ML103610409

2010/12/27-Energy Policy, Valuing the Greenhouse Gas Emissions from Nuclear Power: a Critical Survey

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Valuingthegreenhousegasemissionsfromnuclearpower:AcriticalsurveyBenjaminK.SovacoolEnergyGovernanceProgram,CentreonAsiaandGlobalisation,LeeKuanYewSchoolofPublicPolicy,NationalUniversityofSingapore,469CBukitTimahRoad,Singapore259772,SingaporearticleinfoArticlehistory:

Received25February2008 Accepted21April2008Availableonline2June2008Keywords:NuclearpowerLifecycleanalysis Greenhousegasemissions abstractThisarticlescreens103lifecyclestudiesofgreenhousegas-equivalentemissionsfornuclearpowerplantstoidentifyasubsetofthemostcurrent,original,andtransparentstudies.Itbeginsbybrie"ydetailingtheseparatecomponentsofthenuclearfuelcyclebeforeexplainingthemethodologyofthesurveyandexploringthevarianceoflifecycleestimates.Itcalculatesthatwhiletherangeofemissionsfornuclearenergyoverthelifetimeofaplant,reportedfromquali"edstudiesexamined,isfrom1.4gofcarbondioxideequivalentperkWh(gCO 2e/kWh)to288gCO 2e/kWh,themeanvalueis66gCO 2e/kWh.Thearticlethenexplainssomeofthefactorsresponsibleforthedisparityinlifecycleestimates,inparticularidentifyingerrorsinboththelowestestimates(notcomprehensive)andthehighestestimates(failuretoconsiderco-products).Itshouldbenotedthatnuclearpowerisnot directlyemittinggreenhousegasemissions,butratherthatlifecycleemissionsoccurthroughplant construction,operation,uraniumminingandmilling,andplantdecommissioning.

&2008ElsevierLtd.Allrightsreserved.1.IntroductionThenuclearerabeganwithawhimper,notabang,onDecember7,1942.Amidstthepolishedwooden"oorsofawar-appropriatedsquashcourtattheUniversityofChicago,EnricoFermiinsertedabout50tonofuraniumoxideinto400carefullyconstructedgraphiteblocks.Asmallpuffofheatexhibitedthe"rstself-sustainingnuclearreaction,manybottlesofChiantiwereconsumed,andnuclearenergywasborn(Metzger,1984

).Sincethen,Americanshavedreamedofexoticnuclearpossibilities.Earlyadvocatespromisedafutureofelectricitytoocheaptometer,anageofpeaceandplentywithouthighpricesandshortageswhereatomicenergyprovidedthepowerneededtodesalinatewaterforthethirsty,irrigatedesertsforthehungry,andfuelinterstellartraveldeepintoouterspace.Otherexcitingopportunitiesincludedatomicgolfballsthatcouldalwaysbefoundandanuclearpoweredairplane,whichtheUSFederalGovernmentspent$1.5billionresearchingbetween1946and1961(Munson,2005

Winkler,2001

Duncan,1978

).Whilenucleartechnologiesdidnotful"llthesedreams,nuclearpowerhasstillemergedtobecomeasigni"cantsourceofelectricity.In2005,435nuclearplantssupplied16%oftheworldspower,constituting368GWofinstalledcapacitygenerating2768TWhofelectricity(InternationalEnergyAgency,2007).IntheUSalone,whichhas29.2%oftheworldsreactors,nuclearfacilitiesaccountedfor19%ofnationalelectricitygeneration.InFrance,79%ofelectricitycomesfromnuclearsources,andnuclearenergycontributestomorethan20%ofnationalpowerproductioninGermany,Japan,SouthKorea,Sweden,Ukraine,andtheUnitedKingdom.Advocatesofnuclearpowerhaverecentlyframeditasanimportantpartofanysolutionaimedat"ghtingclimatechangeandreducinggreenhousegasemissions.TheNuclearEnergyInstitute(2007)tellsus,itisimportanttobuildemission-freesourcesofenergylikenuclearandthatnuclearpowerisacarbon-freeelectricitysource(1998).PatrickMoore,co-founderofGreenpeace,haspubliclystatedthatnuclearenergyistheonlynon-greenhousegasemittingenergysourcethatcaneffectivelyreplacefossilfuelsandsatisfyglobaldemand(EnvironmentalNewsService,2005).ThenuclearpowercompanyAreva(2007)claimsthatonecoalpowerstationof1GWeemitsabout6milliontonsofCO 2peryearwhilenuclearisquiteCO 2free.Opponentsofnuclearpowerhaverespondedinkind.Intheir calculation,ISA(2006)arguesthatnuclearplantsarepoorsubstitutestootherlessgreenhousegasintensivegenerators.Theyestimatethatwindturbineshaveone-thirdthecarbon-equivalentemissionsofnuclearpowerovertheirlifecycleandhydroelectricone-fourththeequivalentemissions.TheOxfordResearchGroupprojectsthatifthepercentageofworldnuclearcapacityremainswhatitistoday,by2050nuclearpowerwouldgenerateasmuchcarbondioxideperkWhascomparablegas-"redpowerstationsasthegradeofavailableuraniumoredecreases(BarnabyandKemp,2007a,b

).Whichsideisright?AnalogoustothecriticalsurveysofnegativeexternalitiesassociatedwithelectricityproductionARTICLEINPRESSContentslistsavailableat ScienceDirectjournalhomepage:www.elsevier.co m/locate/enpolEnergyPolicy0301-4215/$-seefrontmatter

&2008ElsevierLtd.Allrightsreserved.

doi:10.1016/j.enpol.2008.04.017Tel.:+6565167501;fax:+6564684186.E-mailaddress:bsovacool@nus.edu.sgEnergyPolicy36(2008)2940-2953 conductedbySundqvistandSoderholm(2002) and Sundqvist(2004),thisarticlescreens103lifecyclestudiesofgreenhousegas-equivalentemissionsfornuclearpowerplantstoidentifyasubsetofthemostcurrent,original,andtransparentstudies.Itbeginsbybrie"ydetailingtheseparatecomponentsofthenuclearfuelcyclebeforeexplainingthemethodologyofthesurveyandexploringthevarianceoflifecycleestimates.Itcalculatesthatwhiletherangeofemissionsfornuclearenergyoverthelifetimeofaplantreportedfromquali"edstudiesexaminedisfrom1.4gofcarbondioxideequivalentperkWh(gCO 2e/kWh)to288gCO 2 e/kWh,themeanvalueis66gCO 2e/kWh.Thearticlethenexplainssomeofthefactorsresponsibleforthedisparityinlifecycleestimates,inparticularidentifyingerrorsinboththelowestestimates(notcomprehensive)andthehighestestimates(failuretoconsiderco-products).Itshouldbenotedthatnuclearpowerisnotdirectlyemittinggreenhousegasemissions,butratherthatthelifecycleinvolvesemissionsoccurringelsewhereandindir-ectlyattributabletonuclearplantconstruction,operation,uraniumminingandmilling,andplantdecommissioning.2.ThenuclearpowerlifecycleEngineersgenerallyclassifythenuclearfuelcycleintotwotypes:once-throughandclosed.Conventionalreactorsoper-ateonaonce-throughmodethatdischargesspentfueldirectlyintodisposal.Reactorswithreprocessinginaclosedfuelcycleseparatewasteproductsfromunused"ssionablematerialsothatitcanberecycledasfuel.Reactorsoperatingonclosedcyclesextendfuelsuppliesandhaveclearadvantagesintermsofstorageofwastedisposal,buthavedisadvantagesintermsofcost,short-termreprocessingissues,proliferationrisk,andfuelcyclesafety(Beckjordetal.,2003).Despitethesedifferences,bothonce-throughandclosednuclearfuelcyclesinvolveatleast"veinterconnectedstagesthatconstituteanuclearlifecycle:thefrontendofthecyclewhereuraniumfuelismined,milled,converted,enriched,andfabri-cated;theconstructionoftheplantitself;theoperationandmaintenanceofthefacility;thebackendofthecyclewherespentfuelisconditioned,(re)processed,andstored;anda"nalstagewhereplantsaredecommissionedandabandonedminesreturnedtotheiroriginalstate.Figs.1and2provideabriefdepictionoftheonce-throughandclosednuclearfuelcycle.2.1.ThefrontendofthenuclearlifecycleThenuclearfuelcycleislongandcomplex.Theprimaryfuelfornuclearpowerplants,uranium,iswidelydistributedintheearthscrustandtheoceaninminutequantities,withtheexceptionofconcentrationsrichenoughtoconstituteore.Uraniumisminedbothatthesurfaceandunderground,andafterextracteditiscrushed,groundintoa"neslurry,andleechedinsulfuricacid.Uraniumisthenrecoveredfromsolutionandconcentratedintosoliduraniumoxide,oftencalledyellowcake,beforeitisconvertedintohexa"uorideandheated.Then,hexa"uoridevaporisloadedintocylinderswhereitiscooledandcondensedintoasolidbeforeundergoingenrichmentthroughgaseousdiffusionorgascentrifuge.2.1.1.UraniumminingStartingatthemine,richoresembodyconcentrationsofuraniumoxideashighas10%,but0.2%orlessisusual,andmosturaniumproducerswillconsiderminingoreswithconcentrationshigherthan0.0004%.Amajorityoftheusablesoftorefoundinsandstonehasaconcentrationbetween0.2%and0.01%,andhardorefoundingranitehasaloweruraniumcontent,usuallyabout0.02%orless.Uraniumminesaretypicallyopencastpits,upto250mdeep,orunderground.Athirdextractiontechniqueinvolvessubjectingnaturaluraniumtoinsituleachingwherehundredsoftonsofsulfuricacid,nitricacid,andammoniaareinjectedintothestrataandthenpumpedupagainafter3-25years,yieldinguraniumfromtreatedrocks.2.1.2.UraniummillingMineduraniummustundergoaseriesofmetallurgicalprocessestocrush,screen,andwashtheore,lettingtheheavyuraniumsettleasthelighterdebrisisfunneledaway.Thenextstepisthemill,oftensituatednearthemine,whereacidoralkalibathsleachtheuraniumoutoftheprocessedore,producingabrightyellowpowder,calledyellowcake,thatisabout75%uraniumoxide(whosechemicalformisU 3 O 8).Inthecaseswhereoreshaveaconcentrationof0.1%,themillingmustgrind1000tonofrocktoextract1tonofyellowcake.Boththeoxideandthetailings(the999tonofremainingrock)remainradioactive,requiringtreatment.Acidsmustbeneutralizedwithlimestone,andmadeinsolublewithphosphates(Fleming,2007

Heaberlin,2003).2.1.3.UraniumconversionandenrichmentNextcomesconversionandenrichment,whereaseriesofchemicalprocessesareconductedtoremoveremainingimpu-rities.Naturaluraniumcontainsabout0.7%uranium-235;therestismainlyuranium-234oruranium-238.InordertobringtheARTICLEINPRESSFig.1.Theonce-throughnuclearfuelcycle.B.K.Sovacool/EnergyPolicy36(2008)2940-29532941 concentrationofuranium-235uptoatleast3.5%fortypicalcommerciallightwaterreactorsandabout4-5%forothermodernreactors,theoxidemustbeenriched,andtheprocessbeginsbyconvertinguraniumtouraniumhexa"uoride,UF 6,orhex.Then,itisenriched,andthetwodominantcommercialenrichment methodsaregaseousdiffusionandcentrifuge.Gaseousdiffusion,developedduringtheSecondWorldWaraspartoftheManhattanProject,accountsforabout45%ofworldenrichmentcapacity.Thediffusionprocessfunnelshexthroughaseriesofporousmembranesordiaphragms.Thelighteruranium-235moleculesmovefasterthantheuranium-238moleculesandhaveaslightlybetterchanceofpassingthroughtheporesinthemembrane.Theprocessisrepeatedmanytimesinaseriesofdiffusionstagescalledacascade,withtheenrichedUF 6 with-drawnfromoneendofthecascadeandthedepletedUF 6removedattheotherend.Thegasmustbeprocessedthroughsome1400stagesbeforeitisproperlyenriched(UraniumInformationCentre,2007).Thegascentrifugeprocess,"rstdemonstratedinthe1940s,feedshexintoaseriesofvacuumtubes,andaccountsforabout45%ofworldenrichmentcapacity.Whentherotorsarespunrapidly,theheaviermoleculeswithuranium-238increaseinconcentrationtowardstheouteredgeofthecylinders,withacorrespondingincreaseinuranium-235concentrationnearthecenter.Toseparatethetwoisotopes,centrifugesrotateatveryhighspeeds,withspinningcylindersmovingatroughlyonemilliontimestheaccelerationofgravity(UraniumInformationCentre,2007

).InUnitedStates,thegaseousdiffusionplantatPaducah,Kentucky,primarilydoesenrichmentwhileEuropeandRussiautilizemostlycentrifugemethods(FthenakisandKim,2007).Theremainingpercentage(10%)ofnuclearfuelcomesfromtherecyclingofnuclearweapons.Afterenrichment,about85%oftheoxidecomesoutaswasteintheformofdepletedhex,knownasenrichmenttails,whichmustbestored.Eachyear,forinstance,Francecreates16,000tonofenrichmenttailsthatarethenexportedtoRussiaoraddedtotheexisting200,000tonofdepleteduraniumwithinthecountry.The15%thatemergesasenricheduraniumisconvertedintoceramicpelletsofuraniumdioxide,UO 2,packedinzirconiumalloytubes,andbundledtogethertoformfuelrodassembliesforreactors.Tosupplyenoughenrichedfuelforastandard1000MWreactorfor1year,about200tonofnaturaluraniumhastobeprocessed(Fleming,2007).Moreover,uraniummustbetrans-portedfromtheminetoprocessingandenrichmentfacilities.Andsetaetal.(1998)foundthatinCanada,theuraniumneededtocreatefuelrodshastraveledmorethan4000kmbeforetheprocessiscomplete.TheIEA(2002)reportsthatinEuropemosturaniumistransported150-805kmbyrailway,1250kmbyboat,or378kmbytruck.2.2.ConstructionTheconstructionphaseofthenuclearlifecycleinvolvesthefabrication,transportation,anduseofmaterialstobuildgen-erators,turbines,coolingtowers,controlrooms,andotherinfrastructure.Atypicalnuclearplantusuallycontainssome50milesofpipingwelded25thousandtimes,and900milesofelectricalcables.Thousandsofelectricmotors,conduits,batteries,relays,switches,operatingboards,transformers,condensers,andfusesareneededforthesystemtooperate.Coolingsystemsnecessitatevalves,seals,drains,vents,gauges,"ttings,nuts,andbolts.Structuralsupports,"rewalls,radiationshields,spentfuelstoragefacilities,andemergencybackupgeneratorsmustremaininexcellentcondition.Temperatures,pressures,powerlevels,radiationlevels,"owrates,coolingwaterchemistry,andequip-mentperformancemustallbeconstantlymonitored.Whilehisestimateisfromanolder1000MWPressurizedWaterReactor, White(1995)calculatesthatthetypicalnuclearplantneeds170,000tonofconcrete,32,000tonofsteel,1363tonofcopper,andatotalof205,464tonofothermaterials.Manyofthesearecarbonintense;1tonofaluminumhasthecarbonequivalentofmorethan10,000tonofC0 2;1tonoflithium,44,000ton;onetonofsilver,913,000ton(White,1995

).ARTICLEINPRESSFig.2.Theclosednuclearfuelcycle.B.K.Sovacool/EnergyPolicy36(2008)2940-2953 2942 2.3.OperationTheoperationphaseofthelifecycleencompassestheenergyneededtomanagethecoolingandfuelcyclesoftheplant,aswellastheenergyneededforitsmaintenanceandthefuelsusedforbackupgenerators.Indirectenergyuseincludestheprovisionofpowerduringreactoroutages,repairs,andshutdowns.Theheartoftheoperatingnuclearfacilityisthereactor,whichgenerateselectricitythroughthe"ssion,orsplitting,ofuraniumandplutoniumisotopes.Inanuclearreactor,the"ssionprocessdoesnottakeplaceoneatomatatime.Uraniumhastherareandproductivepropertythatwhenitisstruckbyaneutron,itsplitsintotwoandproducesmoreneutrons.Ifoneuranium-235atomcollideswithanatomofuranium-238,oneoftheotherisotopesofuranium,itmaystaythereandinduceacoupleofdecaycyclestoproduceplutonium-239.Plutonium-239,sharingthesameprop-ertyofuranium-235,splitswhenstruckbyneutronstoactasadditionalfuel.Theprocesscanbecontrolledbyamoderatorconsistingofwaterorgraphitetospeedthereactionup,andneutron-absorbingcontrolrodstoslowitdown(Fleming,2007

Beckjordetal.,2003).Mostnuclearreactorsaroundtheworldhaveapresentlifetimeof30-40years,butproduceelectricityatfullpowerfornomorethan24years(Fleming,2007

).2.4.ThebackendofthenuclearlifecycleThebackendphaseinvolvesfuelprocessing,interimstorage,andpermanentsequestrationofwaste.Spentfuelmustbeconditionedforreactorsoperatingonaonce-throughfuelcycle,andreprocessedforthoseemployingaclosedfuelcycle.Eventually,radioactiveimpuritiessuchasbariumandkrypton,alongwithtransuranicelementssuchasamericiumandneptu-nium,clogtheuraniumfuelinganuclearreaction.Afterafewyears,fuelelementsmustberemoved,andfreshfuelrodsinserted.Thehalf-lifeofuranium-238,oneofthelargestcomponentsofspentfuel,isaboutthesameastheageoftheearth:4.5billionyears.Spentfuelmustthenbestoredatindividualreactorsitesinlargepoolsofwaterforatleast10years,afterwhichtheyarelocatedinlargeconcretecasksthatprovideair-cooling,shielding,andphysicalprotection.Whiletherearemanydifferentcasktypes,thoseintheUStypicallyhold20-24PressurizedWaterReactorfuelassemblies,sealedinaheliumatmosphereinsidethecasktopreventcorrosion.Decayheatistransferredbyheliumfromthefuelto"nsontheoutsideofthestoragecaskforcooling.The"nalstageofthebackendofthecycleinvolvesthesequestrationofnuclearwaste.Permanentgeologicalrepositoriesmustprovideprotectionagainsteveryplausiblescenarioinwhichradionuclidesmightreachthebiosphereorexposehumanstodangerouslevelsofradiation.Theserisksincludegroundwaterseepingintotherepository,corrosionofwastecontainers,leachingofradionuclides,andmigrationofcontaminatedground-watertowardsareaswhereitmightbeusedasdrinkingwaterorforagriculture.2.5.DecommissioningThelaststageofthenuclearlifecycleinvolvesthedecom-missioninganddismantlingofthereactor,aswellasreclamation oftheuraniumminesite.Afteracoolingoffperiodthatmaylastaslongas50-100years,reactorsmustbedismantledandcutintosmallpiecestobepackedincontainersfor"naldisposal.Proopsetal.(1996)expectnuclearplantstohaveanoperatinglifetimeof40years,butexpectdecommissioningtobe longer,takingatleast60years.Whileitwillvaryalongwithtechniqueandreactortype,thetotalenergyrequiredfordecommissioningcanbeasmuchas50%morethantheenergyneededfororiginalconstruction (Fleming,2007).Attheuraniummine,theoverburdenofrockcoveringtheareamustbereplacedandreplantedwithindigenousvegetation,andradioactivetailingsmustbetreatedandcon-tained.3.ReviewofnuclearlifecyclestudiesToassessthetotalcarbondioxide-equivalentemissionsoverthecourseofthenuclearlifecycle,thisstudybeganbyreviewing103studiesestimatinggreenhousegasemissionsfornuclearplants.These103studieswerenarrowedaccordingtoathree-phaseselectionprocess.First,giventhattheavailabilityofhigh-qualityuraniumorechangeswithtime,andthatmining,milling,enrichment,construction,andreactortechnologieschangeoverthedecades,thestudyexcludedsurveysmorethan10yearsold(i.e.,publishedbefore1997).Admittedly,excludingstudiesmorethanadecadeoldisnoguaranteethatthedatautilizedbynewerstudiesisinfactnew.OneanalysisfromDonesetal.(2004c),forinstance,reliedonreferencesfromthe1980sforthemodelingofuraniummining;datafrom1983formodelinguraniumtailingponds;1996dataforuraniumconversion;and2000dataforuraniumenrichment.Still,excludingstudiesmorethan10yearsoldisanattempttohedgeagainsttheuseofoutdateddata,andtoensure thatrecentchangesintechnologyandpolicyareincludedinlifecycleestimates.Table1listsall40studiesexcludedbytheir date.Second,thestudyexcludedanalysesthatwerenotinthepublicdomain,costmoneytoaccess,orwerenotpublishedinEnglish.

Table2detailstheninestudiesexcludedforlackofaccessibility.Third,35studieswereexcludedbasedontheirmethodology.Thesestudiesweremostfrequentlydiscountedbecausetheyeitherreliedonunpublisheddataorutilizedsecondarysources.Thoserelyingonunpublisheddatacontainedproprie-taryinformation,referenceddatanotpublishedalongwiththestudy,didnotexplaintheirmethodology,werenottransparentabouttheirdatasources,ordidnotdetailgreenhousegasemissionestimatesforseparatepartsofthenuclearfuelcycleingCO 2e/kWh.Thoseutilizingsecondarysourcesmerelyquotedotherpreviouslypublishedreportsanddidnotprovideanynewcalculationsorsyntheticanalysisontheirown.Table3depictsthe35studiesexcludedbymethodology.Excludingdetailedstudiesthatrelyonunpublishedornon-transparentdatadoesruntheriskofincludinglessdetailed(andlessrigorous)studiesrelyingonpublishedandopendata.Simplyplacingastudyinthepublicdomaindoesnotnecessarilymakeitgood.However,theauthorbelievesthatthisriskismorethanoffsetbythepositivebene"tsoftransparencyandaccountability.Transparencyenhancesvalidityandaccuracy;publicknowledgeislesspronetoerrors,andmoresubjecttotheprocessofdebateanddialoguethatimprovesthequalityofinformation.Transpar-ency,saysAnnFlorini,anexpertongovernance,isthemosteffectiveerrorcorrectionsystemhumanityhasyetdevised (Florini,2005,p.16).Furthermore,transparencyisessentialtopromotingsocialaccountability.Societysimplycannotmakeinformeddecisionsaboutnuclearpowerwithoutpublicdiscus-sion;forthesereasons,theauthorbelievesthatonlyresultsinthe publicdomainshouldbeincluded.Theremaining19studiesmetallcriteria:theywerepublishedinthepast10years,accessibletothepublic,transparentabouttheirmethodology,andprovidedclearestimatesofequivalentgreenhousegasemissionsaccordingtotheseparatepartsofthenuclearfuelcycle.Thesestudieswereweighedequally;thatis,ARTICLEINPRESSB.K.Sovacool/EnergyPolicy36(2008)2940-2953 2943 theywerenotadjustedinparticularfortheirmethodology,timeofreleasewithinthepast10years,orhowrigorouslytheywerepeerreviewedorcitedintheliterature.Table4documentstheresultsofthese19studies.Statisticalanalysisofthese19studiesrevealsarangeofgreenhousegasemissionsoverthecourseofthenuclearlifecycleattheextremelylowendof1.4gCO 2e/kWhandtheextremelyhighendof288gCO 2e/kWh.Accountingforthemeanvaluesofemissionsassociatedwitheachpartofthenuclearlifecycle,themeanvaluereportedfortheaveragenuclearpowerplantis66gCO 2 e/kWh.Tables5and6 andFigs.2and3providethecompletebreakdownofthisestimate.AsFig.3depicts,thefrontendcomponentofthenuclearcycleisresponsiblefor38%ofequivalentemissions;decommissioning18%;operation17%;backend15%;andconstruction12%(Fig.4).4.AssessingthedisparityinlifecycleestimatesWhataccountsforsuchawidedisparityamonglifecycleestimatesofgreenhousegasemissionsassociatedwiththenuclearfuelcycle?Studiesprimarilydifferintermsoftheirscope;assumptionsregardingthequalityofuraniumore;assumptionsregardingtypeofmining;assumptionsconcerningmethodofenrichment;whethertheyassessedemissionsforasinglereactororfora"eetofreactors;whethertheymeasured historicalormarginal/futureemissions;assumptionsregardingreactortype,siteselection,andoperationallifetime;andtypeoflifecycleanalysis.4.1.ScopeSomestudiesincludedjustoneortwopartsofthenuclearfuelcycle,whereasothersprovidedexplicitdetailsforevensubcom-ponentsofthefuelcycle.Vorspoolsetal.(2000),forexample,analyzedjusttheemissionsassociatedwithconstructionanddecommissioningforreactorsacrosstheworld,whereas ExternE(1998)assessedthecarbonequivalentfortheconstructionoftheSizewellBnuclearreactorintheUnitedKingdom.Theirestimatesarenearthelowendofthespectrum,atbetween3and11.5gCO 2e/kWh.Incontrast,StormvanLeeuwenetal.(2007)lookedateverysinglesubcomponentofthefuelcycle,andproducedestimatesnearthehighendofthespectrumat112-166gCO 2/kWh.Table7providesabreakdownoftheirestimate,whichtheauthorsemphasizeishighlydependentonthequalityofuraniumorebeingusedtofuelnuclearplants.Ithasbeenincludedherefortworeasons:togivereadersasenseforhowdetailedlifecycleassessmentscanbe,andbecausethisstudyrefersbacktosomeofthenumberspresentedinthistablewhenmakingcomparisonsbelow.StormvanLeeuwenandSmithsestimatehasnotbeenuniversallyaccepted.Dones(2007)pointsoutthatwhileStormvanLeeuwenandSmithsanalysisistransparentenoughthatitcanbecritiqued

-somethingpositive

-hebelievesthattheirestimateistoohigh.Hisownsurveyoflifecyclestudiesfoundarangeof2-230gCO 2e/kWh,butthattherangeof2-77gCO 2 e/kWhwasmostcommon,withonly3studiesgivingaverageestimatesabove40gCO 2e/kWh.DonesalsoarguesthatStormvanLeeuwenandSmithstreatmentofgreenhousegasesassociatedwiththenaturalgassupplychainareinconsistent,thattheyrelyonoutdatedreferencesforsomeoftheirestimates,andthatsomeoftheircostconversionestimatesaretoogeneric.Donesarguesthattheypaynoconsiderationtothecoproductionofminerals,acommonpracticewhereeconomicallyviableminingandmillingoflow-gradeuraniumtakeplacewithotheractivities,meaningARTICLEINPRESSTable1LifecyclestudiesexcludedbydateStudyLocationEstimate(gCO 2 e/kWh)Arronetal.(1991)

CanadaBodansky(1992)World5.7-17Bowersetal.(1987)

--Bude(1985)

--Chapmanetal.(1974)

--Chapman(1975)

--CRIEPI(1995)Japan22DeLucchi(1993)UnitedStates40-69Dones(1995)World-DonesandFrischknecht(1996)World-Donesetal.(1994)World-El-Bassioni(1980)

--ERDA(1976)UnitedStates-ExternE(1995Europe-Held(1977)-20HohenwarterandHeindler(1988)Germany-IAEA(1996a)World-IAEA(1996b)World-IEA(1994)World30-60Kivisto(1995)Finland17-59Mortimer(1989)UnitedKingdom-Mortimer(1991a)World47-54Mortimer(1991b)World47-54Perry(1977)UnitedStates-Proopsetal.(1996)UnitedKingdom2.83Raeder(1977)

--RomboughandKoen(1975)

--Roseetal.(1983)UnitedStates-SandgrenandSorteberg(1994)Norway-ScienceConcepts(1990)UnitedStates30Spreng(1988)

--Taylor(1996)World19.7Tsoulfanidis(1980)UnitedStates-Tunbrantetal.(1996)Sweden-Uchiyama(1994)Japan10.5-47Uchiyama(1996)

--Yasukawaetal.(1992)Japan-Yoshiokaetal.(1994)

JapanWhite(1995)UnitedStates34.1-37.7WhittleandCameron(1977)UnitedStates-Table2LifecyclestudiesexcludedbyaccessibilityStudyLocationEstimate(gCO 2e/kWh)ReasonexcludedANRE(1999)Japan-InJapaneseDonesetal.(2003a,b)

USA5OnlyavailabletoecoinventsubscribersDonesetal.(2004c)Switzerland5-12OnlyavailabletoecoinventsubscribersDones(2003)Europe-InGermanFrischknecht(1995)Germany-InGermanIzunoetal.(2001)Japan-InJapaneseLewin(1993)Germany-InGermanNuclearEnergyAgency(2007)World-OnlyavailableforpurchaseWeisetal.(1990)Germany-InGermanB.K.Sovacool/EnergyPolicy36(2008)2940-29532944 energyexpendituresallocatedtouraniumminingbyStormvanLeeuwenandSmithmaybehigh.Asaresult,DonesconcludesthatStormvanLeeuwenandSmithmayoverestimatetheenergyexpenditures,andthusgreenhousegasemissions,associatedwithnuclearpower.4.2.QualityofuraniumoreStudiesvariedintheirassumptionsregardingthequalityofuraniumoreusedinthenuclearfuelcycle.Low-gradeuraniumorescontainlessthan0.01%yellowcake,andisatleasttentimeslessconcentratedthanhigh-gradeores,meaningittakes10tonoforetoproduce1kgofyellowcake.Putanotherway,ifuraniumoregradedeclinesbyafactoroften,thenenergyinputstominingandmillingmustincreasebyatleastafactoroften(DiesendorfandChristoff,2006

).StormvanLeeuwenetal.(2007)pointoutthatthiscangreatlyskewestimates,asuraniumof10%U 3 O 8 hasemissionsforminingandmillingatjust0.04gCO 2/kWh,whereasuraniumat0.013%gradehasassociatedemissionsmorethan1500 timesgreaterat67gCO 2/kWh.Thesametrendistruefortheemissionsassociatedwithuraniumminelandreclamation.Withuraniumof10%grade,emissionsforreclamationarejust0.07g CO 2e/kWh,butat0.013%,theyare122gCO 2/kWh.4.3.Open-pitorundergrounduraniumminingThetypeofuraniumminingwillalsore"ectdifferentCO 2 eemissions.Open-pitminingoftenproducesmoregaseousradonandmethaneemissionsthanundergroundmines,and Andsetaetal.(1998)notethatminingtechniqueswillreleasevaryingamountsofCO 2basedontheexplosivesandsolventstheyusetopurifyconcentrate.Theyalsopointoutthatthecarboncontentassociatedwithacidleechingusedtoextracturaniumcanvary,aswellastheemissionsassociatedwiththeuseoflimetoneutralizetheresultingleachedtailings.Theemissionsassociatedwithuraniumminingdependgreatlyonthelocalenergysourceforthe

mines.Andsetaetal.(1998)notethatinCanada,uraniumextractedfromminesclosertoindustrialcentersreliesonmoreef"cient,centrallygeneratedpower.Incontrast,remoteminestherehavereliedonlessef"cientdieselgeneratorsthatconsumed45,000tonoffossilfuelperyear/mine,releasingupto138,000tonofcarbondioxideeveryyear(Andsetaetal.,1998

).ARTICLEINPRESSTable3Lifecyclestudiesexcludedbymethodology aStudyLocationEstimate(gCO 2 e/kWh)ReasonexcludedAustraliaCoalAssociation(2001)Australia30-40ReliesonunpublisheddataBarnabyandKemp(2007a)OECDCountries11-130ReliesonsecondarysourcesCommonwealthofAustralia(2006)Australia,France,Germany,Japan,Sweden,Finland,UnitedStates5-60ReliesonsecondarysourcesDelucchi(2003)UnitedStates26ReliesonunpublisheddataDenholmandKulcinski(2004)World10-100ReliesonsecondarysourcesDonesetal.(2004a)World5-80ReliesonsecondarysourcesEchavarri(2007)World2.6-5.5ReliesonsecondarysourcesFleming(2007)World88-134ReliesonsecondarysourcesFritsche(1997)Germany34ReliesonunpublishedGEMISdataFthenakisandAlsema(2006)Europe20-40ReliesonsecondarysourcesGagnonetal.(2002)World15ReliesonunpublisheddataHeede(2005)UnitedStates2.5-5.7ReliesonsecondarysourcesKoch(2000)World2-59ReliesonunpublisheddataKrewittetal.(1998)Europe19.7ReliesonunpublisheddataKulcinski(2002)World15ReliesonsecondarysourcesLeeetal.(2000)SouthKorea2.77ReliesonunpublisheddataLeeetal.(2004)SouthKorea0.198-2.77ReliesonunpublisheddataMeier(2002)UnitedStates17ReliesonsecondarysourcesMeierandKulcinski(2002)UnitedStates15ReliesonsecondarysourcesMeieretal.(2005)UnitedStates17ReliesonsecondarysourcesOntarioPowerAuthority(2005)Canada5-12ReliesonunpublisheddataPembinaInstitute(2007)Canada10-120ReliesonsecondarysourcesRuetheretal.(2004)UnitedStates3ReliesonsecondarysourcesSpadaroetal.(2000)World2.5-5.7ReliesonunpublisheddataSustainableDevelopmentCommission(2006)World2-20ReliesonsecondarysourcesTaharaetal.(1997)Japan1.8ReliesonsecondarysourcesTokimatsuetal.(2000)Japan20.9Doesnotseparatefuelcycleestimatesfor"ssionreactorsUKPOST(2006)UnitedKingdom5ReliesonsecondarysourcesandunpublisheddataUtgikarandThiesen(2006)World2-59ReliesonsecondarysourcesVanDeVate(1997)World9ReliesonunpublishedFENCHdataVanDeVate(2003)World8.9ReliesonunpublishedFENCHdataVattenfall(1997)Sweden3.3ReliesonpublishedutilitydataWorldEnergyCouncil(2004)Australia,Germany,Sweden,Switzerland,andUnited Kingdom3-40ReliesonunpublisheddataWeisser(2007)World2.8-24ReliesonsecondarysourcesWorldNuclearAssociation(2006)Japan,Sweden,Finland6-26Reliesonsecondarysources aThephrasereliesonunpublisheddatameansthatstudiescontainedproprietaryinformation,referenceddatanotpublishedalongwiththestudy,didnotexplaintheirmethodology,werenottransparentabouttheirdatasources,ordidnotdetailgreenhousegasemissionestimatesforseparatepartsofthenuclearfuelcycleingCO 2 e/kWh.Thephrasereliesonsecondarysourcesmeansthatstudiesmerelyquotedotherpreviouslypublishedreportsanddidnotprovideanynewcalculationsorsyntheticanalysisontheirown.B.K.Sovacool/EnergyPolicy36(2008)2940-2953 2945 ARTICLEINPRESSTable4Overviewofdetailednuclearlifecyclestudies aStudyLocationAssumptionsFuelcycleIndividualestimate(gCO 2 e/kWh)Totalestimate(gCO 2 e/kWh)Andsetaetal.(1998)CanadaCANDUheavywaterreactor,40-yearlifecycle,high-qualitynaturaluraniumore, enrichedandchargedwithfossilfuel generatorsFrontend0.6815.41Construction2.22 Operation11.9 Backend-Decommissioning0.61BarnabyandKemp(2007b)United Kingdom35-yearlifecycle,averageloadfactorof85%,uraniumoregradeof0.15%Frontend5684-122Construction11.5Operation-Backend-Decommissioning16.5-54.5Donesetal.(2005)Switzerland100-yearlifecycle, Gosgenpressurizedwaterreactorand LiebstadtboilingwaterreactorFrontend3.5-10.25-12Construction1.1-1.3 Operation-Backend0.4-0.5 Decommissioning-Donesetal.(2003a,b)Switzerland,France,andGermany40-yearlifecycle,existingboilingwaterreactorsandpressurizedwaterreactorsusingUCTEnuclearfuelchainsFrontend6-127.6-14.3Construction1.0-1.3Operation-Backend0.6and1.0 Decommissioning-Donesetal.(2004b)China20-yearlifecycle,once-throughnuclearcycleusingcentrifugetechnologyFrontend7.4-77.49-80Construction1.0-1.4 Operation-Backend0.6-1.2 Decommissioning-ExternE(1998)United KingdomAnalysisofemissionsforconstructionofSizewellBpressurizedwaterreactorintheUnitedKingdomFrontend-11.5Construction11.5Operation-Backend-Decommissioning-FritscheandLim(2006)bGermanyAnalysisofemissionsforatypical1250MWGermanreactorFrontend2064Construction11 Operation-Backend33 Decommissioning-FthenakisandKim(2007)UnitedStates,Europe,and Japan40-yearlifecycle,85%capacityfactor,mixofdiffusionandcentrifugeenrichmentFrontend12-21.716-55Construction0.5-17.7Operation0.1-10.8 Backend2.1-3.5 Decommissioning1.3Hondo(2005)JapanAnalysisofbase-caseemissionsforoperatingJapanesenuclearreactorsFrontend1724.2Construction2.8 Operation3.2 Backend0.8Decommissioning0.4IEA(2002)cSwedenand Japan40-yearlifecycleforSwedishForsmark3boilingwaterreactorand30yearlifecyclefor Japaneseboilingwaterreactor,advanced BWR,andfastbreederreactorFrontend1.19-8.522.82-22Construction0.27-4.83 Operation-Backend1.19-8.52 Decommissioning0.17ISA(2006)dAustraliaAnalysisofemissionsforexistingAustralianlightwaterreactorswithuraniumoreof 0.15%gradeFrontend4.5-58.510-130Construction1.1-13.5 Operation2.6-34.5 Backend1.7-22.2Decommissioning0.1-1.3ISA(2006)dAustraliaAnalysisofemissionsforexistingAustralianheavywaterreactorswithuraniumoreof 0.15%gradeFrontend4.5-5410-120Construction1.1-12.5 Operation2.6-31.8 Backend1.7-20.5 Decommissioning0.1-1.2B.K.Sovacool/EnergyPolicy36(2008)2940-2953 2946 4.4.GaseousdiffusionorcentrifugeenrichmentAnothersigni"cantvariationconcernsthetypeofuraniumenrichment.Donesetal.(2005)notethatgaseousdiffusionismuchmoreenergy-intense,andthereforehashigherassociatedcarbondioxideemissions.Gaseousdiffusionrequires2400-2600kWhperseperativeworkunit(afunctionmeasuringtheamountofuraniumprocessedproportionedtoenergyexpendedforenrichment),ARTICLEINPRESSTable4(continued)StudyLocationAssumptionsFuelcycleIndividualestimate(gCO 2 e/kWh)Totalestimate(gCO 2 e/kWh)Rashadand Hammad (2000)Egypt30yearlifecycleforapressurizedwaterreactoroperatingat75%capacityFrontend23.526.4Construction2.0 Operation0.4Backend0.5Decommissioning-StormvanLeeuwenetal.(2005)WorldAnalysisofemissionsforexistingnuclearreactorsFrontend3684-122Construction12-35 Operation-Backend17 Decommissioning23-46StormvanLeeuwen(2006)WorldAnalysisofemissionsforexistingnuclearreactorsFrontend3992-141Construction13-36 Operation-Backend17Decommissioning23-49StormvanLeeuwenetal.(2007)WorldAnalysisofemissionsforexistingnuclearreactorsassuming0.06%uraniumore,70%

centrifugeand30%diffusionenrichment,and inclusionofinterimandpermanentstorage andminelandreclamationFrontend16.26-28.27112.47-165.72Construction16.8-23.2 Operation24.4 Backend15.51-40.75 Decommissioning39.5-49.1Tokimatsuetal.(2006)eJapan60-yearlifecycle,lightwaterreactorreferencecase,emissionsfor1960-2000Frontend5.9-11810-200Construction1.3-26Operation2.0-40Backend0.7-14 Decommissioning0.1-2Vorspoolsetal.(2000)WorldAnalysisofemissionsforconstructionanddecommissioningofexistingreactorsFrontend-3 Construction2Operation-Backend-Decommissioning1WhiteandKulcinski(2000)UnitedStates40-yearlifecycleof1000MWpressurizedwaterreactoroperatingat75%capacity factorFrontend9.515Construction1.9Operation2.2Backend1.4 Decommissioning0.01 aFrontendincludesminingandmilling,conversion,enrichment,fuelfabrication,andtransportation.Constructionincludesallmaterialsandenergyinputsforbuildingthefacility.Operationincludesenergyneededformaintenance,coolingandfuelcycles,backupgenerators,andduringoutagesandshutdowns.Backendincludesfuelprocessing,conditioning,reprocessing,interimandpermanentstorage.Plantdecommissioningincludesdeconstructionoffacilityandlandreclamation.bStudymentionsatotalof31gkWhfororeextraction,enrichment,andconstruction,andanother33gkWhofothergreenhousegasesotherthancarbon.

cTheIEAstudycombinedupstreamanddownstreamemissionsintheirestimate.Theyhavebeendividedequallyovertheupstreamanddownstreamphases.

dNumbersderivedfrom10to130/120estimateandthenapportionedaccordingtopercentagesgiveninFigs.5.11and5.22.

eNumbersderivedfrom10to200g/kWhestimateandapportionedaccordingtopercentagesprovidedinFig.3(c).Table5Summarystatisticsofquali"edstudiesreportingprojectedgreenhousegasemissionsfornuclearpowerplants a(gCO 2e/kWh)FrontendConstructionOperationBackendDecommissioningTotalMin0.580.270.10.40.011.36Max118354040.7554.5288.25 Mean25.098.2011.589.212.0166.08

N171991513 aFrontendincludesminingandmilling,conversion,enrichment,fuelfabrication,andtransportation.Constructionincludesallmaterialsandenergyinputsforbuildingthefacility.Operationincludesenergyneededformaintenance,coolingandfuelcycles,backupgenerators,andduringoutagesandshutdowns.Backendincludesfuelprocessing,conditioning,reprocessing,interimandpermanentstorage.Plantdecommissioningincludesdeconstructionoffacilityandlandreclamation.B.K.Sovacool/EnergyPolicy36(2008)2940-29532947 comparedtojust40kWhperSWUforcentrifugetechniques.Theenergyrequirementsforthesetwoprocessesaresovastlydifferentbecausegaseousdiffusionisamucholdertechnology,necessitatingextensiveelectricalandcoolingsystemsthatarenotfoundincentrifugefacilities.Emissionswillfurthervaryonthelocalpowersourcesattheenrichmentfacilities.Donesetal.(2004a-c)calculate9gCO 2e/kWhforChinesecentrifugeenrichmentrelayingonamixofrenewableandcentralizedpowersources,butupto80gCO 2e/kWhifgaseousdiffusionispoweredcompletelybyfossilfuels.4.5.IndividualoraggregateestimatesSomestudieslookatjustspeci"creactors,whileothersassessemissionsbasedonindustry,national,andglobalaverages.These obviouslyproducedivergentestimates.Donesetal.(2005)lookatjusttwoactualreactorsinSwitzerland,the Gosgenpressurizedwaterreactorand Liebstadtboilingwaterreactorandcalculateemissionsat5-12gCO 2e/kWh,whereasotherstudieslookatglobalreactorperformanceandreachestimatesmorethan10timesgreater.4.6.Historicalormarginal/futureemissionsYetanotherdifferenceconcernswhetherresearchersassessedhistoric,future,orprototypicalemissions.Studiesassessinghistoricemissionslookedonlyatemissionsrelatedtorealplantsoperatinginthepast;studieslookingatfutureaverageemissionslookedathowexistingplantswouldperformintheyearstocome;studiesanalyzingprototypicalemissionslookedathowadvancedplantsyettobebuiltwouldperforminthefuture.Tokimatsuetal.(2006),forinstance,foundhistoricalemissionsforlightwaterreactorsinJapanfrom1960to2000toberatherhighatbetween10and200gCO 2e/kWh.Others,suchasDonesetal.(2005)

,lookedatfutureemissionsforthenext100yearsusingmoreadvancedpressurizedwaterreactorsandboilingwaterreactors.Stillotherstudiesmadedifferentassumptionsaboutfuturereactors,namelyfast-breederreactorsusingplutoniumandthorium,andotherGenerationIVnucleartechnologyexpectedtobemuchmoreef"cientiftheyeverreachcommercialproduction.4.7.ReactortypeStudiesvariedextensivelyinthetypesofreactorstheyanalyzed.Morethan30commercialreactordesignsexist today,andeachdiffersinitsfuelcycle,output,andcoolingsystem.Themostcommonaretheworlds263pressurizedwaterreactors,usedinFrance,Japan,RussiaandtheUS,whichrelyonenricheduraniumoxideasafuelwithwaterascoolant.Boilingwaterreactorsaresecondmostcommon,with92inoperationthroughouttheUS,Japan,andSweden,ARTICLEINPRESSTable6Meanstatisticsofquali"edstudiesreportinglifecycleequivalentgreenhousegasemissionsfornuclearplantsStudyFrontendConstructionOperationBackendDecommissioningAndsetaetal.(1998)0.682.2211.9-0.61BarnabyandKemp(2007b)5611.5--35.5Donesetal.(2005)6.851.2-0.45-Donesetal.(2003a,b)91.15-0.8-Donesetal.(2004b)42.41.2-0.9-ExternE(1998)-11.5---FritscheandLim(2006)2011-33FthenakisandKim(2007)16.859.15.412.81.3Hondo(2005)172.83.20.80.4IEA(2002)4.862.55-4.860.17ISA(2006)31.57.318.5511.950.7ISA(2006)29.256.817.211.10.65RashadandHammad(2000)23.520.40.5-StormvanLeeuwenetal.(2005)3623.5-1734.5StormvanLeeuwenandWillem(2006)3924.5-1736StormvanLeeuwenetal.(2007)22.272024.428.1344.3Tokimatsuetal.(2006)61.9513.65217.351.05Vorspoolsetal.(2000)-2--1WhiteandKulcinski(2000)9.51.92.21.40.01Mean25.098.211.589.212.01 300 250 200 150 100 50 0 Front End Operation Construction Backend DecommissioningTotalFig.3.Rangeandmeanemissionsreportedfromquali"edstudiesforthenuclearfuelcycle(gCO 2 e/kWh)B.K.Sovacool/EnergyPolicy36(2008)2940-29532948 whichalsorelyonenricheduraniumoxidewithwaterasacoolant.Thencomepressurizedheavywaterreactors,ofwhichthereare38inCanada,thatusenaturaluraniumoxidewithheavywaterasacoolant.Nextcomes26gas-cooledreactors,usedpredominatelyintheUnitedKingdom,whichrelyonnaturaluraniumandcarbondioxideasacoolant.Russiaalsooperates17lightwatergraphitereactorsthatuseenricheduraniumoxidewithwaterasacoolantbutgraphiteasamoderator.Ahandfulofexperimentalreactors,includingfast-breederreactors(cooledbyliquidsodium)andpebblebedmodularreactors(whichcanoperateatfullloadwhilebeingrefueled),stillintheprototypestages,makeuptherestoftheworldtotal(Beckjordetal.2003).Togiveanideaabouthowmuchreactordesigncanin"uencelifecycleemissions,Boczaretal.(1998)commentthatCANDUreactorsarethemostneutronef"cientcommercialreactors,achievingtheiref"ciencythroughtheuseofheavywaterforbothcoolantandmoderator,andrelianceonlow-neutron-absorbingmaterialsinthereactorcore.CANDUreactorsthushavetheabilitytoutilizelow-gradenuclearfuelsandrefuelwhilestillproducingpower,minimizingequivalentcarbondioxideemissions.ThiscouldbewhyAndsetaetal.(1998)concludethatCANDUreactorshaverelativelylowemissions(15gCO 2e/kWh)comparedtotheaverageemissionsfromquali"edstudiesasdescribedbythiswork(66gCO 2e/kWh).Others,suchasStormvanLeeuwenetal.(2007),contestthesenumbersandarguethattheproductionofheavywaterassociatedwithCANDUreactorsisveryenergy-intensiveandcanproduceemissionsmorethanafactorofonegreaterthantheprojectionmadebyAndsetaetal.4.8.SiteselectionEstimatesvarysigni"cantlybasedonthespeci"creactorsiteanalyzed.TheSustainableDevelopmentCommission(2006)arguesthatlocationin"uencesreactorperformance(andcon-sequentialcarbon-equivalentemissions).Someofthewaysthatlocationmayin"uencelifetimeemissionsincludedifferencesin:constructiontechniques,includingavailablematerials,compo-nentmanufacturing,andskilledlabor;localenergymixatthatpointofconstruction;traveldistanceformaterialsandfuelcyclecomponents;associatedcarbonfootprintwiththetransmissionanddis-tribution(T&D)networkneededtoconnecttothefacility;coolingfuelcyclebasedonavailabilityofwaterandlocal hydrology;environmentalcontrolsbasedonlocalpermittingandsiting requirements.Eachofthesecansubstantiallyaffecttheenergyintensityandef"ciencyofthenuclearfuelcycle.ConsidertwoextremesfromTable4.InCanada,thegreen-housegas-equivalentemissionsassociatedwiththeCANDUlifecycleareestimatedatabout15gCO 2e/kWh.CANDUreactorstendtobebuiltwithskilledlaborandadvancedconstructionARTICLEINPRESSFig.4.Meanemissionsreportedfromquali"edstudiesforthenuclearfuelcycle(gCO 2 e/kWh).Table7EmissionsforthenuclearfuelcyclefromstormvanLeeuwenandSmith(2007),ingCO 2/kWhNuclearprocessEstimate(gCO 2/kWh)Frontend (total)16.26-28.27Uraniumminingandmilling(softandhardores)(uraniumgradeof0.06%)10.43Re"ningofyellowcakeandconversiontoUF 62.42-7.49Uraniumenrichment(70%UC,30%diff)2.83-8.03 Fuelfabrication0.58-2.32 Construction (total)16.8-23.2Reactoroperationandmaintenance (total)24.4 Backend (total)15.51-40.75Depleteduraniumreconversion2.10-6.24 Packagingdepleteduranium0.12-0.37 Packagingenrichmentwaste0.16-0.46 Packagingoperationalwaste1.93-3.91 Packagingdecommissionedwaste2.25-3.11Sequestrationofdepleteduranium0.12-0.35Sequestrationofenrichmentwaste0.16-0.44 Sequestrationofoperationalwaste1.84-3.73 Sequestrationofenrichmentwaste1.98-2.74 Interimstorageatreactor0.58-2.32 Spentfuelconditioningfor"naldisposal0.35-1.40 Construction,storage,andclosureofpermanentgeologicrepository3.92-15.68 Decommissioning (total)39.5-49.1Decommissioninganddismantling25.2-34.8 LandReclamationofuraniummine(uraniumgradeof0.06%)14.3 Total112.47-165.72B.K.Sovacool/EnergyPolicy36(2008)2940-29532949 techniques,andtheyutilizeuraniumthatisproduceddomes-ticallyandrelativelyclosetoreactorsites,enrichedwithcleanertechnologiesinaregulatoryenvironmentwithrigorousenviron-mentalcontrols.Bycontrast,thegreenhouse-gas-equivalentemissionsassociatedwiththeChinesenuclearlifecyclecanbeashighas80gCO 2e/kWh.ThiscouldbebecauseChinesereactorstendtobebuiltusingmorelabor-intensiveconstructiontechniques,mustimporturaniumthousandsofmilesfromAustralia,andenrichfuelprimarilywithcoal-"redpowerplantsthathavecomparativelylessstringentenvironmentalandair-qualitycontrols.4.9.OperationallifetimeHowlongtheplantsatthosesitesareoperatedandtheircapacityfactorin"uencestheestimatesoftheircarbondioxide-equivalentintensity.StormvanLeeuwenetal.(2007)notethata30-yearoperatinglifetimeofanuclearplantwithaloadfactorof82%tendstoproduce23.2gCO 2/kWhforconstruction.Switchtheloadfactorto85%andthelifetimeto40years,andtheemissionsdropabout25%to16.8gCO 2/kWh.Thesameistruefordecom-missioning.Aplantoperatingfor30yearsat82%capacityfactorproduces34.8gCO 2/kWhfordecommissioning,butdrop28%to25.2gCO 2/kWhifthecapacityfactorimprovesto85%andtheplantisoperatedfor40years.Mostofthequali"edstudiesreferencedaboveassumelifetimenuclearcapacityfactorsthatdonotseemtomatchactualperformance.Almostallofthequali"edstudiesreportedcapacityfactorsof85-98%,whereactualoperatingperformancehasbeenless.WhilethenuclearindustryintheUShasboastedrecentcapacityfactorsinthe90%range,averageloadfactorsoverthe entirelifeoftheplantsisverydifferent:66.3%forplantsintheUK (AssociationofElectricityProducers,2007)and81%fortheworldaverage(May,2002).4.10.TypeoflifecycleanalysisThetypeoflifecycleanalysiscanalsoskewestimates.Projectionscanbetop-down,meaningtheystartwithoverallestimatesofapollutant,assignpercentagestoacertainactivity(suchascementmanufacturingorcoaltransportation),andderiveestimatesofpollutionfromparticularplantsandindus-tries.Ortheycanbebottom-up,meaningthattheystartwithaparticularcomponentofthenuclearlifecycle,calculateemissionsforit,andmovealongthecycle,aggregatingthem.Similarly,lifecyclestudiescanbeprocess-basedorrelyoneconomicinput-outputanalysis.Process-basedstudiesfocusontheamountofpollutantreleased

-inthiscase,carbondioxideoritsequivalent

-perproductunit.Forexample,iftheamountofhypothesizedcarbondioxideassociatedwitheverykWhofelectricitygenerationforaregionwas10g,andthecementneededforanuclearreactortook10kWhtomanufacture,aprocessanalysiswouldconcludethatthecementwasresponsiblefor100gofCO 2.Input-outputanalysislooksatindustryrelationswithintheeconomytodepicthowtheoutputofoneindustrygoestoanother,whereitservesasaninput,andattemptstomodelcarbondioxideemissionsasamatrixofinteractionsrepresentingeconomicactivity.StormvanLeeuwenetal.(2007),forexample,relyheavilyoncalculatingaverageenergyintensityforvariouspartsofthenuclearfuelcycleandaggregatethosenumbersintoa"nalestimate.Donesetal.(2004a-c)usesprocessanalysistodescribethefulllifecycleofspeci"cindustriesassociatedwiththenuclearfuelcycle,suchasmaterialandchemicalmanufacturing,energyconversion,electricitytransmission,andwastemanagement.TheISA(2006)usesahybridlifecycleassessmentthatcombinesprocessanalysiswithinputandoutputmethodologies.Thesedifferentapproachesproduceunderstandablydifferentresults.5.ConclusionThe"rstconclusionisthatthemeanvalueofemissionsoverthecourseofthelifetimeofanuclearreactor(reportedfromquali"edstudies)is66gCO 2e/kWh,duetorelianceonexistingfossil-fuelinfrastructureforplantconstruction,decommissioning,andfuelprocessingalongwiththeenergyintensityofuraniumminingandenrichment.Thus,nuclearenergyisinnowaycarbonfreeoremissionsfree,eventhoughitismuchbetter(frompurelyacarbon-equivalentemissionsstandpoint)thancoal,oil,andnaturalgaselectricitygenerators,butworsethanrenewableandsmallscaledistributedgenerators(seeTable8).Forexample,Gagnonetal.(2002)foundthatcoal,oil,diesel,andnaturalgasgeneratorsemittedbetween443and1050gCO 2e/kWh,farmorethanthe66gCO 2e/kWhattributedtothenuclearlifecycle.However,Pehnt(2006)conductedlifecycleanalysesfor15separatedistributedgenerationandrenewableenergytechnolo-giesandfoundthatallbutone,solarphotovoltaics(PV),emittedmuchlessgCO 2e/kWhthanthemeanreportedfornuclearplants.InananalysisusingupdateddataonsolarPV, Fthenakisetal.(2008)foundthatcurrentestimatesonthegreenhousegasemissionsfortypicalsolarPVsystemsrangefrom29to35gCO 2e/kWh(basedoninsolationof1700kWh/m 2/yrandaperformanceratioof0.8).Thesecond(andperhapsmoreobvious)conclusionisthatlifecyclestudiesofgreenhousegasemissionsassociatedwiththenuclearfuelcycleneedtobecomemoreaccurate,transparent,accountable,andcomprehensive.Thirty-ninepercentoflifecyclestudiesreviewedweremorethan10yearsold.Ninepercent,whilecitedintheliterature,wereinaccessible.Thirty-fourpercentdidnotexplaintheirresearchmethodology,reliedcompletelyonARTICLEINPRESSTable8Lifecycleestimatesforelectricitygenerators aTechnologyCapacity/con"guration/fuelEstimate(gCO 2 e/kWh)Wind2.5MW,offshore9Hydroelectric3.1MW,reservoir10 Wind1.5MW,onshore10 BiogasAnaerobicdigestion11 Hydroelectric300kW,run-of-river13Solarthermal80MW,parabolictrough13BiomassForestwoodCo-combustionwithhardcoal14 BiomassForestwoodsteamturbine22 BiomassShortrotationforestryCo-combustionwithhardcoal 23BiomassFORESTWOODreciprocatingengine27BiomassWastewoodsteamturbine31 SolarPVPolycrystallinesilicone32BiomassShortrotationforestrysteamturbine35Geothermal80MW,hotdryrock38 BiomassShortrotationforestryreciprocatingengine41 NuclearVariousreactortypes66 NaturalgasVariouscombinedcycleturbines443 FuelcellHydrogenfromgasreforming664 DieselVariousgeneratorandturbinetypes778 HeavyoilVariousgeneratorandturbinetypes778CoalVariousgeneratortypeswithscrubbing960CoalVariousgeneratortypeswithoutscrubbing1050 aWind,hydroelectric,biogas,solarthermal,biomass,andgeothermal,estimatestakenfromPehnt(2006).Diesel,heavyoil,coalwithscrubbing,coalwithoutscrubbing,naturalgas,andfuelcellestimatestakenandGagnonetal.(2002).SolarPVestimatestakenfromFthenakisetal.(2008).Nuclearistakenfromthisstudy.Estimateshavebeenroundedtothenearestwholenumber.B.K.Sovacool/EnergyPolicy36(2008)2940-2953 2950 secondarysources,orwerenotexplicitaboutthedistributionofcarbon-equivalentemissionsoverthedifferentstagesofthenuclearfuelcycle.Allinall,thismeantthat81%ofstudieshadmethodologicalshortcomingsthatjusti"edexcludingthemfromtheassessmentconductedhere.Noidenti"ableindustrystandardprovidesguidanceforutilitiesandcompaniesoperatingnuclearfacilitiesconcerninghowtoreporttheircarbon-equivalentemissions.Regulators,utilities,andoperatorsshouldconsiderdevelopingformalstandardizationandreportingcriteriaforthegreenhousegasemissionsassociatedwithnuclearlifecyclessimilartothosethatprovidegeneralguidanceforenvironmentalmanagementandlifecycleassessment,suchasISO14040and14044,butadaptedexclusivelytothenuclearindustry.Oftheremaining19%ofstudiesthatwererelativelyuptodate,accessible,andmethodologicallyexplicit,theyvariedgreatlyintheircomprehensiveness,somecountingjustconstructionanddecommissioningaspartofthefuelcycle,andothersincludingmining,milling,enrichment,conversion,construction,operation,processing,wastestorage,anddecommissioning.Addingevenmorevariation,studiesdifferedinwhethertheyassessedfutureemissionsforafewindividualreactorsorpastemissionsfortheglobalnuclear"eet;assumedexistingtechnologiesorthoseunderdevelopment;andpresumedwhethertheelectricityneededforminingandenrichmentcamefromfossilfuels,othernuclearplants,renewableenergytechnologies,oracombinationthereof.Furthermore,thespeci"creactorsstudieddiffergreatlythemselves.Someutilizerelativelyhigh-qualityuraniumorelocatedclosetothereactorsite;othersrequiretheimportationoflow-qualityorefromthousandsofkilometersaway.AnuclearplantinCanadamayreceiveitsfuelfromopen-pituraniumminesenrichedatagaseousdiffusionfacility,whereasareactorinEgyptmayreceiveitsfuelfromanundergroundmineenrichedthrough centrifuge.AnuclearfacilityinFrancemayoperatewithaloadfactorof83%for40yearsonaclosedfuelcyclerelyingonreprocessedfuel,whereasalightwaterreactorintheUnitedStatesmayoperatewithaloadfactorof81%for25yearsonaonce-throughfuelcyclethatgeneratessigni"cantamountsofspentnuclearfuel.Ratherthandetailthecomplexityandvariationinherentinthegreenhousegasemissionsassociatedwiththenuclearlifecycle,moststudiesobscureit;especiallythosemotivatedonbothsidesofthenucleardebateattemptingtomakenuclearenergylookcleanerordirtierthanitreallyis.AcknowledgmentsMarkA.DelucchifromtheUniversityofCaliforniaDavis,PaulDenholmfromtheNationalRenewableEnergyLaboratory,RobertoDonesfromtheSwissLaboratoryforEnergySystemsAnalysis,V.M.FthenakisfromBrookhavenNationalLaboratory,PaulJ.MeierfromtheUniversityofWisconsin-Madison,andJanWillemStormvanLeeuwenprovidedinvaluableandoutstandingcommentsandsuggestionsintherevisionofthemanuscript.TwoanonymousreviewersfromEnergyPolicyalsoprovidedextensiveandexceptionalsuggestionsatrevision.Allhavethedeepgratitudeoftheauthor.Despitetheirhelp,ofcourse,allerrors,assumptions,andconclusionspresentedinthearticlearesolelythoseoftheauthor.ReferencesAndseta,S.,Thompson,M.J.,Jarrell,J.P.,Pendergast,D.R.,1998.CANDUreactorsandgreenhousegasemissions.In:Proceedingsofthe19thAnnualConference,CanadianNuclearSociety,Toronto,Ontario,Canada,October18-21,1998.[ANRE]AgencyforNaturalResourcesandEnergy,1999.EvaluationofLifelongMeasureofUtilitiesNuclearPowerStationandFutureConcreteMeasures.

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