coupling the system analysis module to sas4a/sassys-1 · coupling the system analysis module with...

ANL/NE-16/22 (ANL-ART-74)

Coupling the System Analysis Module with SAS4A/SASSYS-1

Nuclear Engineering Division

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ANL/NE-16/22 (ANL-ART-74)

Coupling the System Analysis Module with SAS4A/SASSYS-1

prepared by T. H. Fanning and R. Hu Nuclear Engineering Division, Argonne National Laboratory September 30, 2016

CouplingtheSystemAnalysisModulewithSAS4A/SASSYS-1 September30,2016

i ANL/NE-16/22

ABSTRACT

SAS4A/SASSYS-1isasimulationtoolusedtoperformdeterministicanalysisofanticipatedeventsaswellasdesignbasisandbeyonddesignbasisaccidentsforadvancedreactors,withanemphasisonsodiumfastreactors.SAS4A/SASSYS-1hasbeenunderdevelopmentandinactiveusefornearlyforty-fiveyearsandiscurrentlymaintainedbytheU.S.DepartmentofEnergyundertheOfficeofAdvancedReactorTechnology.AlthoughSAS4A/SASSYS-1containsaverycapableprimaryandintermediatesystemmodelingcomponent,PRIMAR-4,italsohassomeshortcomings:outdateddatamanagementandcodestructuremakesextensionofthePRIMAR-4modulesomewhatdifficult.TheuserinputformatforPRIMAR-4alsolimitsthenumberofvolumesandsegmentsthatcanbeusedtodescribeagivensystem.

TheSystemAnalysisModule(SAM)isafairlynewcodedevelopmenteffortbeingcarriedoutundertheU.S.DOENuclearEnergyAdvancedModelingandSimulation(NEAMS)program.SAMisbeingdevelopedwithadvancedphysicalmodels,numericalmethods,andsoftwareengineeringpractices,howeveritiscurrentlysomewhatlimitedinthesystemcomponentsandphenomenathatcanberepresented.Forexample,componentmodelsforelectromagneticpumpsandmulti-layerstratifiedvolumeshavenotyetbeendeveloped.Noristheresupportforabalanceofplantmodel.Similarly,system-levelphenomenasuchascontrol-roddrivelineexpansionandvesselelongationarenotrepresented.

Thisreportdocumentsfiscalyear2016workthatwascarriedouttocouplethetransientsafetyanalysiscapabilitiesofSAS4A/SASSYS-1withthesystemmodelingcapabilitiesofSAMunderthejointsupportoftheARTandNEAMSprograms.ThecouplingeffortwassuccessfulandisdemonstratedbyevaluatinganunprotectedlossofflowtransientfortheAdvancedBurnerTestReactor(ABTR)design.Therearedifferencesbetweenthestand-aloneSAS4A/SASSYS-1simulationsandthecoupledSAS/SAMsimulations,butthesearemainlyattributedtothelimitedmaturityoftheSAMdevelopmenteffort.

ThesevereaccidentmodelingcapabilitiesinSAS4A/SASSYS-1(sodiumboiling,fuelmeltingandrelocation)willcontinuetoplayavitalroleforalongtime.Therefore,theSAS4A/SASSYS-1modernizationeffortshouldremainahighprioritytaskundertheARTprogramtoensurecontinuedparticipationindomesticandinternationalSFRsafetycollaborationsanddesignoptimizations.Ontheotherhand,SAMprovidesanadvancedsystemanalysistool,withimprovednumericalsolutionschemes,datamanagement,codeflexibility,andaccuracy.SAMisstillinearlystagesofdevelopmentandwillrequirecontinuedsupportfromNEAMStofulfillitspotentialandtomatureintoaproductiontoolforadvancedreactorsafetyanalysis.TheefforttocoupleSAS4A/SASSYS-1andSAMisthefirststepontheintegrationofthesemodelingcapabilities.

CouplingtheSystemAnalysisModulewithSAS4A/SASSYS-1September30,2016

ANL/NE-16/22 ii


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TABLEOFCONTENTS

Abstract....................................................................................................................................................................iTableofContents................................................................................................................................................iiiListofFigures.......................................................................................................................................................ivListofTables........................................................................................................................................................iv1 Introduction...................................................................................................................................................52 SAS/SAMCoupling......................................................................................................................................6

2.1 Strategy.................................................................................................................................................62.2 DataExchangeRequirements.....................................................................................................8

3 CodeModifications......................................................................................................................................93.1 SASCodeModifications..................................................................................................................93.2 SAMCodeModifications.............................................................................................................13

4 CouplingResults........................................................................................................................................174.1 ABTRReferenceModel...............................................................................................................174.2 SAMSystemModel........................................................................................................................224.3 VerificationofCouplingInterface...........................................................................................234.4 UnprotectedLossofFlowTransientSequence................................................................254.5 TransientSimulationResultsofUnprotectedLossofFlow........................................25

5 PathForward..............................................................................................................................................326 References....................................................................................................................................................33


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LISTOFFIGURES

Figure1:TightCouplingSchemeforaGenericTimeStep................................................................7Figure 2:SAS4A/SASSYS Time Step Hierarchy........................................................................................7Figure3:SequentialTwo-WayCouplingSchemeduringaTransient..........................................8Figure4:RelationshipbetweenPRIMAR-4andtheSAS4A/SASSYS-1

Thermal-HydraulicsSolvers....................................................................................................10Figure5:SummaryofSAS4A/SASSYS-1InputRequiredforSAS/SAM

Coupling...........................................................................................................................................12Figure6:ExampleofSAStoSAM.datfileforSAS/SAMCoupling..................................................15Figure7:ExampleofSAMtoSAS.datfileforSAS/SAMCoupling..................................................16Figure8:ExecutionProcessFlowChartofCoupledSASSteadyExecutioner.........................16Figure9:ExecutionProcessFlowChartofCoupledSASTransientExecutioner....................17Figure10:ReferenceABTRCoreConfiguration.................................................................................18Figure11:ChannelAssignmentsfortheSAS4A/SASSYS-1CoreModel..................................19Figure12:ElevationviewoftheABTRPrimarySystem.................................................................20Figure13:PRIMAR-4RepresentationofthePrimary,Intermediate,and

DecayHeatCoolantSystems...................................................................................................21Figure14:SchematicsoftheABTRmodelforcoupledSAS/SAMsimulations.....................23Figure15:CoupledSAS/SAMsimulationresultsofABTRnulltransient................................24Figure16:NormalizedpowerandcoreflowduringtheABTRULOFtransient...................27Figure17:Pooltemperaturesduringthetransient..........................................................................27Figure18:TransienttemperaturesforChannel5.............................................................................28Figure19:Corechannelflowvelocitiesduringthetransient.......................................................28Figure20:TotalcoreflowdifferencesbetweenSAMsurrogatemodeland

SAS4A/SASSYS-1corechannelsimulationresults........................................................29Figure21:Transientreactivityfeedback...............................................................................................29Figure22:Normalizedpowerandcoreflow,comparisonbetweenstand-

aloneSASandcoupledSAS/SAMsimulationresults....................................................31Figure23:TransienttemperaturesforChannel5,stand-aloneSASsimulation..................31Figure24:Transientreactivityfeedback,stand-aloneSASsimulation....................................32

LISTOFTABLES

Table1:DataexchangeflowforSAS/SAMcouplingatthecouplinginterface........................9


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1 IntroductionSAS4A/SASSYS-1isasimulationtoolusedtoperformdeterministicanalysisof

anticipatedeventsaswellasdesignbasisandbeyonddesignbasisaccidentsforadvancedliquid-metal-coolednuclearreactors.[1]WithitsoriginasSAS1Ainthelate1960s,theSASseriesofcodeshasbeenundercontinuoususeanddevelopmentforoverforty-fiveyearsandrepresentsacriticalinvestmentinsafetyanalysiscapabilitiesfortheU.S.DepartmentofEnergy.Incontrast,theUSDOENuclearEnergyAdvancedModelingandSimulationProgram(NEAMS)hasmaderecentinvestmentstoexplorenewsystemsmodelingcapabilitiesinasoftwaretoolreferredtoastheSystemAnalysisModule(SAM).[2]Thisreportdocumentsfiscalyear2016activitiesthatwerecarriedouttocouplethetransientsafetyanalysiscapabilitiesofSAS4A/SASSYS-1withthesystemmodelingcapabilitiesofSAMunderthejointsupportoftheAdvancedReactorTechnology(ART)andNEAMSprograms.

SAS4A/SASSYS-1containsacapableprimaryandintermediatesystemmodelingcomponent,PRIMAR-4.PRIMAR-4canrepresentcomplexarrangementsofcoolantsystemcomponentsincludingpumps,piping,valves,intermediateheatexchangers,airdumpheatexchangers,steamgenerators,etc.SAS4A/SASSYS-1alsocontainsacontrolsystemmodulethatcandynamicallyinteractwithPRIMAR-4basedonuser-definedlogicandcontrols.Controlsignalscanaffectcertainplantstateparameterssuchasscramreactivity,pumpspeed,andvalveactuation.

Inadditiontoitscapabilities,PRIMAR-4hassomeshortcomings.Themostsignificantshortcomingsareintheformofdatamanagement,codestructure,anduserinputlimitations.OutdateddatamanagementandcodestructuremakesextensionofthePRIMAR-4moduledifficult.Addingnewcomponentmodelsrequiresknowledgeofunrelatedcodeinordertoavoidintroducingbugs.Lackofmodularitymeansthatunittestingtovalidateindividualmodelsisnotpossible.TheuserinputformatforPRIMAR-4limitsthenumberofvolumesandsegmentsthatcanbeusedtodescribeagivensystem.CouplingwithSAMwillprovideanalternativetoPRIMAR-4forprimary,secondary,anddecayheatcoolantsystemmodelingcapabilitiesthataremoreflexibleandextensible.

SAMdevelopmentaimsfortheadvancesinphysicalmodeling,numericalmethods,andsoftwareengineeringtoenhanceitsuserexperienceandusability.Tofacilitatethecodedevelopment,SAMutilizesanobject-orientedapplicationframework(MOOSE),anditsunderlyingmeshingandfinite-elementlibrary(libMesh)andlinearandnon-linearsolvers(PETSc),toleveragemodernsoftwareenvironmentsandnumericalmethods.Asanewcodedevelopment,theinitialefforthasbeenfocusedonthemodelingandsimulationcapabilitiesofheattransferandsingle-phasefluiddynamicsresponsesintheadvancedreactorsystems.

DespitetheadvancedsoftwarearchitectureofSAM,itiscurrentlysomewhatlimitedinthesystemcomponentsandphenomenathatcanberepresented.Forexample,componentmodelsforelectromagneticpumpsandmulti-layerstratifiedvolumeshavenotyetbeendeveloped.Noristheresupportforabalanceofplantmodel.Similarly,system-levelphenomenasuchascontrol-roddrivelineexpansionandvesselelongationarenot


ANL/NE-16/22 6

represented.Nevertheless,themodernsoftwaredesignofSAMshouldfacilitaterapiddevelopmentofmodels,andcontinuedinvestmentbyNEAMSwouldeliminatethesegaps.

UntilSAMmaturestoprovidethesamerangeofcomponentsandphenomenathatPRIMAR-4provides,PRIMAR-4willbethepreferredmoduleforprimaryandintermediatecoolantsystemsmodeling.Bycompletingthecoupling,however,apathforwardwillbeavailabletosupportenhancedmodelingcapabilitiesthatarenotcurrentlypossible.

2 SAS/SAMCoupling

2.1 StrategyTocombinetheadvantagesofSAS4A/SASSYS-1andSAM,aninitialcoupling

strategyhasbeendefinedthatretainsthefullcomplementofcore(inthereactorsense)modelingcapabilitiesofSAS4A/SASSYS-1—coolantchannelandsub-channelthermalhydraulics,sodiumboiling,fuelrestructuringandrelocation,in-pinfuelmelting,claddingfailure,andfuelandcladmeltingandrelocation—andaddstheoptiontouseSAMfortheprimary,intermediate,anddecayheatcoolantsystems.Inthisapproach,themodelingcapabilitiesofPRIMAR-4willberetainedtomaintaincontinuityofsimulationcapabilities.

Inallmulti-codecouplingapplications,carefulcontrolofdataexchangeandtimesynchronizationareessentialforanumericallystableandphysicallyvalidsimulation.Whenusingatightcouplingscheme,aninterfaceconsistency,orconvergence,checkisneededtomakesuretheresultsareconsistentatthecouplinginterfacebetweenthetwocodes,asshowninFigure1.Ifthisschemewereadopted,eachtimestepisrepeatedinbothSAMandSAS4A/SASSYS-1untilthedesiredconvergenceisachieved.Tightcouplinginthismannerusuallydoesnotrequiresignificantmodificationstotheunderlyingsolutionschemesofthetwocodes.

However,thisapproachoftenrequiresthemodificationofthetimesteppingcontrolanddatamanagementinthetwocodes,whichisnotalwaysatrivialtask.Forexample,Figure 2showsthatSAS4A/SASSYS-1usesamulti-leveltime-stephierarchytoensurestabilityofthemanydifferentaccidentmodelsavailable.PRIMAR-4itselfusesatheta-weighted,semi-implicitsolutionschemewithtime-stepcut-backcontrolstoavoidexpensiveiterations.Therefore,atightcouplingschemethatrequiresiterationisnotappropriate.

Instead,asequentialtwo-waycouplingschemeisusedforcouplingSAMwithSAS4A/SASSYS-1.ThisapproachisshowninFigure3.Inthisscheme,eachofthetwocodesdrivesitsownportionofthesimulationandcouplinginterfacedataisexchangedatwell-definedpoints.Forsteady-stateinitialization,SAS4A/SASSYS-1willdeterminecoreinletandoutletboundaryconditionsbasedonmodelinput.Thoseconditionswillprovidetheinitialsteady-stateconditionsforSAM.Duringthetransient,theroleswillbereversed.SAMwilldeterminecoolantsystemdynamicchanges,suchaslossoffloworlossofheatsink,andwilldefinetheinterfaceconditionsforthecorechannelmodelsinSAS4A/SASSYS-1.


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Figure1:TightCouplingSchemeforaGenericTimeStep

Figure 2:SAS4A/SASSYS Time Step Hierarchy

SAM$

SAS$

Interface$data$from$SAS$to$SAM$at$tn01$

Interface$data$from$SAS$to$SAM$for$tn+1$

Internal$itera5ons$

Time$Step$N$

Interface$Convergence$

Yes$

No$

Data$from$SAM$to$SAS$at$tn$

Interface$data$from$SAS$at$tn$

DELT%

DT%

DTPRI%

DTIME%

Transient%Time%

Start%of%Main%Time%Step%

TIMCL2%TIMHT2% TIMPR2% TIME2%

Main%Time%Step%

Primary%Loop%Time%Step%Ends%on%Main%Time%Step%

Heat%Transfer%Time%Step%Ends%on%Main%Time%Step%

Coolant%Time%Step%Ends%on%Primary%Loop%and%Main%Time%Step%


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Figure3:SequentialTwo-WayCouplingSchemeduringaTransient

ThisapproachissimilartotheprovenapproachusedbetweentheSAS4A/SASSYS-1corechannelmodelsandPRIMAR-4.InPRIMAR-4,asurrogatecorechannelmodelisusedtoestimatetherateofchangeinthemassflowrateforeachchannel.Additionally,thedifferencesbetweentheestimatedchannelflowsandcomputedchannelflowsareconsideredintheadjustmentsoftheplenacouplingparameters.Inthisway,thenumericalstabilityofthecoupledcodeisassured,whilethemodificationstoSAS4A/SASSYS-1areminimized.

2.2 DataExchangeRequirements

InSAS4A/SASSYS-1,themulti-channelcoremodeliscoupledwithPRIMAR-4attheinletandoutletplena.Whenthecore-channelthermalhydraulicsmodulesinSAS4A/SASSYS-1completeatimestepforthecoresimulationportionofthetransient,theyalsodefinessurrogatemodelsforeachchannel.ThesurrogatemodelsareusedduringthePRIMAR-4timesteptoestimatechangesincorechannelflowratesduringthenextprimarycoolantsystemtimestep.

Thesurrogatemodelsaredefinedbasedonthefollowingequationthatrelateschangesinthecorechannelflowratestochangesintheplenumpressures:

𝑑𝑤𝑑𝑡 = 𝐶! − 𝐶!𝑝in + 𝐶!𝑝out + 𝐶!𝑤 𝑤 (1)

Thecoefficients𝐶!through𝐶!areprovidedbythecorechannelmodeltoPRIMAR-4,whilethepressure(𝑝inand𝑝out)andflow(𝑤)variablesaresolvedbyPRIMAR-4duringtheprimarycoolanttimestep.Solutionsforpressureandflowareestimatesbecausetheyarebasedonthesurrogatemodel.

Fortransientsinwhichthecorechannelcoolantremainssinglephase,theseestimateswillbequiteaccurate.Ifboilinginitiates,theprocessofvoidformationandcoolantexpulsionintroducerapid,non-linearchangesthatrequiresignificantreductionsintime-stepsizesinordertomaintainaccuracy.Also,PRIMAR-4willneedtoadjustplenummass,pressure,temperature,andcover-gasinterfaceelevationstoaccountfordifferencesbetweentheestimatedchannelflowsbasedonthelinearsurrogatemodelandtheactualflowscomputedbythecoolantdynamicsmodels.

! 4!

&Figure 2: Sequential Two-Way Coupling Scheme for a Generic Time Step

This& approach& is& similar& to& the& proven& approach& used& between& the& SAS4A/SASSYSP1&core&channel&models&and&PRIMARP4.&In&PRIMARP4,&a&surrogate&core&channel&model&is&used&to& estimate& the& rate& of& change& in& the&mass& flow& rate& for& each& channel.& Additionally,& the&differences& between& the& estimated& channel& flows& and& computed& channel& flows& are&considered&in&the&adjustments&of&the&plena&coupling&parameters.&In&this&way,&the&numerical&stability& of& the& coupled& code& is& assured,&while& the&modifications& of& SAS4A/SASSYSP1& are&minimized.&

Data*Exchange*Requirements*

In& SAS4A/SASSYSP1,& the& multiPchannel& core& model& is& coupled& with& PRIMARP4& at& the&inlet& and& outlet& plenums.& When& the& corePchannel& thermal& hydraulics& module& in&SAS4A/SASSYSP1&completes&a&time&step&for&the&core&simulation&portion&of&the&transient,&it&also&defines&surrogate&models&for&each&channel.&The&surrogate&models&are&used&during&the&PRIMARP4& time& step& to& approximate& changes& in& core& channel& flow& rates& during& the& next&primary&coolant&system&time&step.&

The&surrogate&models&are&defined&based&on&the&following&equation&that&relates&changes&in&the&core&channel&flow&rates&to&changes&in&the&plenum&pressures:&

!"!" = !! − !!!in + !!!out + !!! ! & (1)&

The&coefficients&!!&through&!!&are&provided&by&the&core&channel&model&to&PRIMARP4,&while&the&pressure&and&flow&variables&are&solved&by&PRIMARP4&during&the&primary&coolant&time&step.&Solutions&for&pressure&and&flow&are&estimates&because&they&are&based&on&the&surrogate&model.&

For&transients&in&which&the&core&channel&coolant&remains&single&phase,&these&estimates&will& be& quite& accurate.& If& boiling& initiates,& the& process& of& void& formation& and& coolant&expulsion& introduce&rapid,&nonPlinear&changes& that&require&significant&reductions& in& timePstep&sizes&in&order&to&maintain&accuracy.&Also,&PRIMARP4&will&need&to&adjust&plenum&mass,&pressure,& temperature,& and& coverPgas& interface& elevations& to& account& for& differences&between&the&estimated&channel& flows&based&on&the& linear&surrogate&model&and&the&actual&flows&computed&by&the&coolant&dynamics&models.&&

SAM& tn* tn+1*

SAS& tn* tn+1*


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Followingcompletionofatimestepfortheprimaryandintermediatecoolantloops,PRIMAR-4providesthefollowinginformationbacktothecorechannelcoolantdynamicsroutinesinSAS4A/SASSYS-1:

𝑝in 𝑡! =inletplenumpressureatthebeginningofthePRIMAR-4timestep

𝑝out 𝑡! =outletplenumpressureatthebeginningofthePRIMAR-4timestep

𝑑𝑝in𝑑𝑡 ,

𝑑𝑝out𝑑𝑡 =timederivativesoftheinletandoutletplenumpressures

𝑇in,𝑇out =inletandoutletplenumtemperatures

Theseparametersprovidetheboundaryconditionsneededtoupdatethecorechannelsolution.

AsimilarcouplingmethodisusedtocoupleSAS4A/SASSYS-1withSAM.Thedataexchangebetweenthetwocodesateachcouplinginterface(corechannel/plenum)issummarizedinTable1.

Table 1: Data exchange flow for SAS/SAM coupling at the coupling interface SAS→SAM(atthebeginningofSAMtimestep)

Foreverychannel: 𝐶!,𝐶!,𝐶!,and𝐶! InletandOutletMassFlowRate InletandOutletTemperature

SAM→SAS(attheendofSAMtimestep)

Foreveryplenum: Pressure Pressurederivatives Temperature

3 CodeModifications

3.1 SASCodeModifications

InSAS4A/SASSYS-1,thePRIMAR-4moduletraditionallycarriesoutthesimulationoftheprimaryandintermediatecoolantloops.ThegoalofthisworkistodevelopacapabilitytousetheNEAMSSystemAnalysisModule(SAM)asanalternativetoPRIMAR-4.ItisfortunatethattheearlydevelopmentofSASwasimplementedastwoseparatecodes:SAS1AthroughSAS4AforsevereaccidentsandSASSYS(includingPRIMAR)forsystemthermalhydraulics.Althoughthecodeshavelongsincemerged,therearestilldiscernableboundariesbetweenthecorechannelmodelsandthePRIMARsystemmodels.ThetraditionalrelationshipbetweenPRIMAR-4andthecorechannelmodelsisillustratedinFigure4.


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Figure4:RelationshipbetweenPRIMAR-4andtheSAS4A/SASSYS-1Thermal-HydraulicsSolvers.

Figure4suggeststhatonlyboundaryconditionsarepassedbetweenPRIMAR-4andthecorechannelmodels.Intheabsenceofobject-orientedprogrammingcapabilities,decadesofdevelopmenthaveresultedinmixedcodesharedbetweenthedifferentmodels.Thiswasparticularlytrueinthemaindriverforsteady-stateinitialization.Overtime,newfeatureswereintroduced—suchascontrol-roddrivelineexpansion,supportformultipleinletandoutletplena,andstructuralgrid-plateexpansion—thatblurredthedistinctionbetweenprimarycoolantsystemandcorechannelsourcecode.

TosupportcouplingwithSAM,thatdistinctionneededtobereinforced.Anewapproachwasbuiltuponmodularobject-orientedconceptsavailableinFortran2003.Anewmodule,namedCoupleSYS,wasdevelopedthatmanagesallboundaryconditioninformationforboththecoreandtheprimarycoolantloop(seeTable1).Foreachcorechannel,themodulemaintainsinformationaboutchannelflow,inletandoutlettemperatures,surrogatemodelparameters,andsodiumvaporenergydischarge.Foreachplenum,themodulemaintainselevation,temperature,pressure,andpressurederivativeinformation.Themodulealsomaintainsamap-typedatastructurethatlinksanynumberofcorechannelstoanynumberofinletandoutletplena.AlthoughthenumberandcomplexityofconnectionsislimitedinPRIMAR-4,theCoupleSYSmoduleimposesnolimitationsonthecomplexityofaSAMmodel.

InSAS4A/SASSYS-1terminology,acoresegmentiscomposedofoneormorechannelsorchannelgroupstorepresentassembliesinthecore.Asegmentalsodefines

SystemThermalHydraulicsPRIMAR-4

Pre-VoidingHydraulics

SodiumBoilingHydraulicsTSBOIL

PointKine:csTSPK

TransientCoreHeatTransferTSHTRNandTSHTRV

corechann

elflow

s

plenumpressuresandtemperatures

corechannelflows

plenumpressuresandtem

peratures

voidingreacEvity

reacEvity

power

iniEalflowsandpressures

coolantflow

coolanttemperatures

cladsurfa

ceheatflux

cladtemperatures

plenumtem

peratures

corechanneloutlettemperatures


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connectionstooneinletandoneoutletplenum.Bycombiningmultiplesegmentsandmultipleplena,morecomplexcoredesignscanberepresented.Anexamplewouldbethehigh-andlow-pressureinletplenainEBR-IIthatresultsintwocoresegments.Userinput,eitherfromPRIMARorforSAM,controlstheseconnectionsthroughcallstoLinkGroupToSegmentIDandLinkSegmentToPlenaIDthatarepartoftheCoupleSYSinterface.

ThecorechannelmodelsincludenotonlythoseinFigure4(transientcoreheattransferandpre-voidingandboilinghydraulics)butalsothefuelmeltingandrelocationmodelsdefinedbyPLUTOandLEVITATE.AllofthesemodelsweremodifiedtocommunicateboundaryconditionstotheCoupleSYSmoduleinsteadoftoPRIMAR.Likewise,thesteady-stateandtransient-statethermal-hydraulicsdrivers(SSTHRMandTSTHRMrespectively)weremodifiedtofetchprimarysystemboundaryconditionsfromCoupleSYSandapplythemtoeverychannel.

Significantcomplicationswereencounteredwhileupdatingthesteady-statedriver,SSTHRM.Unlikemanyothersystemcodes,SAS4A/SASSYS-1directlysolvesthesteady-stateequationsratherthaniterateonthetransientequationsuntilanequilibriumisfound(althoughthatisanoption).Thissimplifiesinputrequirementsfortheuser.Inadditiontopowerandflowdistributions,theuseronlyhastosupplytheinletplenumtemperatureandtheoutletplenumpressure.SSTHRMdeterminesthesolutionforinitialtemperatureandpressuredistributionsandautomaticallyadjuststheorificecoefficientsforeverychannel.Thisapproachrequirescoordinationbetweenthecorechannelmodelsandthesystemmodelsfortheinletandoutletplena.Asaresult,thesourcecodeforthecorechannelandsystemplenummodelshadblendedtogetherinmanyplaces,breakingtheencapsulationthatisneededforobject-orientedprogrammingconstructs.

Toresolvethisissue,nearlyallofthePRIMAR-relatedsteady-statesupportroutinesusedbySSTHRM,particularlythosethatsupportmultipleinletandoutletplenaconfigurations,hadtoberewritten.Inaddition,SSTHRMcantakeoneofseveraldifferentpathsdependingonthetypeandcombinationofcorechannelsbeingused—single-pin(traditional),multiple-pin,andsub-channel—andwhetheranulltransientisneededtoinitializeassembly-to-assemblyheattransfer.Fortunately,therewriteledtotheeliminationofspecializedcodethathandledmultiplecoresegmentsandplenaseparatelyfromtraditional,singlesegmentdesigns.

TocouplewithSAM(oranysystemcodethatsatisfiestherequirementsdefinedinSection0),twoadditionalmoduleswerewritten.Thefirstisaplug-inadditiontotheinputprocessorthathandlesnewinputfordescribingsegmentandplenumconnections.ThesecondisamodulethathandlescommunicationsbetweenSASandSAM.

SAS4A/SASSYS-1inputconsistsofinputblocks.Anewblock,SAMSYS,definestheinputrequirementsforcouplingwithSAM.TheSAMSYSblockallowstwotypesofsub-blocks:PLENUMandSEGMENT.ThePLENUMblockdefinesthezelevationandeithertheinlettemperatureoroutletpressureforaninletoroutletplenum,respectively.TheSEGMENTblockdefinestheassociationbetweenacoresegmentanditsinletandoutletplena.Figure5illustratestheinputrequiredfortheSAMSYSblock.


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TheSAMSYSinputblockundergoesextensiveinputverification.Forexample,aplenumcannotbedefinedmorethanonce,norcanitdefinebothaninlettemperatureandanoutletpressure.Temperaturesandpressuresmustbepositivevalues,andeachsegmentmustconnecttovalidinletandoutletplena.

EachSEGMENTmusthaveauniqueid.Theexistingchannel-dependentinput,NSEGMP,isusedtoassociateacorechannelwithasegmentbasedontheID.Ifleftblank,thesegmentIDwilldefaulttoitssequencenumberintheSAMSYSblock(startingwith1),andNSEGMPwilldefaulttoone(1).Thisallowsthemostcommoncaseofasinglecoresegmenttobedefinedwithminimalinput.

Thefinalmodule,CoupleSAM,launchestheSAMexecutableandhandlescommunicationsbetweenthetwocodes.ItalsohandlesupdatestotheboundaryconditionsmaintainedbytheCoupleSYSmodule.Threekeyinterfacesaredefined.InitWithSurrogateinitializestheCoupleSAMmoduleandpassesareferencetothesurrogateboundaryconditionsinCoupleSYS.Neartheendofthesteady-stateinitializationinSSTHRM,SSInitiscalledtosendtheresolvedsteady-stateboundaryconditionstoSAMforitsownsteady-stateinitialization.Duringeachtransienttimestep,TSStepiscalledtoprovideupdatedsurrogatechannelparameterstoSAMandreceiveupdatedinletandoutletboundaryconditionsforSAS.Additionalinterfacesaredefinedtohandlejobterminationorrestartsituations.

Figure5:SummaryofSAS4A/SASSYS-1InputRequiredforSAS/SAMCoupling

Page 1/1SampleInput.inpSaved: 9/15/16, 10:06:31 PM Printed for: Thomas H. Fanning

SAMSYS "<name>"1

2

path = "<SAM executable path>"3

4

! Define an inlet plenum:5

PLENUM "<name>"6

Zref = Z ! inlet plenum elevation7

Tin = T ! inlet plenum temperature8

END9

10

! Define an outlet plenum:11

PLENUM "<name>"12

Zref = Z ! outlet plenum elevation13

Pout = P ! outlet plenum pressure14

END15

16

! Define a core segment17

SEGMENT "<name>"18

id = # ! needed for core channel models19

inlet = "<name of inlet plenum>"20

outlet = "<name of outlet plenum>"21

END22

23

! [...]24

25

END26

27

28

29


13 ANL/NE-16/22

3.2 SAMCodeModifications

SignificantcodeupdateshavebeenmadefortheimplementationoftheSAS/SAMcouplingstrategyanddataexchangediscussedintheaboveSections.Majorcodeupdatesinclude:

• Implementationofsurrogatecore-channelflowmodelsinSAM;

• Developmentofnewcouplingboundarycomponents,CoupledVolumeBranchandCoupledLiquidVolume,includingadditionalphysicsmodelingassociatedwiththenewComponents;

• DataexchangeandfileI/O;

• DevelopmentofCoupledSASSteadyExecutionerandsteady-stateinitialization;

• DevelopmentofCoupledSASTransientExecutioner.Asurrogatemodel,asdescribedinEq.(1),isimplementedinSAMtoapproximate

theSAScorechannelflowratebasedoncoefficientsC!throughC!providedbySAS,andthestatevariablesintheSAMprimaryloop.

NewcomponentsweredevelopedinSAMtomodelavolumewithadditionalmasssourcesorsinks,whichrepresenttheconnectingpipesmodeledintheothercodessuchasSAS4A/SASSYS-1.ThegoverningequationsofmassandenergyconservationfortheCoupledVolumeBranchandCoupledLiquidVolumeComponentsare

−𝑑 𝜌𝑉𝑑𝑡 + 𝜌𝑢𝐴𝑛 !

!

!!!

+ 𝑚coupled

!

!!!

+𝑚!"# = 0(1)

−𝑑 𝜌𝑉ℎ𝑑𝑡 + 𝜌𝑢𝐴ℎ𝑛 !

!

!!!

+ 𝑚coupledℎcoupled

!

!!!

+𝑚!"#ℎ = 0(2)

where𝜌 = density of the volume component

𝑉 = volume of the volume component

𝑡 = time

𝜌𝑢 = mass flux at the connecting nodes

𝑢 = flow velocity at the connecting nodes

𝐴 = flow area of the connecting components

ℎ = fluid enthalpy of the volume component

𝑚coupled = coupled pipe flow rate

ℎcoupled = coupled pipe flow enthalpy.


ANL/NE-16/22 14

WhencoupledwithSAS4A/SASSYS-1,thecorechannelflowratecalculatedfromthesurrogatemodelwillbeusedas𝑚coupledinthecoupledvolumecomponentmodel.Amassadjustmentterm𝑚!"# isalsoincludedtoaccountforthedifferencesbetweentheSAMsurrogatemodelandtheSAS4A/SASSYS-1corechannelmodelresults.

BecauseSAMisdevelopedinanobject-orientedprograminglanguage,mostofthetermsinthecoupledvolumegoverningequationswereavailablefromthedevelopmentoftheoriginalPBVolumeBranchandPBLiquidVolumecomponents.Onlythenewterms,

m!"#$%&'!!!! and m!"#$%&'h!"#$%&'!

!!! ,areimplementedasnewNodalScalarKernelsinSAM.

ThedataexchangerequirementsdefinedinSection2.2arecurrentlyimplementedinbothSAS4A/SASSYS-1andSAMthroughfileinputsandoutputs.Directdataexchangethroughmemorycouldbeimplementedinthefuturetoimprovethecouplinginterface.Theexamplesofthedatatransferfiles“SAStoSAM.dat”and“SAMtoSAS.dat”areshowninFigure6andFigure7.Afterthedataisexchanged,itwillbepropagatedintoallrelatedMOOSEobjectsinSAM,includingScalarKernelsandAuxScalarKernelstocalculatethesurrogatecorechannelflowratesandtheflowrateadjustments.

AspecialMOOSEExecutioner,CoupledSASSteady,wasdevelopedtoimplementthecouplingstrategybetweenSAMandSASforsteadystateinitialization.ItinheritsmethodsfromtheregularSteadyExecutioner,butaddssimplifiedmodelsforcouplingboundarycomponentsandadditionalprocessesforcommunicatingwiththeSAScode.ItsprocessflowchartisdepictedinFigure8,wheretheregularprocessesinaSteadyExecutionerareontheleft,andthedashedlinesandblocksontherightareadditionalprocessesforthecoupledcodeexecution.

SpecialmodelingoptionsarealsousedintheCoupledVolumeBranchandCoupledLiquidVolumecomponentsforsteady-stateinitialization.Insteadofusingthesurrogatemodeltocalculatethecorechannelflowrates,constantcorechannelflowratesfromSASareused.Additionally,constantpressureandtemperatureareassumedfortheoutletplenum,whilethepressureandtemperatureoftheinletplenumwillbecalculatedbythecode.Onceaconvergedsimulationisobtained,theinletplenumconditionswillbecheckedwithSASresultsforconsistency.

Similarly,atransientExecutioner,CoupledSASTransient,wasdevelopedforcoupledSAM/SAStransientsimulation.ItinheritsmethodsfromtheregularMOOSETransientExecutioner,butaddsadditionalprocessesforcommunicatingwiththeSAScode,asdepictedinFigure9.Ateachtime-step,SAMwillreadintheSASsimulationresults(fromtheprevioustimestep)andcompleteitsowninneriterationsforthetime-step.Itwillalsocheckifthesimulationtimeissynchronizedinthetwocodes.WhentheSAMtimestepisconverged,SAMwillsendtheresultsatthecouplinginterfaces(inletandoutletplenum)toSAS.ThisisthesameprocessasdepictedinFigure3.


15 ANL/NE-16/22

Figure6:ExampleofSAStoSAM.datfileforSAS/SAMCoupling

STEP0.00000000E+002.50000000E-01NSEG1ISEG112NCHN5ICHN11DATA5.02738439E+025.02738439E+026.28150000E+027.92070772E+02-8.98160471E+02-8.98160471E+023.76658339E-023.76658339E-02-3.76658339E-02-3.76658339E-02-5.09810775E-02-5.09810775E-020.00000000E+000.00000000E+000.00000000E+000.00000000E+00ICHN21DATA1.29659670E+021.29659670E+026.28150000E+027.77447007E+02-2.34923308E+02-2.34923308E+029.82586971E-039.82586971E-03-9.82586971E-03-9.82586971E-03-1.99906354E-01-1.99906354E-010.00000000E+000.00000000E+000.00000000E+000.00000000E+00ICHN31DATA5.74500990E+025.74500990E+026.28150000E+027.75603758E+02-1.17500736E+03-1.17500736E+034.91293485E-024.91293485E-02-4.91293485E-02-4.91293485E-02-5.09113676E-02-5.09113676E-020.00000000E+000.00000000E+000.00000000E+000.00000000E+00ICHN41DATA3.34098683E+013.34098683E+016.28150000E+027.96439451E+02-1.22363928E+03-1.22363928E+035.13559913E-025.13559913E-02-5.13559913E-02-5.13559913E-02-1.57402335E+01-1.57402335E+010.00000000E+000.00000000E+000.00000000E+000.00000000E+00ICHN51DATA2.40600920E+012.40600920E+016.28150000E+028.11907475E+02-3.89099428E+01-3.89099428E+011.63764495E-031.63764495E-03-1.63764495E-03-1.63764495E-03-9.68009690E-01-9.68009690E-010.00000000E+000.00000000E+000.00000000E+000.00000000E+00NPLN2IPLN1DATA-6.00000000E-015.48818671E+056.28150000E+020.00000000E+00IPLN2DATA2.30000000E+001.62850000E+057.83578000E+020.00000000E+00DONE


ANL/NE-16/22 16

Figure7:ExampleofSAMtoSAS.datfileforSAS/SAMCoupling

Figure8:ExecutionProcessFlowChartofCoupledSASSteadyExecutioner

preExecute()+

Converged?+

Data+from+SAS+

End+

Solve()+

postSolve()+

postExecute()+

No+

Yes+

Setup+coupling+interface+

Data+to+SAS+

SAS+Execu>on+

Signal+to+SAS+for+SAVE+and+STOP+

STEP999.751000NPLN2IPLN1DATA-0.6194369.17673.627952.5896327IPLN2DATA2.3170465.05817.250982.5916317


17 ANL/NE-16/22

Figure9:ExecutionProcessFlowChartofCoupledSASTransientExecutioner

4 CouplingResultsTotestthecouplinginterface,anexistingSAS4A/SASSYS-1modeloftheAdvanced

BurnerTestReactor(ABTR)conceptualdesignwasused.DetailsofthisdesignareavailableinReference3.Inthefollowingsections,abriefsummaryoftheABTRreferencemodelisprovided,includingtheprimaryandintermediatesystemlayout.TheSAMmodelisthendescribed.ItisthismodelthatreplacesthePRIMAR-4modelfromtheoriginalreferencemodel.Finally,resultsforanunprotectedlossofflow(ULOF)accidentsequencearepresented.TheresultsshowthatkeyfeaturesoftheULOFtransientarecapturedbythecoupledcode,butthatsomeimprovementsareneeded.Inparticular,controlroddrivelineexpansionandcertainoptionsforgridplateexpansionarenotyetsupported.Thesedifferenceswereexpectedfortheinitialcouplingimplementation.

4.1 ABTRReferenceModel

TheABTRdesignconceptisa250MWtpool-typesodiumfastreactorwithmetalalloyfuel.Thecoreconsistsof54driverassemblies,78reflectorassemblies,48shieldassemblies,andtencontrol-rodassemblies.Ninetestassemblylocationsarereservedformaterialandfueltesting.ThecoreconfigurationisshowninFigure10.

PreExecute()+

Converged?+

Data+from+SAS+

End+

Take+Timestep+

PostExecute()+

No+

End+of+Transient?+

Yes+

Yes+

No+

Setup+Coupling+interface+

Data+to+SAS+

SAS+ExecuAon+

Signal+to+SAS+

PreStep()+

Time+step+Advancing+?+

No+

Yes+


ANL/NE-16/22 18

Figure10:ReferenceABTRCoreConfiguration


19 ANL/NE-16/22

FivecorechannelsareusedtorepresentthecoreassembliesinthereferenceSAS4A/SASSYS-1model.Threeofthechannelsaredefinedbasedonassemblytypeandenrichmentzone.Afourthchannelrepresentsreflectorassemblies,andthefifthchannelrepresentsasingle,inner-corepeakassembly.ChannelassignmentsareshowninFigure11.

TheprimaryvesselconfigurationisshowninFigure12andthePRIMAR-4modelfortheprimary,intermediate,anddecayheatcoolantloopsisillustratedinFigure13.Largesodiumvolumesinthecoolantloopsaremodeledascompressiblevolumes(CVs)inPRIMAR-4.Forexample,CV1istheinletplenum,CV2istheoutletplenum(hotpool)andCV3isthecoldpool.Compressiblevolumesareconnectedbyliquidsegments.Inthismodel,segmentone(S1)isthesegmentrepresentingthecore,anditconnectstheinletplenumtotheoutletplenum.Segmentfour(S4)includestheprimarypumpandpipingthatconnectsthecoldpooltotheinletplenum.

Thecoresegment(S1)isuniquebecausePRIMAR-4usesthesurrogateparametersandEq.(1)toestimatecorechannelflowsduringtheprimarycoolantloopcalculations.Oncetheinletandoutletplenumconditionsareknown,theactualcorechannelflowsaredeterminedbythedetailedtransientcoreheattransferandpre-voidingandboilinghydraulicssolvers.

Figure11:ChannelAssignmentsfortheSAS4A/SASSYS-1CoreModel.


ANL/NE-16/22 20

Figure12:ElevationviewoftheABTRPrimarySystem


21 ANL/NE-16/22

Figure13:PRIMAR-4RepresentationofthePrimary,Intermediate,andDecayHeatCoolantSystems.


ANL/NE-16/22 22

4.2 SAMSystemModel

InacoupledSAS/SAMsimulation,thecoresegmentisstillunique.Inthiscase,however,SAMusesthesurrogateparametersandEq.(1)toestimatecorechannelflowsduringtheprimarycoolantloopcalculations.Oncetheinletandoutletplenumconditionsareknown,theactualcorechannelflowsaredeterminedbythedetailedtransientcoreheattransferandpre-voidingandboilinghydraulicssolversofSAS4A/SASSYS-1.

ThechangestothereferenceSAS4A/SASSYS-1inputarestraightforward.AllPRIMAR-4inputisdeleted,andaSAMSYSinputblockwiththefollowinginputisadded:

Thereferenceelevationsandsteady-stateinlettemperatureandoutletpressurearethesameasthevaluesusedintheoriginalmodel.

Figure14showstheschematicsoftheSAMABTRmodelforthecoupledSAS/SAMsimulation.Theprimarycoolantsystemconsistsoftheinletpiping(pumpoutletandpumpdischarge),thelowerplenum,thereactorcoremodel,theoutletplenum,andtheintermediateheatexchanger.FivecorechannelsweremodeledinSAStodescribethereactorcore.CoupledLiquidVolumeandCoupledVolumeBranchcomponentsareusedtorepresentthecoreoutletplenum(hotpool)andtheinletplenum.BothareconnectedtoimaginarymasssourceandsinksrepresentingtheflowfromandtotheSAScorechannels.Theintermediateloop,thesecondaryloop,andtheDRACSlooparemodeledwithgreatsimplicities.Single-phasecountercurrentheatexchangermodelsareimplementedtomimicthefunctionoftheintermediateloopheatexchanger(IHX),DRACSheatexchanger(DHX),andsecondaryloopheatexchanger(SHX)totransferheatamongtheprimary,intermediate,secondary,andDRACSloops.

Page 1/1untitled text

SAMSYS "ABTR System Model"1

2

path = "<executable path>"3

4

PLENUM "Inlet Plenum"5

Zref = -0.606

Tin = 628.157

END8

9

PLENUM "Outlet Plenum"10

Zref = 2.3011

Pout = 1.6285E+0512

END13

14

SEGMENT "ABTR Core"15

id = 116

inlet = "Inlet Plenum"17

outlet = "Outlet Plenum"18

END19

20

END21

22

23

24


23 ANL/NE-16/22

Figure14:SchematicsoftheABTRmodelforcoupledSAS/SAMsimulations

4.3 VerificationofCouplingInterface

SteadystatesimulationoftheABTRmodelwasfirstperformedtoassurethecorrectinitializationoftheoperatingconditionspriortotransientsimulation.TheprimarypumpheadsatnormalconditionsareadjustedintheSAMmodeltomatchthepressureconditionsinthecoreinletandoutletplenafromSAS4A/SASSYS-1steadystateresults.MajorABTRoperationparameterswereconfirmedinthecoupledSAS/SAMmodel.

Additionally,anulltransientsimulationwasperformedtofurtherverifythefunctionalityoftheSAS/SAMcouplinginterface.ThenulltransientresponsesofmajoroperationparametersareshowninFigure15,whichshowsthatthecoupledSAS/SAMmodelholdssteadystateduringthenulltransient.IdenticalcorechannelflowratesareobtainedfromtheSAMsurrogatemodelandSAScorechannelcalculations,asshowninFigure15d.

TDV$

TDJ$

DHX$

Cold$Pool$Inlet$Plenum$

Outlet$Plenum$(Hot$Pool)$

TDV$

TDJ$

Pump$

IHX$ Na9CO2$HX$

Core$Channels$Modeled$in$SAS$

TDV$


ANL/NE-16/22 24

(a)Massflowrates

(b)Pooltemperatures

(c)Poolpressures

(d)DifferenceincorechannelflowratesbetweenSAMsurrogatemodelandSAS

calculationsFigure15:CoupledSAS/SAMsimulationresultsofABTRnulltransient

0"

200"

400"

600"

800"

1000"

1200"

1400"

0"10"

20"

30"

40"

50"

Mass$Flow$Rate$(kg/s)$

Time$(s)$

IHX_

Prim

aryFlow"

CH1_Flow

"CH

2_Flow

"CH

3_Flow

"CH

4_Flow

"CH

5_Flow

"

600#

620#

640#

660#

680#

700#

720#

740#

760#

780#

800#

0#10#

20#

30#

40#

50#

Temperature)(K))

Time)(s))

Hot#P

ool#

Inlet#P

lenu

m#

0.E+00%

1.E+05%

2.E+05%

3.E+05%

4.E+05%

5.E+05%

6.E+05%

0%10%

20%

30%

40%

50%

Pressure&(Pa)&

Time&(s)&

Cold%Poo

l%Ho

t%Poo

l%Inlet%P

lenu

m%

!0.1%

!0.08%

!0.06%

!0.04%

!0.02%0%

0.02%

0.04%

0.06%

0.08%

0.1%

0%10%

20%

30%

40%

50%

Differences)in)Flow)Rates)(kg/s))

Time)(s))


25 ANL/NE-16/22

4.4 UnprotectedLossofFlowTransientSequence

Thebasicaccidentsequenceanalyzedisthelossofnormalpowertothereactorandintermediatecoolantpumpswithfailureoftheemergencypowersupplies.Theresultisalossofforcedflowintheprimaryandintermediatecoolantcircuits.Inaddition,itisassumedthattheflowrateinthepowercycleloopisreducetozeroimmediatelyfollowingtheaccidentsothattheonlyheatremovalpathisthroughtheemergencydirectreactorauxiliarycoolingsystem(DRACS).Itisalsoassumedthatthereactorsafetysystemisnotactivated,i.e.controlrodsarenotinsertedtoreducereactorpowerimmediately.Thissequenceisanunprotectedloss-of-flow(ULOF)accident.

ThenaturalcirculationDRACSismodeledasasimpleheatexchangerinthisdemonstrationproblem.Inletflowrate,inlettemperature,andoutletpressurearefixedonthesecondarysideasboundaryconditions.TheDRACSisdesignedtoremove0.5%offullpower(1250kW)atnormaloperatingtemperaturesassumingfailureofoneDRACSunit.Initialconditionsfortheaccidentsequencearenormaloperationsatfullpowerandflow.Withthelossofpumpingpower,flowintheprimarycircuitcoastsdownaccordingtothespinninginertiaofthepumpsandmotors.Followingflowcoastdown,naturalcirculationflowisestablished.Withthelossofpower,forcedflowintheintermediatecoolantsystemisalsolost,andcoastsdownaccordingtothecharacteristicsoftheintermediatepumps,whichisassumedtobesimilartotheprimarypumps.

IntheULOFsequence,thereactorsafetysystemfailstoscramthereactor,thusthereactorremainsatfullpowerinitially.Immediatelyfollowingtheaccident,reactortemperaturesincreaseasthecoolantflowratedecreases,andvariousreactivityfeedbackmechanismsreducethereactorpower.Ascoolantflowcontinuestodecrease,asecondtemperaturepeakoccursafterthefullstopofprimarypumpsandbeforefullnaturalcirculationisestablished.Oncenaturalcirculationisestablishedintheprimaryloop,thetemperaturescontinueincreasingslowlybecausetheDRACShasinsufficientheatremovalcapacitytoovercomeboththeearlydecayheatproductionandthestoredheatintheprimarycoolantsystem.Eventually,thedecayheatfallsbelowtheDRACScapacity,andthesystemtemperaturesdecline.

4.5 TransientSimulationResultsofUnprotectedLossofFlow

ResultsfromanalysisoftheearlypartoftheULOFtransient,duringthepumpcoastdownandtransitiontonaturalcirculation,areshowninFigure16–Figure21.ThenormalizedcorepowerandflowrateareshowninFigure16.Thistransientisinitiatedbyacompletelossofforcedcoolantflowintheprimaryandintermediateloops.Boththeprimaryandintermediatepumpsaredesignedwithsufficientflowinertiaanddonotceaseoperationuntilabout420secondsafterthestartofthetransient,followedbyatransitiontonaturalcirculation.Thepower-to-flowimbalanceresultsinsignificanttransientreactorheatingduringthefirst200seconds.

Thetemperaturesatthecoreinletplenum,outletplenum,andthecoldpoolareshowninFigure17.Shortlyafterthetransient,theonlyheatremovalisthroughtheDRACS.Therapidcoreflowreductionduetothepumptripleadstoarapidincreaseofthecoolantandfuelrodtemperaturesinthecoreandthentheoutletplenum.Thedropin


ANL/NE-16/22 26

reactorpowerduetoinherentreactivityfeedbackstabilizesthehotpooltemperature.ColdpooltemperaturescontinuerisingduringthewholetransientbecausethehotcoolantcontinuesenteringthecoldpoolfromtheIHXoutlet.ThiswillcontinueuntiltheDRACSheatremovalcapabilitybecomesequaltothedecayheatproduction,whichwilloccuratabout5hours.Afterthat,thecoldpooltemperaturewilldecreaseasthewholesystemcools.Theinletplenumtemperatureresponsefollowsthesimilartrendofthecoldpooltemperatureresponse,butwithsomedelay.

Peakfuel,peakclad,andcoolantoutlettemperaturesforchannel5(innercorepeakfuelassembly)areshowninFigure18.Thepeakfuel,cladding,andcoolanttemperaturesremainwellbelowthecoolantsaturation(boiling)temperature,withaminimummargintocoolantboilingofnearly300°C.Thissuggeststhatthecorewouldsurviveanunprotectedloss-of-flowaccidentwithoutpinfailuresorfueldamage.Figure19showsthemassflowrateinallcorechannelsduringthetransient.Similarbehaviorsarefound,andtheestablishmentsofthenaturalcirculationflowsoccuratthesametimeforallchannels.

ThetotalcoreflowdifferencesbetweentheresultsfromtheSAMsurrogatemodelandSAS4A/SASSYS-1corechannelmodelareshowninFigure20.Differencesbetweenthetwomodelsareverysmallthroughoutthetransientandarelessthan0.1kg/smostofthetime.Thisdemonstratesthatthesurrogatemodelisabletoaccuratelyestimatethecorechannelflowrate,whichiscrucialfortheconvergencespeedandtheconsistencyinthecoupledSAS/SAMsimulationusingasequentialtwo-waycouplingscheme(asdiscussedinSection2).

ThereactivityfeedbacksduringthetransientareshowninFigure21.AxialandRadialexpansionarethemaincontributorstotheinitialnegativereactivityfeedback,whichcausespowerandfueltemperaturestodecline.ReducedfueltemperaturesprovideapositiveDopplerfeedback,althoughthemagnitudeismodestduetothehighthermalconductivityandrelativelylowoperatingtemperaturesofmetallicfuel.Notethatthereactivityfeedbackduetothecontrol-roddrivelineexpansionarealwayszerointhecoupledSAS/SAMsimulationasthecontrolroddrivelineexpansionisnotsupportedthecurrentcoupling.Negativereactivityduetocontrol-roddrivelineexpansionwouldbeexpectedasthecontrol-roddrivelinesareheatedbyhighertemperaturecoolantshortlyaftertheonsetofthetransient.


27 ANL/NE-16/22

Figure16:NormalizedpowerandcoreflowduringtheABTRULOFtransient

Figure17:Pooltemperaturesduringthetransient

0.01$

0.1$

1$

0$ 200$ 400$ 600$ 800$ 1000$

Normalized

+Pow

er+and

+Flow+

Time+(s)+

Normalized$Core$Power$

Normalized$Core$Flow$

600#

650#

700#

750#

800#

850#

0# 200# 400# 600# 800# 1000#

Tempe

rature)(K

))

Time)(s))

Hot#Pool#

Inlet#Plenum#

Cold#Pool#


ANL/NE-16/22 28

Figure18:TransienttemperaturesforChannel5

Figure19:Corechannelflowvelocitiesduringthetransient

600#

700#

800#

900#

1000#

1100#

1200#

1300#

1400#

0# 200# 400# 600# 800# 1000#

Tempe

rature)(K

))

Time)(s))

Satura0on#Peak#Clad#Temperature#Peak#Fuel#Temperature#Outlet#Temperature#Inlet#Temperature#

0.001$

0.01$

0.1$

1$

0$ 200$ 400$ 600$ 800$ 1000$

Normalized

+Mass+F

low+Rate++

Time+(s)+

CH1$CH2$CH3$CH4$CH5$


29 ANL/NE-16/22

Figure20:TotalcoreflowdifferencesbetweenSAMsurrogatemodelandSAS4A/SASSYS-1

corechannelsimulationresults

Figure21:Transientreactivityfeedback

!1#

!0.8#

!0.6#

!0.4#

!0.2#

0#

0.2#

0.4#

0.6#

0.8#

1#

0# 200# 400# 600# 800# 1000#

Diffe

rences)in)Flow)Rates)(k

g/s))

Time)(s))

!0.5%

!0.4%

!0.3%

!0.2%

!0.1%

0%

0.1%

0% 200% 400% 600% 800% 1000%

Reac%v

ity*($

)*

Time*(s)*

Net% Doppler% Axial% Radial% CRDL% Coolant%


ANL/NE-16/22 30

Thestand-aloneSAS4A/SASSYS-1simulationresultsoftheABTRULOFtransientarealsocomparedwiththecoupledSAS/SAMresults.ForconsistencywiththeSAMprimaryloopmodeling,theperfectmixingpoolmodelsareusedinthestand-aloneSAS4A/SASSYS-1simulation.

NormalizedcorepowerandflowratearecomparedinFigure22.Verysimilarcorepowersandflowrateswerepredictedthroughoutthetransientinthetwosimulations.Verysmalldifferencesinreactorpowerwerefoundintheinitial50sduetodifferencesinreactivityfeedbackduetocontrol-roddrivelineexpansion,andbetween390and410softhetransientduetodifferencesincoreflowratesandtemperatures.Thecoreflowrateswerealmostidenticalforthefirst150seconds,butdeviateslightlyfromeachotherlaterduetothedifferencesinpumpandloopfrictionmodeling.Thelargerdifferencesinflowratesbetween390and410sareattributedtodifferencesinmodelingthepumpresistanceafterthefullstopofthepumpimpeller.

Peakfuel,peakclad,andcoolantoutlettemperaturesforchannel5inthestand-aloneSAS4A/SASSYS-1simulationareshowninFigure23,andthereactivityfeedbacksareshowninFigure24.Notethatthereactivityfeedbacksduetocontrol-roddrivelineexpansionwereincludedinthestand-aloneSASsimulation.ComparingtheseresultstothecoupledSAS/SAMsimulation(Figure18andFigure21),thetransientresponse(bothtrendsandmagnitudes)areverysimilarbetweenthetwosimulations.

ThisdemonstrationsimulationfocusesontheearlystageoftheULOFtransient.ItshowsthatmajorphysicsphenomenaintheprimarycoolantloopcanbecapturedbythecoupledSAS4A/SASSYS-1andSAMsimulations.SomedifferenceswerefoundinthecoupledSAS/SAMsimulationresults.Thesecanbereducedbyaddressingtheknownmodelingdifferencesbetweenthetwosimulations.


31 ANL/NE-16/22

Figure22:Normalizedpowerandcoreflow,comparisonbetweenstand-aloneSASand

coupledSAS/SAMsimulationresults

Figure23:TransienttemperaturesforChannel5,stand-aloneSASsimulation

0.01$

0.1$

1$

0$ 200$ 400$ 600$ 800$ 1000$

Normalized

+Pow

er+and

+Flow+

Time+(s)+

Coupled0Core$Power$

Coupled0Core$Flow$

SAS$StandAlone0Core$power$

SAS$StandAlone0Core$Flow$

600#

700#

800#

900#

1000#

1100#

1200#

1300#

1400#

0# 200# 400# 600# 800# 1000#

Tempe

rature)(K

))

Time)(s))

Satura0on##Peak#Clad#Temperature#Peak#Fuel#Temperature#Outlet#Temperature#Inlet#Temperature#


ANL/NE-16/22 32

Figure24:Transientreactivityfeedback,stand-aloneSASsimulation

5 PathForwardSAS4A/SASSYS-1withPRIMAR-4willcontinuetobethemainworkhorseforSFR

safetyanalysisinthenearterm.AndthesevereaccidentmodelingcapabilitiesinSAS4A/SASSYS-1(sodiumboiling,fuelmeltingandrelocation)willcontinuetoplayavitalroleforalongtime.Therefore,theSAS4A/SASSYS-1modernizationeffortshouldremainahighprioritytaskundertheARTprogramtoensurecontinuedparticipationindomesticandinternationalSFRsafetycollaborationsanddesignoptimizations.Ontheotherhand,SAMisanadvancedsystemanalysistool,withimprovednumericalsolutionschemes,datamanagement,codeflexibility,andaccuracy.SAMisstillinearlystagesofdevelopmentandwillrequirecontinuedsupportfromNEAMStofulfillitspotentialandtomatureintoaproductiontoolforadvancedreactorsafetyanalysis.TheefforttocoupleSAS4A/SASSYS-1andSAMisthefirststepontheintegrationofthesemodelingcapabilities.ContinueddevelopmentonSAS/SAMcouplingwillbeneededtoincludethemissingreactivityfeedbacks(controlroddrivelineexpansionandvesselelongation),themissingcomponentmodels,andtoimprovetheefficiencyofthecouplinginterface.Overtime,theadvancedmodelingandsimulationcapabilitiesprovidedbyNEAMSareexpectedtoplaymoreandmoresignificantrolesinadvancedreactorsafetyanalyses.

!0.4%

!0.35%

!0.3%

!0.25%

!0.2%

!0.15%

!0.1%

!0.05%

0%

0.05%

0.1%

0% 200% 400% 600% 800% 1000%

Reac%v

ity*($

)*

Time*(s)*

Net% Doppler% Axial% Radial% CRDL% Coolant%


33 ANL/NE-16/22

6 References1. T.H.Fanning,ed.,TheSAS4A/SASSYS-1SafetyAnalysisCodeSystem,ANL/NE-12/4,

NuclearEngineeringDivision,ArgonneNationalLaboratory,January31,2012.2. R.Hu,T.H.Fanning,T.Sumner,Y.Yu,“StatusReportonNEAMSSystemAnalysisModule

Development,”ANL/NE-15/41,ArgonneNationalLaboratory,December2015.

3. Y.Chang,P.Finck,andC.Grandy,“AdvancedBurnerTestReactorPreconceptualDesignReport,”ANL-ABR-1,ArgonneNationalLaboratory,Sept.5,2006.

Argonne National Laboratory is a U.S. Department of Energy laboratory managed by UChicago Argonne, LLC

Nuclear Engineering Division Argonne National Laboratory 9700 South Cass Avenue, Bldg. 208 Argonne, IL 60439-4842 www.anl.gov

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