ML18026A417

From kanterella
Revision as of 04:46, 29 June 2018 by StriderTol (talk | contribs) (Created page by program invented by StriderTol)
Jump to navigation Jump to search
Forwards Revised Response to NRC Station Blackout Safety Evaluation Dtd 920114,revising Diesel Generator Target Reliability to 0.975,based on NRC Position.Resolution of Cabinet Temp Concern Will Be Submitted by 920501
ML18026A417
Person / Time
Site: Susquehanna  Talen Energy icon.png
Issue date: 03/13/1992
From: KEISER H W
PENNSYLVANIA POWER & LIGHT CO.
To: MILLER C L
Office of Nuclear Reactor Regulation
Shared Package
ML17157B098 List:
References
PLA-3745, TAC-M68613, TAC-M68614, NUDOCS 9203230281
Download: ML18026A417 (34)
v • d • e


Text

.,ACCELERATED DISTRIBUTION DEMONST$A.TIONSYSTEMREGULA.YINFORMATION DISTRIBUTIO.

SYSTEM(RIDS),~'7ACCESSION NBR:9203230281 DOC.DATE:

92/03/13NOTARIZED:

NODOCKETFACIL:50-387 Susquehanna SteamElectricStation,Unit1,Pennsylva 0500038750-388Susquehanna SteamElectricStation,Unit2,Pennsylva 05000388AUTH.NAMEAUTHORAFFILIATION KEISERgH.W.

Pennsylvania Power&LightCo.RECIP.NAME REC1PIENT AFFILIATION MILLER.C.L.

ProjectDirectorate I-2R

SUBJECT:

ForwardsutilrevisedresponsetoStationBlackoutRuleperNRC920114SafetyEvaluation w/answers attachedtoallbutIoneNRCrecommendation.

QueryonCRinstrument cabinettemptobeanswerednolaterthan920501.D,DISTRIBUTION CODE:A050DCOPIESRECEIVED:LTR ENCLjSIZE:g5f~f$TITLE:ORSubmittal:

StationBlackout(USIA-44)10CFR50.63, MPAA-22/0500038705000388ADRECIPIENT IDCODE/NAME PD1-2PDINTERNAL:

ACRSNRRPD2-4PMTAMNRR/DST/SELB NRR/DST/SRXB8E EXTERNAL:

NRCPDRNOTES:COPIESLTTRENCL11111133111122RECIPIENT IDCODE/NAME RALEIGHiJ.

AEOD/DSP/TPAB NRR/DET/ESGB 8DNRRDST/PLB8D1GFILE01NSICCOPIESLTTRENCL111122331111DDNOTETOALL"RIDS"RECIPIENTS:

PLEASEHELPUSTOREDUCEWAS'ONTACT THEDOCUMENTCONTROLDESK.ROOMPl-37(EXT.20079)TOELIMINATE YOURNAMEFROMDISIRIBUTION LINISFORDOCUMENTS YOUDON'TNEED!ADDTOTALNUMBEROFCOPIESREQUIRED:

LTTR19ENCL19 Pennsylvania Power8LightCompanyTwoNorthNinthStreet~Allentown, PA18101-1179

~215/774-5151 HaroldW.KeiserSeniorVicePresident-Nuclear 215/774<194 NRl31992DirectorofNuclearReactorRegulation Attention:

Mr.C.L.Miller,ProjectDirectorProjectDirectorate I-2DivisionofReactorProjectsU.S.NuclearRegulatory Commission Washington, D.C.20555SUSQUEHANNA STEAMELECTRICSTATIONRESPONSETOSTATIONBLACKOUTSAFf"TYEVALUATION PLA-3745FILER41-2

Reference:

RESPONSETOTHESTATIONBLACKOUTRULEFORSUSQUEHANNA STEAMELECTRICSTATION,UNIT1AND2PACNOS.M68613ANDM68614)DatedJanuary14,1992.

DearMr.Miller:

ThisletterprovidesthePennsylvania Power&LightCompany(PP&L)revisedresponsetotheStationBlackout(SBO)Ruleasrequiredbythereferenced NRCSafetyEvaluation.

Thisresponse(attached) revisesdieselgenerator targetreliability to0.975basedonyourposition, andprovidestherequested justification tosupportPP&L'soriginalpositionthatSSESisonlyrequiredtocopewithaSBOeventfor4hours.However,itshouldbenotedthatathoroughevaluation wasundertaken toreviewthestaffsconcernsregarding theneedandabilityforSSEStocopefor8hours.Resultsofthisevaluation concluded SSEShasthecapability tocopefor8hoursandlongerifrequired.

Withtheexception ofafinaltechnical resolution toyourquestionregarding ControlRoominstrument cabinettemperatures, theattachment respondsinfulltoeachofyourrecommendations.

Ourresolution tothecabinettemperature concernwillbeforwarded toyounolaterthanMay1,1992.9203230281 920313PDRADOCK05000387PPDR FILER41-2PLA-3745Mr.C.L.MillerQuestions regarding thisrevisedresponseshouldbedirectedtoMr.A.K.Maronat(215)774-7852.

Verytrulyyours,H.W.KeiserAttachment cc:NRC3)ocnment:Control DeaR(original)

NRCRegionIMr.G.S.Barber,NRCSr.ResidentInspector

-SSESMr.J.J.Raleigh,NRCProjectManager-Rockville

~~q~,9203230281 ATTACHMENT TOPLA-3745I~NTRDUCTINTheStationBlackoutRule(10CFR50.63)wasinstituted in1988andrequiredlicensees toassesstheirabilitytocopewithastationblackout(SBO)ofaspecified duration.

In1989,PP&Lsubmitted theresultsofourcopingstudytotheNRC,concluding thatSusquehanna SES(SSES)mustbeabletocopewithastationblackoutfor4hoursandmaintainanEmergency DieselGenerator (EDG)reliability of0.975(97.5%).InFebruaryof1991,PP&LreviseditsEDGtargetreliability valuefrom0.975to0.95basedonaspraypondbypassvalvemodification.

OnJanuary14,1992,NRCissueditsSafetyEvaluation oftheSSESSBOsubmittal concluding thatSSESwasan8hourcopingplantrequiring EDGreliability bemaintained at0.975.Thefollowing isanitembyitemresponsetotherecommendations identified intheNRCSafetyEvaluation.

c-".STATION,::::>SL'ATCKOUT:;,::::DUR'ATION>".l tNRRKMMENDATION:

ThelicenseeneedstochangetheEDGreliability targetfrom0.95to0.975andthecopingdurationfrom4hoursto8hours.P~PRLRA)CopingDurationOneinputtothedetermination ofrequiredSBOcopingdurationisthe"returntime"ofextremely highwinds(>125 mph).Aspartofouroriginalcopingassessment, PP&Lcontracted withDames&MooreConsulting Engineers forthecalculation ofthis"returntime"forSSES.Dames&Mooredetermined thisvaluetobe-6.7E-4/yr.

(aboutoncein1500years)usingdataspecifictoSSES.Anyreturntimevaluelessthan1.OE-3/yr, coupledwithoursevereweatherandoff-sitepowerdesignclassification, placesSSESina4hourcopingcategory.

TheNRCevaluation didnotcredituseofsitespecificdataduetothisdatabeingapplicable forwindsat10metersofftheground,ratherthantherequiredassessment heightof30metersfromtheground(averagetransmission towerheight).Itwastherefore concluded, basedonNUMARCTable3.2,thatthereturntimeforSSESwasmorefrequentthanonceper1000yearsandthatSSESmustcopewithaSBOfor8hours,Page1

~)~~(

ATTACHMENT TOPLA-3745Toaddressthiscopingdurationconcern,PP&Linvestigated thebasisofTable3.2inNUMARC87-00andcontracted againwithDames&Mooretodetermine thereturntimeofwindspeedsat30meters.Conversations withbothNUMARCpersonnel andNRCstaffindicated thattheuseofsitespecificdataisacceptable.

TheNRCcautioned thattheuseofsuchdatashouldaccountforwindspeedsof125mphat30metersandconsiderNationalBureauofStandards (NBS)publications 118and124,aswellasseveralNationalOceanicandAtmospheric Administration (NOAA)documents.

Notethattheuseofsitespecificdataisencouraged inNUMARC87-00.NBS118providesamethodofscalingwindspeedstovariousheightsandprovidesmeasuredweatherdatafrom129meteorological stationsacrosstheUSmainland.

ItisthisdatawhichPP&LandDames&Moorebelieveprovidesthebestestimates ofwindspeedreturntimesatSSES.UsingthemethodofNBS118,the125mph"fastestmile"windspeedat30metersisscaledtoa"fastestmile"windspeedof107mphat10meters(thenormalized heightofallreportedweatherdata).Usingthedataformeteorological stationsclosesttoSSES,NBS118providesthefollowing "returntimes"forvariousfastestmilespeeds:FastestMileWindSpeed(mph)ReturnTimeears1,0005,00010,00050,000100,000500,0001,000,000 Scranton60.8667.3470.1276.5879.3685.8288.6095.0697.84Harrisburg 70.5780.4984.7594.6498.90108.79113.05122.95127.21Page2 ATTACHMENT TOPLA-3745Inaddition, Dames&Moorehavecalculated theprobability ofexceeding variouswindspeedswithin1000years,alsobasedonthedataandmethodsinapaperbyH.C.S.Thorn:

Probability ofExceedance in1000rsScrantonHarrisburg FastestMileWindSpeed(mph)0.5000.2500.1000.0500.0057275798292879299103117Fromthefirsttableabove,onecanseethatthereturntimeofawindspeedof107mphat10metersisexpectedtobegreaterthan1millionyearsatScrantonandalmost50,000yearsatHarrisburg.

Table2shows'that theprobability ofexceeding the107mphwindspeedwithin1000yearsislessthan1%atScrantonandabout3%atHarrisburg.

UsingthedatafromHarrisburg inTable1,theexpectedreturntimeofa125mphwindat30metersis-37,500years.PP&Lalso-reviewed NBS,124forapplicability.

NBS124reliesontheextrapolation ofcoastalweatherdatatoinferwindspeedsinland.Further,thismethodofextrapolation assumesintervening terraintobeopenandgrasscovered.SinceSSESislocatedwithinavalleyseparated fromthecoastbyapproximately 100milesofhillsandforest,theextrapolation ishighlyinaccurate.

Thus,PP&LviewsNBS124asvalidonlyforscopingcalculations andshouldonlybeusedintheabsenceofbettertechniques/data.

PP&Lconsiders thepreceding arguments anddatasufficient justification fornotusingTable3.2ofNUMARC87-00fordetermining ourESWcategory.

Further,thisdatashowsthatthereturntimeofwindsinexcessof125mphatSSESishighlylikelytobegreaterthan1000years.Thus,itisconcluded thattheESWcategoryof"2"originally reportedinourcopingstudyisfullyjustified (thedataactuallyjustifies anESWclassification of"1"),andthatSSESremainsa"Pl"plant(perNUMARC87-00)requiring aSBOcopingtimeof4hours.B)EDGTargetReliability In1991,PP&LinformedtheNRCthatforpurposesofcomplying withtheSBOruleourtargetEDGreliability wastobe0.95(95%).Inmakingthisdetermination, PP&Lreliedontheuseof"staggered operation" ofRHRpumpstocoolbothsuppression pools.Staggered operation isrequiredbecause,althoughinprinciple anytwoEDGscancoolbothunits,inactuality therearetwocombinations ofEDG's(AandC,orBandD)whichresultinonlyoneRHRpumpineachunitavailable toalternately coolthesuppression pools.Page3 i

eATTACHMENT TOPLA-3745TheNRCnotedthattheuseofstaggered operation didnotmeetthe"connectability criterion" andwasdetermined tobeanunacceptable increaseinoperatorburden.Thiscriterion wasexplained indocumentation providedbytheNRCtoNUMARCaftersubmittal oftheSSESSBOanalysis.

TheNRCconcluded thattoavoiduseofstaggered operation, 3ofthe4EDG'swouldberequired.

Further,theNRCnotedthatifonlydieselsAandBstart,nocontrolstructure HVACwouldbeavailable.

PP&Lhasperformed acalculation ofsteadystatecontrolroomtemperature usingthemethodinNUMARC87-00andassumingthatthemeasured, normalcontrolroomheatloadexists.Theresultofthiscalculation isthatthecontrolroomtemperature willnotriseabove111'FintheabsenceofnormalHVAC.Becausetemperature remainslessthan120'F,thecontrolstructure environment remainsacceptable.

Basedontheinability totakecreditforstaggered operation, PP&Lconcurswiththestaff'spositionin"requiring 3of4EDGsandthereliability targetvalueof0.975.:;::ST@'TIOÃ:;::'.SL'A'CEO'::,:,::COPINO.":..:.CAPASILITY::,::,::,'=:,',ll NRRECMMENDATIN'heNRCmadethefollowing fourrecommendations basedontheirpreviousdetermination thatPP&LhadtoaddresstheneedforSSEStocopewithan8hourStationBlackout.

1)Thelicenseeneedstoconformtoan8hourcopingdurationandincreasetheEDGreliability targetfrom0.95to0.975.2)Thelicenseeshouldprovideaprocedure torefilltheCSTfromtheRWSTduringanSBOevent.3)ThelicenseeshouldaddtheportableACgenerator tothelistofSBOequipment, provideprocedures foritsutilization, andapplytoitanappropriate QAprogram.Theportableacgenerator shouldmeetthecriteriainAppendixBofNUMARC87-00.Alsothelicenseeshouldreplacebattery1D650withahighercapacitybatteryorprovidechargingcapability totheexistingbatterytoextenditssupportforthe8hourSBOduration, andrecoverythereafter.

Thelicenseeshouldincludealltheanalysesandrelatedinformation insupporting documentation thatistobemaintained bythelicenseeforpossiblestaffreview.4)Thelicenseeshouldprovideforstaffreviewafulldescription, including thenatureandobjectives ofanymodification required.

Theanalysesandrelatedinformation shouldalsobeincludedinthesupporting documentation thatistobemaintained bythelicenseeinsupportoftheSBOsubmittals.

Page4 Slipl(ii0

~RP~PLRNR'2RATTACHMENT TOPLA-3745Asaddressed intheinitialsectionofthisresponse, PP&Lconcludes thatSSESmustcopewithaSBOeventfor4hours.Thisconclusion issupported by.theuseofsitespecificweatherdata(attherequiredassessment height).AsfortheEDGreliability targetvalue,PP&LhasreviewedtheNRCconcernsandhasconcurred withthestaff'sfindingthattheconfiguration ofSSESmandatesanEDGreliability targetvalueof0.975.Thisreliability valuehasbeenincludedintheEDGReliability Programdeveloped inaccordance withNUMARC87-00AppendixD.PP&Lhasthoroughly evaluated theabilityofSSEStocope8hourswithanSBOevent,including allareasofconcernidentified intheNRCSafetyEvaluation.

PP&Lisconfident thatSSEShastheabilitytocopefor8hoursandlongerifrequired.

SincePP&Lhasdemonstrated thatSSESisa4hourcopingplantthisinformation willnotbeprovidedinsupportofourrevisedsubmittal, butisavailable forreview.';"':;EFFECTS::.".,"OF.,:,:LOSS:;OF..'",VENTILh;TION~:;i NRRECMMENDATIThelicenseeshould:I)provideadditional information and/ortechnical justification fortheinitialconditions andassumptions usedintheheat-upanalysisforeachareaofconcern,2)withregardtoCOTTAPcomputercode,providedetailedinformation toaddressthestaff'sconcernsasidentified above,and3)re-perform theheat-upanalysisforeachareaofconcernandforan8hourcopingdurationtakingintoaccountthenon-conservatism asidentified intheSAICTER.P~PRLRNR-CCPPAP2C1TheuseoftheCompartment Temperature Transient AnalysisProgram(COITAP)computercodehasbeenpresented tothestaffaspartofoursubmittals toresolvesteamleakdetection Technical Specification changes.Attachment Acontainsauser'smanualfortheCOTTAPcomputercodeandacopyofarecentpaperpublished inNuclearTechnology whichdescribes themethodology usedintheCOTI'APprogramandpresentssomeoftheverification calculations whichhavebeenperformed.

Theuser'smanualpresentssomeofthecalculations whichwereperformed againstproblemsthathaveexactanalytical solutions.

Thereferredpaperpresentsthemethodology alongwithcalculations whichhavebeenbenchmarked againstcalculations performed withtheCONTAINcomputerprogram.Inaddition, theprogramandcomputation packagehavebeenindependently reviewedbyGilbertAssociates.

PP&Lalsomaintains aQualityAssurance file/package fortheCOTTAPcomputercode.APage5

~tof ATTACHMPIT TOPLA-3745Intheoriginalcopingassessment, twobasicCOTTAP2calculations wereperformed:

anassessment ofDominantAreasofConcern(DACs);andanevaluation ofcontrolroomcabinets.

ForBWRs,theDACsaretheHPCIandRCICrooms,andthemainsteamtunnel(NUMARC87-00).Themainsteamtunnelisconsidered because,apparently atsomeplants,HPCIandRCICareisolatedonhightemperature inthetunnel.AtSSES,theHPCVRCICisolations donotcomefrommainsteamtunneltemperature butfromsensorslocatedonthe683footelevation ofthereactorbuildingcommontobothHPCIandRCICpiping.DuringSBO,onlytheRCICisolation logicispowered.Thus,forSSES,themainsteamtunnelisnotatrueDAC.Thecommonpipingarea,calledtheRHRpipingareainthecalculation, isaDAC.PP&Lrecalculated theDACtemperatures usingCO1TAP2and"conservative" inputs.Inputsincludeduseof"maximumnormal"roomtemperatures pertheFSAR.Outsideairtemperature wasassumedtobeaconstant95'F.Theinfluence.

ofhotpiping(including fluedheads)wasaddedtotheHPCI,RCIC,RHRpipingarea,andthemainsteamtunnel.(TheabsenceofthishotpipeloadingcausedthecooldownofthemainsteamtunnelnotedintheSAICTechnical Evaluation Report).Noengineering reference foracon'crete thermal'conductivity of0.7couldbefound.However,thisvaluewaschangedfrom1.0to0.7,pertheTER.Theactualinputdeck,andthejustification forallinputvaluesused,appearsinthedetailedcalculation.

TheresultsoftheCOTTAP2calculations arepresented inthetablesbelow.OriginalSubmittal:

Temperature

('F)NewCalculation:

ROOM8hours72hours8hours72hoursHPCIRCICRHRPipingMSTunnel113118123114117117114107125150119130171FromTable3,thetemperatures oftheDACsremainlessthanthe180'Foperability limit,evenat72hours.Theinclusion ofthehotpipe.loadsdoescause,significant increases intunneltemperatures.

Page6 0ATTACHMENT TOPLA-3745Temperature

('F)ROOMRHRPipingMSTunnelCOTTAP2at72hours130171NUMARC87-00176Table4presentsacomparison ofthetwohottestDACtemperatures ascalculated bybothCOTTAP2andthemethodofNUMARC87-00.WhileitappearsthattheNUMARCmethodproduces"conservative" results,itmustbenotedthattheNUMARCcalculation producesasteadystate,infinitetimeresult.TheCOTTAP2resultsarenotsteadystatebuttimedependent, andat72hoursthetemperatures intheseroomsarestillincreasing.

Atlongerandlongertimes,onewouldexpectbetteragreement betweenthetwomethods.Theresultsoftheabovetableshowthattheagreement betweenthetwomethodsisquitegood.TheTERmadereference to"oscillatory" temperature profiles.

ReviewoftheoriginalCOTI'AP2workrevealednosuchprofiles.

Thereviewers maybereferring totemperature profileswhichpeakanddropintheshortterm,thencontinuealongtermtemperature rise(Figure1).ThelargeearlypeakiscausedbyACmotorheatloadswhichdecayaway.Atlatertimes,theroomisheatedbysurrounding walls.Thisresultisconsistent withexpectedbehavior.

Thereviewers questioned PP&L'suseofCOTTAP2forcalculation ofinstrument cabinettemperatures andseveralassumptions usedinthesecalculations.

TheoriginalimpetusforusingCORI'AP2tocalculate cabinettemperatures wasthedesiretoavoidopeningcontrolstructure cabinetdoorsandnotimposeunnecessary operatorburden.PP&LconcurswiththeNRCthatmodifications areneededtotwoassumptions usedinthecabinettemperature calculations.

TheNRCquestioned ouruseof120'Fasthecontrolroomtemperature, implyingsuchatemperature wasoverlyconservative.

Inresponse, theinfinitetimecontrolroomtemperature, assumingmeasurednormaloperating heatloads,hasbeencalculated usingthemethodofNUMARC87-00.Theresulting controlroomtemperature is111'F.TheTERquestioned useof180'Fastheoperability limitofcontrolroominstruments.

Basedoninformation receivedfromequipment manufacturers, wecurrently believethecorrectlimitis140'F,andareperforming areevaluation onthisbasis.Thisevaluation willbecompleted andsubmitted totheNRCnolaterthenMay1,1992,Page7

<r ATTACHMENT TOPLA-3745';:;CONTAPC41i22lT,!ISOLATION','R REMMENDATION'helicenseeshouldlistthevalvesidentified inanappropriate procedure andidentifytheactionsnecessary toensurethatthesevalvescanbefullyclosed,ifcontainment isolation isrequiredduringanSBOevent.Thevalveclosureshouldbeconfirmed bypositionindication (local,mechanical, remote,processinformation, etc.)P&LRThepenetrations whichhavebeenidentified bytheNRCasrequiring tobeproceduralized aretheResidualHeatRemoval(RHR)andCoreSpray(CS)suctionlinesalongwiththeContainment Sprayline.Containment isolation oftheselineshasbeenaddressed andapprovedbytheNRCpriortothissubmittal.

Thefollowing identifies thatapprovedapproach.

Susquehanna SESFSARsection6.2.4.3.6 statesinpartthat"Containment isolation provisions forcertainlinesinengineered safetyfeatureorengineered safetyfeature-related systemsmayconsistofasingleisolation valveoutsidecontainment.

Asingleisolation valveisconsidered acceptable ifitcanbeshownthatthesystemreliability isgreaterwithonlyoneisolation valveintheline,thesystemisclosedoutsidecontainment, andasingleactivefailurecanbeaccommodated withonlyoneisolation valveintheline."Additionally, section6.2.4.3.6.3 states,"Although strictlyspeakingtheHPCI,RCIC,CS,andRHRpumpsuctionlinesdonotconnectdirectlytotheprimarycontainment, theyarenevertheless evaluated to10CFR50AppendixA,GeneralDesignCriteria56.Theselinesareeachprovidedwithoneremotemanuallymotoroperatedgatevalveexternaltothecontainment andusetherespective pipingsystemsasthesecondisolation, barrier..

FortheRHRandCSvalvesthehandswitchesarekeylocked".Furtherinvestigation intothisissuerevealsthatsection6.2.4oftheNRCSafetyEvaluation Report(NUREG0776)forSusquehanna SSESdocuments theNRCapprovalofmeetingthealternative acceptance criteriaspecified insection6.2.4oftheStandardReviewPlan.Thissectionsummarizes thesealternative acceptance criteriaalongwithspecifically identifying thelinesfoundacceptable viathismethod.Basedontheaboveexplanation webelievethatcontainment isolation isestablished andcontainment integrity willbemaintained.

Page8 tg~04'L ATTACHMENT TOPLA-3745:1'R'O.CEDURFS.:;::lANDl, TRAXNING,',

REMMEATIThestaffexpectsthelicenseetoimplement theappropriate trainingtoassureaneffective responsetoanSBOevent.PP&LRNEAppropriate plantpersonnel willbetrainedonanyneworrevisedprocedures inaccordance withtherequirements ofInitiative 2,NUMARC87-00andReg.Guide 1.155,section3.4.'-;:QUALITY>'A'SSUR'A'NCE'"'.AND;:::TECHggCAL"'-::,SPECIPICATION~):'R REMMEATIThestaffexpectsthattheplantprocedures willreflecttheappropriate testingandsurveillance requirements toensuretheoperability ofthenecessary SBOequipment,

'P&L'f4ItisPP&LsintenttosatisfytheQualityAssurance (QA)requirements ofReg.Guide1.155byupgrading anexistingprocedure toincorporate StationBlackout.

Thisprocedure addresses alltheReg.GuideQArequirements andwillrequirethenecessary Inspections andTeststobeperformed inaccorda'nce withtheOperational QualityAssurance Program.::-;ED6'!RELIA'SILIIYiPRO GRAM::::..":

NRRKMMENDATIN'helicenseeshouldcompletetheimplementation ofanEDGreliability programwhichmeetstheguidanceofRG1.155,Section1.2andprovideascheduleforitscompletion.

Confirmation thatsuchaprogramisinplaceorwillbeimplemented shouldbeincludedinthedocumentation supporting theSBOsubmittals thatistobemaintained bythelicensee.

Page9 00'I0 ATTACHMENT TOPLA-3745PP&LRReg.Guide1.155specifies thateachutilityestablish anEDGperformance monitoring program.NUMARC87-00AppendixDcontainsguidanceforthedevelopment andimplementation ofsuchaprogram.PP&Lhascommitted toimplement aprogramofreliability monitoring and,asindicated above,PP&LmustmaintainanEDGreliability atorabove97.5%aspartofourSBOcopingstrategy.

TheReg.GuideandNUMARCprovide"triggervalues"fordetermining compliance withtargetreliability.

NRCreviewers indicated thatlackofthisdatainoursubmittal hinderedassessment ofSSESEDGreliability.

Atthe97.5%reliability level,compliance isassumedifthefailurestostart/load arelessthanorequalto3,4,and5outofthelast20,50and100startattempts, respectively.

Asof2/10/92thefailurestostart/load ineachcategorywere0,0,and3,respectively.

Thus,today,PP&Lcanaccepttheincreased reliability targetof97.5%.PP&L'sEmergency DieselGenerator reliability monitoring programhasbeendeveloped anddocumented inNuclearDepartment Administrative Procedure-QA-0401 entitled"Emergency DieselGenerator Monitoring Program."

Thisprocedure complieswiththereliability requirements delineated inAppendixDofNUMARC87-00,Rev.1.Reliability willbemonitored againstasetof"triggervalues"withactionsspecified forvariouslevelsoftriggervalueexceedance.

Page10 l~rvO.d4 ROOMTEMPERATURE RESPONSETOASTATIONBLACKOUT200180160140~I-120I-1008010203040TIME(HRS)50607080LegendgHVACEQUIPRM0EXHfANRM~HVACEQUIPRM0HVACEQUIPRM6RECIRCPLENUM COTTAP:ACOMPUTERCODEFORSIMULATION OFTHERMALTRANSIENTS INSECONDARY CONTAINMENTS OFBOILINGWATERREACTORS~~~"7MARKA.CHAIKOandMICHAELJ.MURPHYPennsylvania Power&LightCompany,Allentown, Pennsylvania 18101ReceivedDecemberI,1989AcceptedforPublication September 12,1990TheCompartment Transient Temperature AnalysisProgram(COTTAP)wasdeveloped bythePennsylva-niaPower&LightCompanyforpostaccident boilingwater'reactor (BWR)secondary containment thermalanalysis.

Thecodemakesuseofpreviously developed implicittemporalintegration methodsandsparsema-trixinversion techniques toallowmodelingofanen-tireBWRsecondary containment.

Investigations weremadewithamodelconsisting of121compartments and767heat-conducting slabs.Thesimulation pre-sentedinvolvesthenumerical integration of20101or-dinarydifferential equations overa30-hsimulation period.TwohoursofCPUtimewererequiredtocarryoutthecalculation onanIBM3090computer.

TheCOTTAPcodeconsiders naturalconvection andradi-ationheattransferbetweencompartment airandwalls'hroughadetailedflnite difference solutionoftheslabconduction equations.

Heatadditionfromhotpipingandoperating equipment, andcoolingeffectsassociated withventilation flowsandcompartment heatremovalunitsarealsoincluded.

Additional capabilities ofCOTTAPincludemodelingofcompartment heatupre-sultingfromsteamline breaksandsimulation ofnat-uralcirculation coolingincompartments withflowpathsatdiffering elevations.

I.INTRODUCTION Underpostaccident conditions, boilingwaterreac-tor(BWR)secondary containment ventilation systemstypically isolatetopreventfissionproductreleasetotheenvironment.

Sincecooledairisnolongercircu-latedthroughthesecondary containment, increased compartment temperatures result.Predictions ofpost-accidentcompartment temperatures arenecessary todetermine whethersafety-related equipment issub-jectedtotemperatures that'exceed itsmaximumdesignvalues.Safety-related equipment mustbeoperableun-derpostaccident conditions inordertoeffectthesafeshutdownofthereactor.Afteranaccident, thesecondary containment ventilation systemoperatesinarecirculation modetopromoteairmixingbetweencompartments andtodilutelocallyconcentrated radioactive isotopes.

Originaldesigncalculations forPennsylvania Power&LightCompany's (PP&L)Susquehanna SteamElectricStation(SSES)assumedthatairrecircula-tionprovidedenoughmixingtoproduceafairlyuniformtemperature distribution throughout allsec-ondarycontainment compartments.

Forthisreason,asingle-compartment transient.

modelwasusedinthesimulation ofpostaccident conditions.

Recentinvesti-gationsbasedonsteady-state calculations haveshown,however,thatsignificant temperature variations canexistbetweencompartments.

Thesetemperature variations werelargeenoughtopromptadetailedNUCLEARTECHNOLOGY VOL.94APR.199l ChaikoandMurphyPOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSISmulticompartment transient analysisofthesecondary containment.

Toreanalyze thepostaccident transient behavioroftheSSESsecondary containment, PP&Ldeveloped theCompartment Transient Temperature AnalysisPro-gram(COTTAP).

Development ofthisprogrambeganafteranevaluation ofavailable codesrevealedthatnonewerecapableofperforming asufficiently detailedsimulation owingtothelargenumberofheat-conduct-ingstructures foundintheSSESsecondary contain-ment.Forexample,theCONTEMPTcode,'hich isprobablythemostwidelyusedcontainment analysisprogram,canmodelasmanyas999compartments butislimitedto99heat-conducting slabs.Incontrast, COTTAPcanmodelupto1200heat-conducting slabsand300compartments.

Italsocontainsmodelsthatdescribeheatdissipation fromoperating electrical equipment andprocesspiping.ACOTTAPmodeloftheSSES-1and-2secondary containment structures consistsof-120compartments and800heat-conduct-ingslabs.TheCONTAINcode2isamorerecentlydeveloped containment simulation programwithcomplexmod-elingcapabilities.

Itis,however,designedspecifically forprimarycontainment simulation andisnotwellsuitedforsecondary containment modelingbecauseithasnoprovisions forenergyinputtocompartments fromheatloadssuchaselectrical panels,lighting, mo-tors,andhotpiping.Adescription oftheCOTTAPcode,including as-sumptions, governing equations, numerical solutionmethods,andcodelimitations isgiveninSec.II.Rep-resentative resultsoftheSSES-1and-2secondary con-tainmentanalysisarepresented inSec.III,andcodeverification isdiscussed inSec.IV.II.DESCRIPTION OFTHECOTTAPCODEII,A.Compartment MassandEnergyBalancesTheCOTTAPcodeallowsforairandwatervapormasstransferbetweencompartments bymeansofforcedventilation, leakage,andnatural,circulation flows.Aforcedventilation flowmodeldescribes heat-ing/ventilating/air conditioning systems,andaleakagemodelsimulates intercompartment flowsthathregen-eratedbypressuredifferentials.

Inaddition, anaturalcirculation modelsimulates gravity4riven flowsbetweencompartments connected byflowpathsatdiffering elevations.

Steamcanalsobeaddedtoacompart-mentasaresultofpipebreaksorremovedthroughcondensation andrain-out.

Airandwatervapormassconservation equations foracompartment withNventilation paths,NIleakagepaths,andN,naturalcir-culationpathsaregivenbyHNcVgWojYoj+gWgYIJ+gWoj(Y<jY)J-1j~ijmianddpIvuJvlV-"=gWj(1-Y,j)+gWg(1-YIJ)dljaijaiH~+gWy(Y-Ycj)+W~-Woold-Wlo>j=l(2)whereV=compartment volume(m3)t=time(s)pp=compartment airandwatervapordensities, respectively (kg/m3)WJWIJWj-massflowratesassociated withj'thventilation, leakage,andcir-culationpaths,respectively (kg/s)Y=massfractionofairwithincom-partmentYj,YIJ--airmassfractions indonorcom-partments forventilation pathjandleakagepathj,respectively Y~--massfractionofairinadjoining compartment associated withcir-.culationpathjWq,=rateofsteamadditionduetopipebreaks(kg/s)Wd=steamcondensation rate(kg/s)W=rain-outrate(kg/s).ThevaluesWjandWljarepositiveforflowintothecompartment andnegativeforflowoutofthecom-partment, whereasthecirculation rateWjisalwaysapositivequantity.

Ventilation pathsaredescribed by'heirassociated massflowratesandidentification numbersofsourceandreceiving compartments.

Ven-tilationflowscanbetrippedofforonatanytimedur-ingatransient bysupplying appropriate trip-logic data.Leakage,circulation, andpipebreakmodelsaredis-cussedinSec.II.Calongwithotherspecialpurposemodels.Informulating thecompartment energybalance,itisassumedthatairbehavesasanidealgas.Moreover,-'or thetransients ofinterest, partialpressures ofwa-tervaporaretypically (Iatm.Therefore, itisassumedthatthesteamspecificenthalpydependsonlyontem-perature, i.e.,thevaporenthalpyisequaltotheen-thalpyofsaturated steamatthetemperature ofthe.gasmixture.Thepartialpressureofwatervaporwithinacompartment iscomputedfromtheidealgasequationofstate,andthetotalcompartment pressureiscalcu-latedasthesumoftheairandwatervaporpartialpressures.

Withtheseassumptions, thecompartment energybalancebecomesNUCLEARTECHNOLOGY VOL.94APR.1991 Pb,k=totalcompartment pressureifpipecontainssaturated liquid(Pa)Pb<<ak=pipefluidpressureifpipecontainssaturated steam(Pa)hg(Pb,k)

=specificenthalpyofsaturated watervaporatpressurePb,k(J/kg)hi(T)=specificenthalpyofsaturated liquidwaterattemperature T(J/kg)TJ,T>--donorcompartment temperatures forventilation pathjandleakagepathj;respectively (K)TJ--temperature inadjoining compart-mentassociated withcirculation pathj(K).Compartment heatloadsfromlighting, electrical pan-els,motors,andmiscellaneous equipment aremain-tainedconstantunlesstheyaretrippedon,off,orexponentially decayedduringthetransient.

Hotpipingandroomcoolerloadsvarywithcompartment temper-atureandcanalsobetrippedonoroff.Inaddition, hotpipingheatloadscanbeexponentially decayedusingtheheatloaddecaymodeldiscussed inSec.(3)II.C.7.+(1-Yy)hg(T))

-(1-Y)hg(T)],whereChaikoandMurphyPOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSISVPaT+PaCpa(T)dhg(T)dT+P>rdTdr=-VTC(T)--Vh(T)-dPadP~dCdj'VTR-"+R,-+Qligitt+Qpanel+Qmotor+Qcooler+Qpiping+Qmisc+Qslab+Qbreak+Wbsilg(Pbreak)

Wro)1J(T)-Wcoadhg(T)iVu+gWt>J[Y>>r)To)Cpa(Ttrj)

+(IYoj)hg(Tpj)]

J>>>1iVI+gWlj[Yi)TJJCpa(Tj))+(1Yg)hg(T(J)])=INc+gWcj[Yc)TcJCpa(TcJ)

YTCpa(T)J=lT=compartment gastemperature (K)Cp,(T)=specificheatofairattemperature T(J/kgK)hg(T)=specificenthalpyofsaturated watervaporattemperature T(J/kg)R,=idealgasconstantforair(288.7J/kgK)R=idealgasconstantforwater(461.4J/kgK)Qligbt,Qpanel>>Qmotor>Qcooler>>Qpiping>Qrnisc=compartment heatloadsduetolight-ing,electrical panels,motors,aircoolers,hotpiping,andmiscellane-ousequipment (J/s)Q,i,b=rateofheattransfertocompartment air/water vapormixturefromsur-roundingslabs(J/s)II.B.SlabModelInthesecondary containment ofaBWR,compart-mentwalls,ceilings, andfloorsaregenerally concreteslabsthatrangeinthickness from-0.3to-2m.Todetermine theheattransferratebetweenacompart-mentatmosphere andtheboundingconcreteslabs,theone-dimensional heatconduction equation(4)issolvedforeachslab.Here,T,(K)istheslabtemper-ature,andx(m)isthespatialcoordinate.

Sincethethermaldiffusivity ns(m/s)issuppliedasinputforeachslab,materials otherthanconcretecanbemod-eledprovidedthatslabsareofuniformmaterialcom-position.

Thisone-dimensional description assumesthatslabedgeeffectsdo.notsignificantly affecttheoverallrateofheattransfer.

Boundaryconditions onslabtemperature aregivenbyQb,k=heattransferratetoair/water vapormixturefromliquidexitingbreakasitcoolstocompartment temperature (J/s)and[Tl(r)Ts(0r)]aT,h,BxoksWb,--massflowrateofsteamexitingbreak(kg/s)46NUCLEARTECHNOLOGY VOL.94APR.1991 ChaikoandMurphywhereT>(t),T2(t)=temperatures ofcompartments ad-jacenttotheslabk,=slabconductivity (J/msK)L,=slabthickness (m)h~,h2=heattransfercoefficients (J/mzsK).ThesolutionofEq.(4)subjecttoEqs.(5)and(6)givestheratesofenergytransferfromtheslabsurfacestotheadjacentgasmixtures.

Thecoefficients hiandhzaccountfornaturalconvection, radiation, andcondensation heattransfer.

Intheabsenceofcondensation, thecoefficient hlcanbeexpressed ashi--ht+h/p,(7)whereh>andh~,arethenaturalconvection andra-diationcomponents, respectively.

Naturalconvection coefficients areexpressed intermsoftheNusseltnumber,whichinturnisafunc-tionoftheRayleighandPrandtlnumbers.Fortheco-efficient hl,theappropriate relationisNu=-=f(Ra,Pr),

h)Ct.k(g)(~,+1)h/I:'4+a+b-c)elm,auaTau

~(10)wherewhereCt.--slabcharacteristic lengthk=gasthermalconductivity andtheRayleighandPrandtlnumberstureare,respectively, definedbyo=Stefan-Boltzmann constant(5.669x10sJ/mzsK4)e,=slabemissivity T,=averagetemperature, whichisdefinedbyTau=[(T"+Tsurf)/2)

',(l1)forthegasmix-gpCI.lTs(0,t)-TI(t)ldvierp~ITICk(9)wherePOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSISfreeconvection fromaverticalplate.Forhorizontal slabs,free-convection coefficients dependonwhetherthesurfaceisbeingheatedorcooledbythesurround-inggasmixture.Asrecommended byHolman,4thecorrelation ofFujiiandImurasisusedwiththemod-ifiedcharacteristic lengthproposedbyGoldstein etal.~tocomputethecoefficient foranarbitrarily shapedslabwithheatedsurfacefacingupwardorcooledsur-facefacingdownward.

Incaseswheretheuppersur-faceiscooledorthelowersurfaceisheated,thecorrelations ofLloydandMoran7areused.Diatomicgasessuchasnitrogenandoxygenarees-sentially transparent tothermalradiation; however,theemissivity ofwatervaporwithrespecttothermalradi-ationissignificant.

InCOTTAP,radiantenergyex-changebetweenaslabsurfaceandwatervaporcontained withinthesurrounding gasmixtureismodeledthroughtheuseofaneffective radiation heattransfercoeffi-cient[seeEq.(7)].Fortheapplications ofinterest, tem-peraturedifferences betweenaslabsurfaceandthesurrounding gasmixturearerelatively small(typically (5K).Therefore, thefollowing approximate relationproposedbyHottelandSarofimforsmalltempera-turedifferences isusedtocomputetheradiation coef-ficient:whereg=acceleration duetogravity(9.8m/sz)p=coefficient ofthermalexpansion (K')v=kinematic viscosity (mz/s)n=thermaldiffusivity (m/s)p=dynamicviscosity (kg/ms)Cv=specificheatoftheairhvater vapormixture-~(J/kgK).T=gastemperature (K)T~=slabsurfacetemperature (K)e,=emissivity ofwatervaporevaluated atT,u.TheCess-Lian'quations, whichgiveananalytical approximation totheemissivity chartsofHottelandEgbert,"areusedtocomputethewatervaporemis-sivity.InEq.(10),chasthevalue0.45,andaandbareobtainedthroughdifferentiation oftheCess-Lian emis-sivityequations Gasmixtureproperties usedinthecalculation offreeconvection coefficients areevaluated atthethermalboundarylayertemperature, whichistakenastheav-erageoftheslabsurfacetemperature andthebulkgastemperature.

Forverticalslabs,coefficients arecalculated fromthecorrelation proposedbyChurchill andChu3forand81n[e(T,PP,PL

)]aBin(PL)8ln[e(T,PP,PL,)]8ln(T)(12)NUCLEARTECHNOLOGY VOL.94APR.199147 losure',forin-ndcondensa-gwalls.Fora-nsationalonebecomingsat-ain-out)formgsmpartment rel-ativehumiditylessthanorequaltounity,therainoutrateW(kg/s)iscalculated fromthefollowing empir-icalmodel:surfacetemperature dropsbelowthedewpoint(thesaturation temperature ofwaterevaluated atthepar-tialpressureofwatervaporinthecompartment) oftheair/water vapormixture.Heattransfercoefficients forcondensation conditions arecalculated usingtheexper-imentally determined Uchida"correlation, whichin-cludesthediffusional resistance effectofnoncondensible W,=200(RH-0.99)max(WC,i) ifRH)0.99andgasesonsteamcondensation rates.InCOTTAP,initialcompartment temperatures, pressures, andrelativehumidities arespecified asin-putdata.Aninitialslabtemperature profileisdeter-minedbycomputing thesteadysolutiontoEqs.(4),(5),and(6)corresponding totheinitialcompartment conditions.

Thisimpliesthatcompartments havebeenmaintained attheirinitialconditions longenoughforslabstoattainsteady-state temperature profiles.

W,=0.0ifRHs0.99,(16)whereRH=relativehumidityWs=totalsteamflowrateintothecompartment (kg/s)C,i=constantthatissuppliedaspartoftheinputdata(kg/s).ChaikoandMurphyFOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSISwhereisolation ofapipebreak(duetovalvecP,=a'rpat'alprcssue(Pa)stance)acompartment beginstocoolationcontinues tooccuronsurroundin P=watervaporpartialpressure(Pa)sufficiently fastcooldownrate,condedoesnotpreventcompartment airfromurated,andthusmoisturedroplets(rCondensation onaslabsurfaceoccurswhenthewithintheamixture.TomaintaincoII.C.SpecialPurposeModelsTheCOTTAPcodeincludesspecialized modelstosimulatetheeffectsofpipebreaks,hotpiping,andcompartment aircoolers.Leakageandnaturalcircu-lationmodelsarealsoincludedtodescribeintercom-partmentmasstransfer.

Inaddition, thecodeincludesasimplified slabmodel,aheatloaddecaymodel,andacompartment modelinwhichtemperature,

pressure, andrelativehumidityarespecified asafunctionoftime.II.C.l.PipeBreakModelWithinthescopeofthepresentmodel,pipesmaycontainsteamorsaturated liquidwater.Inputdatade-finethetotalmassflowthroughthebreakWb,(kg/s)alongwiththetimeatwhichthebreakdevelopsandthelengthoftimeoverwhichfluidlossoccurs.Forpipescontaining saturated liquid,thesteamflowrateWb,exitingthepipe(kg/s)iscalculated fromtheen-ergybalanceWbihy(P>)

=Wbslig(P)

+(Wbi-Wbs)h/(P),

(14)whichdescribes theisenthalpic expansion offluidfrompipepressureP~tocompartment pressureP.Theliq-uidfraction, whichdoesnotflashasitleavesthepipe,isassumedtocooltocompartment temperature, andthedissipated sensibleheatistransferred directlytothecompartment air/water vapormixture.Forthecasewhereapipecontainssteam,allofthemassandenergyexitingthebreakisdeposited directlyintothecompart-mentgasmixture.Rain-outphenomena canbeimportant incompart-mentscontaining pipebreaks.Forexample,following 48II.C.2.HotPipingModelInmanysecondary containment compartments, themajorheatsourceconsistsofpipingthatcontainsreactorsteamorcoolant.Theheatadditionratetoacompartment airhvater vapormixturefromahotpipeiscalculated fromalp(<gUp7rLpDp[Tj'(t)]>(I7)where.~Up=overallheattransfercoefficient (J/m2sK)L~=pipelength(m)D~=outsidediameterofthepipe(orinsulation ifthepipeisinsulated)

(m)Tj--pipefluidtemperature (K)T=compartment temperature.

Theoverallheattransfercoefficient iscalculated bythecodebasedoninitialcompartment conditions; theco-efficient isthenmaintained constantthroughout thetransient.

II.C.3.AirCoolerModelCoolingunitsareusedinanumberofsecondary containment compartments toremoveheatgenerated byequipment suchasemergency corecoolingsystems(ECCS)injection pumpsandhigh-voltage busesandtransformers.

Heatremovalratesofcoolingunitsarecalculated fromQcool(t)Ccool(T(t)Tcool(t)j~(Ig)NUCLEARTECHNOLOGY VOL.94APR.199t ChaikoandMurphyPOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSISwhereT,/(t)=averageoftheinletandoutletcoolingwatertemperatures C,/=constantthatiscomputedfromspec-ifiedinitialvaluesofthecoolingloadQ,/,theinletcoolingwatertempera-ture,thecoolingwaterflowrate,andthecompartment temperature T.Anenergybalanceonthecoolingwateryieldstheout-letcoolingwatertemperature.

II.C.4.LeakageModelsTheCOTTAPleakagemodelsimulates pressure-inducedintercompartmental masstransferthroughopeningssuchasdoorwaysandventilation ducts.In-tercompartment leakageiscalculated bybalancing thepressuredifferential betweenthecompartments withanirreversible pressureloss.Thus,theleakageratesat-isfiesP(t)-P,(t)Kinesia(t)[

Win(t)](19)2p//(l)Aw whereP1,Pz=pressures ofthecompartments associated withtheleakagepath(Pa)WN=leakagerate(kg/s)K~=irreversible pressurelosscoefficient A//,--leakagearea(m)p//,=gasdensitywithinthecompartment sup-plyingtheleakageflow(kg/m).Itisassumedthatinertialeffectsdonotsignificantly affectleakagerates.II.C.5.NaturalCirculation ModelAnaturalcirculation modelsimulates gravity-drivenmixingincompartments connected byflowpathsatdiffering elevations.

Thecirculation rateW,(kg/s)isobtainedfromThismodelalsodescribes intercompartment, gravity-drivencirculation flowsthatcandevelopatopendoor-ways(seetheanalysisofBrownandSolvason'.

II.C.6.ThinSlabModelThedetailedslabmodeldiscussed inSec.II.Bisnotrequiredtodescribeheattransferthroughthinslabsthathavelittlethermalcapacitance.

Slabsofthistype,e.g.,refueling floorwalls,havenearlylineartem-peratureprofiles, andthustheheatflowthroughathinslabcanbecalculated bytheuseofanoverallheattransfercoefficient U.Therateofheattransferthroughathinslabisobtainedfromq/s(r)=UisA[T1(>)-T2(/)],(21)whereA=thinslabheattransferarea(m)TjTz=temperatures ofthecompartments sepa-ratedbytheslab(K).ValuesofU(J/msK)aresuppliedaspartofthecodeinputdata(onevalueforeachverticalslabandtwovaluesforeachhorizontal slab).Forhorizontal slabs,twovaluesofUarerequiredbecausefree-convection filmcoefficients dependonthedirection, upwardordownward, ofheatflowthroughtheslab.II.C.7.Heal-Load DecayModelCoolingofacomponent suchasapipefilledwithhotstagnantfluidorapumpthathasceasedoperat-ingissimulated throughtheuseofalumped-param-eterheattransfermodel.Mostcompartments inthesecondary containment havealargethermalcapacitybecauseoftheboundingconcreteslabs.Itistherefore assumedthatthecomponent temperature changesonafastertimescalethanthecompartment airtemper-ature;i.e.,theairtemperature isassumedtoremainfairlyconstantduringthecooldownofthecomponent.

Withthisassumption, thecomponent heatdissipation rateQc(t)isgovernedby7'Q'"=-Q(/)(22)d/W-g['()'()](")K//[Alp2(t)]+KN/[ANpi(/)]JwhereQc(/o)=Qco(23)wherep1,pz--densities oftheair/water vapormixtureswithinthetwoadjacentcompartments (kg/m)(hereitisassumedthatp2isthegasdensityforthecoolercompartment)

E,E/--elevations oftheupperandlowerflowpaths(m)A,A/--upperandlowerflowpathareas(m).NUCLEARTECHNOLOGY VOL.94APR.1991McCwVcUcAc(24)whereM,=massofthecomponent (kg)Ci~=specificheatofthecomponent (J/kgK)49and7,(s'),thethermaltimeconstantofthecompo-nent,isgivenby ChaikoandMurphyPOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSISU,=overallheattransfercoefficient (J/m2.sK)A,=component heattransferarea(m2).InEq.(23),to(s)isthetimeatwhichthecooldownprocessbegins,andQ<<,whichissuppliedasinputdata,istheheatdissipation ratepriortocooldown.

So-lutionofEqs.(22)and(23)givestheexponential-decay approximation usedinCOTTAPtomodelheatdissi-pationofcoolingcomponents.

Thecomponent timeconstanty,isspecified asinputdataexceptinthecaseofhotpiping,whereitiscalculated bythecodefromthepipingdescription data.II.C.8.Time-Dependent Compartment ModelWiththetime-dependent compartment (TDC)model,environmental conditions withinacompart-mentarespecified asafunctionoftime;i.e.,temper-ature,pressure, andrelativehumidityversustimearesuppliedastabularinputdata.Thismodelisparticu-larlyusefulforrepresenting outsideairconditions, in-cludingsolarandthermalradiation effects.Theinfluence ofsolarandlong-wave atmospheric radiation onexteriorbuildupsurfacescanbedescribed byspec-ifyingtheeffective Sol-Airtemperature'n theTDCinsteadoftheactualoutsideairtemperature.

Insec-ondarycontainment

analysis, theTDCmodelisalsousefulfordescribing transient conditions withintheprimaryreactorcontainment, whicharegenerally knownfromtheresultsofdetailedlicensing basiscal-culations.

dTsl=GTpssxx(25)wherei=1,2,3,...,N, thenumberofequallyspacedgridpointsTp--slabtemperature atgridpointiTp=finitedifference approximation tothesecond-order spatialderivative atgridpointi.Following theapproachusedbyPirkleandSchiesser'3 intheMOLsolutionofparabolic equa-50II.D.Numerical SolutionNlethodsAnenergybalanceandtwomassbalancesaresolvedforeachcompartment todetermine gastemperature, airmass,andwatervapormass.Inaddition, theone-dimensional heatconduction equationissolvedforeachslab.Beforecomputing thenumerical solutionofthegoverning equations, partialdifferential equations describing heatflowthroughslabsareapproximated bysetsofordinarydifferential equations (ODEs).Thisisaccomplished throughapplication ofthemethodoflines(MOL).IntheMOL,afinite.difference approx-imationisappliedonlytothespatialderivative inEq.(4),givingtions,fourth-order centraldifference formulasareusedtocomputeTtatinteriorgridpoints:Asix-point slopingdifference formulaisusedtoap-proximate Tpati=2andi=N-1:ITsxx2=-2(10Tsi15Ts24Ts3+14Ts4-'6T,s+T,6)+O(~)(27)and1TsxxNl2(10TSN15TsN-l4TsN-2+14TsN-3-6TsN-4+TsN-5)+O(~4).(28)Fortheendpoints,wherethenormalderivatives arespecified throughconvective boundaryconditions, thefollowing finitedifference approximations, recom-mendedbyPirkleandSchiesser,'3 areusedtocom-puteTI41532T=---Ti+96T2-36T3+-T4sxxt12626ssS3sTss50t3,Tsxl

+O(h)(29)34andI415TsN=---TN+96TNi-36TN2sxx323+-TsN-3--TsN-4+506TsxN2+O(a)(30)InEqs.(29)and(30),thenormalderivatives TsxiandT~areevaluated inaccordance withEqs.(5)and(6),theconvective boundaryconditions; i.e.,hiTsxl-(TlTsI)sandh2Tsx2----(TsN-T2)s(31)NUCLEARTECHNOLOGY VOL.94APR.199l1Tsxxi=122(-Tsi-2+16Tsi-i-30Tsi+16Tsl+i128,-Ts'+2)+O(h),(26)wherei=3,4,...,N-2 6=spacingbetweengridpoints.

ChaikoandMurphyPOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSISAllgovernirig equations arenowexpressed intermsofODEsoftheformdy-=F(y,t)withy(0)=yedL'32)Solutions ofEq.(32)exhibitrapidinitialadjust-mentsincompartment airtemperature causedbytherelatively smallthermalcapacitance oftheaircontained withinthecompartment.

Moreover, slabtemperatures undergorapidinitialchangesinnarrowregionsneartheboundaries, resulting intheformation ofspatialthermalboundarylayers.Inthenumerical integration ofEq.(32),smalltimestepsarerequiredtosimulatetheseinitialtransients.

Astheinitialtransient responsedecays,however,itisdesirable toincreasestepsizesinordertoreducethecomputation timerequiredtofol-lowtheslowlyvaryingpartofthesolution.

Equations, suchasEq.(32),whichexhibitinitialtemporalbound-arylayerstructures aretermedstiffdifferential systems(seethediscussion inRef.16),andbecauseofstabil-itylimitations, theycannotbesolvedefficiently withexplicitintegration schemes.Forthisreason,anim-plicitschemewasselectedforCOTTAP.Numerical integration ofthegoverning Eq.(32)iscarriedoutwiththeLSODEScode,'hich usestheimplicitbackwarddifferentiation methodsproposedbyGearforthesolutionofstiffsystems.TheLSODEScodealsoemployssparse'matrix inversion techniques insolvingtheimplicitfinitedifference equations.

Withthesenumerical integration

features, itisfeasibletocarry'outtheintegration ofthelargedifferential sys-temsthatariseinthesimulation ofsecondary contain-menttransients.

Asanillustration oftheproblemdimension, simulation oftheSSES-1and-2secondary containments underpostaccident conditions requiredthesolutionof20101coupledODEs.Fortheselarge-scale

problems, reevaluation ofcode-calculated slabheattransfercoefficients ateverytimestepleadstounacceptably longcomputation times.Toalleviate thisdifficulty-,

thefrequency ofre-evaluation (numberofstepsbetweenreevaluation ofcoefficients) isaparameter suppliedasinputtothecode.Sensitivity calculations onsmall-scale problemsrepresentative ofpostaccident secondary containment transients indicatethatcoefficients canbereevaluated asinfrequently asoncepertenstepswithoutintroducing significant errorsintheresults.TheCPUtimerequire-mentswerereducedbyafactorof4whencoefficients werereevaluated ateverytenthtimestep.1.Fissionproducttransport amongcompartments isnotmodeled.II.E.CodeLimitations.

inModelingAccidentScenarios Thefollowing modelinglimitations havebeeniden-tifiedinthecurrentversionoftheCOTTAPcode:2.Coolermodelingdoesnotdescribemoisturere-movalunderconditions wherethecoolingcoiltemper-.atureisbelowthedewpointoftheinletgasmixture.3.Pipebreakmodelingisvalidonlyforlinescon-tainingsteamorsaturated liquid;breaksinvolving thereleaseofsubcooled liquidcannotbedescribed.

4.Compartment floodingeventscannotbesimu-latedbecauseallliquidisassumedtoexitthroughcom-partmentfloordrains.III.RESULTSOFSSESSECONDARY CONTAINMENT ANALYSISFORPOSTACCIOENT CONDITIONS Thissectiongivesrepresentative resultsforaCOT-TAPsimulation ofthecombinedSSES-1and-2sec-ondarycontainments underpostaccident conditions.

Thethermalresponses oftheUnits1and2secondary containments arecoupledbyheattransferthroughcommonwallsthatseparatethetwostructures.

TheSSESmodelconsists.

of105compartments, 16time-dependent compartments, 767slabs,38thinslabs,and505heatloads.Thesimulation wascarriedoutfor30handrequired124minofCPUtimeonanIBM3090computer.

NotethatmostoftheCPUtimeisrequiredtosimulatetherapidlyvaryingpartofthetransient thatoccurswithinthefirstfewhoursoftheevent.Thus,substantially longersimulation timesdonotsig-niflcantly increaseCPUtimerequirements.

Forthisanalysis, itisassumedthataloss-of-coolantaccident(LOCA)occursinSSES-1andafalseLOCAsignal(aspurioussignalthatindicates lossofreactorcoolantandleadstoventilation systemisola-tionandoperation ofECCSinjection pumps)isgen-eratedonSSES-2.Underpostaccident conditions, ECCSinjection pumpscomprisethekeyequipment withinthesecondary containment structure.

TheECCSconsistsoftheresidualheatremoval(RHR),corespray,andhigh-pressure coolantinjection (HPCI)sys-tems.Thesesystemsreceiveelectrical powerfromhigh-voltagebusescontained withinemergency switchgearandloadcenterrooms.FigureIshowsthecalculated temperature responsewithinaSSES-1RHRpumproom(eachunitcontainstwoRHRpumproomsandtwocorespraypumprooms).Initially, theairtemper-atureincreases rapidlybecauseofthesmallthermalca-pacitance oftheairwithinthecompartment.

Asairtemperature increases, abalancebetweencompartment heatsourcesandlossestocompartment aircoolersandslabsbeginstodevelop.Atthistime,air.temperature startstoincreaseontheslowtimescalegovernedbytheslabthermalcapacityandtransport properties.

Aninitialrapidtemperature risefollowedbyamuchslowertemperature increaseischaracteristic ofallcom-partmentheatuptransients.

After1hofoperation, thisparticular RHRpumpswitchesfromtheinjection modeofoperation tothesuppression poolcoolingNUCLEARTECHNOLOGY VOL.94APR.199151-ChaikoandMurphyPOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSIShC320E316I-E3316o314312051015202530Time(h)Fig.1.Simulation ofpostaccident temperature responsewithinSSES-IRHRpumproomforLOCAonSSES-IandfalseLOCAonSSES-2.317~316.~~315I-314Eo313E312Q311X310051015202530Time(h)Fig.3.Simulation ofpostaccident temperature responsewithinSSES-IHPCIpumproomforLOCAinSSES-IandfalseLOCAinSSES-2.mode.Asaresultofincreased compartment heatloadsassociated withthechangeinoperating mode,thetem-peratureagainincreases rapidlyuntilanewbalancebetweentheheat-generation andheat-loss ratesisat-tained.Thetemperature responsewithinaSSES-IcorespraypumproomisshowninFig.2.Coresprayop-erationbeginsatthestartoftheeventandceasesIhlater.Temperature decreases rapidlyatthispointbe-cause,oncepumpoperation isterminated, nosignif-icantheatloadsremaininthecompartment.

Figure3illustrates thetemperature responseoftheSSES-IHPCIsystem,whichalsobeginsoperation atthestartoftheaccident.

Inthiscase,however,compartment temperature continues toincreasewhenthesystemceasesoperation atIhintothetransient.

Thisoccursbecausepipingheatloadswithinthiscompartment aresubstantial.

WhenHPCIpumpoperation stops,anas-sociatedroomcoolingunitalsoceasesoperation.

Uponshutdownofthecoolingunit,slowlydecayingpipingheatloadsrapidlyincreasecompartment temperature untilabalancebetweenheatgeneration andheatlossestocompartment slabsisapproached.

Figure4givesthetemperature withinaSSES-Iloadcenterroomthat~317PE~316I-E3315CC~314V)313O051015202530Time(h)Fig.2.Simulation ofpostaccident temperature responsewithinSSES-IcorespraypumproomforLOCAinSSES-IandfalseLOCAinSSES-2.-309ejE308I-E3cc~3078CO306051015202530Time(h)Fig.4.Simulation ofpostaccident temperature responsewithinSSES-IloadcenterroomforLOCAinSSES-IandfalseLOCAinSSES-2.52NUCLEARTECHNOLOGY VOL.94APR.1991 supplieselectrthiscompartmstantthroughout thetransient.

Fromtheresultsofthisanalysis, itisdetermined thatunderpostaccident conditions, someoftheequip-mentwithinthesecondary containment wouldbeex-posedtotemperatures thatexceedtheirqualification values.Consequently, components werereassessed foroperation athighertemperatures, andinsomein-stancesequipment wasrelocated tocompartments withlesssevereenvironmental conditions.

Furthermore, aprocedure wasdeveloped toinstructplantoperators toshednonessential electrical loadswithin24hafteranaccidentinordertomoderatethetemperature re-sponseswithinsecondary containment compartments.

K310P~~305COTTAP---CONTAIN300IChaikoandMurphyPOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSISicalpowertoemergency equipment.

In315ent,heatloadsremainessentially con-IV.EVALUATION OFCODEACCURACYAspartoftheverification processfortheCOT-TAPcode,calculational resultswerecomparedwiththoseobtainedwiththeCONTAIN(Ref.2)program,whichhasbeenverifiedthroughcomparison withex-perimental data.'AlthoughtheCONTAINcodedoesnotaccommodate adirectheatinput(suchasfromoperating mechanical orelectrical equipment) toacompartment, usefulproblemscannevertheless beformulated inordertoinvestigate themodelingandcomputational accuracyofCOTTAP.Twosuchprob-lemswereformulated forcodeverification.

ThefirstproblemteststheCO%I'APcompartment massanden-ergybalancecalculations andtheslabheattransfersimulation.

Thisproblemconsistsofasinglecompart-mentthathasa1000-m3volumeandcontainsairat300Kand101325-Painitialtemperature andpressure.

Concreteslabs,whichrangeinthickness from0.1to1m,formthewallsofthecompartment.

Allslabshaveauniform,initialtemperature of300K.Toaddheattothecompartment, theairincontactwiththeoutersurfaceofoneslab(theslabthatis0.1mthick)issud-denlyincreased to400Katt=0.Inaddition, at50sintothetransient, airwithatemperature of500Kisin-jectedintothecompartment ata0.26kg/sflowrate.Outersurfacetemperature riseandairinjection con-ditionswereselectedtoeffectsignificant, butnotex-cessive,temperature andpressureresponse.

Figures5and6presentacomparison oftheCOT-TAPandCONTAINcalculation resultsforthefirsttestproblem.Thetemperature andpressuresimula-tionsbothshowexcellent agreement; notethatthepressureresponsecurvesgiveninFig.6completely overlap.In-Fig.5,theinitialtemperature

increase, whichisduetoinjection ofhotairintothecompart-ment,beginstoleveloffat-0,5h.Heatadditionbymeansofconduction throughtheexternally heatedslabthenbeginstooccur,causingafurtherbutlessrapidincreaseintemperature.

Thesecondtestproblemconsidered forcodever-0.200.180.160.14Q-0.12-COTTAP---CONTAIN0.100246810Time(h)Fig.6.Comparison ofCOTTAPandCONTAIN.compart-mentpressuresimulations fortestprobleml.ification involvesmodelingofcompartment tempera-tureandpressurebehaviorunderconditions wherehigh-energy steamisinjectedintothecompartment.

Inthisproblem,condensation effectsstronglyinfluence therateoftemperature andpressureincrease.

Com-partmentphysicaldescription dataarethesameasthatfortestproblem1.Inthiscase,however,theonlyheatsourceisthesteamenteringthecompartment ata0.20kg/sflowrateanda2.7756x106J/kgenthalpy.

Thisflowrateandenthalpyarecharacteristic ofasmallsteamleakwithinasecondary containment com-partment.

Figures7and8showacomparison ofthe0246810Time(h)Fig.5.Comparison ofCOTTAPandCONTAINcompart-menttemperature simulations fortestproblemI,NUCLEARTECHNOLOGY VOL.94APR.I99t53 ChaikoandMurphyPOSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSIS450~4oo'50300-COTTAP---CONTAINACKNOWLEOGMENTS TheauthorsthankJackG.Refling,JamesE.Agnew,MarkR.Mjaatvedt, andLeonardJ.Westfortheirmanyhelpfulsuggestions duringthecourseofthiswork.WealsothankLisaWalshfortypingthemanuscript.

REFERENCES 1.C.C.LIN,C.ECONOMOS, J.R.LEHNER,G.MAISE,andK.K.NG,"CONTEMPT4/MOD4:

AMulti-compartment Containment SystemAnalysisProgram,"

BNL-NUREG-51754, Brookhaven NationalLaboratory (1984).05101520Timelh)Fig.7.Comparison ofCOTTAPandCONTAINcompart-menttemperature simulations fortestproblem2.0.6osg0.4IPn0.3-Q.2.K.K.MURATAetal.,"User's.ManualforCONTAIN1.1:AComputerCodeforSevereNuclearReactorAccidentContainment Analysis,"

NUREG/CR-5026, SandiaNa-tionalLaboratories (1989).3.S.W.CHURCHILL andH.H.S.CHU,"Correlating Equations forLaminarandTurbulent FreeConvection fromaVerticalPlate,"Int.J.HeatMassTransfer, 18,1323(1975).4.J.P.HOLMAN,HeatTransfer, 4thcd.,p.250,McGraw-Hill BookCompany,NewYork(1976).5.T.FUJIIandH.IMURA,"NaturalConvection HeatTransferfromaPlatewithArbitrary Inclination,"

Int.J.HeatMassTransfer, 15,755(1972).6.R.J.GOLDSTEIN, E.M.SPARROW,andD.C.JONES,"NaturalConvection MassTransferAdjacenttoHorizontal Plates,"Int.J.HeatMassTransfer, 16,1025(1973).0.20.1COTTAP---CONTAIN7.J.R.LLOYDandW.R.MORAN,"NaturalConvec-tionAdjacenttoHorizontal SurfaceofVariousPlanforms,"

ASME74-WA/HT-66, AmericanSocietyofMechanical Engineers (1974).05101520Time(h)Fig.8.Comparison ofCOTTAPandCONTAINcompart-mentpressuresimulations fortestproblem2.COTTAPandCONTAINsimulation results.There-sultsshowgoodagreement eventhoughthecodesem-ployconsiderably different approaches inthecalculation ofcondensation ratesonslabsurfaces.

TheCOTTAPcodeusestheexperimentally determined Uchida'ondensation coefficient, whileCONTAINcarriesoutadetailedcomputation ofthethermalre-sistances associated withthegasboundarylayerandthecondensate film.8.D.Q.KERN,ProcessHeatTransfer, p.690,McGraw-HillBookCorupany, NewYork(1950).9.H.C.HOTTELandA.F.ballot'tM, Radiative

Transfer, McGraw-Hill BookCompany,NewYoit(1967)'1~10.R.D.CESSandM.S.LIAN,"ASimpleParameteriza-tionfortheWaterVaporEmissivity,"

Int.J.HeatTransfer, 98,676(1976).11.H.C.HOTTELandR.B.EGBERT,"RadiantHeatTransmission fromWaterVapor,"Am.Inst.Chem.Eng.,38,531(1942).12.H.UCHIDA,A.OYAMA,andY.TOGO,"Evalua-tionofPost-Incident CoolingSystemsofLight-Water PowerReactors,"

Proc.3rdInt.Conf.PeacefulUsesofAtomicEnergy,Geneva,Switzerland, 1964,Vol.13,p.93,UnitedNations(1965).54NUCLEARTECHNOLOGY VOL.94APR.1991 ChaikoandMurphy13.W.G.BROWNandK.R.SOLVASON, "NaturalCon-vectionThroughRectangular OpeningsinPartitions-I Ver-ticalPartitions,"

Int.J.HeatMassTransfer, 5,859(1962).14.ASHRAEHandbook1985Fundamentals, AmericanSocietyofHeating,Refrigerating andAir-Conditioning En-gineers,Atlanta,Georgia.15.J.C.PIRKLE,Jr.andW.E.SCHIESSER, "DSS/2:ATransportable FORTRAN77CodeforSystemsofOrdinaryandOne,TwoandThree-Dimensional PartialDifferential Equations,"

presented at1987SummerComputerSimula-tionConference,

Montreal, Canada,1987.18.K.K.MURATAandK.D.BERGERON, "Experimen-talValidation oftheCONTAINCode,"Proc.11thLWRSafelyInformation Mtg.,Gaithersburg,
Maryland, October24-28,1983,SAND-83-1911C, SandiaNationalLaborato-ries(1983).19.K.K.MURATAetal.,"CONTAIN:

RecentHighlights inCodeTestingandValidation,"

Proc.Int.Mtg.LightWaterReactorSevereAccidentEvaluation, Cambridge, Massa-chusetts, August28-September I,1983,AmericanNuclearSociety(1983).16.C.W.GEAR,Numerical InitialValueProblemsin Or-dinaryDifferential Equations, Chap.11,Prentice-Hall, En-glewoodCliffs,NewJersey(1971).POSTACCIDENT BWRSECONDARY CONTAINMENT THERMALANALYSIS17.A.C.HINDMARSH, "ODEPACK, ASystematized Collection ofODESolvers,"

Scientific Computing, Vol.I,p.55,R.S.STEPLEMAN etal.,Eds.,IMACSTransac-tionsonScientific Computation, North-Holland Publishing Company,Amsterdam (1983).MarkA.Chaiko[BS,1980,andMS,1983,chemicalengineering, Penn-sylvaniaStateUniversity (PSU);PhD,appliedmathematics, LehighUniver-sity,1989]isaprojectengineer-nuclear systemsatthePennsylvania Power&LightCompany.Hiscurrenttechnical interests includeboilingwaterreactorstability analysisandthermal-hydraulic modelingofreactorsystems.MichaelJ.Murphy(BS,mechanical engineering, 1982,andMS,nuclearengineering, 1986,PSU)isaprojectengineer-nuclear systemswiththePenn-sylvaniaPower&LightCompany.Heiscurrently involvedinsimulation ofanticipated transient withoutscramandsevereaccidentanalysis.

NUCLEARTECHNOLOGY VOL.94APR.199155

Retrieved from "https://kanterella.com/w/index.php?title=ML18026A417&oldid=732723"