RG1.011 穿透一回路反应堆安全壳的仪表管线 1971

3/10/71SAFETYGUIDE11INSTRUMENTLINESPENETRATINGPRIMARYREACTORCONTAINMENTA.IntroductionGeneralDesignCriteria55and56requirethateachlinethatpenetratesprimaryreactorcontainmentandispartofthereactorcoolantpressureboundaryorthatisconnecteddirectlytothecontainmentatmospherehaveoneautomaticvalveinsideandoneautomaticvalveoutsidecontainmentunlessitcanbedemonstratedthatthedesignisacceptableonsomeotherdefinedbasis.ThisguidedescribesasuitablebasiswhichmaybeusedtoimplementGeneralDesignCriteria55and56fordemonstratingtheacceptabilityofaparticulargroupoftheselines,namely,instrumentlines.B.DiscussionValvingprovidedforeachinstrumentlinepenetratingorconnectedtoprimaryreactorcontainmentmustreflecttheimportanceoftwosafetyfunctions:(1)thefunctionthelineperformsand(2)theneedtomaintaincontainmentleaktightintegrity.Theprobabilityofachievingthefirstfunctionisenhancedbyinclusionoffewervalves(e.g.,oneratherthantwo),whereasthatofthesecondfunctionisenhancedbyadditionalvalves.Intheeventofaruptureofanycomponentintheinstrumentlineoutsideprimarycontainment,itisimportanttoassurethattheintegrityandfunctionalperformanceofsecondarycontainmentanditsassociatedfiltrationsystemsaremaintained.Itisalsodesirabletokeeptherateandextentofcoolantlossfromtherupturedcomponentwithinthecapabilityofreactorcoolantmakeupsystem.Theprobabilityofsucharuptureisconsideredtobesufficientlyhighthatthecalculatedoffsiteexposuresthatmightresultfromsuchasinglefailureduringnormaloperationshouldbesubstantiallybelowtheguidelinesof10CFR100.TherateofcoolantlossfromaninstrumentSlineruptureoutsidecontainmentcanbereducedbyincludingflowrestrictions,suchasorifices,intheinstrumentline.Theflowrestrictionsshouldbesizedtoreducethisrateofcoolantlosstotheextentpracticalwithoutadverselyaffectingthecapabilityoftheconnectedinstrumentstoperformtheirfunctions.Inparticular,itmustbeassuredthattheresponsetimeoftheinstrumentsdoesnotbecomeunacceptablylongbecauseofsuchflowrestrictionsandthattheflowrestrictionswillnotbecomeplugged.Itisalsodesirablethatflowrestrictionsintheinstrumentlinebelocatedascloseaspracticaltowheretheinstrumentlineconnectstothereactorcoolantsystem.Iftheconditionsofthetwoprecedingparagraphsaresatisfied,anacceptablecapabilityforisolatinginstrumentlinespenetratingorconnectedtoprimaryreactorcontainmentcanbeprovidedbyasingleisolationvalvecapableofautomaticoperation(nodependenceonoperatoractions)orcapableofremoteoperationbytheoperatorinthecontrolroomoranotherappropriatelocation.Aselfactuatedexcessflowcheckvalveisacceptableasanautomaticallyoperatedvalveifithastheotherfeaturesneededforthisservice.Itisdesirablethattheisolationvalvebelocatedoutsidecontainmentforgreateraccessibility.Forpoweroperatedvalves,whichmayprovideasafetyfunctionineithertheopenorclosedposition,onbalance,greatersafetywillbeaffordedbydesigningthisvalvetoremainas-is(usuallyopen)ifpowerislost.Eliminationoftheisolationvalveinsidecontainmentmakesitimportantthattherebeahighdegreeofassurancethatthepipingfromthecontainmentuptoandincludingtheoutsidevalveretainitsintegrityduringnormalreactoroperationandunderaccidentconditions.Thisassurancecanbeprovidedbylocatingthevalveasclosetocontainmentaspractical,byadoptingaconservativeapproachinthedesignofthissectionof,piping,bysuitablequalityassuranceprovisions,andbysuitablevisualinserviceinspections.Performinginserviceinspections11.1shouldnotincreasetheprobabilityofdamagingtheinstrumentlines.Inaddition,provisionsmaybeneededtoprotectagainstaccidentaldamageoflinesandtoassurethatfailuresofonelinewillnotinducefailureofanyotherlinebypipewhip,missiles,orsomeothermechanism.Sufficientexperiencewithvalvesofasimilartypeshouldbeavailabletoassureahighprobabilitythatthevalvewillnotclosewhentheinstrumentlineisintactanditssafetyfunctionisrequired,butthatitwillcloseiftheinstrumentlineisruptureddownstream.Intheeventofarupturedownstreamofthevalve,thevalveshouldcloseautomaticallyorbecapableofbeingclosedduringnormalreactoroperationandunderaccidentconditions.Inaddition,thevalveshouldreopenautomaticallyorbecapableofbeingreopenedreadilyundertheconditionsthatprevailwhenreopeningisappropriate.Itshouldnotbenecessarytobreakalinetoreopenaclosedvalve.Itisdesirabletohavevalvestatus(openedorclosedindicatedinthecontrolroombecausewithoutsuchanindication,avalvemaybeclosedandtheeffectivenessoftheinstrumentimpairedforlongperiodsoftime.Forremotelyoperablevalves,theoperatorneedssufficientinformationregardingthestatusofthevalveandtheconditionofthelinesothathecantakeproper,timelyactions.Linesconnectedtoinstrumentsthatarepartoftheprotectionsystemareextensionsofthatsystemandshouldsatisfytherequirementsforredundancy,independence,andtestabilityfortheprotectionsystem,toassurethattheprotectivefunctionwillbeaccomplished.Linesconnectedonlytoinstrumentsthatarenotpartoftheprotectionsystemneednotmeettherequirementsoftheprotectionsystem.Fortheselines,theassurancethatisolationcanbeeffectedwhenrequiredisofgreaterimportancetosafetythanthecapabilityoftheconnectedinstrumentfunction;therefore,moreextensivevalvingisacceptable.C.RegulatoryPositionT