ML16314C691

Diablo Canyon, Units 1 and 2 - Enclosure, Statement of the Problem Concerning PWR Primary Coolant System Pipe Rupture

ML16314C691
Person / Time
Site:	Diablo Canyon
Issue date:	11/09/2016
From:	Pacific Gas & Electric Co
To:	Office of Nuclear Reactor Regulation
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Download: ML16314C691 (12)

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EKCLOSORESTATEMENZOFTHEPROBLEM1IntheunlikelyeventofaPHRprimarycoolantsystempiperuptureintheimmediatevicinityofthereactorvessel,transientloadsoriginatingfromthreeprincipalcauseswillbeexertedonthereactorvesselsupportsystem.Theseare:1.Blowdownjetforcesatthelocationoftherupture(reactionforces),2.3.Transientdifferentialpressuresintheannularregion"betweenthevesselandtheshield,andTransientdifferentialpressuresacrossthecorebarrelwithinthereactorvessel.Theblowdownietforcesareadegvatelyunderstoodanddesiqnproceduresareavailabletoaccountforthem.Bothofthe"differentialpressure"forces,however,arethree-dimensionalardtimedependentandrequiresophisticatedanalyticalprocedurestotranslatethemintoloaosactingonthe'eactorvesselsupport'system.Alloftheloadsareresistedbytheinertiaandbythe.'supportmembersandrestraintsof'thercomponentsoftheprimarycoolant:.systemincludingthereactorpressurevesselsupports.Thetransientdifferentialpresureactiniexternallyonthereactorvesselisaresultoftheflowof,theblowdowneffluentinthe"reactorcavity.Themaqnitudeandthetimedependenceoftheresultinaforcesdependsonthenatureandthesizeof~thepiperupture,theclearancebetweenthevesselandtheshieldandthesizeandlocationcftheventopeningsleadingfromthecavitytothecontainmentasawhole.Forsometimerefinedanalyticalmethodshavebeenavailableforcalculatinqthesetransientdifferentialpressures(multi-nodeanalyses).Theresultsofsuchanalysesindicatethattheconseauentloadsonthevesselsupportsystemcalculatedbylesssophisticatedmethodsmaynctbeasconservativeasoriginallyintendedforearlierdesigns.Attachment1tothisenclosureprovidesforyourinformationalistofinformationrequestsforwhichresponsescouldbeneededforaproperassessmentoftheimpactofthecavitydifferentialpressureonthedesignadeauacyofthevesselsupportsystemfora.powerplant.

Thecontrollingloadsfordesianpurposes,however,appearintypicalcasestobethoseassociatedwiththeinternaldifferentialpressuresacrossthecorebarrel.Theinternallygeneratedloadsareduetoamomentarydifferentialpressurewhichiscalculatedtoexistacrossthecorebarrelwhenthepressureinthereactorannularregionbetweenthecorebarrelandvesselwallinthevicinityoftherupturedpipeisassumedtorapidlydecreasetothesaturationpressureoftheprimarycoolantduetotheoutflowofwater.Althou'ahthedepressurizationwavetravelsrapidlyaroundthecorebarrel,thereisafiniteperiodoftimeduringwhichthepressureintheannularregionoppositethebreaklocationisassumedtoremainat,ornear,theoriginalreactoroperatingpressure.Thus,transientasymmetricalforcesareexertedonthecorebarrelandthevesselwallwhichultimatelyresultintransientloadonthesupportsystems.Thesearetheloadswhichwereunderestimated.bythelicenseeoriginallyreportingthisproblemandwhichmaybeunderestimatedinothercases.Theyarethereforeofgenericconcerntothestaff.Attachment2tothisenclosureprovidesforyourinformationalistofinformationrequestsforwhichresponseswouldbeneededforaproperassessmentoftheimpactthatthevesselinternaldifferentialpressure,inconjunctionwiththeotherconcurrentloads,couldhaveonthedesignadeauacyofthesupportsystem.Inthatthereareconsiderabledifferencesinthereactorsupportsystemdesignsforvaiiousfacilitiesand'probablyinthedesignmarginsprovidedbythedesionersofolder.facilities,theunderestimationofthese'differ-entialpressure"loadsmayormaynotresultinadeterminationthattheadeouacyofthevesselsupportsystemforaspecificfacilityisguestion-able.Sincelocalfailuresinthevesselsupports(suchasplasticdeformation)donotnecessarilyleadtothefailureofthesupportsasanintegralsystem,theremaybesomelimitedreactor.vesselmotionprovidedthatnofurther,sionificantconseguenceswould,ensueandtheemergencycorecooling;systems(ECCS)wouldbe.abletoperformtheirdesignfunctions,r

.~ATTACt<l1ENT1CONTAINMFNTSYSTEMSBRANCHREUESTFORADDITIONALINFORMATIONIntheunlikelyeventof.apiperupture.insidemajorcomponentsubcompartments,theinitialblowdowntransientwouldleadtonon-uniformpressureloadingsonboththestructuresandenclosedcomponents.Toassuretheintegrityofthesedesignfeatures,werequestthatyouperformacompartmentmulti-nodespressureresponseanalysistoprovidethefollowinginformation:(a)Theresultsofanalysesofthedifferentialpressuresresultingtfromhotlegandcoldleg(pumpsuctionanddischarge),reactorcoolantsystempiperuptureswithinthereactorcavityandpipepenetrations.(b)Describethenodalization,sensitivitystudyperformedtodetermine'heminimumnumberofvolumenodesrequiredto,.conservativelypredictthemaximumpressurewithinthe.reactorcavity.The'odalizationsensitivitystudyshouldincludeconsiderationofspatialpressurevariation;e.g.,'ressurevariationscircumferentially,axially,and.radially,withinthereactorcavity.(c)Provideaschematicdrawingshowingthenodalizationofthereactorcavity.Provideatabulationofthenodalnetfreevolumes.and,interconnectingflowpathareas.(d)Providesufficientlydetailedplanandsectiondrawingsforseveralviewsshowingthearrangementof,thereactorcavitystructure,reactorvessel,piping,andothermajorobstructions,,andventareas,topermitverificationofthereactorcavitynodalizationandventlocations.(e)Provideandjustifythebreaktypeandareausedineachanalysis. (f)Provideandjustifyvaluesofventlosscoefficientsand/o'rfrictionfactorsusedtocalculateflowbetweennodalvolI>mes.llhenalosscoefficientconsistsofmorethanonecomponent,identifyeachcomponent,itsvalueandtheflowareaatwhichthelosscoefficientapplies.(g)Discussthemannerinwhichmovableobstructionstoventflow(suchasinsulation,ducting,plugs,andseals)w'ere'treated.Provideanalyticaljustificationfortheremovalofsuchitemstoobtainventarea.Providejustification'tha'tventareaswi1notbepartiallyorcompletelypluggedbydisplacedobjects.(h)Provideatableofblowdownmassflowrateandenergyreleaserateasafunctionoftimeforthereactorcavitydesignbasisaccident.(i)Graphicallyshowthepressure(psia)'nddifferentialpressure(psi)responsesasfunctionsoftimeforeachnode.Discussthebasis'orestablishingthedifferentialpressures.(j)Providethepeakcalculateddifferentialpressureandtimeofpeakpressureforeachnode,andthedesigndifferentialpressure(s)forthe5react'orcavity.Discusswhetherthedesigndifferential"pressureisuniformlyappliedtothereactorcavityorwhetheritisspatiallyvaried.(StandardReviewPlan6.2.1.2,SubcompartmentAnalysisattached,providesadditionalguidanceinestablishingacceptabledesignvalues,fordeterminingtheacceptabilityofthecalculatedresults.)

P.U.S.NUCLEARREGULATORYCOMMISSIONST%,INDE,IR9REVIEWPLANOFFICEOFNUCLEARREACTORREGULATIONFebruary,1975SECTION6.2.1.2SUBCOHPARTHENTANALYSISREVIEWRESPONSIBILITIESPrimary-ContainmentSystemsBranch(CSB)Secondary-HechanicalEngineeringBranch(HEB)CorePerformanceBranch(CPB)AuxiliaryandPowerConversionSystemsBranch(APCSB)I.AREASOFREVIEWTheCSBreviewstheinformationpresentedbytheapplicantinthesafetyanalysisreportconcerningthedeterminationofthedesigndifferentialpressurevaluesforcontainmentsub-compartments.Asubcompartmentisdefinedasanyfullyorpartiallyenclosedvolumewithintheprimarycontainmentthathouseshighenergypipingandwouldlimittheflowoffluidtothemaincontainmentvolumeintheeventofapostulatedpiperupturewithinthisvolume.Ashort-termpressurepulsewouldexistinsideacontainmentsubcompartmentfollowingapiperupturewithinthisvolume.Thispressuretransientproducesapressuredifferentialacrossthewallsofthesubcompartmentwhichreachesamaximumvaluegenerallywithinthefirstsecondafterblowdownbegins.Themagnitudeofthepeakvalueisafunctionofseveralparameters,whichincludeblowdownmassandenergyreleaserates,subcompartmentvolume,ventarea,andventflowbehavior.Atransientdifferentialpressureresponseanalysisshouldbeprovidedforeachsubcompartmentorgroupofsubcompartmentsthatmeetstheabovedefinition.TheCSBreviewincludesthemannerinwhichthemassandenergyreleaserateintothebreakcompartmentweredetermined,nodalizationofsubcompartments,subcompartmentventflowbehavior,andsubcompartmentdesignpressuremargins.ThisincludesacoordinatedrevieweffortwiththeCPB.TheCPBisresponsiblefortheadequacyof'theblowdownmodel.TheCSBreviewofthemassandenergyreleaseratesincludesthebasisfortheselectionofthepipebreaksizeandlocationwithineachsubcompartmentcontainingahighenergylineandtheanalyticalprocedureforpredictingtheshort-termmassandenergyreleaserates.TheCSBreviewofthesubcompartmentmodelincludesthebasisforthenodalizationwithineachsubcompartment,theinitialthermodynamicconditionswithineachsubcompartment,thenatureofeachv'entflowpathconsidered,andtheextentofentrainmentassumedintheventflowmixture.Thereviewmayalsoincludeananalysisofthedynamiccharacteristicsofcomponents,suchasdoors,blowoutpanels,orsandplugs,thatmustopenorberemovedtoUSNRCSTANDARDREVIEWPLANStandenlreviewplansaroproparedforthecurdsneooftheOfficeofNuclearReactorReps4tlonstaffresponsibleforthoreviewofapplicationstoconstmctondoperatenuclearpowerp4nts.ThesedocumentseremadeavailabletothopublloespertofthoCommission'spoucytoInformthonuclearIndustryandtheSenorslpubdeofregulatoryproceduresendpollclos.Standardreviewp4nseronotsubstltutseforredu4torySuldssorthoCommlmlon'srepu4tlonsendCOmpllancowiththemisnetrortulrod.ThostandardreviewplansectionssrokeyedtoRevfa4n2ofthoStandardFormatsndContentofSafetyAnalysisReportsforNuclearPowerPlants.NotstlsectionsofthoStandardFormathavesconospondlnpreviewplan.Publishedstandardreviewplanswillborev4edperlodlcally,asappropriate.toaccommodatecommentsondtorellectnewinformationsndoaperlonco.copiesofmsndardrovfowplansmaybaobtainedbyrecusaltothoU.S.NuclearResu4toryCommlmlon.Wathlnston,O.C.20MS.Attention:OfficeofNudasrReactorRadulation.CommentssndeucsostlonsforImprovementwillboconsideredondshouldalsobosenttothoOfficeofNuclearReactorRadutatlon.

~.provideaventflowpath,andthemethodsand'resultsofcomponentstestsperformedtodemonstratethevalidityoftheseanalyses.Theanalyticalproceduretodeterminethelosscoefficientsforeachventflowpathandtopredicttheventmassflowrates,includingflowcorrelationsusedtocomputesonicandsubsonicflowconditionswithinavent,isre-viewed.Thedesignpressurechosenforeachsubcompartmentisalsoreviewed'nrequestfromtheAPCSB,theCSBevaluatesorperformspressureresponseanalysesforsubcompartmentsoutsidecontainment.TheHEBisresponsibleforreviewiitheacceptabilityofthebreaklocationschosenandofthedesigncriteriaandprovision.methodsemployedtojustifylimitedpipemotionforbreakspostulatedtooccurwithin.'ubcompartments(SeeStandardReviewPlan3.6.2).II.ACCEPTANCECRITERIA1.Thesubcompartmentanalysisshouldincorporatethefollowingassumptions:a.Breaklocationsandtypesshouldbe,chosenaccordingtoRegulatoryGuide1.46forsubcompartmentsinsidecontainmentandtoBranchTechnicalPositionMEB3-1(attachedtoStandardReviewPlan3'.2)forsubcompartmentsoutsidecontainment.Anacceptablealternateprocedureistopostulateacircumferentialdouble-endedruptureofeachhighpressuresystempipeinthesubcompartment.b.'fseveralbreakspostulatedonthebasisofa,above,thebreakselectedasthereferencecaseforsubcompartmentanalysisshouldyieldthehighestmassandenergyreleaserates,consistentwiththecriteriaforestablishingthebreaklocationandarea.c.Theinitialplantoperatingconditions,suchaspressure,temperature,waterinventory,andpowerlevel,shouldbeselectedtoyieldthemaximumblowdownconditions~.Theselectedoperatingconditionswi11beacceptableifitcanbeshownthatachangeofeachparameterwouldresultinalesssevereblowdownprofile.2.Theanalyticalapproachusedtocomputethemassandenergyreleaseprofilewillbeacceptedifboththecomputerprogramandvolumenodingofthepipingsystemaresimilartothoseofanapprovedemergencycorecoolingsystem(ECCS)analysis.ThecomputerprogramsthatarecurrentlyacceptableincludeSATAN-VI(Ref.24),CRAFT(Ref.23),CEFLASk-4(Ref.25),andRELAP3(Ref.21),whenaflowmultiplierof1.0isusedwiththeapplicablechokedflowcorrelation.Analternateapproach,whichisalsoacceptable,istoassumeaconstantblowdownprofileusingtheinitialconditionswithanacceptablechokedflowcorrelation.WhenRELAP-4isacceptedbythestaffasanoperationalECCSblowdowncode,itwillbeacceptable'forsubcompart-mentanalyses'.Theinitialatmosphericconditionswithinasubcompartmentshouldbeselectedtomax-imizetheresultantdifferentialpressure.Anacceptablemodelwouldbetoassumeairatthemaximumallowabletemperature,minimumabsolutepressure,andzeropercentrel-ativehumidity.Iftheassumedinitialatmosphericconditionsdifferfromthese,theselectedvaluesshouldbejustified.6.2.1.2-2 Anothermodelthatisalsoacceptable,forarestrictedclassofsubcompartments,in-volvessimplifyingtheairmodeloutlinedabove.Forthismodel,theinitialatmos-pherewithinthesubcompartmentis.modeledasahomogeneouswater-steammixturewithanaveragedensityequivalenttothedryairmodel.Thisapproachshouldbelimitedtosubcompartmentsthathavechokedflowwithinthevents.However,theadequacyofthissimplifiedmodelforsubcompartmentshavingprimarilysubsonicflowthroughtheventshasnotbeenestablished.'4..Subcompartmentnodalizationschemesshouldbechosensuchthatthereisnosubstantialpressuregradientwithinanode,i.e,thenodalizationschemeshouldbeverifiedbyasensitivitystudythatincludesincreasingthenumberofnodesuntilthepeakcal-culatedpressuresconvergetosmallresultantchanges.5.Ifventflowpathsareusedwhicharenotimmediatelyavailableatthetimeofpiperupture,thefollowingcriteriaapply:c~Theventareaandresistanceasafunctionoftimeafterthebreakshouldbebasedonadynamicanalysisofthesubcompartmentpressureresponsetopiperuptures.Thevalidityoftheanalysisshouldbesupportedbyexperimentaldataoratestingprogramshouldbeproposedattheconstructionpermitstagethatwillsupportthisanalysis.Theeffectsofmissilesthatmaybegeneratedduringthetransientshouldbeconsideredinthesafetyanalysis'.Theventflowbehaviorthroughallflowpathswithinthenodalizedcompartmentmodelshouldbebasedonahomogeneousmixtureinthermalequilibrium,withtheassumptionof100Kwaterentrainment.Inaddition,theselectedventcriticalflowcorrelationshouldbeconservativewithrespecttoavailableexperimentaldata:Currentlyaccept-ableventcriticalflowcorrelationsarethe"frictionlessHoody"withamultiplierof0.6forwater-steammixtures,andthethermalhomogeneousequilibriummodelforair-steam-watermixtures,7.Attheconstructionpermitstage,afactorof1.4shouldbeappliedtothepeakdifferentialpressurecalculatedinamannerfoundacceptabletotheCSBforthesubcompartment.Thecalculatedpressuremultipliedby1.4shouldbeconsideredthedesignpressure.Attheoperatinglicensestage,thepeakcalculateddifferentialpressureshouldnotexceedthedesignpressure.Itisexpectedthatthepeakcalcu-lateddifferentialpressurewillnotbesubstantiallydifferentfromthatoftheconstructionpermitstage.However,improvementsintheanalyticalmodelsorchangesintheas-builtsubcompartmentmayaffecttheavailablemargin.III.REVIEWPROCEOURESTheproceduresdescribedbelowarefollowedforthesubcompartmentanalysisreview.Thereviewerselectsandemphasizesmaterialfromtheseproceduresasmaybeappropriatefor6~2.1.2-3 aparticularcase.Portionsofthereviewmaybecarriedoutopagenericbasisorbyadoptingtheresultsofpreviousreviewsofplantswithessentiallythesamesubcompartmentandhighpressurepipingdesign.TheCSBreviewstheinitialconditionsselectedfordeterminingthemassandenergyreleaseratetothesubcompartments~Thesevaluesarecomparedtothespectrumofallowableopera-tingconditionsfortheplant.TheCBSwillascertaintheadequacyoftheassumedconditionsbasedonthisreview.TheCSBconfirmswiththeHEBthevalidityoftheapplicant'sanalysisofsubcompartmentscontaininghighenergylinesandpostulatelpipebreaklocations,usingelevationandplandrawingsofthecontainmentshowingtheroutingoflinescontaininghighenergyfluids.TheCSBdeterminesthatanappropriatereferencecaseforsubcompartmentanalysishasbeenidentified.Intheeventapipebreakotherthanadouble-endedpiperuptureispostulatedbytheapplicant,theHEBwillevaluatetheapplicant'sjustificationforassumingalimiteddisplacementpipebreak.TheCSBmayperformconfirmatoryanalysesoftheblowdownmassandenergyprofileswithi'nasubcompartment.TheanalysisisdoneusingtheRELAP3computerprogram(SeeReference21foradescriptionofthiscode).Thepurposeoftheanalysisistoconfirmthepredic-tionsofthemassandenergyreleaseratesappearinginthesafetyanalysisreport,andtoconfirmthatanappropriatebreaklocationhasbeenconsideredinthisanalysis.TheuseofRELAP3willcontinueuntiltheRELAP4computercodehasbeenapprovedbythestaffasanacceptableblowdowncode.Atthattime,theCSBwillreplaceRELAP3withRELAP4forallsubsequentanalyses./TheCSBdeterminestheadequacyoftheinformationinthesafetyanalysisreportregardingsubcompartmentvolumes,ventareas,andventresistances.Ifasubcompartmentmustrelyondoors,blowoutpanels,orequivalentdevicestoincreaseventareas,theCSBreviewstheanalysesandtestingprogramsthatsubstantiatetheiruse.TheCSBreviewsthenodalizationofeachsubcompartmenttodeterminetheadequacyofthecalculationalmodel.Asnecessary,CSBperformsiterativenodalizationstudiesforsub-compartmentstoconfirmthatsufficientnodeshavebeenincludedinthemodel.TheCSBcomparestheinitialsubcompartmentairpressure,temperature,andhumiditycondi-tionstothecriteriaoFII,above,toassurethatconservativeconditionswereselected.TheCSBreviewsthebases,correlations,andcomputer'odesusedtopredictsubsonicandsonicventflowbehaviorandthecapabilityofthecodetomodelcompressibleandun-compressibleflow.Thebasesshouldincludecomparisonsofthecorrelationstobothexperimentaldataandrecognizedalternatecorrelationsthathavebeenacceptedbythestaff.6.2.1.2-4 4,0Usingthenodalizationofeachsubcompartmentasspecifiedinthesafetyanalysisreport,theCSBperformsanalysesusingoneofseveralavailablecomputerprogramstodeterminetheadequacyofthecalculatedpeakdifferentialpressure.Thecomputerprogramusedwilldependuponthesubcompartmentunderreviewaswellastheflowregime.Atthe'presenttime,thetwoprogramsusedbytheCSBareRELAP3(Ref.21)andCONTEHPT-LT(Refs.*7,8,and9).Amulti-volumecomputercodeiscurrentlyunderdevelopment.Attheconstructionpermitstage,theCSBwillascertainthatthesubcompartmentdesignpressuresincludeappropriatemarginsabovethecalculatedvalues,asgiveninII,above.IV.EVALUATIONFINDINGSTheconclusionsreachedoncompletionofthereviewofthissectionarepresentedinStandardReviewPlan6.2.1~V.REFERENCESThereferencesforthisplanarethoselistedinStandardReviewPlan6.2.1,togetherwiththefollowing:la.RegulatoryGuide1.46,"ProtectionAgainstPipeWhipInsideContainment."2a.StandardReviewPlan3,6.2,"DeterminationofBreakLocationsandDynamicEffectsAssociatedwiththePostulatedRuptureofPiping,"andattachedBranchTechnicalPositionNEB3-1,"PostulatedBreakandLeakageLocationsinFluidSystemPipingOutsideContainment."46.2.1.2-5 0l ATTACHiiEHT2MECHANICALENGINEERINGBRANCHREVESTFORADDITIONALINFOlMTIONRecentanalyseshaveshown'thatreactorpressurevesselsupportsmaybeVIsubjectedtopreviouslyunderestimatedlateralloadsundertheconditionsthatwouldexistifaninstantaneousdoubleendedbreakispostulatedinIthereactorvesselcoldlegpipeatthevessel.nozzle.Itisthereforenecessarytoreassessthecapabilityofthereactorcoolantsystemsupportstolimitthecalculatedmotionofthereactorvesselduringapostulatedcoldlegbreakwithinboundsnecessarytoassureahigh-probabilitythatthereactorcouldbebrought.safelytoacoldshutdowncondition.'XThe,followinginformationisrequired'forpurposesofmakingthenecessaryv<reassessmentofthereactorvesselsupports:nI1.Provideengineeringdrawingsofthereactorsupportsystemsufficienttoshowthegeometryofall.principleelementsandmaterials6feon-1struction.2;Specify.thedetaildesignloadsusedintheoriginaldesignanalysesofthereactorsupportsgivingmagnitude,directionofapplicationandthebasisforeachload.Alsoprovidethecalculatedmaximumstressineachprincipleelementofthesupportsystemandthecorrespondingallowablestresses.3.Providetheinformationrequestedin2abovefortheRYsupportscon-sideringapostulatedbreakatthecoldlegnozzle.Includeasummaryoftheanalyticalmethodsemployedandspecificallystatetheeffectsof,Ishorttermpressuredifferentialsacrossthecorebarrelincombination.

withallexternalloadingsca1culatedtoresultfromtherequiredpostulate.Thisanalysisshouldconsider:(a)limiteddisplacementbreakareaswhereapplicable(b)considerationoffluidstructureinteraction(c)useofactualtimedependentforcingfunction(d)reactorsupportstiffness.4.Iftheresultsoftheanalysesrequiredby3.aboveindicatesloadsleadingtoinelasticactioninthereactorsupportsordisplacementsexceedingpreviousdesignlimitsprovideanevaluationofthefollowing:(a)Yieldbehavior(effectsofpossiblestrainenergybuildup)ofthematerialusedinthereactorsupportdesignandtheeffectontheloadstransmittedtothereactorcoolantsystemandthebackupstructurestowhichthereactorcoolantsystemsupportsareattached.(b)Theadequacyofthereactorcoolantsystempiping,controlroddrives,steamgeneratorandpumpsupports,structuressurroundingthereactoi"coolantsystem,reactorinternalsandECCSpipingtoassurethatthereactorcanbesafelybroughttocoldshutdown.