Development of Advanced Reprocessing Technologies purex1.pdf

Development of Advanced Reprocessing Technologies

Introduction

Currentlyabout10500tHM(tonnesofheavymetal)ofspentfuelaredischargedannuallyfrom

nuclear power reactors worldwide. Although this spent fuel still contains substantial fissionable

material(uraniumandplutonium)thatcanbereprocessedandrecycledasfuel,only15%iscurrently

reprocessed.Formostofnuclearpower’shistory,reprocessingandrecyclingoftheseparatedUand

Puinfastreactorshasbeenthefavouredstrategyforthebackendofthefuelcycle.Whilemost

countrieshaveadopteda‘waitandsee’strategyonthismatter,somecountrieshavedecided,dueto

proliferationconcernsandalackofeconomicstimulus,toregardthespentfuelaswasteandpreferto

disposeofitafter3040years’storagewithoutreprocessing.Lately,however,insomeofthese

countriestherehasbeenaresurgenceofinterestinreprocessingandrecyclingaskeycomponentsof

developingfuturesustainablenuclearenergysystems[Ref.1,2].

Themainpurposeofreprocessingistobetterutilisenaturalresourcebyrecyclingtheremaining

uraniumandplutonium,thusreducingdemandsonfreshuraniumminingandmillingandensuringa

moresustainableandlongtermuseofnuclearenergy.Reprocessingandrecyclinginfastreactorshas

thepotentialtoreducetheuraniumdemandperkWhbyafactorof50–100.Reprocessingoffuelfrom

lightwaterreactorsandgascooledreactorsandrecyclingoftheseparatedplutoniumasmixedoxide

(MOX)fuelistodaycommerciallyavailable.

Table1:Compositionofspentfuelfromthermalreactors:associatedissuesandplausiblesolutions

Constituent

Composition in

percentage

Issue

Disposition path

Uranium

~ 95 - 96

An energy resource.

Separated uranium could be

recycled as fuel in reactors.

Plutonium

~ 1.0

An energy resource, but also the

major contributor to long term

radio-toxicity (and heat-load) of

the waste. Separated Pu

constitutes a major proliferation

concern.

Separated Pu could be

recycled in reactors as fuel.

Proliferation concerns could

be reduced by not separating

pure Pu.

Minor actinides

(MAs) primarily

Np, Am, and Cm

~ 0.1

Important contributors to long-

term radio-toxicity of the waste.

Proliferation concerns exist

concerning separated Np.

MAs can be burnt alone or in

combination with Pu in fast

reactors.

Stable or short-

lived FPs (fission

products)

~ 3 - 4

Some FPs such as Cs and Sr are

the primary contributors to the

short term radio-toxicity and heat

source in the waste. Other FPs,

e.g. noble metals, could become

valuable.

Storage of high level waste

(HLW) for a few hundred

years or separation of Cs and

Sr for separate disposal after a

few hundred years storage.

Separated Cs has industrial

applications.

Long-lived fission

products (LLFPs)

viz., Tc and I

~ 0.1

Contributors to the long term

radio-toxicity of the waste.

No industrial process to limit

the problem has been

developed.

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FigureIV1showshowtherelativeradiotoxicity 1 ofthedifferentcomponentsofspentnuclearfuel

variesovertime.Forthefirst100yearsafterspentfuelisdischarged,itsradiotoxicityisdetermined

bythefissionproducts.Itisthendeterminedbyplutonium.Iftheplutoniumisremoved,theminor

actinidesdeterminethelongtermradiotoxicity.Itshouldbenotedthatbothscalesarelogarithmic.

FIG. IV-1. Relative radio-toxicity of the different components in spent nuclear fuel from a light water

reactor irradiated to 41 MWd/kgU with respect to the radio-toxicity of the corresponding uranium

ore. [Ref. 3,4]

Incomparisonwithdirectdisposalofspentfuel,presentdayreprocessingalsoprovidessomepositive

effectsontheremainingradioactivewastethatneedsdisposal.Theseinclude:

•

Longtermradiotoxicityisreduced.Thisreduceslongtermconcernsfortherepository,which

couldsimplifytherepositorydesignandincreasepublic acceptance.

•

Longtermheatproductionisreduced,whichincreasesthecapacityofarepository,asthe

packagingdensityinmostcasesisdeterminedbytheheatload.

Theseeffectscanbefurtherenhancedinadvancedreprocessingsystems,whereminoractinidesare

alsoseparatedwiththepurposeofburningthem,therebyfurtherreducingthelongtermradiotoxicity

andheatloadintheremainingwaste.Inaddition,somevaluablefissionproductmaterials,e.g.

caesiumandplatinumgroupmetals,couldbeextractedforindustrialuse.Heatreductionismainly

achievedbyremovingthecaesiumandstrontiumfollowedbyplutoniumandamericium.

Thevolumeofhighlevelwasteisreduced.

___________________________________________________________________________

1 Radio-toxicity is calculated by dividing the radioactivity (Ci) of a nuclide in the spent fuel by the maximum

permissible concentration (Ci/m 3 ) of that radionuclide in drinking water.

•

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PUREX – current industrial reprocessing technology

Allcurrentcommercialreprocessingplantsusethe PUREX 2 process.Itwasdevelopedforcivil

applicationsduringthe1960s,followingexperiencegainedfrommilitaryprogrammes.

InthePUREXprocess(whichissummarizedinFig.IV2),thespentfuelisfirstchoppedintosmall

piecesandthendissolvedinnitricacidandsubjectedtoasolventextractionprocessusingtrinbutyl

phosphate(TBP).UraniumandplutoniumareselectivelytakenupintheTBPphaseresultingingood

separationfromtherestofthefissionproductsandminoractinides 3 ,whichareretainedintheinitial

acidmedium.TheUandPuarethenseparatedinmultistageextractioncyclesandpurified.The

presentstateoftheartinPUREXreprocessingprovidesa99.9%separationofUandPu.Insome

variantsofthePUREXprocessthePuiscoprecipitatedwithuraniumtoavoidtheseparationofpure

plutonium.ThisisthecaseintheJapanesereprocessingplantatRokkasho.Thewastestream(the

liquidhighlevelwaste)thatcontainsfissionproducts,minoractinidesandactivationproducts,is

processedandvitrified,i.e.mixedwithglassmaterialtoformaborosilicateglass,andencapsulatedin

asteelcontainer.

Spent Fuel Storage

Off-gas Treatment

Mechanical

Disassembly

Hulls (HLW)

High Level Waste

Acid recovery

Acid dissolution

Solvent Extraction

Solvent Treatment

Fission Product

Consolidation (HLLW)

High Level Liquid Waste

Solvent Extraction

& Partitioning

Uranium Oxide

Conversion

Plutonium Oxide

Conversion

Reprocessed

Uranium

Plutonium

FIG. IV-2. Key steps in the PUREX process.

InaPUREXreprocessingfacilitythespentfuelisthusseparatedintoitsfourcomponents:uranium,

plutonium,highlevelwastecontainingfissionproductsandothertransuranicelements,andmetallic

wastefromthefuelrodsandassemblies.

ThePUREXtechnologyisactivelyusedonalargescaleinFrance,Japan,India,Russia,andthe

UnitedKingdom.Itisusedtoreprocessuraniumandmixedoxide(MOX)fuelfromdifferenttypesof

reactors (LWR, PHWR, GCR and LMFR 4 ) and also fuel with different chemical forms and

enrichments, e.g. from research reactors. Around 90000tHM have been reprocessed in civilian

___________________________________________________________________________

2 Plutonium-Uranium Extraction (PUREX)

3 The main minor actinides are neptunium, americium and curium

4 LWR = light water reactor, PHWR = pressurized heavy water reactor, GCR = gas cooled reactor and LMFR = liquid

metal cooled fast reactor.

Page 4

reprocessing facilities. The current annual industrial reprocessing capacity is around 4600 tHM

globally,anditisexpectedthatanadditional2000tonnesmightbeaddedinthenext10years.

Developments in reprocessing technologies

The current generation of reprocessing plants has been continuously improved in regard to the

following[Ref.5]:

ii)

reductionofeffluentdischargesandimpactsontheenvironment;

iii)

reduction of occupational exposure (e.g. during preventive maintenance and

inspections);

iv)

reductionsinwastevolumes(ofbothHLWandintermediatelevelwaste(ILW));

simplificationoftheprocess(e.g.throughreducingthenumberofcyclesneeded);

vi)

increasedsafetythroughreducedcriticalityhazards,andbetterproliferationresistance

byrealtimeaccountingofnuclearmaterials.

Neverthelessreprocessingsystemsstillhavetoaddresssomemorechallengingconcerns,namely:

proliferationissuesassociatedwithproducingseparatedplutonium;

ii)

issuesassociatedwithhighlevelwaste,owingtothepresenceofminoractinidesand

longlivedfissionproducts(LLFP);

iii)

economicsandcosts;and

iv)

theprocessingoftransuranicrichfuelsthatarebeingdevelopedforfutureadvanced

nuclearreactors.

Muchoftheongoingdevelopmentworkforreprocessingtechnologiesdealswiththeseissues.The

economiccompetitivenessofreprocessingandrecyclingoffissilematerialsdependsonthepriceof

naturaluraniumandonthepossiblegainsfromreduceddemandsforrepositories.

Collaborative international efforts are underway, including INPRO and GIF 5 , for developing

innovativereactorsandfuelcyclesthatarecompetitiveandsafe,withsimplifiedproceduresfor

managing radioactive waste and with features to increase the proliferation resistance of nuclear

materials.Similartotheevolutionofinnovativenuclearreactordevelopment,reprocessingtechnology

isevolvinginstages.

NewwetprocessesareunderdevelopmentinwhichalsotheminoractinidesandsomeLLFPsare

separatedforlaterdestruction(incineration)indifferenttypesofreactors,includingfastreactorsand

acceleratordrivensystems.Othermethodsarealsobeingdevelopedinwhichplutoniumisnever

separatedinapureformbutalwaysmixedwithminoractinidesforproliferationresistance.Inalonger

time perspective different dry reprocessing technologies are also being developed, e.g. pyro

processing,whichcouldprovidebenefitsintermsofeconomics,sizeandfuelcycleflexibilitythrough

theirhigherradiationresistance.Severaldifferentlinesofdevelopmentarebeingconsideredand

testedonalaboratoryscale.Insomecasesthesteptowardsindustrialimplementationisfairlyshort,

whileotherswillrequiresubstantialworkbeforetheycanbeintroducedatanindustriallevel.The

followingsectiongivessomeexamplesofadvancedprocesses.

___________________________________________________________________________

5 INPRO = International Project on Innovative Nuclear Reactors and Fuel Cycles; GIF = Generation IV International

Forum

flexibility(adaptationstoincreasedburnup,MOXtreatment);

Page 5

C.1.

Wet processes developments

Forwetprocessestherearetwodifferentlinesofapproach:(i)advancedseparationofdifferent

componentsinthehighlevelliquidwaste(HLLW)generatedbythePUREXprocess(advanced

separation)or(ii)changingthechemistryinthefirstseparationstepsothatonlyuraniumisseparated,

while keeping plutonium, minor actinides and fission products in the waste solution for later

processing(e.g.UREX 6 ).

Advanced separation

Thepurposeoftheongoingdevelopmentworkonadvancedseparationmethodsistoremoveminor

actinidesandsomefissionproductsfromtheHLLWinordertoreducetheradiotoxicityandheatload

inthefinalhighlevelwaste.Theminoractinideswillbeincorporatedinreactorfuelfortransmutation

(nuclearincineration),whiletheseparatedfissionproductsareconditionedforlongtermstorageor

separatedisposal.

Theprocessestypicallyinvolvethefollowingsteps:

•

recoveringminoractinides(MA)andlanthanidefissionproducts

•

purifyingtheMAsfromthelanthanides

•

individuallyseparatingtheMAs

•

recoveringCsandSr

Severalprocessesusingdifferenttypesofextractantsandsolventshavebeenstudiedindifferent

countriesandtestedinhotfacilities.SomeexamplesarelistedinTable2.Eachprocessusesits

specificextractantandsolvent.Veryhighseparationefficiencieswillberequiredtoreducethelong

termradiotoxicityoftheremainingHLLWbyasignificantfactor.Inadditiontohighseparation

efficiencytheminimisationofsecondaryprocesswaste,e.g.byusingamidesinsteadofphosphorous

reagents,isalsoanimportantgoal.

Table2:Reviewofadvancedaqueouspartitioningmethods[Ref.1,6,7,8,9,10]

Process Purpose

Country Specialaspects

DIAMEX Extractionofminor

actinidesand

lanthanidesfrom

HLLW

France DiamideExtractionProcess

Solventbasedonamidesasalternateto

phosphorousreagent

Generatesminimumorganicwasteasthesolvent

istotallycombustible

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6 URanium EXtraction

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