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HandbookofSmallModular NuclearReactors ModularNuclearReactors SecondEdition
Editedby
DanielT.Ingersoll
FormerDirectorofResearchCollaborationsat
MarioD.Carelli
FormerChiefScientistforResearch&Technology
WoodheadPublishingisanimprintofElsevier
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Copyright©2021ElsevierLtd.Allrightsreserved.
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ThisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythePublisher (otherthanasmaybenotedherein).
Notices Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchandexperiencebroaden ourunderstanding,changesinresearchmethods,professionalpractices,ormedicaltreatmentmaybecome necessary.
Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluatingand usinganyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuchinformation ormethodstheyshouldbemindfuloftheirownsafetyandthesafetyofothers,includingpartiesforwhom theyhaveaprofessionalresponsibility.
Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors,assumeany liabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproductsliability,negligenceor otherwise,orfromanyuseoroperationofanymethods,products,instructions,orideascontainedinthe materialherein.
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ISBN:978-0-12-823916-2(print)
ISBN:978-0-12-823917-9(online)
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Dedication Thisbookisdedicatedtoallpioneers,practitioners,andfirstadoptersof smallmodularreactorswhoarecollaboratingtocreatethefutureof nuclearenergy.
Contributors KathleenArau ´ jo EnergyPolicyInstitute,BoiseStateUniversity,Boise,ID, UnitedStates
RobertA.Bari BrookhavenNationalLaboratory,Upton,NY,UnitedStates
NicholasJ.Barron ReactorCoreTechnology,NationalNuclearLaboratory, Sellafield,UnitedKingdom
RandallJ.Belles OakRidgeNationalLaboratory,OakRidge,TN,UnitedStates
GeoffreyBlack DepartmentofEconomics,CollegeofBusinessandEconomics, BoiseStateUniversity,Boise,ID,UnitedStates
RichardL.Black Consultant,McLean,VA,UnitedStates
S.Boarin PolitecnicodiMilano,Milan,Italy
ShannonM.Bragg-Sitton IdahoNationalLaboratory,IdahoFalls,ID,UnitedStates
M.D.Carelli FormerlyofWestinghouseElectricCo.,Pittsburgh,PA,USA
Lap-YanCheng BrookhavenNationalLaboratory,Upton,NY,UnitedStates
SuhnChoi KoreaAtomicEnergyResearchInstitute,Daejeon,RepublicofKorea
DaraCummins IndependentContractor,Loudon,TN,UnitedStates
DarioF.Delmastro NationalAtomicEnergyCommissionandUniversidadNacional deCuyo,SanCarlosdeBariloche,Rı´oNegro,Argentina
D.Goodman Consultant,USA
KevinW.Hesketh FuelandCore,NationalNuclearLaboratory,Preston,United Kingdom
JacquesHugo JacquesHugoAssociates,Pretoria,SouthAfrica
DanielT.Ingersoll NuScalePowerLLC(retired),OakRidge,TN,UnitedStates
VladimirKuznetsov Consultant,Austria
S.Lawler Rolls-Royceplc,Derby,UK
G.Locatelli UniversityofLincoln,Lincoln,UK
M.Mancini PolitecnicodiMilano,Milan,Italy
GaryMays OakRidgeNationalLaboratory,OakRidge,TN,UnitedStates
TsutomoOkubo JapanAtomicEnergyAgency(retired),Oarai-Machi,Japan
BojanPetrovic GeorgiaInstituteofTechnology,Atlanta,GA,UnitedStates
Edward(Ted)Quinn TechnologyResources,DanaPoint,CA,UnitedStates
M.Ricotti PolitecnicodiMilano,Milan,Italy
DavidShropshire NuclearScienceandTechnologyDirectorate,IdahoNational Laboratory,IdahoFalls,ID,UnitedStates
DanrongSong NuclearPowerInstituteofChina,Chengdu,People’sRepublicof China
NeilTodreas MassachusettsInstituteofTechnology,Cambridge,MA,UnitedStates
N.Town Rolls-Royceplc,Derby,UK
AndrewWorrall OakRidgeNationalLaboratory,OakRidge,TN,UnitedStates
MetinYetisir AdvancedReactorTechnologies,CanadianNuclearLaboratories, ChalkRiver,ON,Canada
Preface Themoderneraofsmallmodularnuclearreactorsbeganroughlyattheturnofthe millennium.Smallersizednuclearreactorshavebeenapartofthenuclearheritage fromitsbeginninginthe1950s.However,designingofnewnuclearplants,small andlarge,waslargelysuspendedduringthe1990swhencountriessuchastheUnited Statesexperiencedalowdemandfornewgeneratingcapacityandothercountriessuch asFrance,Japan,andtheRepublicofKoreaproceededtodeploystandardizedplant designs.Neartheconclusionofthe1990s,theUSgovernmentinitiatedaresearchprogramtostimulatetheidlednuclearindustryandspecificallytargetedthedevelopment ofsmaller,morerobustnuclearplantdesigns.
OneofthedesignsthatemergedfromtheUSresearchinitiativewastheInternationalReactorInnovativeandSecure(IRIS)design,whichwasdevelopedbyaninternationalconsortiumofpartnersthateventuallyspannedmorethan20organizationsin 10countries.TheteamwasledbyDr.MarioCarelli,ChiefScientistatWestinghouse ElectricCompany(WEC),andconsistedofadiversesetofacademic,research,and industrialpartners.OneofthosepartnerswasOakRidgeNationalLaboratory (ORNL).Dr.DanielIngersoll,aSeniorProgramManageratORNL,ledORNL’sparticipationintheIRISprojectuntil2008whenhewasassignedtechnicalleadershipofa newprograminitiatedbytheUSDepartmentofEnergyfocusedonresearchand developmentofsmallmodularreactors.
Bytheendof2010,severalnewSMRdesignshademergedintheUnitedStatesand globally,andcustomerinterestinanewgenerationofdesignswasexpandingrapidly. Inlate2011CarelliwasapproachedbyWoodheadPublishingtoserveasEditorfora newprojecttopublishahandbookonsmallmodularnuclearreactors.Giventhesize oftheprojectandthedynamicnatureofthetopic,CarelliinvitedIngersolltojoinas coeditor.Atthesametime,IngersollleftORNLandmovedtoNuScalePower,arelativelynewcompanydedicatedtothedesignofanespeciallyinnovativeSMR.Carelli andIngersollcollaboratedtodevelopthescopeandorganizationoftheHandbookand amassedacollectionof20expertstocontributespecificchaptersfocusedonmany differentaspectsofSMRs.Thefirsteditionofthe HandbookofSmallModular NuclearReactors wasreleasedattheendof2014.
AsecondeditionoftheHandbookwasrequestedbythepublisherin2019.The resultisthisnewlyupdatedandexpanded HandbookofSmallModularNuclearReactors.Significantchangesincorporatedintothissecondeditionincludethefollowing:
– ThecreationofafinalPartVdevotedtobroadinternationalmarketsandperspectives.
– Theupdatingofmostchapterstoincludenewdevelopmentsoccurringduringthe5years sincereleaseofthefirstedition.
Theadditionofthreenewchapters:twoinPartIV(R&DactivitiesinCanadaandtheUnited Kingdom)andoneinPartV(globalmarketassessment).
Theenergylandscapeandespeciallythenuclearenergylandscapecontinuestoevolve inaverydynamicandsomewhatunpredictablefashionasenergydemandchanges, oldtechnologiesareabandoned,newtechnologiesareintroduced,andsociopolitical policiesfluctuate.ItisourhopethatthisupdatedHandbookwillprovidethereader withthebest,mostaccurateunderstandingofthestateoftheartinsmallmodular nuclearreactors.
TheEditors
Introduction Thishandbookprovidesathoroughandauthoritativeintroductiontotoday’shottest newdevelopmentinnuclearplantdesignanddeployment:smallmodularreactors (SMRs).Buildingontheglobalsuccessoflargenuclearplants,SMRsofferthepotentialtoexpandtheuseofclean,reliablenuclearenergytoabroaderrangeofcustomers andenergyapplications.
Theearlycommercialnuclearpowerreactorsdesignedandbuiltfromthe1950s and1960swerelow-powerplants(uptoafewhundredmegawatts)andwerebuilt todemonstratethecommercialviabilityofnuclearenergy.Theseplantswerecomparablewiththeirfossil-fueledcounterparts,bothinoutputandconstructiontime(afew years).Theyweremoderatelysuccessful;however,theirunitcapitalcosts($/kW) weresubstantiallyhigherthanforcomparablefossilplants.Asthenuclearplantcost keptincreasingtoimproveperformanceandsafety,itbecamenecessarytoalso increasetheoutputpowertomaintaincompetitiveenergyprices;thustheplantsize increasedrapidlyfromafewhundredsofmegawattstonearly2000MWtoday.Sucha drasticincreasehadseveraleffects:Onlyafewmanufacturers,eitherlargeconglomeratesorstate-ownedenterprises,remainedinoperationworldwide;plantcosts becamestratospheric,creepingintotensofbillionsdollars;andthetimefromcontract signingtoinitiatingpowerproductionexceededadecade.
Startinginthe1990snewSMRdesignsemergedworldwideandhavegained increasingmomentuminthenewmillenniumwiththeintenttocomplementlarge plantsandofferamorediverseoptiontopotentialcustomers.Thenewsmallplants haveseveraltraitsincommonwithearlierdesigns,suchassize(fromtenstoafew hundredsofmegawatts),relativesimplicity,andashorterconstructiontimeowing toincreasedfactory-basedfabrication.Also,SMRscancoverawiderangeofapplicationsanddeploymenttimes.Thoseproposedforpower-producingapplicationsin theshorttermaredesignsofthelightwaterreactor(LWR)type,whileSMRsbest suitedforotherapplicationssuchasfuelbreedingandwasteburningemploydifferent coolantsandaredeployableoverthelongterm.
ManydevelopersofSMRs,eventhenear-termLWRs,arequitedifferentfromthe largeLWRmanufacturers.Theyincludesmaller-sizedmanufacturersandnewenterprises.Forexample,thetwoLWR-basedSMRvendorsintheUnitedStatesarecurrentlyNuScalePower,anentirelynewenterprisededicatedtoaspecificSMRdesign, andHoltecInternational,arecognizedleaderinfuelstoragefacilitiesbutnewtoreactordesign.TheinternationalSMRdevelopmentcommunityreflectsasimilardemographicwithmanydesignsevolvingfromtheresearchcommunityornontraditional suppliers.
Thishandbookiscomposedof23chaptersstructuredintofiveparts,eachchapter beingauthoredbyarecognizedexpertinthefield.
l PartI(FundamentalsofSMRs)providesacomprehensiveintroductiontoSMRtechnologies,existingcommercialdesigns,andfundamentaldesignstrategies.ThethreeauthorscontributingtothissectionhavebeeneminentproponentsofSMRssincethe1990sandhaveled thedevelopmentofintegralpressurizedwaterreactor(iPWR)designs,whicharetheprevailingdesignstrategyforSMRsandthefocusofthishandbook.PartIisarticulatedover threechapters:overviewofSMRfeaturesandtechnologies,reviewofseveralcurrentSMRs beingdevelopedanddeployedworldwide,andanintroductiontoiPWRsasaspecificSMR designcategory.
l PartII(SMRtechnologies)reviewsthekeytechnologiesthatarefundamentaltotheiPWR design,focusingonwhatisnewanddifferentwhilealsoprovidinginsightonpotential opportunitiesandchallenges.Sixchapters,writtenbyinternationallyrecognizedauthorities intheirfield,addressseveralbasicSMRtechnologies:thereactorcoreandfuel,reactorsystemcomponents,performancemonitoringandcontrol,human-systeminterfaces,safety,and proliferationresistanceandphysicalprotection.
l PartIII(Implementationandapplications)addressesfourkeyareascriticaltosuccessful deploymentofSMRs:economicsandfinancing,hybridenergysystemsusingSMRs,licensing,andmanufacturingmethods.AswithPartIIthefourauthorsofPartIIIarerecognized authoritiesintheirfield.
l PartIV(InternationalR&Danddeployment)reviewsstate-of-the-artprojectsandprograms forSMRdevelopmentanddeployment.Eightchaptersfocusoncountriesthataremost activeinthedevelopmentanddeploymentofSMRs,presentedinalphabeticalorder:Argentina,Canada,China,Japan,RepublicofKorea,Russia,theUnitedKingdom,andtheUnited States.Theauthorsareaccomplishedresearchersanddirectlyinvolvedintheircountry’s SMRactivities.
l PartV(Globalperspectives),composedofjusttwochapters,providesatimelysnapshotof theglobalmarketforSMRsandalsooffersatimelessperspectiveonhowSMRdeployment mightimpacteconomicgrowthandenvironmentalconditionsindevelopingcountries.Itisa reminderthatSMRspromisenotonlytobeabetterandmoreeconomicalsolutionfornew energybutalsopromoteimprovedopportunitiesandqualityoflifeinemergingeconomies.
ThishandbookisintendedtobeusefultothosewithageneralinterestinSMRs,aswell astothoselookingfordetailedtechnicalinformation.Itisfurtherintendedthatthis handbookservesasaguide,throughitscopiousreferences,tofurtherlearningonthe subject.
Smallmodularreactors(SMRs) forproducingnuclearenergy: Anintroduction NeilTodreas
MassachusettsInstituteofTechnology,Cambridge,MA,UnitedStates
1.1Introduction 1 Justwhataresmallmodularreactors(SMRs)?Thisquestionisfirstansweredsimply alongwithabriefhistoryoftheevolutionofthisclassofreactors.Subsequentsections detailtheincentivesandchallengestoachievingsuccessfulcommercialdeployments, thedifferenttypesofSMRsbasedoncoolantsemployed,and,finally,thecurrent statusandfuturetrendsintheworldwideefforttodevelopanddeploythisreactortype.
1.1.1DefiningSMRs “Small”referstothereactorpowerrating.Whilenodefinitiverangeexists,apower ratingfromapproximately10–300MWehasgenerallybeenadopted.Theminimum ratingassuresthatthereactordeliverspowersuitableforthepracticalindustrialapplicationofinterest.Themaximumratingconstrainsthesedesignstopowerlevels atwhichtheexpectedadvantagesofserialproductionandincrementaldeployment aswellasthematchtoelectricgridsitingopportunitiesandconstraintscanbe realized.InadditiontoagrowinginterestinSMRs,therehasbeenarecentsurge ofinterestinnuclearreactorswithoutputbelow10MWe,whicharecommonly referredtoasmicroreactors.
“Modular”referstotheunitassemblyofthenuclearsteamsupplysystem(NSSS), which,whencoupledtoapowerconversionsystemorprocessheatsupplysystem, deliversthedesiredenergyproduct.Theunitassemblycanbeassembledfrom oneorseveralsubmodules.Thedesiredpowerplantcanthenbecreatedfromone orseveralmodulesasnecessarytodeliverthedesiredpowerrating.Importantly thedeploymentofmodulescanalsobesequencedovertimebothtomatchregional loadgrowthandtolevelizethetimingofcapitalspendingoveraprescribedtimehorizon.Constructionoftheplantbyassemblyoffactory-builtelementsormodulesisthe techniqueofmodularconstruction.Althoughitisanintegralpartoftheconstruction strategyenvisionedforallSMRs,thistechniqueisnotuniquelyappliedtoSMRs. Rather,itisnowbeingemployedforrelevantconstructionelementsofnuclearpower plantsofallpowerratings,althoughthemodulesforlargeplantsareconsiderablydifferentinsize,nottypicallyamenabletorapidassemblyasisbeingproposedforSMRs.
“Reactor”isatermmorebroadlyappliedtovesselsinwhichallmannerofchemicalprocessesareconducted.However,inourcase,reactorreferstoasysteminwhich acontrollednuclearfissionprocessisconducted.
1.1.2StrategyfordevelopmentofSMRs Smallreactorsandthemodularconstructionofreactorsarenotnew.Historically, earlyreactorsforcommercialproductionofelectricitywereofsmallsize,aconsequenceoftheprudentengineeringprocessofconstructingplantsstartingatsmall ratingstogaintheneededconstructionandoperatingexperiencenecessarytomove confidentlytolargerratings.Now,afterahalf-centuryofexperience,commercial civilreactorsarebeingdeployedwithratingsupto1660MWe.Additionally,small unitswerebuiltforterrestrialdeploymenttoprovideelectricpowerforremote, vulnerablemilitarysites;foroceandeployment;forpropulsionofsubmarines,naval, andcommercialships;andforaircraftpropulsion.Modularconstructiontechniques historicallyhavealsobeenusedforserialproductionofselectedproducts.However, whatisnewisthevisionofsmallratedpowerreactorscomposedofasingleormultiplemodulessizedtomarketsofsmall-orlarge-sizedelectricgrids,therebycreating newnucleargeneratingsites,whichrequiresignificantlyreducedcapitalinvestments andcapitalinvestmentrates.Thefurthereconomicpremiseisthatelectricgeneration costcanbemadesufficientlycomparabletothatofexistinglarge-sizedplants byemployingastrategyofeconomyofnumbers(manufactureofmultipleidentical modules)andsimplificationofdesignversusthetraditionaleconomyofscale.
1.1.3EvolutionofSMRs Commercialelectricpowerbeganwithsmallreactorsoflightwater-cooleddesign.Key examplesaretheShippingport,60-MWereactordesignedbytheWestinghouseoperatedBettisNavalAtomicPowerLaboratory,whichstartedoperationin1958; theYankeeRowereactor,185MWe(Westinghouse)in1960;theIndianPointOne reactor,275MWe(B&W)in1962(allpressurizedwaterreactor[PWR]designs); andDresden210MWe(GeneralElectric)in1960(aboiling-waterreactor(BWR) design).
TheeightmilitaryreactorsforterrestrialapplicationdevelopedbytheUSArmy NuclearPowerProgramincluded(1)thestationaryplantsoperatedatFortBelvoir,Virginia,whichstartedoperationinApril1957,7monthsbeforeShippingportand5years beforecriticalityoftheFt.Greely,Alaskareactor;(2)theportablereactoroperatedat McMurdoSoundattheSouthPolein1962;and(3)abarge-mountedreactoroperatedoff thecoastofPanamaCity,Panama,in1967.Theseplantsrangedfrom1.75to10MWe andperformedeitheraheatingordesalinizationfunctioninadditiontothegenerationof electricity.AnotherexampleofaportablereactoristheRussianPAMIRreactor designedprimarilytopowerremotemilitaryradaroutposts.ThefirstwastheTES-3, a2MWenuclearplantcompletedin1961.Thedesignwasmodifiedinthe1980sto asmaller,moremobile630kWreactor. 4
ThemuchlargerUSnavalprogram,whichpioneeredtheapplicationofnuclear powerforthepropulsionofsubmarinesandsurfaceships,hasproducedmultiple pressurizedwaterreactorsandonesodium-cooledreactorofsmallratings.Additionally, severalcountrieshavefollowedsuitwithnavalpropulsion—mostnotablyRussia, whichexpandeditsdevelopmentofwater-cooledsubmarinereactorstosubmarines usinglead-bismuthcoolantandhasalsobuiltnuclearpowerednavalsurfaceships andicebreakers.
Commercial(merchantmarine)propulsionhasalsobeenexploitedthroughthe developmentofoceanfreightersandicebreakers.Fourfreighters,allwithreactors oflightwaterdesign,havebeenbuiltandoperatedalbeitwithoutcommercialsuccess: (1)the USSavannah,74MWt,ineffectiveservicestarting1962;(2)theGerman Otto Hahn,38MWt,1968;(3)theJapanese Mutsu,36MWt,1972;and(4)theonlyvessel stillinoperationundernuclearpower,theRussian Sevmorput,135MWt,deliveredin 1988,whichalsohasice-breakingcapability.
The OttoHahn reactordesignisofspecialinterestsinceitsintegraldesigncharacteristicisthetypicalconfigurationbeingexploitedbyseveralmodernPWRSMR vendors.Asextensivelyelaboratedin Chapter3,thetermintegraldesignmeansthe colocationofallcomponentsandpipingoftheprimarycoolantsysteminthesingle pressurevessel.Bycontrastthetypicallarge-ratedPWRsareloopsystemswiththe primarysystemcomponents,forexample,thesteamgenerators,primarycoolant pumpsandpressurizerconnectedbypipingtoeachother,andthepressurevessel, whichhousesthereactorcoreandthecontrolelements.
TodateRussiaalonehasconstructedandoperatedninenuclear-poweredicebreakers,startingin1959withthe Lenin.Twovesselclasseshavebeenbuilt:theArktika class,eachvesselwithtwoOK-900Areactorseachof171MWt,andtheTaymyclass, eachvesselwithasingleKLT-40Mreactorof135MWt.(NB:Allreactorsofthe oceanvesselsnotedpreviouslydrivepropulsionshafts;thustheirratingsareonly inMWt.)Also,Russiahasconstructedanonself-propelledfloatingnuclearpower station,theAkademikLomonosov,toprovidepowersupplytoremotecoastaltowns. ThereactorstationwhichachievedcommercialoperationinMay2020consistsof twomodifiedice-breakerreactors,eachaKLT-40Sreactorof35MWe.Withthese reactorsthestationcanprovideeither70MWeofpower,300MWtofdistrictheating, or240,000m3/dayoffreshwater.
Thedevelopmentofanuclearpropulsionsystemformilitaryaircraftwasinitiated in1946astheUSNuclearEnergyforthePropulsionofAircraft(NEPA)projectand continuedunderthenameoftheAircraftNuclearPropulsion(ANP)program.Two differentsystemsfornuclear-poweredjetengineswerepursued—adirectaircycle conceptdevelopedbyGeneralElectricandanindirectaircyclebyPrattandWhitney. Onlythedirectaircycleprogramadvancedsufficientlytoproducereactors.Thefirst productoftheGEprogramwastheAircraftReactorExperiment(ARE),whichoperatedfor1000hin1954.Itwasa2.5-MWtnuclearreactorexperimentusingmolten fluoridesalt(NaF-ZrF4-UF4)asfuel,aberylliumoxide(BeO)moderator,andliquid sodiumasasecondarycoolant.In1955thisprogramproducedthesuccessfulX-39 enginewithheatsuppliedbytheHeatTransferReactorExperiment-1(HTRE-1). TheHTRE-1wasreplacedbytheHTRE-2andeventuallytheHTRE-3unitpowering
thetwojetturbines.Additionally,anoperatingreactornamedtheaircraftshieldtest reactor(ASTR)wasflownaboardamodifiedB-36bombertotestshieldingratherthan poweringtheplane.TheHTRE-3usedashieldsystemofflight-typedesignbutwas nottakentopowerbeforetheprogramwascanceledin1961.
Experiencewiththeseearlierreactorshasledtothecurrentinterestinreducedsize modularpowerplants. Table1.1 listsseveralcurrentSMRsunderdevelopment,which encompassallcoolanttechnologiesbeingexploitedforlargernuclearreactors.
Additionalreactordesignsnotincludedin Table1.1 areunderdevelopmentby nationalresearchinstitutionsbuthavenotyetreachedthecommercializationstage. Forexample,thefluoride-salt-cooledhigh-temperaturereactor(FHR)(Forsberg
Table1.1 Examplesofcurrentsmall(>10MWe)modularreactorsproposedbycommercial industries.
Reactor design Powerrating (MWe)CountryVendor/AE
Lightwater-cooled(PWR)
ACP100100 China CNNC/Guodian CAREM27 Argentina CNEA/INVAP
KLT-40S35 Russia OKBM NuScale60 UnitedStatesNuScalePower/Fluor RITM-20050 Russia OKBM
SMART100 S.Korea KAERI SMR-160160 UnitedStatesHoltec
Lightwater-cooled(BWR)
BWRX-300300 UnitedStates/JapanGE-Hitachi VK-300250 Russia NIKIET
Gas-cooled
EM2 265 UnitedStatesGeneralAtomics GT-MHR288 Russia OKBM HTR-PM105 China INETTsinghuaUniversity Xe-10075 UnitedStatesXEnergy,LLC
Sodium-cooled
4S 10/50 Japan Toshiba PRISM311 UnitedStatesGE-Hitachi
Lead-cooled
SVBR-100100 Russia JSCEDB BREST300 Russia AKME-engineering
Moltensalt-cooled
IMSR190 Canada TerrestrialEnergy,Inc. LFTR250 UnitedStatesFlibeEnergy,Inc.
etal.,2013)isa180-MWereactorwith700°Cpeakoperatingtemperaturecoupledto anair-Braytoncombinedcyclesystem.
1.2Incentivesandchallengesforachievingcommercial deploymentsuccess ThequestionariseswhyinterestinSMRshasreemergedandburgeonedoverthelast decade.ThereasonisthatSMRsofferanattractivevehicletosurmountthecurrent barrierstodeploymentofthecurrentgenerationoflarge-ratedadvancedlightwater plants(theGenerationIII+designs)andalternativecoolant(GenerationIV)plants. Principalamongthesebarriersisthelargeinitialinvestmentrequiredtoconstructa reactor,theattendantsignificantfinancialrisktotheinvestor,andthemismatchof reactorsizetotheelectricpowergridservicedbymanyelectricity-generatingentities.
GiventheincentivesforSMRdeployment,whatarethechallenges?Themajor uncertaintiesaretheabilitytoreducethefinancialrisksufficientlytoattractinvestors, theabilitytoreducetheprojectedlevelizedunitelectricitycost(LUEC)differential betweenthatofSMRsandthecompetitionofferedbylower-costnaturalgaspower plantsandlargenuclearplants,andcompatibilityoffuelcycleswithexistingfacilities. Theseincentivesandchallengesareelaboratednext.
1.2.1Incentives
ThetwomajorincentivesforSMRdeploymentareasfollows.
1.2.1.1Reductionofinitialinvestmentandassociated financialrisk
Themodularconceptallowstheinvestortoachievetheleveloftotalpowersupply desiredbytime-sequencedconstructionincrements.Eachmoduleincrementnotonly doescostlessthanthatofthelargemonolithiccompetitorplant,butalsothetimeprofileofcapitalinvestmentscanbesomewhatoffsetbyrevenuesfromtheearliestmoduledeploymentsastheyachievecommercialoperation.However,whenmodule constructionisstaggered,greatcaremustbetakentoinsurethatconstructiondoes notadverselyimpactthesafetyoftheoperatingSMR.
1.2.1.2Improvedmatchtosmallerelectricpowergrids
Asignificantnumberofpotentialnuclearpowerplantcustomershaveconstraintsonthe sizeofallowableandneededincrementsofpowercapacityadditions,whicharesmaller thanthe1000MWeandlargerratingsofcurrentlyofferedadvancedreactors.The allowablesizeofadditionsreflectsthesomewhatcontortedgridlayoutand interconnectionsinseveralUSregions.Neededsizeincrementsreflectanticipated growthinloaddemandandincentivestoreplaceolder,smallgeneratingstations,mostly coalburning,withthoseusingotherfuels.Also,sincethesmallerSMRsshouldtakeless timetobuildthan1000MWeunits,demandforecastsneedtobeprojectedforfewer
yearsoutthanarepresentlyneeded.Furthermarketsforsmallnuclearunitsareemerginginsmallerdevelopingcountries,whichhavenotpreviouslyembarkedonnuclear powerutilization.Indevelopedcountrieswithwell-establishednuclearpowerprograms,remoteregionsandsitesvitalfornationalsecurityexist,whichhavepowerneeds thatcanideallybesuppliedbySMRs.Additionally,SMRsinthesecountriescansupply processheatonthescaleappropriatetocommercialchemicalprocessingplantneeds. ThesemajorincentivesforSMRsarebuttressedbyseveralotherdesirablefactors derivingfromthesmallSMRcharacteristics:
l effectiveprotectionofplantinvestmentfromthepotentialtoachieveareactordesignwith enhancedsafetycharacteristics;
l possiblereductionofthecurrent10-mileemergencyplanningzonebyvirtueofthesmaller coreinventoryandpotentialforaddedsafetydesignfeatures;
l reductionoftransmissionrequirementsandamorerobust,morereliablegrid;
l useofcomponentsthatdonotrequiretheultraheavyforgingsoftoday’sgigawatt-scale nuclearpowerplantsandarerailshippable,whichcouldbesuppliedbyareinvigorated USheavyindustry;and
l suitabilityforthedistrictheatingmission.
1.2.2Challenges ThethreemajorchallengesforSMRdeploymentareasfollows.
1.2.2.1Sufficientreductionoffinancialrisk
Theinvestor-perceivedfinancialriskarisesfromthreekeyfactors:
l NRClicensingrequirements,whichcouldaffectthecapitalandoperatingcostofthese SMRsregardingplantstaffing,securityrequirements,insuranceandlicensingfees,and decommissioningfunding;
l thevalidityoftheexpectedlearningcurvetoreducecapitalcoststhroughfactory manufacture;
l themoretypicalnuclearconstructionconcerns,suchasthefollowing: constructionandcommercialoperationscheduledelayduetoregulatoryrelateddelays, constructioncostoverrunduetoconstructorinexperiencesuchastherecentEPRFinnish andFrenchconstructionactivitiesandunforeseenmandateddesignenhancementssuch asthosearisingfromtheFukushimaaccident, lossofinvestmentduetooperationalandmaintenancecostescalationoroccurrenceofa severereactoraccident.
Allreactorsareequallydesignedtoatoplevelsetofregulatoryrequirements,which howeverarenotfullyharmonizedinternationally.IntheUnitedStates,theserequirementshavebeenmademuchmoreexplicitforwater-cooledreactors,sinceamongthe othercoolants,onlytheFortSt.Vrainhelium-cooledreactorreceivedaUSNuclear RegulatoryCommission(NRC)(commercial)operatinglicense.Theexplicitexisting definitionofwater-cooledreactorregulatoryrequirementsisamajorbenefittolight waterreactor(LWR)SMRsincomparativelyassessingthelicensabilityofotherSMR coolanttypes.However,evenforLWRSMRs,thefollowingfactorssignificantto
potentialcostreductionscomparedwithcurrentGWestationsandregulatoryacceptancewillneedtoberesolved:
l thereactorcontrolstrategyleadingtoreductioninthenumberofrequiredoperators,
l thereactivitycontrolissuesrelatedtothedesiredlongdurationoftheirradiationcycletobe accomplishedbysomedesignswithouttheuseofsolublepoisons,
l thedefinitionofthemechanisticsourcetermforfissionproductreleaseinasevereaccident,
l thepotentialforandconsequencesofmultimoduleinteractions,
l establishmentofemergencyplanningandpreparednessconsistentwiththereducedpower ratingandfootprintofSMRs.
Finally,LWRplantvendorsareassumingthattheirdesignswillbeacceptedina timelymannerbytheregulator.Theybasetheiroptimismonthecontentionthat theirdesignsemployproven,currentlicensedconceptsusingprovencomponents andsystemsconfigurationsatpowerlevelssufficientlylowtoallowtheenhanced useofpassivesafetyfeatures,whichhavealreadybeenreviewedandapprovedfor thelargerGenerationIII+advancedlightwaterreactor(ALWRs).Thisassumption, evenifprovencorrect,needstoreflectregulatoryacceptanceofatleastsomeof thefactorsnotedpreviouslycastinamanneryieldingeconomicbenefittotheSMR.
ForSMRsusingnontraditionalcoolantssuchashelium,sodium,lead-bismuth,or moltensalts,theregulatorychallengeismoredifficultsincetheNRCstafflackfamiliaritywiththesereactordesigns.Additionally,giventhestilllargelyprescriptive natureoflightwater-basedregulationsintheUnitedStates,thelicensingprocessis notamenabletothenewermoreinnovativedesigns.Therehavebeencallsforusing atechnology-neutrallicensingprocesstolicensethesenewreactorconceptssuchthat theinherentdesignfeaturescanberecognizedbytheregulator.Thedevelopmentof suchaprocessisunderwaybutisproceedingslowly.
1.2.2.2ProjectedLUEC Theimpactoftheconceptofmodularityinreducingthecostofsmall,replicated,and mostlyfactory-builtunitsisparamount.Proponentsrefertothisasthecompetition betweenthetraditionaleconomyofscale,whichhasledtoGWe-sizedplantsand theneweconomyofnumbers,whichcharacterizestheconstructionofSMRs.
FurtherthedramaticallyreducedpowerratingofSMRsprovidessignificantpotentialforpassivesafetysystems,whichsimplifyoreliminateactivesafetysystemscomparedwiththoseofcurrent-generationreactors.AlsotheSMRscaneliminate theirrelianceuponsupportsystemsascomparedwiththecurrentLWRs’needforsuch systems.TheAmericanNuclearSociety’sreportonSMRgenericlicensingissues (see Tables1.3and1.4 in AmericanNuclearSociety,2010)identifiesspecificcandidatesafetyandsupportsystemsforsuchsimplificationsandeliminations.However, projectionsamonganalystsvaryastowhetherSMRscanachievelowerLUECsthan traditionallargeplants.Forexample,theOECDhasreported(OECD,2011)that theinvestmentcomponentofLUECfromanSMRwouldprobablybehigherthan thatofalargeplant,eventakingintoaccounttheSMRreducedconstructionschedule, shopfabrication,andlearningcurve.FurthertheOECDconcludedthatSMRs,
includingtwin-unitandmultimoduleplants,generallyhavehighervaluesofLUEC thannuclearpowerplantswithlargerreactors.Thusachievementofacompetitive SMRLUECwillbeverydifficulttoaccomplish:referencetoindependentlyvalidated projectionsisessentialfordevelopingrealisticcostestimates.
1.2.2.3Fuelcyclecompatibilitywithfacilitiesandstrategy TheSMRsofdifferentcoolanttypesemployverydifferentfueltypes.Thewatercooledandthelead-/bismuth-cooledSMRsuseuraniumdioxide(UO2)ceramicfuel; thegas-cooledSMRsusegraphiteandsiliconcarbide-coatedUO2 particlesingraphite compactsorpebbles;thesodium-cooledreactorusesmetallicUZrwithminoractinides;andthelead-cooledSMRusesmononitride-mixedfuel(UN-PuN).The water-cooledSMRfuelisthesameasthatoftheoperatingplantsandoftheGEN III+plantscurrentlybeingdeployed.Alltheliquidmetal-cooledreactorfuelswill haveanenrichmentsignificantlymorethanthe5%ofcurrentwater-cooledfuel.
AlthoughaUSnationalrepositoryisnotyetidentified,thiswater-cooledSMRfuel willbehandledconsistentwiththeanticipatedUSpolicyyettobefinalized.ThegascooledSMRfuel,thesameasthatusedintheFortSt.Vrainreactor,hassignificantly morevolumeperunitenergygenerationbutlowerheatloadperunitvolumethanLWR UO2 fuel.Thecharacteristicofthisfuelwillrequireadifferentoveralldisposalstrategy, althoughitwouldlikelybecompatiblewiththestrategyofthenationalrepositoryfor ceramicUO2-zircaloycladfuelsincethetristructuralisotropic-type(TRISO)fuelparticlesformgoodbarriersthatprovideexcellentfissionproductretention.
Thefuelofsodium-andlead-cooledSMRreactorsexploitstheinherentincentiveof thesefastneutronspectrumreactorstoundergoreprocessingandrecycling.Thisfuel cyclewillentailconstructionandoperationofreprocessingandfuelfabricationfacilities,whilemostlikelyitwouldalsobeintegratedwithreprocessingofsomelightwater fleetfuelsasfeedstockfortheplutoniumneededforinitialloadingofagrowingfleetof fastreactors.Thespentfuelconstituentsultimatelyrequiringdisposalwillbepredominantlyfissionproductsofmuchlessvolumethanthespentfuelbundlesofthermalspectrumwaterreactorsperequivalentunitofenergygenerated.However,thedeployment offastspectrumSFRsbasedontheclosedfuelcyclewouldrequiresignificantexpansionofreprocessingandfuelfabricationfacilitiescomparedwiththeneedsfortheexistingLWRfleetandLWRSMRsoperatingontheonce-throughfuelcycle.
1.3OverviewofdifferenttypesofSMRs Aswiththecurrentlarge-ratedreactors,SMRcoolantscanbelightwater,gas,orliquidmetal.KeySMRexamplesoftheseprimarysystemcoolanttypeswiththeirprincipaldesignparametersarepresentedin Table1.2.Thecoolantpropertiesthatdictate thedifferentdesigncharacteristicsoftheseSMRsarepresentedin Table1.3.Principal amongthemareasfollows:
l theveryhighoutlettemperature(750–950°C)ofthehigh-temperaturegasreactor(HTGR) possiblewiththeuseofheliumascoolantandgraphiteastheprincipalcorematerial,
Table1.2 Reactorcharacteristicsbycoolant.
Powerdensity(kWt/lcore)6939.53.2
FuelgeometryRodsRodsPebblesPrismatic graphiteblocks RodsRodsRods
Fuelmaterial/claddingUO2/Zr-4UO2/ZrUO2/TRISOUCO/TRISO(U+Pu)/SS(U+Pu)N/SSUO2 1,h
Primarysystemtemperature inlet/outlet(°C) 295/319190/285250/750325/750360/499420/540340/490
Plantthermalefficiency(%)3433.3424537432
NA,notapplicablesincetheBWRonlyhasaprimarysystem. Numericalvaluesofcharacteristicsarerounded.
a Pers.Comm,D.Langley(mPower)toN.Todreas(MIT),January2013.
b VK-300—Gabaraevetal.(2004); Kuznetsovetal.(2001).
c PRISM—Triplettetal.(2012).
d HTR-PM—Zhangetal.(2009); Zhang(2012).
e SC-HTGR—AREVA(2012)
f BREST—Smirnov(2012); Glazovetal.(2007)2.
g SVBR-100—ToshinskyandPetrochenko(2012);MOXandNfueloptionsproposed1
h LikelyEP823orEP450.
Table1.3 Reactorcoolantpropertiesofsignificancea.
a Typicalreactorvalues.
b PropertyvaluesatPWRaverageandBWRinletconditionsfrom TodreasandKazimi(2012).
c Propertyvaluesat537°Cand6MPafrom Petersen(1970)
d Propertyvaluesat450°Cfrom Hejzlaretal.(2009).
yieldingahighplantthermalefficiencyandsupplyofreactorheatforprocessesrequiring hightemperatureheat;
l thelowprimaryoperatingpressureoftheliquidmetalreactorspermittedbythelowvapor pressureoftheirprimarycoolantattheirhighoperatingtemperature;
l thehighpowerdensityofthesodium-cooledreactorpossiblebecauseofitsoperationwitha fastneutronspectrumcoupledwithaveryhighheattransfercoefficientthatallowstight packingofitsfuelpins.
Thepredominantuseoflightwaterinbothpressurizedandboiling-waterlarge-rated reactorscurrentlyinusecanbereadilyreplicatedforSMRapplication.Thesmaller primarysystemcomponentsofpressurizedwaterSMRsallowstheirarrangement withinthepressurevesselasisalreadydoneevenforlargepowerratedBWRs.This PWRconfiguration,theintegralreactor,waspioneered(asdiscussedin Section1.1.3) inthecommercialmerchantvessel,theGerman OttoHahn,andisaprincipalconfigurationofcurrentPWRSMRsaselaboratedin Chapter3
HeliumhasbeenthegascoolantofSMRchoice,althoughcarbondioxideisused inadvancedgasreactors(AGRs)operatingintheUnitedKingdom,whicharecurrentlyslatedforretirement.TheliquidmetalcoolantsofSMRchoicearesodium,lead, andlead-bismuth.Sodiumhasbeenexploitedsignificantlyforlarge-ratedreactors basedonearlyworkwithsodium-potassiumandsodium,whilemoreexoticcoolants suchaslithiumhavebeenusedforelectricity-generatingspacereactors,forexample, theSystemsforNuclearAuxiliaryPower(SNAP)series.ForSMRs,attention isfocusedonsodiumandthevariantsofleadcooling—bothpureleadandlead-bismutheutectic.
Differentiationamongreactortypesandspecificreactordesignswithinacoolanttypedesignisbasedontheirsatisfactionofaselectedmissionandthenasetofcriteria includingoperationalreliability,protectionofpublichealthandsafety,and finallyeconomiccompetitiveness.ThesalientcharacteristicsoftheSMRreactors astheyrelatetothesefactorsarepresentednext. Chapter2 andthechapters inPartFourelaboratethedetailedtechnicalfeaturesofSMRscoveringthisrange ofprimarycoolants.
1.3.1Reactormission TheprincipalmissionadoptedforcommercialSMRshasbeenthegenerationofelectricity.Allreactorcoolanttypesaddressthismission.Forthoseplantsdesignedtobe deployabletoremotelocations,whetherplacedterrestriallyordispatchedasbargemountedreactors,theaddedcogenerationcapabilitiesfordesalinizationanddistrict heatingexist.Ofthewater-cooledSMRs,theRussianPWRandBWRsystemshave beendesignedfortheseadditionalmissions.Additionally,propulsionasaccomplished byRussianice-breakervesselsusingtheKLT-40Sreactoranditsplannedreplacement,theRITM-200reactor,isafurtherreactormission.
Theheliumgas-cooledreactorcanoperateathighenoughoutletcoolanttemperature,750°Cininitialdesigns,toprovideaprocessheatcapability.Thisprocessheat canbeuseddirectlyforvariousindustrialprocessessuchasshaleoilrecoveryandthe productionofhydrogenbyrelativelyhigh-temperaturethermochemicalcycles.
Hydrogenproductionfromwaterbyelectrolysiscanbeaccomplishedattheloweroutlettemperatureofthesodium-andlead-cooledreactors,ontheorderof500–550° C,buttheseSMRshavenotembracedthismissionduetocurrentshrinking USinterest.
1.3.2Operationalreliability Certainly,thiscriterionisbestmetbyreactorconceptsusingconventionalcomponentsandsystemsoperatingatcoolanttemperaturesandpressureswithintheenvelope ofsignificantoperatingexperience.WaterasacoolantforSMRshasbeenselected explicitlybecauseofthesatisfactionoftheseconditions.Experiencewithwaterreactorsusingtheessentialdesignfeaturesselectedforwater-cooledSMRsgoesback tothebeginningsofthenuclearelectricitygenerationandpropulsionage.Themajor caveatregardingtheachievablereliabilityofwater-cooledSMRsrelatestothose havingselectedtheintegralconfiguration,theplacementofallNSSScomponents, andpipingwithinasinglepressurevessel.Whilethe OttoHahn merchantvesselsuccessfullyusedthisreactorconfigurationandoperatedcommerciallyfor9years,the potentialreductioninoperationalreliabilityofthisconfigurationduetoitslimited accessibilityforprimarysystemcomponentmonitoring,maintenance,andrepair canbeconfidentlyassessedonlythroughmanymoreyearsofoperatingreactor experience.
Sodium-cooledreactorshavegenerallyhadamixed,albeitlimited,recordofoperatingexperience.TheUSExperimentalBreederReactorII(EBR-II)andBritish DounreayFastReactor(DFR)recordswereexemplary,theRussianBOR-60and BN-600andtheFrenchPhenixreactorexperiencewasonbalancesatisfactory,while theJapaneseMonjuexperiencehasbeenverytroubled,principallyduetoasodium leakageeventaswastheSuperphenixexperience.Similarlythelead-/bismuth-cooled Russiansubmarinereactorsoperatedreliablybutwiththeneedforcarefulattentionto coolantchemistrycontrolandfreezepreventionafterthemajoraccidentin1968 beforeadequateunderstandingexistedoftheneedforrigorouscontrolofcoolantoxygenconcentrationtopreventleadoxideslagformation(ToshinskyandPetrochenko, 2012).Helium-cooledreactors,forexample,theexperimentalreactorsAVRand THTRinGermanyandthecommercialFortSt.VrainunitintheUnitesStates,also havehadamixedoperatingrecord.
Hence,itcanbeconcludedthat,basedonoperatingexperience,thewater-cooled SMRclasshasasignificantadvantageovertheothercoolanttypeswithregardtoits promiseofoperationalreliability.Theoperationalreliabilityofnonwatercooledreactorswillbeuncertainuntilsufficientdemonstrationplantoperationalexperienceis accumulated.
Theprincipalcoolantcharacteristicsinfluencingthisoperationalexperience—for example,coolanttoxicity,corrosioneffectonboundingsurfaces,andcoolantfreezing andboilingtemperatures—areshownin Table1.4.Coolanttoxicityhasbeen expressedintermsofradiological,biological,andchemicalfactors.
Biologicalconsequencesarisefromdecayof 210Bi,whichyields 210Po.ThepoloniumthenchemicallycombineswithleadasPbPo(s).Shouldwaterentertheprimary
Table1.4 Inherentcoolantcharacteristicsaffectingoperationalreliability.
Radiological 16O(n,p)16N
16N ! 16O+5to7MeVγ
(T1/2 ¼ 7.1s)
Nonebuterosion createddust liftofffrom sudden depressurization cancause mechanical clogging
23Na(n, γ )24Na (T1/2 ¼ 15h)
1.38,2.76MeV γ s
23Na(n,2n)22Na (T1/2 ¼ 2.6year) 1.28MeV γ
204Pb(n, γ )205Pb (T1/2 ¼ 51.5days) 1.28MeV γ
Sameasleadplus
209Bi(n, γ )
210Bi(e) 210Po
210Po(α, γ low prob.) 206Pb (T1/2 ¼ 138days)
5.3MeV α; 805keV γ
Toxicity
Biological 6Li(n, α)3T
10B(n,2α)3T
10B(n, α)7Li(n,nα)3T (T1/2 ¼ 12.3years)
NoneNoneTraceamountsofPo from 205Pbto 210Poby neutroncaptureand β decay
ChemicalNoneAsphyxiation hazard
NoneExposuretohighlevels ofleadthrough inhalation,ingestionor occasionallyskincontact canleadtothemedical conditionknownaslead poisoning
PbPo(s)
+H2O ¼ PbO
+H2Po(g) (volatilealphaemittingaerosol)
Sameasforlead
Continued
Table1.4 Continued
CorrosionPreventionofstress corrosioncrackingof stainlesssteelrequires significantattention.Also significantcorrosioninducedcrudformation potential
NoneSodiumis practically noncorrosivewith respecttostainless steel.Corrosionis lowerthanforlead orwater
Aggressivecorrosionby: P directdissolutionbya surfacereaction P intergranularattack Oxidefilmformation tendstoinhibitthe corrosionrates.Needto limitvelocitytoabout 3m/stoavoidcladding corrosion
Sameasforlead
Melting (freezing)/ boiling points (°C)
a Lin(1996).
b Todreasetal.(2008)
0/100NA98/883327/1737
Highfreezingtemp— needtraceheating 125/1670
Lowerfreezing temperature advantageous versuslead
systemduetoafailureoftheingresspenetrationbarriercoincidentwithasteamgeneratortubeleak,itwouldreactwiththePbPo(s)toproduceH2Po(g),avolatilealphaemittingaerosolofbiologicalinhalationconcern.Thedesignersofthelead-/bismuthcooledSVBR-100reactor(see Table1.2),whoarewellversedinRussiansubmarine experience,citethatoperatingexperiencehasresultedinthedevelopmentofmeasures forprovidingadequateradiationsafety.Forwater-cooledreactors,waterchemistry measurestypicallyincludeintroductionofboronandlithiumintheformofboricacid andlithiumhydroxideforcorrosioncontrol,althoughsomeSMRs,forexample,the B&WmPowerdesign,haveeliminatedtheuseofsolubleboronforreactivitycontrol. Neutronactivationof 6Liand 10Bproducestritium, 3T,albeitinsmallquantities, whichneverthelessisabiologicalhazardifingested.
Occupationalcontacthazardsofachemicalnatureexistforleadthroughhigh levelsofexposureduetoinhalationandoccasionallyskincontact.Similarly,asphyxiationduetoaccidentalimmersioninhelium(orinnitrogentypicallyusedtoinert BWRcontainments)isapotentialhazard.Themoresignificant,well-recognized chemicaloxidationreactionsofzirconiumcladdingandsodiumarecoveredasa safetyconcernunderpotentialenergyreleasein Section1.4.1.
Ofallthecoolants,helium,becauseitisaninertgas,posestheleastcorrosion potential,anditsactivationisminimalas demonstratedbytheFortSt.Vrainexperiencethatshowedverylowactivityinthecoolantcomparedtolightwaterreactors. Theaggressiveattackofleadandlead-bismuthonmetalcladding(e.g.,inHT-9and theRussianequivalentsEP823andEP450)hasforcedthelimitationofcoolant velocityinlead-andlead-/bismuth-c ooledcoredesignsto3m/s.Thisinturnhas necessitatedthepr ovisionofalargecoolantflowareatoboundcorecoolanttemperaturerise.Hence,leadandlead-bismuthcoreshavefuelpinsspacedwithalarge pitch/diametersquarelatticearray.However,thedevelopment(ShortandBallinger, 2012)ofacompositematerialforcladdingandstructuralapplicationmaymitigate suchlimitations.
Finallytheoperabilityofliquidmetalcoolantsystemsrequirestraceheaters aroundpipingandcomponentsofsodium,leadandlead-bismuthreactorstopreventcoolantfreezingwheninsufficientheatisavailablefrompoweroperationor decayheat.Thehighfreezingtemperatureoflead,327 ° C,comparedwiththemodestvaluesforsodium,98 °C,andlead-bismuth,125 °C,rendersleaddisadvantageousasareactorcoolantinthisregard.However,withthesehighfreezing temperaturesbothleadandlead-bismutheutecticwillsolidifyinambientair,providingameansforsealingsmallleaks intheprimarycoolantboundary.Onthe otherhandthehighboilingpointswiththeattendantlowvaporpressuresofthese liquidmetalcoolantsallow reactoroperationatatmosp hericpressurewithoutthe sourceofstoredenergyassociatedwithahigh-pressurecoolant.Operationatlow pressureallowsreductionoftherequiredthicknessofthepressurevesselandother primarypressureboundarycomponents.Nevertheless,fortheheavyleadcoolant, thedimensioningofthesevesselsmustbecarefullyevaluatedtosatisfyseismic designcriteria.
1.3.3EconomicimplicationsofSMRtechnologies Theeconomiccharacteristicsoflargewaterpowerreactorsareknownfromyearsof constructionandoperatingexperience.Thecostofsodium-cooledreactorsbasedon deploymentsofdemonstrationunitsinthelate1900shasledtocapitalcostestimates of110%–125%thatofwater-cooledreactors(Waltaretal.,2012).Experiencewith gas-cooledandcertainlylead/lead-/bismuth-cooledreactorshasnotbeensufficient toallowacomparableprojectionofovernightcapitalcostscomparedwithwatercooledreactorexperience.Hence,whileitisacceptedthatthecapitalcostofindividualSMRunitswillbefarlowerthanthatofthelarge-ratedreactorsemployingthe samecoolant,thecapitalcostperKWeforSMRscomparedwithlarge-ratedreactors, althoughlikelylarger,isasyetnotestablished.Wecanonlyprojectcomparativecosts ofSMRsemployingthevariouscoolantsonthebasisofthepreviouslynotedlargeratedreactorexperience.
Otherpotentialmeasuresofcomparativeeconomiccharacteristicsofvariously cooledSMRsarethefundamentalparametersofcorepowerdensityandspecific power.Thepowerdensity,kilowatts/liter,reflectsthecorevolumeandhenceisoften ameasureofthevesselcontainmentandplantsizenecessaryforagivenpowerrating. Exceptionsdoexistifthereactorvesselorcontainmentsizeisdictatedbyconsiderationsotherthancorepowerdensity.Forexample,theSPRISMsodium-cooledfast reactorvesselissizedtoaccommodatedecayheatremovalthroughanair-cooled chimneyoutsidetheguardvessel:BWRcontainmentsbyvirtueoftheiruseofincontainmentcoolantpoolsforpressuresuppressionaremuchsmallerthanthoseof PWRs,whichcontrolpressurebylargeair-filledcontainmentvolume.Thepowerdensityisthusarelativeindicationofcapitalcost,albeitforplantsusingcomparable designstrategiesandprincipalmaterials.Thespecificpower,kW/kgIHM,reflects themassofinitialheavymetal(IHM)orfuelneededforagivenpowerrating.The specificpoweristhusarelativeindicationoffuelcyclecost,butforplantsusing comparablefuels.
However,itisclearthatnotallSMRsemployingthevariouscoolantsofinterest usecomparablematerialsorfuels.Hencetherelativevaluesofpowerdensityand specificpowerpresentedin Table1.5 forvariouscoolantsdonotnecessarilyforecast thecomparativeeconomiccharacterofreactorsemployingvariouscoolants.Nevertheless,theseparametersprovideaninsightregardingthesignificantbenefitto sodium-cooledreactorsfromtheirhighrelativeparametricvalues,abenefitwhich likelykeepstheircostsclosetowater-cooleddesignseventhoughtheyuseanexotic liquidmetalcoolantrequiringconsiderablecostlyinstrumentationandpurification systems,andtheirenrichmentismuchhigherthanthatofwater-cooleddesigns.
Table1.5 NominalaveragepowerdensityandspecificpowerofSMRsofvariouscoolants.
PWRBWRHeliumSodiumLead
Powerdensity(kW/l)100516280110 Specificpower(kW/kgIHM)38271006045
