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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~~BACKGROUND INFORMATION FORREACTORVESSELHEADVENTOPERATION REVISION0FEBRUARY19818i072i0423 8i07i5PDRADOCK05000315PPDR REACTORVESSELHEADVENTOPERATION I.GENERALDISCUSSION A.~PuroseTheoperatoractionsandprecautions specified inthisguideline arethoseinstructions necessary fortheremovalof'gasesfromthereactorvesselheadbyoperation ofthereactorvesselheadventsystem.8;Guideline Assumptions Thespecificdesignofthereac.orvsse'.',-ead ventsys-;eausedinthisguideline includesasirg!ecornec.'.ion to~i:avesselheadwithredundant flowpathsandisolation valves.extending fromacommonline.Thecommonlineincludesa3/8".orifice whichlimitstheflowratetowithinthemakeupcapability ofthechemicalandvolumecontrolsystem..Theredundant flowpathsdischarge tothereacto~containment building.

Notethatthoseplants,whichhaveventsystemsinstalled whichventtothepressure~

erorth"r=ssur-.=er relieftankmaydesirotomodifyormake'd"i:icos

-o:heexistingguideline inordertoincorporate theplantspecificdesign.2.Althoughtheguideline doesnotrequireareactorvessellevelsystemitisrecomnended thatanyventingoperation beperformed incon5unction withanaccuratevessellevelindication forbothwithandwithoutreactorcoolantpumpoperation.

Forplantswithoutalevelsystem,theperformance ofAppendixA,"RCSGaseousVoidDetection andSizing"mayprovideanestimateofthetotalvolumeofgaseousvoidsintheRCS(otherthanthepressurizer).

February, 1981Revision0'Page1 b3.Thereactorcoolantsystemcanbestabilized withaconstantpressurizer levelandadequatereactorcoolantsub-cooling established.

Theseconditions arerequiredtoensureadequatecore-cooling ismaintained duringtheventingperiod.4.Thepressurizer levelandpressurerequirements throughout theguideline donotincludeerrorallocations duetoanadversecontaihment environment.

Therefore, itisassumed.-that containment temperature isnearnormaloperating conditions.

5.Anyventingoperation mustbep'rformed priortotheinitiation-

'ofsafetyinjection flowthrottl'ing duringaPOST-LOCA-cooldownanddepressurizaticn "peraton.Sever.lg"Ide;incactionsrequiresheinitiation osafe-:.y~n'ect".:-n

':-ressurizer levelcannotberestore.TheO'.ST-LOCA co.lccwn"nddoresuri-zationoperation beginstothrottlesafe-.yinjecti"n.lowand-therefore fullSIflowcouldnotbedelivered totheRCSwhenrequired.

6.Theheadventsystemisnotdesi'gned forandshouldnot.beusedastheprimarymeans.o<<mitigate aninadequate tcorecoolingevent.Theventflcwpa.h'.snotsi:edtoproviCe"'his capability andshouldonlybeusedincon'unction witntheInadequate CoreCoolingGuidelines.

C.~S~ot~ms0Thefollowing aresymptomsthatmayindicatethepresenceofagaseousvoidinthereactorcoolantsystem.Notethatanyoneorcombination ofsymptomsmayindicatethatavoidexists.February, 1981Revision0Page2

ForPlantswithaRVlevelindication:

1.Reactorvessellevelindication lessthan(plantspecific) percentofspan.Theplantspecificvalueshoul'dincludeanallowance fornormalchannelaccuracy.

Ifthelevelsystemdoesnotincludeareference

'1egtemperature compensator

'hananadditional allowance should.beincludedforconditions wheretheRCStemperature isnotequaltothechannelcalibration

~'Vtemperature.

ForPlants~ith/without aRYlevelindication:

2.Variations fromthenorm-1pressur.,zer pressureandlevelrosponseCueto::omanchar"ingand.s".ray',ng over=.".".",.s maynotbeobserveairagaseousvoide"istsn"he.-":CS.Thepressurizer levelmaydecreasedur',ngaRCSpressurization fromchargingduetogaseousvoid.contraction andlevelmayriserapidlyduringasprayingoperation duetoagaseousvoidexpansion.

3.Anindication ofreactorvesselheadtempera'tures equaltoorgreaterthansaturation temperature warrantsthepresenceofasteambubblebeinggenerated int.",eRCS.'4.Gasesinthereactorcoolantsystemmayresultfromseveraltypesofplantevents.Anaccumulator tank"discharge oracoreuncoverymayresultinnon-condensible gases(e.g.nitrogenandhydrogen) beingtrappedintheRCS.ArapidRCScooldownmayresultinthevesselheadtemperature beinggreaterthantheprimarysaturation temperature andresultinasteambubblebeingdeveloped.

TheoperatorshouldsuspectthepresenceofgasesintheRCSifany.oftheaboveeventsoccur.February, 1981Revision0Page3 II.BASISFORSUBSEQUENT ACTIONSTheCAUTIONprecedtng Step'Iearnstheoperatortomatntatntheextsttngmodeofcorecoo11ngdurIngtheperformance ofthesubsequent actions.Trippinganoperating reacto~coolantpumpcouldresultingasesinthereactorcoolantloopscollecting inthesteamgenerator U-tubesandmaydisturbnaturalcirculation andprimarytosecondary heattransfer.'Starting reactorcoolantpumpswoulddisperseanygasesalreadycollected inthevesselheadandmaketheirremovalmorediffscult.

Therefore, theexistingstatusofthereactorcoolantpumpsshouldbemaintained duringtheventfngoperation.

Ifpossibleandifconditions requireso,thenareactorcoolantpumpshouldbestartedfo]lowing thecompl.so>>ofheventingoperation.

TheNOTEpreceding Stepidenti.'es cer"nsteps-(markeabyanasterisk,'hich arenotapplicable ifsafetyin~mection hasbeeninitiated andthesestepsshouldbeskippedduringtheventingoperatione l.Onceagaseousvoidisdetectedorsuspected intheRCS,thenanychangesbeingmadetotheprfnarysystemshouldbetermfnated andasteady-state condition shouldbeestablished.

ThisstepreferstoeventslikeaFCST-LOCA

cooldown, anormalplantcooldown, oraplantrecoveryfromz.'esignbasisevent.TheintentistoaIIowtheRCStostabHfzesothatthesizeandpositionofthevoidcanbedetermined.

NotethatanormaI-pressurizer pressurecontrolcondition'may notbeattainable duetothereasonsstatedinsymptom2.2.ThefirstactiontakentoremoveanygasesfromtheRCSfstoattempttorecombine anycondensfble gasesbyincreasing RCSpressure.

Thisstepmaybeslowactingandifaupwardtrendfswitnessed onthevessellevelindicator thenmafntafnthismodeuntiltheheadisrefilledortheupwardtrendstops-thisstepissuccessful infillingthehead,thenreturntotheappropriate operating instruction.

Ifthisstepisnotsuccessful, thenproceedtoStep4.February, 1981Revision0Page4 TheCAUTIONa'lertstheoperatorthatchargingfioumayresultinasuddencol'lapse ofsteambubblesintheRCSandcausearapiddecreaseinpressurizer level.Thelevelshouldberestoredbyincreasing theRCSmakeupflowrate.

Iftheincreased makeupflowfailstorestorelevelthensafetyinjection shouldbeinitiated andtheoperatoristoproceedtoEOI-O,Immediate ActionsandDiagnostics.

3.Theventingoperation willresultinRCSgasesbeingventedtothecontainment.

Therefore thec'ontainment purgeandexhaustsystemshouldbeisolatedtopreventthereleaseofanyradioactive gasestotheenvironment.

Allavailable containment aircircula-.icn ecuipment si.oui"".es;ar".adoprevens-.anyhydirognfromfor-irgagasoockezandtoersureare"rsanttivehydro".Ten concentrat';n isobtainedinS:p5.4.Increasing thereactorcoolantsub-cooling 50'Fabovetheminimum~plantspecificvalueensuresthatreactorcoolantsub-cooling willbemaintained overtheentirerangeofRCSoperating conditions iftheventingoperation isterminated following a200psidecreaseinRCSpressure.

Thepreferred method-ofobtaining theadditional sub-cooling isincreasing RCSpressurtsincethis~illaidincondensing anysteambubblespresen"..

Iftheadditioral 5C'Fsub-cooling isalreadyestablished thenproceedtoStep5.5.TheactionsofAppendixS"VentingTimePeriod"determine themaximumallcwable timeperiodforventingwhichwilllimitthecontainment hydrogenconcentration tolessthan3volumepercent.Thislimitisrequiredtopreventapotentially explosive hydrogenconcentration frombeingdeveloped insidethecontainment.

(Thisstepmaynotbeapplicable forplantswhichventtothepressurizer orpressurizer relieftank.)February, 1981Revision0Page5

  • 6.Pressurizer levelisincreased togreaterthan50"forthepurposeofmaintaining RCSmassinventory duringtheventingperiod..Theoperatorisinstructed toisolateletdownin"ordertoobtainthelevelincrease.

Letdownwillremainisolateduntiltheventingoperation iscomplete.

a7.Thisstepandthefollowing CAUTIONearnstheoperatorthatRCS.pressurewilldecreaseduringtheventingandifin.itialpressureisnearthelowpressuresafetyinjection actuation

setpoint, thenSImay.beautomatically initiated duringtheventing.Theoperatorisinstructed:to blockthelowpressurSIactuation ifand/orwhentheblockpermissive isene.gzedtopreventaninadventn.SI.*8.Chargingflowisincrsed.omaximumtolimitthenemassdepletion oftheRCSduringtheventingperiod.Aseondc~ar,r.'g',",pimpshouldbestartedifitwillprovideadditional make-.pflou..Ifthesafetyinjection systemisin;.operation thenmaintainthecurrentplantconfiguration untiltheventingiscomplete.

Theresponses indicated intheNOTEwill'provide theprobablestatJsoftheRCSforthoseplantswithoutalevelsys:em.majalsoiden=ifythepresencecfvoidsintheRCSotherthanthereactorvesselheadorpressurizer.

a)Duringadepressurization, anygaseousvoidsthatexistintheRCS,otherthanthevesselhoad,willrapidlyexpand'ndresult.inanincreaseinthepressurizer level.b).Theorificeintheheadventdischarge lineissizedtolimitwaterrelieftowithinthemake-upcapability ofacharging'pump.Therefore, ifnogasesarepresentinthevesselhead,thentheventflowratewil.lmatchthechargingflowrateandthepressurizer levelwillremainconstant.

February, 1981Revision0Pag'e6 c)Theventingofgaseswillresultinarapiddecreasefnpressurizer levelduetothemassflowrateofthegasesbeinggreaterthanthenthemassinputbeingprovidedbythemakeupflow.9.Bothisolation va1vesinoneventflowpathmustbeopenedtoinitiatetheventingoperation.

TheNOTEinstructs the.operatortoclosebothisolation valvesintheflowpathff..':oneor,bothofthevalvesfailtoopen.'Thefsolatfon valvesfntheredundant flowpathshouldthen.beopened.Thfspreventstwoflowpaths'being openifthefailedvalvesuddenlyopens.10.Theventingis'terminated whenthereactorvess=lheadfsrefilledorwhenthefollowing criteriaareme=.b)lhemaximumtimeperiodallowable forventingwhicnli..itsccntainment hydrogenconcentration-to lessthan3volumepercent(determined byAppendixB,"VentingTimePeriod").c,d;e)Theselimitingconditions areconsistent withthesafetyfngection re-initiation criteriaoftheemergency operating instructions.

Theyprovidesuffjcient ope.atingmarginfortheventingan'datthesametime,providei'mtscnt.".etransient whichensuresadequate'system controlcanbemaintained.

rf)Oncethereactorvesselheadisventedandrefilledthenwaterreliefth~oughtheventpathwillbegin.Atthistime,therateofRCSdepressurization andtherateofpressurizer leveldecreaseshouldchangeanymayeventerminate.

Thismaybeusedonani'ndication that.theheadhasbeen'refilled forthoseplantswithoutavessellevelsystem.Bothisolation valvesintheventflowpathshouldbeclosedtoterminate theventing.February, 1981Revision0Page7 TheCAUTIONinstructs theoperatortomaintaintheRCSventingiflossofreactorcoolantpumpoperation occurs.Theventingismaintained toremoveasmuchgasaspossiblefromthevesselheadduringtheRCPcoastdown andonsoughtofnatural'irculation.

Thiswillminimizetheamountofgasbubblesinthereactorcoolantloopsandsteamgenerator U-tubes.TheoperatorshouldrefertoAOI-4"NaturalCirculation" toensureadequatecorecoolin'gisbeingmaintained.

  • II.Nornialpressurizer pressureandlevelcontrolisrestoredafterthecompletion oftheventing.Astablelevelandpressureshouldbemaintained while,itisdetermined iffurtherventingisreouired.

I"12.Ifa'gasbubbleexistednthevesselheadandtheventingwasterminated priortothevesselheadbeingcomolezely

f'.llthen*theoperatorshouldreturntoStep4andrepeattheventingoperation untilthereactorvesselheadhasbeencompletely refi1Ied.TheNOTEalertstheoperatorthatif~thetimeperiodforventingdetermined inAppendix8ismetheft<rethevesselhad'.sre-,illted,;

thenthecontainment hydrogenconcentration musbereducedandanewventingperiodcalcula:ed priortoperforming additional

.Nventing.Thehydrogenconcentration couldbereducedthroughtheuse,ofthecontainment hydrogenre-combiners orbythepurge'.andexhaustsystemifradioactive gasconcentrations arewithinlimits.Thenewventingperiodwillbebaseduponthereducedhydrogenconcentration.

13.Theoperatorshouldreturntotheappropriate operating instruction following thesuccessful completion ofventing'thereactorvesselhead.If,duringsubsequent actions,agaseousbubblereformsinthevesselhead,thentheoperatorshouldreturntoStepIandrepeattheventingoperation.

February, 1981Revision0Page8 III.BASISFORAPPENDIXA"RCSGASEOUSVOIDDETECTION ANDSIZING"PIfgasesarepresentinthereactorcoolant'system,thenthepressurizer pressureandlevelcontrolswillnotrespondastheynormallywould.Thetotalgasvolumecanbeestimated byperforming aroutinepressurizer controloperation andthencomparing theexpectedresultswith.theactualresults,,:This isthetechnique utilizedinthefallowing steps..Ifthesafetyinjection systemisinservice,thenthefoll'owing stepsarenotapplicable sincenormalpressurizer controlwillnotbemaintained.

1,Theop"=rator isinstructed toachievo=-.-.-ablepressurizer pressurewithnormalcontrolsbeingmainai.;ed.2.Systempressureandlevelareplacedon.rendrecorde.s"'.oachievebetteraccuracyforrecording theirvalves.;hcransie",-.

isnotexpectedtoexceeda150psi.or.'.1NofspanchargeinRCSconditions.

3..Theserecordings willbecometheinitialparameters inthefollow'.ng calculation.

4.Letdownflowisisolated, pressurizer heatersaretriooe",andpressurizer sprayisterminated toestablish acondit".on wherethepressurizer levelwillchangeonlyasaresultofmassbeinginjectedintotheRCS.UII5.Theoperatorisinstructed toallowthesystempressuretoincrease100psiorthepressurizer levelincreaseby5percentofspan(pressurizer levelisthepreferred response).

Theseconditions areobtainedbyaslowcontinuous chargingrate.6.Theserecordings willbecomethefinalparameters inthefollowing calculation.'ebruary, 1981Revision0Page9 7.NormalRCSpressureandlevelcontrolsarere-established andmaintained untilotherwise directedbystepsofthisinstruction.

8.Theoperatorisinstructed tocalculate thetotalvolumeofthepressurizer vaporspace.Thetotalcylindrical pressurizer vol.:meisthetotalvolumeofthepressurizer excluding theupperandlowersph'erical domes.9.ThetotalchargedvolumeintotheRCSisthedifference betweenthe(charging andsealinjection flows)andthesealleakoffflowandthenconverted tocubicfe't;Anexpectedpressurizer levelchangecanLedeirminedthetotalchargedvolumeinthepreced'.rc s-.ep.11.Iftheactualpressurizer levelchangeislessthantheexpec.edchange(orifnolevelchangewaswitnessed}

thengaseousvoidsexistinthereactorcoolantsystem.~Thisisaresultofthegaseousvoidscontracting whenthepressurewasincreased bythechargingflow.Thiswilllimit,orpreventanormalpressurizer, levelincrease.

Thevoidcontractio;.

mayevenbelargeenougr.tocausear.actualdecreaseinthepressuriz rlevel.Step12shouldthenbeperformed toestimatethetotalvolumeofthegasvoids.intheRCS..12.TheRCSvoidvolumecontraction, isequaltothechangeinpressurizer levelconverted tovolume.AlsotheratiooffinalvoidvolumetoinitialvoidvolumeisequaltotheratioofinitialRCSpressuretofinalRCSpressure.

Fromthesetwoequations thetwounknown(initialandfinalRCSvoidvolume)canbedetermined byinserting oneequationintoanother.The.initialvoidvolumeifcalculated firstandthenfitintothevolume/pressure ratiotodetermine thefinalvoidvolume.February, 1981Revision0Page10 IY.BASISFORAPPEHOIX8YEHTINGTIi"IEPERIOD'uring acoreuncoveryevent,thereexiststhepotential forasignificant amount'of hydrogengenerated inthecorewhichcouldbetrappedinthereactorvesselheadandreleasedtothecontainment atmosphere duringtheventingoperation.

Thecontainment hydrogenconcentration islimitedtolessthan4volumepercenttopreventapotential explosive mixturewithoxygen,therefore, theamountofhydrogenthat,.canbeventedtothecontainment isrestricted.

Amaximumallowable timeperiodforventingisdetermined tolimitthecontainment hydrogen..'oncentration.

1.Theto.alcontainment volumeincubicfeetis-.'rs=de:a~ne"andthenconvrtedtostancard.e..oera..r'e andorossurec"nditons.Ho.e"'..atthepressure~ermfor:neconvetsionisi..iya"iicabietosub-atmospheric containments andcanbedeleted;-'ar='..eremaining

plants.'2,Thecontainment hydrogenconcentration, isthendetermined involumepercert'units.

Thisvaluecanbefoundbydirectsamplingorbyhydrogenmonitors.

Sufficient timeshouldbeallowedfortheaircirculation equipment tomixthecontainmnta--..osph reprio~tosamplinginor"ertodetermine arepresenta iveconcentration.

aTheNOTEidentifies totheoperatorthatthecontainment hydrogenconcentration willbeinsignificant iftherehasbeennoleakagefromtheRCStothecontainment.

Theoperatormayassumethe.HZconcentration tobe.0volumepercent.3.Themaximumvolumeofhydrogenthatcanbeventediscalculated whichwilllimitthecontainment hydrogenconcentration tolessthan3volume.percent.February, 1981Revision0'page11 0L'~~l~,l,

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