ML17319A961

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Background Info for Reactor Vessel Head Vent Operation.
ML17319A961
Person / Time
Site: Cook  American Electric Power icon.png
Issue date: 02/28/1981
From:
INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:
Shared Package
ML17319A959 List:
References
PROC-810228, NUDOCS 8107210423
Download: ML17319A961 (15)
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~~BACKGROUNDINFORMATIONFORREACTORVESSELHEADVENTOPERATIONREVISION0FEBRUARY19818i072i04238i07i5PDRADOCK05000315PPDR REACTORVESSELHEADVENTOPERATIONI.GENERALDISCUSSIONA.~PuroseTheoperatoractionsandprecautionsspecifiedinthisguidelinearethoseinstructionsnecessaryfortheremovalof'gasesfromthereactorvesselheadbyoperationofthereactorvesselheadventsystem.8;GuidelineAssumptionsThespecificdesignofthereac.orvsse'.',-eadventsys-;eausedinthisguidelineincludesasirg!ecornec.'.ionto~i:avesselheadwithredundantflowpathsandisolationvalves.extendingfromacommonline.Thecommonlineincludesa3/8".orificewhichlimitstheflowratetowithinthemakeupcapabilityofthechemicalandvolumecontrolsystem..Theredundantflowpathsdischargetothereacto~containmentbuilding.Notethatthoseplants,whichhaveventsystemsinstalledwhichventtothepressure~erorth"r=ssur-.=errelieftankmaydesirotomodifyormake'd"i:icos-o:heexistingguidelineinordertoincorporatetheplantspecificdesign.2.Althoughtheguidelinedoesnotrequireareactorvessellevelsystemitisrecomnendedthatanyventingoperationbeperformedincon5unctionwithanaccuratevessellevelindicationforbothwithandwithoutreactorcoolantpumpoperation.Forplantswithoutalevelsystem,theperformanceofAppendixA,"RCSGaseousVoidDetectionandSizing"mayprovideanestimateofthetotalvolumeofgaseousvoidsintheRCS(otherthanthepressurizer).February,1981Revision0'Page1 b3.Thereactorcoolantsystemcanbestabilizedwithaconstantpressurizerlevelandadequatereactorcoolantsub-coolingestablished.Theseconditionsarerequiredtoensureadequatecore-coolingismaintainedduringtheventingperiod.4.Thepressurizerlevelandpressurerequirementsthroughouttheguidelinedonotincludeerrorallocationsduetoanadversecontaihmentenvironment.Therefore,itisassumed.-thatcontainmenttemperatureisnearnormaloperatingconditions.5.Anyventingoperationmustbep'rformedpriortotheinitiation-'ofsafetyinjectionflowthrottl'ingduringaPOST-LOCA-cooldownanddepressurizaticn"peraton.Sever.lg"Ide;incactionsrequiresheinitiationosafe-:.y~n'ect".:-n':-ressurizerlevelcannotberestore.TheO'.ST-LOCAco.lccwn"nddoresuri-zationoperationbeginstothrottlesafe-.yinjecti"n.lowand-thereforefullSIflowcouldnotbedeliveredtotheRCSwhenrequired.6.Theheadventsystemisnotdesi'gnedforandshouldnot.beusedastheprimarymeans.o<<mitigateaninadequatetcorecoolingevent.Theventflcwpa.h'.snotsi:edtoproviCe"'hiscapabilityandshouldonlybeusedincon'unctionwitntheInadequateCoreCoolingGuidelines.C.~S~ot~ms0Thefollowingaresymptomsthatmayindicatethepresenceofagaseousvoidinthereactorcoolantsystem.Notethatanyoneorcombinationofsymptomsmayindicatethatavoidexists.February,1981Revision0Page2

ForPlantswithaRVlevelindication:1.Reactorvessellevelindicationlessthan(plantspecific)percentofspan.Theplantspecificvalueshoul'dincludeanallowancefornormalchannelaccuracy.Ifthelevelsystemdoesnotincludeareference'1egtemperaturecompensator'hananadditionalallowanceshould.beincludedforconditionswheretheRCStemperatureisnotequaltothechannelcalibration~'Vtemperature.ForPlants~ith/withoutaRYlevelindication:2.Variationsfromthenorm-1pressur.,zerpressureandlevelrosponseCueto::omanchar"ingand.s".ray',ngover=.".".",.smaynotbeobserveairagaseousvoide"istsn"he.-":CS.Thepressurizerlevelmaydecreasedur',ngaRCSpressurizationfromchargingduetogaseousvoid.contractionandlevelmayriserapidlyduringasprayingoperationduetoagaseousvoidexpansion.3.Anindicationofreactorvesselheadtempera'turesequaltoorgreaterthansaturationtemperaturewarrantsthepresenceofasteambubblebeinggeneratedint.",eRCS.'4.Gasesinthereactorcoolantsystemmayresultfromseveraltypesofplantevents.Anaccumulatortank"dischargeoracoreuncoverymayresultinnon-condensiblegases(e.g.nitrogenandhydrogen)beingtrappedintheRCS.ArapidRCScooldownmayresultinthevesselheadtemperaturebeinggreaterthantheprimarysaturationtemperatureandresultinasteambubblebeingdeveloped.TheoperatorshouldsuspectthepresenceofgasesintheRCSifany.oftheaboveeventsoccur.February,1981Revision0Page3 II.BASISFORSUBSEQUENTACTIONSTheCAUTIONprecedtngStep'Iearnstheoperatortomatntatntheextsttngmodeofcorecoo11ngdurIngtheperformanceofthesubsequentactions.Trippinganoperatingreacto~coolantpumpcouldresultingasesinthereactorcoolantloopscollectinginthesteamgeneratorU-tubesandmaydisturbnaturalcirculationandprimarytosecondaryheattransfer.'Startingreactorcoolantpumpswoulddisperseanygasesalreadycollectedinthevesselheadandmaketheirremovalmorediffscult.Therefore,theexistingstatusofthereactorcoolantpumpsshouldbemaintainedduringtheventfngoperation.Ifpossibleandifconditionsrequireso,thenareactorcoolantpumpshouldbestartedfo]lowingthecompl.so>>ofheventingoperation.TheNOTEprecedingStepidenti.'escer"nsteps-(markeabyanasterisk,'hicharenotapplicableifsafetyin~mectionhasbeeninitiatedandthesestepsshouldbeskippedduringtheventingoperationel.OnceagaseousvoidisdetectedorsuspectedintheRCS,thenanychangesbeingmadetotheprfnarysystemshouldbetermfnatedandasteady-stateconditionshouldbeestablished.ThisstepreferstoeventslikeaFCST-LOCAcooldown,anormalplantcooldown,oraplantrecoveryfromz.'esignbasisevent.TheintentistoaIIowtheRCStostabHfzesothatthesizeandpositionofthevoidcanbedetermined.NotethatanormaI-pressurizerpressurecontrolcondition'maynotbeattainableduetothereasonsstatedinsymptom2.2.ThefirstactiontakentoremoveanygasesfromtheRCSfstoattempttorecombineanycondensfblegasesbyincreasingRCSpressure.Thisstepmaybeslowactingandifaupwardtrendfswitnessedonthevessellevelindicatorthenmafntafnthismodeuntiltheheadisrefilledortheupwardtrendstops-thisstepissuccessfulinfillingthehead,thenreturntotheappropriateoperatinginstruction.Ifthisstepisnotsuccessful,thenproceedtoStep4.February,1981Revision0Page4 TheCAUTIONa'lertstheoperatorthatchargingfioumayresultinasuddencol'lapseofsteambubblesintheRCSandcausearapiddecreaseinpressurizerlevel.ThelevelshouldberestoredbyincreasingtheRCSmakeupflowrate.IftheincreasedmakeupflowfailstorestorelevelthensafetyinjectionshouldbeinitiatedandtheoperatoristoproceedtoEOI-O,ImmediateActionsandDiagnostics.3.TheventingoperationwillresultinRCSgasesbeingventedtothecontainment.Thereforethec'ontainmentpurgeandexhaustsystemshouldbeisolatedtopreventthereleaseofanyradioactivegasestotheenvironment.Allavailablecontainmentaircircula-.icnecuipmentsi.oui"".es;ar".adoprevens-.anyhydirognfromfor-irgagasoockezandtoersureare"rsanttivehydro".Tenconcentrat';nisobtainedinS:p5.4.Increasingthereactorcoolantsub-cooling50'Fabovetheminimum~plantspecificvalueensuresthatreactorcoolantsub-coolingwillbemaintainedovertheentirerangeofRCSoperatingconditionsiftheventingoperationisterminatedfollowinga200psidecreaseinRCSpressure.Thepreferredmethod-ofobtainingtheadditionalsub-coolingisincreasingRCSpressurtsincethis~illaidincondensinganysteambubblespresen"..Iftheadditioral5C'Fsub-coolingisalreadyestablishedthenproceedtoStep5.5.TheactionsofAppendixS"VentingTimePeriod"determinethemaximumallcwabletimeperiodforventingwhichwilllimitthecontainmenthydrogenconcentrationtolessthan3volumepercent.Thislimitisrequiredtopreventapotentiallyexplosivehydrogenconcentrationfrombeingdevelopedinsidethecontainment.(Thisstepmaynotbeapplicableforplantswhichventtothepressurizerorpressurizerrelieftank.)February,1981Revision0Page5

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6.Pressurizerlevelisincreasedtogreaterthan50"forthepurposeofmaintainingRCSmassinventoryduringtheventingperiod..Theoperatorisinstructedtoisolateletdownin"ordertoobtainthelevelincrease.Letdownwillremainisolateduntiltheventingoperationiscomplete.a7.ThisstepandthefollowingCAUTIONearnstheoperatorthatRCS.pressurewilldecreaseduringtheventingandifin.itialpressureisnearthelowpressuresafetyinjectionactuationsetpoint,thenSImay.beautomaticallyinitiatedduringtheventing.Theoperatorisinstructed:toblockthelowpressurSIactuationifand/orwhentheblockpermissiveisene.gzedtopreventaninadventn.SI.*8.Chargingflowisincrsed.omaximumtolimitthenemassdepletionoftheRCSduringtheventingperiod.Aseondc~ar,r.'g',",pimpshouldbestartedifitwillprovideadditionalmake-.pflou..Ifthesafetyinjectionsystemisin;.operationthenmaintainthecurrentplantconfigurationuntiltheventingiscomplete.TheresponsesindicatedintheNOTEwill'providetheprobablestatJsoftheRCSforthoseplantswithoutalevelsys:em.majalsoiden=ifythepresencecfvoidsintheRCSotherthanthereactorvesselheadorpressurizer.a)Duringadepressurization,anygaseousvoidsthatexistintheRCS,otherthanthevesselhoad,willrapidlyexpand'ndresult.inanincreaseinthepressurizerlevel.b).Theorificeintheheadventdischargelineissizedtolimitwaterrelieftowithinthemake-upcapabilityofacharging'pump.Therefore,ifnogasesarepresentinthevesselhead,thentheventflowratewil.lmatchthechargingflowrateandthepressurizerlevelwillremainconstant.February,1981Revision0Pag'e6 c)Theventingofgaseswillresultinarapiddecreasefnpressurizerlevelduetothemassflowrateofthegasesbeinggreaterthanthenthemassinputbeingprovidedbythemakeupflow.9.Bothisolationva1vesinoneventflowpathmustbeopenedtoinitiatetheventingoperation.TheNOTEinstructsthe.operatortoclosebothisolationvalvesintheflowpathff..':oneor,bothofthevalvesfailtoopen.'Thefsolatfonvalvesfntheredundantflowpathshouldthen.beopened.Thfspreventstwoflowpaths'beingopenifthefailedvalvesuddenlyopens.10.Theventingis'terminatedwhenthereactorvess=lheadfsrefilledorwhenthefollowingcriteriaareme=.b)lhemaximumtimeperiodallowableforventingwhicnli..itsccntainmenthydrogenconcentration-tolessthan3volumepercent(determinedbyAppendixB,"VentingTimePeriod").c,d;e)Theselimitingconditionsareconsistentwiththesafetyfngectionre-initiationcriteriaoftheemergencyoperatinginstructions.Theyprovidesuffjcientope.atingmarginfortheventingan'datthesametime,providei'mtscnt.".etransientwhichensuresadequate'systemcontrolcanbemaintained.rf)Oncethereactorvesselheadisventedandrefilledthenwaterreliefth~oughtheventpathwillbegin.Atthistime,therateofRCSdepressurizationandtherateofpressurizerleveldecreaseshouldchangeanymayeventerminate.Thismaybeusedonani'ndicationthat.theheadhasbeen'refilledforthoseplantswithoutavessellevelsystem.Bothisolationvalvesintheventflowpathshouldbeclosedtoterminatetheventing.February,1981Revision0Page7 TheCAUTIONinstructstheoperatortomaintaintheRCSventingiflossofreactorcoolantpumpoperationoccurs.TheventingismaintainedtoremoveasmuchgasaspossiblefromthevesselheadduringtheRCPcoastdownandonsoughtofnatural'irculation.ThiswillminimizetheamountofgasbubblesinthereactorcoolantloopsandsteamgeneratorU-tubes.TheoperatorshouldrefertoAOI-4"NaturalCirculation"toensureadequatecorecoolin'gisbeingmaintained.*II.Nornialpressurizerpressureandlevelcontrolisrestoredafterthecompletionoftheventing.Astablelevelandpressureshouldbemaintainedwhile,itisdeterminediffurtherventingisreouired.I"12.Ifa'gasbubbleexistednthevesselheadandtheventingwasterminatedpriortothevesselheadbeingcomolezely;f'.llthen*theoperatorshouldreturntoStep4andrepeattheventingoperationuntilthereactorvesselheadhasbeencompletelyrefi1Ied.TheNOTEalertstheoperatorthatif~thetimeperiodforventingdeterminedinAppendix8ismetheft<rethevesselhad'.sre-,illted,;thenthecontainmenthydrogenconcentrationmusbereducedandanewventingperiodcalcula:edpriortoperformingadditional.Nventing.Thehydrogenconcentrationcouldbereducedthroughtheuse,ofthecontainmenthydrogenre-combinersorbythepurge'.andexhaustsystemifradioactivegasconcentrationsarewithinlimits.Thenewventingperiodwillbebaseduponthereducedhydrogenconcentration.13.Theoperatorshouldreturntotheappropriateoperatinginstructionfollowingthesuccessfulcompletionofventing'thereactorvesselhead.If,duringsubsequentactions,agaseousbubblereformsinthevesselhead,thentheoperatorshouldreturntoStepIandrepeattheventingoperation.February,1981Revision0Page8 III.BASISFORAPPENDIXA"RCSGASEOUSVOIDDETECTIONANDSIZING"PIfgasesarepresentinthereactorcoolant'system,thenthepressurizerpressureandlevelcontrolswillnotrespondastheynormallywould.Thetotalgasvolumecanbeestimatedbyperformingaroutinepressurizercontroloperationandthencomparingtheexpectedresultswith.theactualresults,,:Thisisthetechniqueutilizedinthefallowingsteps..Ifthesafetyinjectionsystemisinservice,thenthefoll'owingstepsarenotapplicablesincenormalpressurizercontrolwillnotbemaintained.1,Theop"=ratorisinstructedtoachievo=-.-.-ablepressurizerpressurewithnormalcontrolsbeingmainai.;ed.2.Systempressureandlevelareplacedon.rendrecorde.s"'.oachievebetteraccuracyforrecordingtheirvalves.;hcransie",-.isnotexpectedtoexceeda150psi.or.'.1NofspanchargeinRCSconditions.3..Theserecordingswillbecometheinitialparametersinthefollow'.ngcalculation.4.Letdownflowisisolated,pressurizerheatersaretriooe",andpressurizersprayisterminatedtoestablishacondit".onwherethepressurizerlevelwillchangeonlyasaresultofmassbeinginjectedintotheRCS.UII5.Theoperatorisinstructedtoallowthesystempressuretoincrease100psiorthepressurizerlevelincreaseby5percentofspan(pressurizerlevelisthepreferredresponse).Theseconditionsareobtainedbyaslowcontinuouschargingrate.6.Theserecordingswillbecomethefinalparametersinthefollowingcalculation.'ebruary,1981Revision0Page9 7.NormalRCSpressureandlevelcontrolsarere-establishedandmaintaineduntilotherwisedirectedbystepsofthisinstruction.8.Theoperatorisinstructedtocalculatethetotalvolumeofthepressurizervaporspace.Thetotalcylindricalpressurizervol.:meisthetotalvolumeofthepressurizerexcludingtheupperandlowersph'ericaldomes.9.ThetotalchargedvolumeintotheRCSisthedifferencebetweenthe(chargingandsealinjectionflows)andthesealleakoffflowandthenconvertedtocubicfe't;AnexpectedpressurizerlevelchangecanLedeirminedthetotalchargedvolumeinthepreced'.rcs-.ep.11.Iftheactualpressurizerlevelchangeislessthantheexpec.edchange(orifnolevelchangewaswitnessed}thengaseousvoidsexistinthereactorcoolantsystem.~Thisisaresultofthegaseousvoidscontractingwhenthepressurewasincreasedbythechargingflow.Thiswilllimit,orpreventanormalpressurizer,levelincrease.Thevoidcontractio;.mayevenbelargeenougr.tocausear.actualdecreaseinthepressurizrlevel.Step12shouldthenbeperformedtoestimatethetotalvolumeofthegasvoids.intheRCS..12.TheRCSvoidvolumecontraction,isequaltothechangeinpressurizerlevelconvertedtovolume.AlsotheratiooffinalvoidvolumetoinitialvoidvolumeisequaltotheratioofinitialRCSpressuretofinalRCSpressure.Fromthesetwoequationsthetwounknown(initialandfinalRCSvoidvolume)canbedeterminedbyinsertingoneequationintoanother.The.initialvoidvolumeifcalculatedfirstandthenfitintothevolume/pressureratiotodeterminethefinalvoidvolume.February,1981Revision0Page10 IY.BASISFORAPPEHOIX8YEHTINGTIi"IEPERIOD'uringacoreuncoveryevent,thereexiststhepotentialforasignificantamount'ofhydrogengeneratedinthecorewhichcouldbetrappedinthereactorvesselheadandreleasedtothecontainmentatmosphereduringtheventingoperation.Thecontainmenthydrogenconcentrationislimitedtolessthan4volumepercenttopreventapotentialexplosivemixturewithoxygen,therefore,theamountofhydrogenthat,.canbeventedtothecontainmentisrestricted.Amaximumallowabletimeperiodforventingisdeterminedtolimitthecontainmenthydrogen..'oncentration.1.Theto.alcontainmentvolumeincubicfeetis-.'rs=de:a~ne"andthenconvrtedtostancard.e..oera..r'eandorossurec"nditons.Ho.e"'..atthepressure~ermfor:neconvetsionisi..iya"iicabietosub-atmosphericcontainmentsandcanbedeleted;-'ar='..eremaining:plants.'2,Thecontainmenthydrogenconcentration,isthendeterminedinvolumepercert'units.Thisvaluecanbefoundbydirectsamplingorbyhydrogenmonitors.Sufficienttimeshouldbeallowedfortheaircirculationequipmenttomixthecontainmnta--..osphreprio~tosamplinginor"ertodeterminearepresentaiveconcentration.aTheNOTEidentifiestotheoperatorthatthecontainmenthydrogenconcentrationwillbeinsignificantiftherehasbeennoleakagefromtheRCStothecontainment.Theoperatormayassumethe.HZconcentrationtobe.0volumepercent.3.Themaximumvolumeofhydrogenthatcanbeventediscalculatedwhichwilllimitthecontainmenthydrogenconcentrationtolessthan3volume.percent.February,1981Revision0'page11 0L'~~l~,l,
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