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
References
Download: ML16314C691 (12)

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EKCLOSORESTATEMENZ OFTHEPROBLEM1IntheunlikelyeventofaPHRprimarycoolantsystempiperuptureintheimmediate vicinityofthereactorvessel,transient loadsoriginating fromthreeprincipal causeswillbeexertedonthereactorvesselsupportsystem.Theseare:1.Blowdownjetforcesatthelocationoftherupture(reaction forces),2.3.Transient differential pressures intheannularregion"betweenthevesselandtheshield,andTransient differential pressures acrossthecorebarrelwithinthereactorvessel.Theblowdownietforcesareadegvately understood anddesiqnprocedures areavailable toaccountforthem.Bothofthe"differential pressure" forces,however,arethree-dimensional ardtimedependent andrequiresophisticated analytical procedures totranslate themintoloaosactingonthe'eactor vesselsupport'system.

Alloftheloadsareresistedbytheinertiaandbythe.'support membersandrestraints of'thercomponents oftheprimarycoolant:.

systemincluding thereactorpressurevesselsupports.

Thetransient differential presureactiniexternally onthereactorvesselisaresultoftheflowof,theblowdowneffluentinthe"reactorcavity.Themaqnitude andthetimedependence oftheresultina forcesdependsonthenatureandthesizeof~thepiperupture,theclearance betweenthevesselandtheshieldandthesizeandlocationcftheventopeningsleadingfromthecavitytothecontainment asawhole.Forsometimerefinedanalytical methodshavebeenavailable forcalculatinq thesetransient differential pressures (multi-node analyses).

Theresultsofsuchanalysesindicatethattheconseauent loadsonthevesselsupportsystemcalculated bylesssophisticated methodsmaynctbeasconservative asoriginally intendedforearlierdesigns.Attachment 1tothisenclosure providesforyourinformation alistofinformation requestsforwhichresponses couldbeneededforaproperassessment oftheimpactofthecavitydifferential pressureonthedesignadeauacyofthevesselsupportsystemfora.powerplant.

Thecontrolling loadsfordesianpurposes, however,appearintypicalcasestobethoseassociated withtheinternaldifferential pressures acrossthecorebarrel.Theinternally generated loadsareduetoamomentary differential pressurewhichiscalculated toexistacrossthecorebarrelwhenthepressureinthereactorannularregionbetweenthecorebarrelandvesselwallinthevicinityoftherupturedpipeisassumedtorapidlydecreasetothesaturation pressureoftheprimarycoolantduetotheoutflowofwater.Althou'ah thedepressurization wavetravelsrapidlyaroundthecorebarrel,thereisafiniteperiodoftimeduringwhichthepressureintheannularregionoppositethebreaklocationisassumedtoremainat,ornear,theoriginalreactoroperating pressure.

Thus,transient asymmetrical forcesareexertedonthecorebarrelandthevesselwallwhichultimately resultintransient loadonthesupportsystems.Thesearetheloadswhichwereunderestimated

.bythelicenseeoriginally reporting thisproblemandwhichmaybeunderestimated inothercases.Theyaretherefore ofgenericconcerntothestaff.Attachment 2tothisenclosure providesforyourinformation alistofinformation requestsforwhichresponses wouldbeneededforaproperassessment oftheimpactthatthevesselinternaldifferential

pressure, inconjunction withtheotherconcurrent loads,couldhaveonthedesignadeauacyofthesupportsystem.Inthatthereareconsiderable differences inthereactorsupportsystemdesignsforvaiiousfacilities and'probably inthedesignmarginsprovidedbythedesioners ofolder.facilities, theunderestimation ofthese'differ-entialpressure" loadsmayormaynotresultinadetermination thattheadeouacyofthevesselsupportsystemforaspecificfacilityisguestion-able.Sincelocalfailuresinthevesselsupports(suchasplasticdeformation) donotnecessarily leadtothefailureofthesupportsasanintegralsystem,theremaybesomelimitedreactor.vesselmotionprovidedthatnofurther,sionificant conseguences would,ensueandtheemergency corecooling;systems (ECCS)wouldbe.abletoperformtheirdesignfunctions, r

.~ATTACt<l1ENT 1CONTAINMFNT SYSTEMSBRANCHREUESTFORADDITIONAL INFORMATION Intheunlikelyeventof.apiperupture.insidemajorcomponent subcompartments, theinitialblowdowntransient wouldleadtonon-uniform pressureloadingsonboththestructures andenclosedcomponents.

Toassuretheintegrity ofthesedesignfeatures, werequestthatyouperformacompartment multi-node spressureresponseanalysistoprovidethefollowing information:

(a)Theresultsofanalysesofthedifferential pressures resulting tfromhotlegandcoldleg(pumpsuctionanddischarge),reactor coolantsystempiperuptureswithinthereactorcavityandpipepenetrations.

(b)Describethenodalization, sensitivity studyperformed todetermine

'heminimumnumberofvolumenodesrequiredto,.conservatively predictthemaximumpressurewithinthe.reactorcavity.The'odalization sensitivity studyshouldincludeconsideration ofspatialpressurevariation; e.g.,'ressure variations circumferentially, axially,and

.radially, withinthereactorcavity.(c)Provideaschematic drawingshowingthenodalization ofthereactorcavity.Provideatabulation ofthenodalnetfreevolumes.and,interconnecting flowpathareas.(d)Providesufficiently detailedplanandsectiondrawingsforseveralviewsshowingthearrangement of,thereactorcavitystructure, reactorvessel,piping,andothermajorobstructions,,and ventareas,topermitverification ofthereactorcavitynodalization andventlocations.

(e)Provideandjustifythebreaktypeandareausedineachanalysis. (f)Provideandjustifyvaluesofventlosscoefficients and/o'rfrictionfactorsusedtocalculate flowbetweennodalvolI>mes.

llhenalosscoefficient consistsofmorethanonecomponent, identifyeachcomponent, itsvalueandtheflowareaatwhichthelosscoefficient applies.(g)Discussthemannerinwhichmovableobstructions toventflow(suchasinsulation, ducting,plugs,andseals)w'ere'treated.

Provideanalytical justification fortheremovalofsuchitemstoobtainventarea.Providejustification'tha't ventareaswi1notbepartially orcompletely pluggedbydisplaced objects.(h)Provideatableofblowdownmassflowrateandenergyreleaserateasafunctionoftimeforthereactorcavitydesignbasisaccident.

(i)Graphically showthepressure(psia)'nd differential pressure(psi)responses asfunctions oftimeforeachnode.Discussthebasis'orestablishing thedifferential pressures.

(j)Providethepeakcalculated differential pressureandtimeofpeakpressureforeachnode,andthedesigndifferential pressure(s) forthe5react'orcavity.Discusswhetherthedesigndifferential "pressure isuniformly appliedtothereactorcavityorwhetheritisspatially varied.(Standard ReviewPlan6.2.1.2,Subcompartment Analysisattached, providesadditional guidanceinestablishing acceptable designvalues,fordetermining theacceptability ofthecalculated results.)

P.U.S.NUCLEARREGULATORY COMMISSION ST%,INDE,IR9 REVIEWPLANOFFICEOFNUCLEARREACTORREGULATION

February, 1975SECTION6.2.1.2SUBCOHPARTHENT ANALYSISREVIEWRESPONSIBILITIES Primary-Containment SystemsBranch(CSB)Secondary

-Hechanical Engineering Branch(HEB)CorePerformance Branch(CPB)Auxiliary andPowerConversion SystemsBranch(APCSB)I.AREASOFREVIEWTheCSBreviewstheinformation presented bytheapplicant inthesafetyanalysisreportconcerning thedetermination ofthedesigndifferential pressurevaluesforcontainment sub-compartments.

Asubcompartment isdefinedasanyfullyorpartially enclosedvolumewithintheprimarycontainment thathouseshighenergypipingandwouldlimittheflowoffluidtothemaincontainment volumeintheeventofapostulated piperupturewithinthisvolume.Ashort-term pressurepulsewouldexistinsideacontainment subcompartment following apiperupturewithinthisvolume.Thispressuretransient producesapressuredifferential acrossthewallsofthesubcompartment whichreachesamaximumvaluegenerally withinthefirstsecondafterblowdownbegins.Themagnitude ofthepeakvalueisafunctionofseveralparameters, whichincludeblowdownmassandenergyreleaserates,subcompartment volume,ventarea,andventflowbehavior.

Atransient differential pressureresponseanalysisshouldbeprovidedforeachsubcompartment orgroupofsubcompartments thatmeetstheabovedefinition.

TheCSBreviewincludesthemannerinwhichthemassandenergyreleaserateintothebreakcompartment weredetermined, nodalization ofsubcompartments, subcompartment ventflowbehavior, andsubcompartment designpressuremargins.Thisincludesacoordinated revieweffortwiththeCPB.TheCPBisresponsible fortheadequacyof'theblowdownmodel.TheCSBreviewofthemassandenergyreleaseratesincludesthebasisfortheselection ofthepipebreaksizeandlocationwithineachsubcompartment containing ahighenergylineandtheanalytical procedure forpredicting theshort-term massandenergyreleaserates.TheCSBreviewofthesubcompar tmentmodelincludesthebasisforthenodalization withineachsubcompartment, theinitialthermodynamic conditions withineachsubcompartment, thenatureofeachv'entflowpathconsidered, andtheextentofentrainment assumedintheventflowmixture.Thereviewmayalsoincludeananalysisofthedynamiccharacteristics ofcomponents, suchasdoors,blowoutpanels,orsandplugs,thatmustopenorberemovedtoUSNRCSTANDARDREVIEWPLANStandenlreviewplansaroproparedforthecurdsneooftheOfficeofNuclearReactorReps4tlonstaffresponsible forthoreviewofapplications toconstmctondoperatenuclearpowerp4nts.Thesedocuments eremadeavailable tothopublloespertofthoCommission's poucytoInformthonuclearIndustryandtheSenorslpubdeofregulatory procedures endpollclos.

Standardreviewp4nseronotsubstltutse forredu4tory SuldssorthoCommlmlon's repu4tlons endCOmpllanco withthemisnetrortulrod.

ThostandardreviewplansectionssrokeyedtoRevfa4n2ofthoStandardFormatsndContentofSafetyAnalysisReportsforNuclearPowerPlants.NotstlsectionsofthoStandardFormathavesconospondlnp reviewplan.Published standardreviewplanswillborev4edperlodlcally, asappropriate.

toaccommodate commentsondtorellectnewinformation sndoaperlonco.

copiesofmsndardrovfowplansmaybaobtainedbyrecusaltothoU.S.NuclearResu4tory Commlmlon.

Wathlnston, O.C.20MS.Attention:

OfficeofNudasrReactorRadulation.

Commentssndeucsostlons forImprovement willboconsidered ondshouldalsobosenttothoOfficeofNuclearReactorRadutatlon.

~.provideaventflowpath,andthemethodsand'results ofcomponents testsperformed todemonstrate thevalidityoftheseanalyses.

Theanalytical procedure todetermine thelosscoefficients foreachventflowpathandtopredicttheventmassflowrates,including flowcorrelations usedtocomputesonicandsubsonicflowconditions withinavent,isre-viewed.Thedesignpressurechosenforeachsubcompartment isalsoreviewed'n requestfromtheAPCSB,theCSBevaluates orperformspressureresponseanalysesforsubcompartments outsidecontainment.

TheHEBisresponsible forreviewiitheacceptability ofthebreaklocations chosenandofthedesigncriteriaandprovision.

methodsemployedtojustifylimitedpipemotionforbreakspostulated tooccurwithin.'ubcompartments (SeeStandardReviewPlan3.6.2).II.ACCEPTANCE CRITERIA1.Thesubcompartment analysisshouldincorporate thefollowing assumptions:

a.Breaklocations andtypesshouldbe,chosenaccording toRegulatory Guide1.46forsubcompartments insidecontainment andtoBranchTechnical PositionMEB3-1(attached toStandardReviewPlan3'.2)forsubcompartments outsidecontainment.

Anacceptable alternate procedure istopostulate acircumferential double-ended ruptureofeachhighpressuresystempipeinthesubcompartment.

b.'fseveralbreakspostulated onthebasisofa,above,thebreakselectedasthereference caseforsubcompartment analysisshouldyieldthehighestmassandenergyreleaserates,consistent withthecriteriaforestablishing thebreaklocationandarea.c.Theinitialplantoperating conditions, suchaspressure, temperature, waterinventory, andpowerlevel,shouldbeselectedtoyieldthemaximumblowdownconditions~

.Theselectedoperating conditions wi11beacceptable ifitcanbeshownthatachangeofeachparameter wouldresultinalesssevereblowdownprofile.2.Theanalytical approachusedtocomputethemassandenergyreleaseprofilewillbeacceptedifboththecomputerprogramandvolumenodingofthepipingsystemaresimilartothoseofanapprovedemergency corecoolingsystem(ECCS)analysis.

Thecomputerprogramsthatarecurrently acceptable includeSATAN-VI(Ref.24),CRAFT(Ref.23),CEFLASk-4(Ref.25),andRELAP3(Ref.21),whenaflowmultiplier of1.0isusedwiththeapplicable chokedflowcorrelation.

Analternate

approach, whichisalsoacceptable, istoassumeaconstantblowdownprofileusingtheinitialconditions withanacceptable chokedflowcorrelation.

WhenRELAP-4isacceptedbythestaffasanoperational ECCSblowdowncode,itwillbeacceptable

'forsubcompart-mentanalyses'.

Theinitialatmospheric conditions withinasubcompartment shouldbeselectedtomax-imizetheresultant differential pressure.

Anacceptable modelwouldbetoassumeairatthemaximumallowable temperature, minimumabsolutepressure, andzeropercentrel-ativehumidity.

Iftheassumedinitialatmospheric conditions differfromthese,theselectedvaluesshouldbejustified.

6.2.1.2-2 Anothermodelthatisalsoacceptable, forarestricted classofsubcompartments, in-volvessimplifying theairmodeloutlinedabove.Forthismodel,theinitialatmos-pherewithinthesubcompartment is.modeledasahomogeneous water-steam mixturewithanaveragedensityequivalent tothedryairmodel.Thisapproachshouldbelimitedtosubcompartments thathavechokedflowwithinthevents.However,theadequacyofthissimplified modelforsubcompartments havingprimarily subsonicflowthroughtheventshasnotbeenestablished.

'4..Subcompar tmentnodalization schemesshouldbechosensuchthatthereisnosubstantial pressuregradientwithinanode,i.e,thenodalization schemeshouldbeverifiedbyasensitivity studythatincludesincreasing thenumberofnodesuntilthepeakcal-culatedpressures convergetosmallresultant changes.5.Ifventflowpathsareusedwhicharenotimmediately available atthetimeofpiperupture,thefollowing criteriaapply:c~Theventareaandresistance asafunctionoftimeafterthebreakshouldbebasedonadynamicanalysisofthesubcompartment pressureresponsetopiperuptures.

Thevalidityoftheanalysisshouldbesupported byexperimental dataoratestingprogramshouldbeproposedattheconstruction permitstagethatwillsupportthisanalysis.

Theeffectsofmissilesthatmaybegenerated duringthetransient shouldbeconsidered inthesafetyanalysis'.

Theventflowbehaviorthroughallflowpathswithinthenodalized compartment modelshouldbebasedonahomogeneous mixtureinthermalequilibrium, withtheassumption of100Kwaterentrainment.

Inaddition, theselectedventcriticalflowcorrelation shouldbeconservative withrespecttoavailable experimental data:Currently accept-ableventcriticalflowcorrelations arethe"frictionless Hoody"withamultiplier of0.6forwater-steam

mixtures, andthethermalhomogeneous equilibrium modelforair-steam-water

mixtures, 7.Attheconstruction permitstage,afactorof1.4shouldbeappliedtothepeakdifferential pressurecalculated inamannerfoundacceptable totheCSBforthesubcompartment.

Thecalculated pressuremultiplied by1.4shouldbeconsidered thedesignpressure.

Attheoperating licensestage,thepeakcalculated differential pressureshouldnotexceedthedesignpressure.

Itisexpectedthatthepeakcalcu-lateddifferential pressurewillnotbesubstantially different fromthatoftheconstruction permitstage.However,improvements intheanalytical modelsorchangesintheas-builtsubcompartment mayaffecttheavailable margin.III.REVIEWPROCEOURES Theprocedures described belowarefollowedforthesubcompartment analysisreview.Thereviewerselectsandemphasizes materialfromtheseprocedures asmaybeappropriate for6~2.1.2-3 aparticular case.Portionsofthereviewmaybecarriedoutopagenericbasisorbyadoptingtheresultsofpreviousreviewsofplantswithessentially thesamesubcompartment andhighpressurepipingdesign.TheCSBreviewstheinitialconditions selectedfordetermining themassandenergyreleaseratetothesubcompartments

~Thesevaluesarecomparedtothespectrumofallowable opera-tingconditions fortheplant.TheCBSwillascertain theadequacyoftheassumedconditions basedonthisreview.TheCSBconfirmswiththeHEBthevalidityoftheapplicant's analysisofsubcompartments containing highenergylinesandpostulatel pipebreaklocations, usingelevation andplandrawingsofthecontainment showingtheroutingoflinescontaining highenergyfluids.TheCSBdetermines thatanappropriate reference caseforsubcompartment analysishasbeenidentified.

Intheeventapipebreakotherthanadouble-ended piperuptureispostulated bytheapplicant, theHEBwillevaluatetheapplicant's justification forassumingalimiteddisplacement pipebreak.TheCSBmayperformconfirmatory analysesoftheblowdownmassandenergyprofileswithi'nasubcompartment.

TheanalysisisdoneusingtheRELAP3computerprogram(SeeReference 21foradescription ofthiscode).Thepurposeoftheanalysisistoconfirmthepredic-tionsofthemassandenergyreleaseratesappearing inthesafetyanalysisreport,andtoconfirmthatanappropriate breaklocationhasbeenconsidered inthisanalysis.

TheuseofRELAP3willcontinueuntiltheRELAP4computercodehasbeenapprovedbythestaffasanacceptable blowdowncode.Atthattime,theCSBwillreplaceRELAP3withRELAP4forallsubsequent analyses.

/TheCSBdetermines theadequacyoftheinformation inthesafetyanalysisreportregarding subcompartment volumes,ventareas,andventresistances.

Ifasubcompartment mustrelyondoors,blowoutpanels,orequivalent devicestoincreaseventareas,theCSBreviewstheanalysesandtestingprogramsthatsubstantiate theiruse.TheCSBreviewsthenodalization ofeachsubcompartment todetermine theadequacyofthecalculational model.Asnecessary, CSBperformsiterative nodalization studiesforsub-compartments toconfirmthatsufficient nodeshavebeenincludedinthemodel.TheCSBcomparestheinitialsubcompartment airpressure, temperature, andhumiditycondi-tionstothecriteriaoFII,above,toassurethatconservative conditions wereselected.

TheCSBreviewsthebases,correlations, andcomputer'odes usedtopredictsubsonicandsonicventflowbehaviorandthecapability ofthecodetomodelcompressible andun-compressible flow.Thebasesshouldincludecomparisons ofthecorrelations tobothexperimental dataandrecognized alternate correlations thathavebeenacceptedbythestaff.6.2.1.2-4 4,0Usingthenodalization ofeachsubcompartment asspecified inthesafetyanalysisreport,theCSBperformsanalysesusingoneofseveralavailable computerprogramstodetermine theadequacyofthecalculated peakdifferential pressure.

Thecomputerprogramusedwilldependuponthesubcompartment underreviewaswellastheflowregime.Atthe'present time,thetwoprogramsusedbytheCSBareRELAP3(Ref.21)andCONTEHPT-LT (Refs.*7, 8,and9).Amulti-volume computercodeiscurrently underdevelopment.

Attheconstruction permitstage,theCSBwillascertain thatthesubcompartment designpressures includeappropriate marginsabovethecalculated values,asgiveninII,above.IV.EVALUATION FINDINGSTheconclusions reachedoncompletion ofthereviewofthissectionarepresented inStandardReviewPlan6.2.1~V.REFERENCES Thereferences forthisplanarethoselistedinStandardReviewPlan6.2.1,togetherwiththefollowing:

la.Regulatory Guide1.46,"Protection AgainstPipeWhipInsideContainment."

2a.StandardReviewPlan3,6.2,"Determination ofBreakLocations andDynamicEffectsAssociated withthePostulated RuptureofPiping,"andattachedBranchTechnical PositionNEB3-1,"Postulated BreakandLeakageLocations inFluidSystemPipingOutsideContainment."

46.2.1.2-5 0l ATTACHiiEHT 2MECHANICAL ENGINEERING BRANCHREVESTFORADDITIONAL INFOlMTION Recentanalyseshaveshown'that reactorpressurevesselsupportsmaybeVIsubjected topreviously underestimated lateralloadsundertheconditions thatwouldexistifaninstantaneous doubleendedbreakispostulated inIthereactorvesselcoldlegpipeatthevessel.nozzle.Itistherefore necessary toreassessthecapability ofthereactorcoolantsystemsupportstolimitthecalculated motionofthereactorvesselduringapostulated coldlegbreakwithinboundsnecessary toassureahigh-probability thatthereactorcouldbebrought.safelytoacoldshutdowncondition.'

XThe,following information isrequired'for purposesofmakingthenecessary v<reassessment ofthereactorvesselsupports:

nI1.Provideengineering drawingsofthereactorsupportsystemsufficient toshowthegeometryofall.principle elementsandmaterials 6feon-1struction.

2;Specify.thedetaildesignloadsusedintheoriginaldesignanalysesofthereactorsupportsgivingmagnitude, direction ofapplication andthebasisforeachload.Alsoprovidethecalculated maximumstressineachprinciple elementofthesupportsystemandthecorresponding allowable stresses.

3.Providetheinformation requested in2abovefortheRYsupportscon-sideringapostulated breakatthecoldlegnozzle.Includeasummaryoftheanalytical methodsemployedandspecifically statetheeffectsof,Ishorttermpressuredifferentials acrossthecorebarrelincombination.

withallexternalloadingsca1culated toresultfromtherequiredpostulate.

Thisanalysisshouldconsider:

(a)limiteddisplacement breakareaswhereapplicable (b)consideration offluidstructure interaction (c)useofactualtimedependent forcingfunction(d)reactorsupportstiffness.

4.Iftheresultsoftheanalysesrequiredby3.aboveindicates loadsleadingtoinelastic actioninthereactorsupportsordisplacements exceeding previousdesignlimitsprovideanevaluation ofthefollowing:

(a)Yieldbehavior(effectsofpossiblestrainenergybuildup)ofthematerialusedinthereactorsupportdesignandtheeffectontheloadstransmitted tothereactorcoolantsystemandthebackupstructures towhichthereactorcoolantsystemsupportsareattached.

(b)Theadequacyofthereactorcoolantsystempiping,controlroddrives,steamgenerator andpumpsupports, structures surrounding thereactoi"coolantsystem,reactorinternals andECCSpipingtoassurethatthereactorcanbesafelybroughttocoldshutdown.