NuclearEnergyandTechnology2(2016)114–118
www.elsevier.com/locate/nucet
Evolution
of
the
CYCLE
code
for
the
system
analysis
of
the
nuclear
fuel
cycle
A.G.
Kalashnikov
∗,
A.L.
Moseev
,
V.M.
Dekusar
,
V.V.
Korobeynikov,
P.A.
Moseev
Joint Stock Company "State Scientific Centre of the Russian Federation – Institute for Physics and Power Engineering named after A. I. Leypunsky" (IPPE), 1, Bondarenko Sq., Obninsk, Kaluga Region, 249033 Russia
Availableonline24May2016
Abstract
The CYCLEcodeis intendedto simulatemathematically theoperationof anuclearpowersystem (NPS)withthermal andfast reactors inanopenor closednuclearfuelcycle,to developscenariosofefficientnuclearpower evolutionin Russiaandto analyzetrendsin global nuclearpower.Thecode isbasedonawell-knownsoftwareprogram,WIMSD-5B,broadlyusedforthedesignofthermalreactorcells,and ona2D multi-group softwaresystem,RZA, forthefast neutronreactor simulation.The CYCLEcode wasdevelopedatIPPEinObninsk. ThispaperpresentsabriefreviewofthecapabilitiesandinformationonthecurrentstatusoftheCYCLEcode.Thecodeallowssimulationof keyfacilities oftheexternalfuelcycle(fuelfabricationandreprocessingfacilities,SNFstorage,uranium,plutonium,neptunium,americium and curium stores, RW long-term storage sites), nuclear reactors, including RBMK-1000 reactors, existing and advanced VVER reactors (usingdifferentfueltypes),and fastreactors(bothexisting andinnovative).Asanimportantfeature,theCYCLEcode allowstheevolution ofthefuel’snuclidecompositionbothinreactorsandattheexternalfuelcyclephasetobeconsideredin details.Offeredasanextraoption isthe capabilityto calculateavarietyof thenuclearfuelcyclecostparameters fornuclearpowerplantswiththermaland fastreactors.For years,the code hasbeensuccessfullyusedaspartof INPRO,aninternationalinnovativenuclearreactorand fuelcycleproject.Theresults ofstudiesintotheRussianNPSevolutionscenarioswerepresentedatGlobal2011.SomeotheroftheCYCLE-basedsimulationresultswere presentedatGlobal2015.
Copyright© 2016,NationalResearchNuclearUniversityMEPhI(Moscow EngineeringPhysicsInstitute).Productionandhostingby ElsevierB.V.Thisisanopenaccess articleunderthe CCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Fuelcycle;Simulation;Modeling;Code;Scenario;Thermalreactor;Fastreactor;Nuclidecomposition;Recycling;Plutoniumequivalenting;Store; Minoractinides.
Introduction
The CYCLE code is intended to simulatemathematically nuclearfuel cycles, developscenarios for effective evolution of nuclearpower inRussia,andanalyzetrendsin global nu-clearpower.Thesystemhasbeensuccessfullyusedin interna-tionalstudiesaspartof INPRO,aninnovativenuclearreactor andfuel cycle project. A greatdeal of emphasiswas placed
∗ Correspondingauthor.
E-mail addresses: [email protected](A.G.Kalashnikov),[email protected]
(A.L.Moseev),[email protected](V.M.Dekusar),[email protected](V.V. Ko-robeynikov),[email protected](P.A.Moseev).
Peer-reviewunderresponsibilityofNationalResearchNuclearUniversity MEPhI(MoscowEngineeringPhysicsInstitute).
Russian textpublished:Izvestia VisshikhUchebnikh Zavedeniy. Yader-nayaEnergetika(ISSN0204-3327),2016,n.1,pp.91-99.
in the development of the CYCLE code on the description andconsideration of peculiarities inherent insimulation of a closednuclearfuel cycle(CNFC)withfast andthermal reac-tors.Thecode wasdevelopedatIPPEinObninsk.Theinitial developmentstage of the CYCLE code (CYCLETR) was
de-scribed in[1] .The activitiesatthat stagewerelimited tothe simulation of the VVER-type reactor fuel cycle (NFC) with the fuel isotopic composition and radiological and environ-mentalcharacteristics trackedin the followingchain: mining ofnaturaluranium– conversion– enrichment– fuelassembly (FA) fabrication– reactor – spentnuclear fuel (SNF) pool– interimstorage – SNFlong-termstorage(or disposal).Itwas alsopossibletosimulateVVERreactorspartiallyloadedwith MOX fuel, with a constant isotopic composition of loaded plutonium.Since then, thefunctionality of thecode hasbeen expanded drastically andisdescribed herein.
http://dx.doi.org/10.1016/j.nucet.2016.05.008
2452-3038/Copyright© 2016,NationalResearchNuclearUniversityMEPhI(MoscowEngineeringPhysicsInstitute).ProductionandhostingbyElsevier B.V.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).
EvolutionoftheCYCLEcode
Presently, the CYCLE code allows modeling a two-component nuclearpowersystem(NPS) themodel of which, in addition to thermal reactors with uranium oxide (UOX) fuel, includes fast reactors and enables multiplerecycling of plutonium, uranium and minor actinides. It is also possible tousemixeduranium-plutoniumoxide(MOX)fuel ornitride fuel witha variableuraniumand plutonium contentfor ther-mal reactors. A fuel cycle with a fuel processing capability, including the use of natural, depleted and reprocessed ura-nium, plutonium, neptunium, americium and curium stores, is considered.
Thesimulationresultsforthefuelcycleofthermalreactors withUOXfuel(TRUOX),involvingtheformationof uranium,
plutonium and MAstores,are used as the input for the sim-ulation of the plutonium fuel reactor operation as part of a nuclear powersystem.
Plutonium fuel reactors are started both using plutonium generated in power reactors and plutonium obtained from other sources. The latter suggests that the initial character-istics of the given plutonium store should be given rather than calculated. Different physical and logical topologies of plutonium storesarepossible.Thus,itis possibletosimulate the evolution of nuclearpower based oncombined operation of TRUOX, thermal reactors with a partial MOX fuel load
(TRMOX) and fast reactors. And thermalreactors with a
par-tial MOX load are assigned the role of plutonium burners, while fast reactors (FR) enable degradation of the plutonium isotopic vector to be stopped during plutonium recycling in thermalreactors.AsimplifiedflowchartoftheNFCsimulated in theCYCLE code is presentedin Fig. 1.
Calculationresults
The major calculation results are the time dependence of materialflowsattheNFCstagesandtheevolutionofisotopic vectors. Besides, the following characteristics are calculated: fuel activity (Bq), radiotoxicity by air (Sv), radiotoxicity by water (Sv), neutronsource dueto spontaneous fission of ac-tinides (n/s), neutron source due to oxygen-based (α,n) re-action (n/s), total neutron source (n/s), actinide heat (kW), fission fragmentheat (kW), totaldecay heat.
Thenuclidelistincludesallheavynuclideswithahalf-life ofover46days,includingstableisotopesofleadandbismuth. The rest of the nuclides are assumed to be in equilibrium with their precursors. The concentrations thereof are taken into account for the calculationof other fuel characteristics: activity, radiotoxicity, neutronsource andheat.
Reactor commissioning
Reactors of the specified type are commissioned and de-commissioned inaccordancewiththe giventimedependence and reactor operating time. In the process of operation, it is possible to convert thermal reactors with uranium fuel to a
partial MOX fuel load for burning the plutonium built up in the system.
Fuel cycle’spre-reactor stages
The fuel is enriched uranium or mixed fuel. The pre-reactor stages are: uranium mining, conversion, enrichment, FAfabrication(foruraniumfuel),retrievaloffuelcomponents fromstores, repeatedremoval of americium fromplutonium, andFA fabrication(for mixed uranium-plutonium fuel).
Annualand integral valuesare determined for the follow-ing:
− consumption of natural uranium and other fuel compo-nents;
− separativework;
− accumulation of depleteduranium;
− accumulation of americium from its possible repeated re-movalfrom plutonium;
− consumption of mixedfuel components from stores; − demandsfor UOX andmixed fuel fabrication.
− uranium,plutoniumandMAlossesattheabovefuelcycle stages.
Forreactors with mixed uranium-plutonium fuel,retrieval of fuel components from uranium, plutonium, neptunium, americiumand curium stores is modeled. It shouldbe noted that components may be retrieved starting from “older” or freshbatchesor evenly.The contentof plutoniuminthe fab-ricatedfuel,inthe eventitsnuclidecomposition differsfrom the base composition, is adjusted. The adjustment is based onthe condition of maintaining thereactor cycle durationin accordancewiththeplutoniumequivalentingprocedure[2] or byuse of direct calculations.
The following istaken into account inthe fuel fabrication
− achangeinthenuclidecompositionofthefuelcomponents inthe courseof storage;
− possible repeated removal of americium from the pluto-niumretrieved from the plutonium store;
− lossesofcomponentsduringfactory-basedfuelfabrication; − achangeinthe nuclidecompositionof fuelfrom thetime
of the fabricationtillthe loading intothe reactor. The lossesof fuel components are shipped for disposal.
Fuel cycle’sreactor stages
− Calculationof the heavy metal quantities loaded annually for the reactor startup and refueling as specified by the givenscenario.
− Calculation of the spent fuel nuclide composition in a rangefrom thorium isotopes tocurium isotopes.
− The input and output nuclide compositions may be given as initialdata.
Fig.1. ModeldiagramofaCYCLE-simulatedNFC.
− Changes in the isotopic composition in fast reactors are simulated by direct calculationof the reactor,with regard for its partial refueling, and those for a thermal reactor are simulatedthroughthecalculationofthe burnupinfuel assemblies (FA). This involves the use of the following external procedures:
° for fast reactors – the RZA 2D multi-group software system[3] ,tosimulatethereactoroperationina steady-state mode withregard for refueling;
° for thermal reactors – the WIMSD-5B reactor FA cal-culation software package [4] ,using WIMSD-IAEA, a 172-group library [5] .
Fuel cycle’spost-reactor stages
Changes in the nuclide composition (nuclides of heavy metals in a range from Pb to Cm with a half-life of over 46days)andsuch SNFcharacteristics asactivity (Bq),water andairradiotoxicity (Sv),neutronsourceanditscomponents (n/s), and decay heat components (kW) are modeled at the followingNFC stages:
− inthe spentfuel pool;
− duringintermediateSNF storage;
− during SNF retrieval from storage and SNF reprocessing at areprocessingfacility;
− when batches of reprocessed uranium, plutonium, neptu-nium, americiumandcurium received at stores– changes
in the nuclide composition, depending on time, are ac-counted for all stores;
− inside a repositoryor long-term storage (for a repository, characteristics are traced for up to107 years).
SNFreprocessing plants
Aspart of theCNFC, irradiatedfuel is reprocessedin ac-cordance with the given reprocessing plant capacity, while extractedplutonium,uranium,neptunium,americium,curium andfission products (FP)are shipped to stores.
Handling ofuranium stores
Uranium inventoriesare formed bythree components: (a)depleteduraniumresultingfromenrichment ofuranium
for thermal reactors, depleted uranium resulting from enrichment of uranium for the BN-350, BN-600, re-search andotherreactors, or from othersources; (b) reprocessed uranium resulting from reprocessing of
thermalandfast reactor fuel; (c)natural uranium.
Plutonium store balance
The plutonium inventory minimization algorithm used in the CYCLEcode todevelopnuclearpower evolution scenar-ios is described in[6] .
Fig.2. NFCflowchart.
Handling of plutoniumstores
The simplest case is accumulation of extracted power-grade plutonium from fast and thermal reactors at one cen-tralized store.A morecomplex fuel cycle permitsthe use of up to three stores to keep plutonium from different sources with a possibility to change the store handling logic in the scenario modeling process.
An option to handle stores for extracted plutonium from different sources is shown in Fig. 2 as an NFC flowchart which, provided there is aparticular ratio betweenthe num-bers of reactorsof different types, enableselectricity genera-tion tobestabilized atacertainlevelachieved withcomplete SNF reprocessingand plutonium utilization.
Economics
The CYCLEcodesupportsacalculationprocedurefor se-lected cost indicators of the nuclear fuel cycle for a nuclear power plantwith fast andthermalreactors.
The procedure is used primarilyto calculate the constant levelized cost of afuelcycle per kWof electricitygenerated for the entire NPP operating time.
Cost indicators of the nuclearfuel cycle
Theoperationsinvolvedinanuclearfuelcycleandin han-dlingof respectivewaste,inarange fromthe miningof ura-nium ore to the final disposal of high-level waste, normally encompassaperiodof50to100years.Asarule,these opera-tions aredivided intotwo stages:the initialstageor frontend (when nuclear fuel is prepared for being used in the reac-tor) andthe finalstage or backend(including irradiated fuel handling).
Thefrontendincludesprocessesrangingfromthepurchase of uraniumore tothesupplyof finishedFAstothe NPP.The backend starts from the transfer of spent nuclear fuel to a detachedstorageor toaspentfuelreprocessingsiteandends withthe final disposalof vitrified high-level wastefollowing the reprocessing (aclosed fuel cycle) or immediately encap-sulated SNF (direct disposal option).
Normally, a comparative analysis of different fuel cycles includes a comparison based on the cumulative cost of the fuel cycle frontendand backendknown as the levelized unit fuel cost (LUFC) of electricity.
The costat the fuel in-reactorstage isnormally classified as operating cost.
AcalculationoftheLUFC forelectricityusesaprocedure developedbytheNuclearEnergyAgencyoftheOrganization for Economic Cooperation and Development (OECD/NEA) based on generalized practices for the calculation of the in-vestment cost at different nuclear fuel cycle stages used in market economies [7] . This procedure is based on the net present value concept that takes into account the disparities in the money expenditures during fuel handling and in the earningsfrom electricitygeneration.
Thisinvolves the followingassumptions:
− the cash flows in time are known during the project im-plementation;
− the interest (discount) rate has been determined based on whichfunds maybe investedin the givenproject. The cost islevelized withrespect to the selected baseline date for each cycle stage given the time range covering the stageinquestion.
The fuel cost is the relation of the total of the levelized expenditures for the entire NPP nuclear fuel lifecycle tothe levelized electricityoutput for the sameperiod.
Thenotionofthe levelizedfuelcostisoneof therequired estimationtoolstocomparetheeconomicefficiencyof differ-entfuelcyclesandthepowerplantsassuchatthetechnology selectionstage.
Inmoredetails,theprocedureusedandtheprogram mod-ulesdeveloped onits basis are described in[8] .
Amortizationand Operation & Maintenancecosts
The Levelized Unit Amortization Cost (LUAC) and the LevelizedUnitOperation&Maintenance(LUAM)costofthe unitelectricity generationare estimated basedon theINPRO procedure[9] .
Levelized UnitEnergyCost
The Levelized UnitEnergy Cost (LUEC) is found as the totalof three components:
LUEC=LUFC+LUAC+LUOM. NFCsimulation results
Someoftheresultstoillustratethemodelingofthenuclear powerevolutioninRussiaandinotherex-USSRcountriesare presented in[10–13] .
CYCLEcode status
Since 2010, the code has been broadly used in analyti-cal feasibility studies for the introduction of the CNFC in Russia’sNPS. ThemodelingresultswerepresentedatGlobal 2011 and Global 2015, and were also used to analyze the NPS evolutionscenariosusing the INPRO methodology.
In2013,theRussianFederationregistrationcertificatewas obtained for the code.The copyright holder isIPPE.
In conclusion, the authors express their acknowledgment to V.Ye. Korobitsyn, Ye.N. Kapranova and Z.N. Chizhikova for cooperation.
References
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[2] A.M.Yatsenko,A.N.Chebeskov,V.S.Kagramanyan,A.G.Kalashnikov, Izv.Vuzov.YadernayaEnerg.(1)(2012)31–41(inRussian).
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[4] NEA-1507/04,WIMSD-5B.12,Deterministic Multigroup Reactor Lat-tice Calculations. Available at http://www.oecd-nea.org/tools/abstract/ detail/nea-1507/,(25.02.04).
[5] WIMS-D Library Update: Final Report of a Coordinated Re-search Project,InternationalAtomicEnergyAgencyPubl.,Vienna,2007.
[6] P.A.Moseev,V.V.Korobeynikov,A.L.Moseev,Izv.Vuzov.Yadernaya Energ.(2)(2013)123–132(inRussian).
[7] TheEconomicsoftheNuclearFuelCycle,OECD,1994.
[8]Dekusar V.M., Kolesnikova M.S., Chizhikova Z.N. Metodika i pro-gramma rascheta toplivnoy sostavlyayushchey stoimosti proizvodstva elektroenergii naAESsteplovymi i bystrymireaktorami.(AMethod andaCodefortheElectricityFuelCostCalculationatNPPswithFast and ThermalReactors). PreprintSSC RF-IPPE-3243, IPPE,Obninsk, 2014(inRussian).
[9]INTERNATIONAL ATOMIC ENERGY AGENCY, Guidance for the Application of an Assessment Methodology for Innovative Nuclear Energy Systems, INPRO Manual – Economics, Volume 2 ofthe Fi-nalReport ofPhase 1 ofthe International ProjectionInnovative Nu-clear Reactorsand Fuel Cycles(INPRO), IAEA,Vienna, 2008 TEC-DOC-1575/Rev.1.
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[13]V.Kagramanyan,V.Usanov,A.Kalashnikov,S.Kvyatkovskiy,in: Pro-ceedings of theGlobal 2015,Paris (France), September 20-24, 2015 Paper5115.
