegulatoryCommission,Washington,DC20555-0001,orbyfaxto(301)415-2289,orbyemailtoDISTRIBUTION@NRC.GOV.Manyregulatoryguidesare alsoavailableontheinternetatNRC'shomepageat<WWW.NRC.GOV>.U.S.NUCLEARREGULATORYCOMMISSIONRevision3December1999REGULATORYGUIDEOFFICEOFNUCLEARREGULATORYRESEARCHREGULATORYGUIDE1.105(DraftwasDG-1045)SETPOINTSFORSAFETY-RELATEDINSTRUMENTATION
A. INTRODUCTION
Criterion13,"InstrumentationandControl,"
1ofAppendixA,"GeneralDesignCriteriaforNuclearPowerPlants,"to10CFRPart50,"DomesticLicensingofProductionandUtilizationFacilities,"requires, amongotherthings,thatinstrumentationbeprovidedtomonitorvariablesandsystemsandthatcontrolsbe providedtomaintainthesevariablesandsystemswithinprescribedoperatingranges.Criterion20,"ProtectionSystemFunctions,"ofAppendixAto10CFRPart50requires,amongotherthings,thattheprotectionsystembedesignedtoinitiateoperationofappropriatesystemstoensurethat specifiedacceptablefueldesignlimitsarenotexceeded.Paragraph(c)(1)(ii)(A)of§50.36,"TechnicalSpecifications,"of10CFRPart50requires,inpart,that,wherealimitingsafetysystemsettingisspecifiedforavariableonwhichasafetylimithasbeenplaced, thesettingbesochosenthatautomaticprotectiveactionwillcorrecttheabnormalsituationbeforeasafety limitisexceeded.Italsorequires,amongotherthings,thatthelicenseenotifytheNRCifthelicensee determinesthatanautomaticsafetysystemdoesnotfunctionasrequired.Thelicenseeisrequiredtothen reviewthematterandrecordtheresultsofthereview.
2CopiesmaybeobtainedfromtheInstrumentSocietyofAmerica,67AlexanderDrive,ResearchTrianglePark,NC
20779.2ThisguidedescribesamethodacceptabletotheNRCstaffforcomplyingwiththeNRC'sregulationsforensuringthatsetpointsforsafety-relatedinstrumentationareinitiallywithinandremain withinthetechnicalspecificationlimits.TheguideisbeingrevisedtoendorsePartlofISA-S67.04-1994,
"SetpointsforNuclearSafety-RelatedInstrumentation."
2Thisstandardprovidesabasisforestablishingsetpointsfornuclearinstrumentationforsafetysystemsandaddressesknowncontributingerrorsinthe
channel.Theinformationcollectionscontainedinthisregulatoryguidearecoveredbytherequirementsin10CFRPart50,whichwereapprovedbytheOfficeofManagementandBudget,approvalnumber3150-
0011.TheNRCmaynotconductorsponsor,andapersonisnotrequiredtorespondto,acollectionof informationunlessitdisplaysacurrentlyvalidOMBcontrolnumber.
B. DISCUSSION
Instrumentsetpointuncertaintyallowancesandsetpointdiscrepancieshaveledtoanumberofoperationalproblems.Operatingexperienceindicatesthatsetpointsforsafety-relatedinstrumentationmay allowplantstooperateoutsidethelimitingconditionsofoperationspecifiedintheirtechnical specifications.Licenseeshavediscoveredconflictsbetweenexistingsetpointsandengineering calculations.Thecausesforthesesetpointdiscrepancieswereproblemswithindustrypracticesthatledto errorsincalibrationproceduresandalackofunderstandingoftherelationshipofthesetpointtothe allowablevalue.Additionalproblemsnotedincludedvaryingsetpointmethodologiesforengineering calculations,alackofaconsistentdefinitionofallowablevaluebetweendifferentsetpointmethodologies, andimproperunderstandingoftherelationshipoftheallowablevaluetoearliersetpointterminology, procedures,andoperabilitycriteria.Furtherproblemswerenotedwhenprocedures(thesetpointprocess)
(1)failedtoprovideanadequatemarginbetweentheinstrumentas-leftcriteriaandthevalues(tripset pointorallowablevalues)requiredperthetechnicalspecifications,(2)didnotalwaysreflectcurrent designcriteria,and(3)didnotensurethatrevisedinstrumentloopswereverifiedtotheoriginaldesign requirementsorthatinstrumentmodificationswereevaluatedfortheireffectonsetpointcalculations.It hasalsobeennotedthatlicenseesdonottypicallyverifywhethersetpointcalculationdriftassumptions haveremainedvalidforthesystemsurveillanceinterval.ISA-S67.04wasrevisedin1987toprovideclarificationandtoreflectindustrypractice.Theterm"tripsetpoint"wasmadeconsistentwiththeterminologyusedbytheNRCstaff.Thestandardwasrevisedfurtherin1994.Theeffectsofuncertaintyallowancesanddiscrepanciesinsetpoints,alongwithoperationalexperience,wereappropriatelyaddressedduringthisrevisionofISA-
S67.04.ThisrevisionofthestandardalsoreflectstheImprovedTechnicalSpecificationprogram(a cooperativeeffortbetweenindustryandtheNRCstaff)andreflectcurrentindustrypractice.Thisstandard providesabasisforestablishingsetpointsfornuclearinstrumentationforsafetysystemsandaddresses knowncontributingerrorsinaparticularchannelfromtheprocess(includingtheprimaryelementand sensor)throughandincludingthefinalsetpointdevice.Theterm"tripsetpoint"isretainedinISA-S67.04-1994.However,Figure1inISA-S67.04-1994(forconvenience,thisfigurehasbeenreproducedasFigure1inthisguide)hasbeenrevisedtodepict region"E,""aregionofcalibrationtolerance."Thecalibrationtoleranceuncertaintiesdepictedbyregion
3Singlecopiesofregulatoryguides,bothactiveanddraft,maybeobtainedfreeofchargebywritingtheOfficeofAdministration,Attn:ReproductionandDistributionServicesSection,U.S.NuclearRegulatoryCommission,Washington,DC20555,orbyfaxto(301)415-2289,orbyemailto<DISTRIBUTION@NRC.GOV>.CopiesarealsoavailableforinspectionorcopyingforafeefromtheNRCPublicDocumentRoomat2120LStreetNW.,
Washington,DC;thePDR'smailingaddressisMailStopLL-6,Washington,DC20555;telephone(202)634-3273;
fax(202)634-3343.
3"E"shouldbedefinedandaccountedforinthelicensee'ssetpointmethodology.Atripsetpointvalueidentifiedtobeoutsideregion"E"regardlessofdirectionrequiresreadjustmenttosatisfythesetpoint methodologyanduncertaintiesidentifiedinFigure1(acceptableas-leftcondition).Itshouldbenotedthat thisstandarddoesnotdefine"nominal"tripsetpoint.ThetripsetpointasdepictedinFigure1isconsistent withtheterm"nominal"tripsetpointasshownaboutadefinedcalibrationtoleranceband.Figure1ofthestandardprovidessetpointrelationshipsfornuclearsafety-relatedsetpoints.Thefiguredenotesrelativepositionandnotdirection,butitshouldbenotedthattheuncertaintyrelationships depictedbyFigure1donotrepresentanyoneparticular method(direction,combination,orrelationshipofuncertaintygroupings)forthedevelopmentofatrip setpointorallowablevalue.Section4ofISA-S67.04-1994statesthatthesafetysignificanceofvarioustypesofsetpointsforsafety-relatedinstrumentationmaydiffer,andthusalessrigoroussetpointdeterminationmethodmaybe appliedforcertainfunctionalunitsandlimitingconditionsofoperation(LCOs).Asetpointmethodology canincludesuchagradedapproach.However,thegradingtechniquechosenbythelicenseeshouldbe consistentwiththestandardandshouldconsiderapplicableuncertaintiesregardlessofthesetpoint application.Additionally,theapplicationofthestandard,usinga"graded"approach,isalsoappropriate fornon-safetysysteminstrumentationformaintainingdesignlimitsdescribedintheTechnical Specifications.Examplesmayincludeinstrumentationreliedoninemergencyoperating procedures(EOPS),andformeetingapplicableLCOs,andformeetingthevariablesinRegulatoryGuide
1.97,"InstrumentationforLight-Water-CooledNuclearPowerPlantsToAssessPlantandEnvirons ConditionsDuringandFollowinganAccident."
3TheindustryconsensusstandardANSI/ANS-10.4-1987,"GuidelinesfortheVerificationandValidationofScientificandEngineeringComputerProgramsfortheNuclearIndustry,"provideshelpful informationonthequalificationofsetpointmethodologysoftware.ISA-S67.04-1982hasbeenusedbylicenseesforsetpointmethodologyandinstrumentdriftevaluations.ISA-S67.04-1994provideslimitedguidanceondriftevaluationsanduncertaintyterm developmentfortheevaluationofaninstrumentsurveillanceinterval.The
4ADEBCSafetyLimitAnalyticalLimitNote:Thisfigureisintendedtoproviderelative positionandnotto implydirection.Allowancedescribedinparagraph4.3.1Allowancedescribedinparagraph4.3.1Regionwherechannelmaybedeterminedinoperable Plantoperatingmargin Regionofcalibrationtolerance(acceptableasleftcondition)
describedinparagraph4.3.1 A.B.C.
D.
E.AllowableValue(LSSS)TripSetpoint(LSSS)NormalFigure1.NuclearSafety-RelatedSetpointRelationships
5(ReproducedfromISA-67.04-1994)
6staffhasgenerallyaccepteddriftevaluationsbasedonstatisticalpredictiontechniques.However,significantvariabilityhasbeenobservedinlicensees'surveillanceintervalevaluationswithregardtodrift, setpointmethodology,andcompleteness.ThefollowingconcernswereidentifiedduringtheNRCstaff review,buttheyhavebeenresolvedduringthedevelopmentofISA-S67.04-1994.Limitedinstrumentdriftdatawereincludedinthelicenseesetpointstudy.Driftdataaccountforalldatapointsfromasurveillancecalibration(i.e.,nine-pointcheck)asindependentdata,butinadequatejustificationisprovidedforthisassumption.Driftdatapoints alsoincludedinterimcalibrations.Alargenumberofdatapointswasprovidedforalimitednumberofinstruments.Flawedoutlieranalysisresultedinvaliddatabeingremovedfromthedataset.Driftdependencyontimewasassumedtobenegligibleovertheintervalselected,andinadequatejustificationwasprovidedwhenextrapolatingtoanextendedsurveillanceinterval(e.g.,24
months).Setpointmethodologyassumesnormaldistributionofdatawhensuchanassumptionwasnot verified.Instrumentationevaluations(historical,maintenance,drift)wereincomplete.Driftprojections,includingthosebasedonregressionanalyses,maynotaccountforpenaltiesforuncertaintyprojection(extendedsurveillanceinterval-drift)beyondthetimerangeforthedata
collected.Instrumentapplicationandprocessorinstallationvariableswerenotevaluated.Theuncertaintiesassumedforinstrumentation,includingprimaryelements,weresubsequentlynotverifiedorcontrolledthroughsurveillancetesting,qualification,ormaintenanceprograms.Theacceptabilityofpoolinggenericdriftdatawithplant-specificdataorweighingthedataaccordingtothesourceofthedatawasnotjustified.Allavailableapplicabledatawerenotutilizedintheanalysis.Section4.3ofISA-S67.04-1994statesthatthelimitingsafetysystemsetting(LSSS)maybethetripsetpoint,anallowablevalue,orboth.Forthestandardtechnicalspecifications,thestaffdesignatedthe allowablevalueastheLSSS.Inassociationwiththetripsetpointandlimitingconditionsforoperation (LCOs),theLSSSestablishesthethresholdforprotectivesystemactiontopreventacceptablelimitsbeing exceededduringdesignbasisaccidents.TheLSSSthereforeensuresthatautomaticprotectiveactionwill correcttheabnormalsituationbeforeasafetylimitisexceeded.Alicensee,withjustification,may proposeanalternativeLSSSbasedonitsparticularsetpointmethodologyorlicense.Thestandardprovidesfortheaccountingofmeasurementandtestequipment(MTE)uncertainties,butMTEcriteriaarenotspecificallyidentifiedwithinthestandard.CriteriaXIandXIIinAppendixBto
710CFRPart50providerequirementsforqualityregardingtesting.RegulatoryGuide1.118,"PeriodicTestingofElectricPowerandProtectionSystems,"
3providesguidanceonperiodicsurveillancetesting.PartII,"MethodologiesfortheDeterminationofSetpointsfortheNuclearSafety-RelatedInstrumentation,"ofISA-S67.04-1994isnotaddressedbythisregulatoryguide.C.REGULATORYPOSITIONConformancewithPart1ofISA-S67.04-1994,"SetpointsforNuclearSafety-Related Instrumentation,"
2withthefollowingexceptionsandclarifications,providesamethodacceptabletotheNRCstaffforsatisfyingtheNRC'sregulationsforensuringthatsetpointsforsafety-related instrumentationareestablishedandmaintainedwithinthetechnicalspecificationlimits.
1.Section4ofISA-S67.04-1994specifiesthemethods,butnotthecriterion,forcombininguncertaintiesindeterminingatripsetpointanditsallowablevalues.The95/95tolerancelimitisan acceptablecriterionforuncertainties.Thatis,thereisa95%probabilitythattheconstructedlimitscontain
95%ofthepopulationofinterestforthesurveillanceintervalselected.
2.Sections7and8ofPart1ofISA-S67.04-1994referenceseveralindustrycodesandstandards.IfareferencedstandardhasbeenincorporatedseparatelyintotheNRC'sregulations,licensees andapplicantsmustcomplywiththatstandardassetforthintheregulation.Ifthereferencedstandardhas beenendorsedinaregulatoryguide,thestandardconstitutesamethodacceptabletotheNRCstaffof meetingaregulatoryrequirementasdescribedintheregulatoryguide.Ifareferencedstandardhasbeen neitherincorporatedintotheNRC'sregulationsnorendorsedinaregulatoryguide,licenseesandapplicants mayconsiderandusetheinformationinthereferencedstandardifappropriatelyjustified,consistentwith currentregulatorypractice.
3.Section4.3ofISA-S67.04-1994statesthatthelimitingsafetysystemsetting(LSSS)maybemaintainedintechnicalspecificationsorappropriateplantprocedures.However,10CFR50.36states thatthetechnicalspecificationswillincludeitemsinthecategoriesofsafetylimits,limitingsafetysystem settings,andlimitingcontrolsettings.Thus,theLSSSmaynotbemaintainedinplantprocedures.Rather, theLSSSmustbespecifiedasatechnical-specification-definedlimitinordertosatisfytherequirementsof
10CFR50.36.TheLSSSshouldbedevelopedinaccordancewiththesetpointmethodologysetforthin thestandard,withtheLSSSlistedinthetechnicalspecifications.
4.ISA-S67.04-1994providesadiscussiononthepurposeandapplicationofanallowablevalue.Theallowablevalueisthelimitingvaluethatthetripsetpointcanhavewhentestedperiodically, beyondwhichtheinstrumentchannelisconsideredinoperableandcorrectiveactionmustbetakenin accordancewiththetechnicalspecifications.Theallowablevaluerelationshiptothesetpointmethodology andtestingrequirementsinthetechnicalspecificationsmustbedocumented.
D. IMPLEMENTATION
ThepurposeofthesectionistoprovideinformationtoapplicantsandlicenseesregardingtheNRCstaff'splansforusingthisregulatoryguide.
8ExceptinthosecasesinwhichanapplicantorlicenseeproposesanacceptablealternativemethodforcomplyingwithspecifiedportionsoftheNRC'sregulations,themethodsdescribedinthisguidewillbe usedintheevaluationofsubmittalsinconnectionwithapplicationsforconstructionpermits,operating licenses,andcombinedlicenses.Itwillalsobeusedtoevaluatesubmittalsfromoperatingreactor licenseeswhovoluntarilyproposetoinitiatesystemmodificationsifthereisaclearnexusbetweenthe proposedmodificationsandthisguidance.
9VALUE/IMPACTSTATEMENTAdraftvalue/impactstatementwaspublishedwiththedraftproposedRevision3ofthisguidewhenitwaspublishedforpubliccomment(DG-1045,October1996).Nochangeswerenecessary,soa separatevalue/impactstatementforthefinalguidehasnotbeenprepared.Acopyofthedraftvalue/impact statementisavailableforinspectionorcopyingforafeeintheNRC'sPublicDocumentRoomat2120L
StreetNW.,Washington,DCundertaskDG-1045.