Impact limits of partitioning and transmutation scenarios on the radiotoxicity of actinides in ...

15 Pages·2003·0.56 MB·English

NuclearEnergy,2003,42,No.5,Oct.,263–277
Impact limits of partitioning and
transmutation scenarios on the radiotoxicity
of actinides in radioactive waste
*
J. Magill,y V. Berthou,y D. Haas,y J. Galy,y R. Schenkel,y H.-W. Wiese,z
G. Heusener,z J. Tommasi} and G. Youinou}
{EuropeanCommission,JointResearchCentre,InstituteforTransuraniumElements,Karlsruhe,Germany
{Forschungszentrum,Karlsruhe,Germany
}CEA-Cadarache,DER/SPRC/LEPh,France
The used fuel discharged from nuclear power plants Theusedfueldischargedfromnuclearpowerplants
constitutes the main contribution to nuclear waste in constitutes the main contribution to nuclear waste in
countrieswhichdonotundertakereprocessing.Assuch, countrieswhichdonotundertakereprocessing.Most
its disposal requires isolation from the biosphere in of the hazard from the spent fuel stems from only a
stable deep geological formations for long periods of few chemical elements, namely plutonium, neptu-
time (some hundred thousand years) until its radio- nium, americium, curium, and some long-lived
activity decreases through the process of radioactive fission products such as iodine, caesium and tech-
decay.Waysforsignificantlyreducingthevolumesand netium.Atpresentapproximately2500tofspentfuel
radiotoxicitiesofthewasteandtoshortentheverylong are produced annually in the EU, containing about
times for which the waste must be stored safely are 25t of plutonium, and 3.5t of the ‘minor actinides’
being investigated. This is the motivation behind the neptunium, americium and curium, and about 3t of
partitioningandtransmutation(P&T)activitiesworld- long-livedfissionproducts.
wide.ThispaperaddressesthepotentialimpactofP&T Theseradioactiveby-products,althoughpresentin
on the long-term disposal of nuclear waste. In particu- relatively low concentrations in the used fuel, are a
lar,itevaluateshowrealisticP&Tscenarioscanleadto hazard to life forms when released into the environ-
a reduction in the time required for the waste to be ment. As such, their disposal requires isolation from
storedsafely.Thecalculationshavebeendoneindepen- thebiosphereinstabledeepgeologicalformationsfor
dently by three research groups: ITU and FZK in long periods of time (some hundred thousand years)
Germany,andbytheCEAinFrance. untiltheirradioactivitydecreasesthroughtheprocess
ofradioactivedecay.
Keywords:naturalanalogues,partitioning&transmu- Forthisreason,intheeyesofsomemembersofthe
tation, radioactivity, research & development, waste public, nuclear waste disposal could be difficult to
management&disposal acceptbecauseoftheverylongtimesinvolvingmany
generationsduringwhichthiswastemustbeseparated
from the biosphere to avoid possible harmful effects.
Introduction
Inthiscontext,itisinterestingtonote,however,that
Nuclear energy provides a significant contribution local communities in the Port Hope area (Canada)
to the overall energy supply in Europe. With 145 have recently indicated their willingness to accept
operating reactors producing a total power of nuclear waste on a long-term basis in waste manage-
125GWe, the resulting energy generation of mentfacilities.1
850TWhperyearprovides35%ofthetotalelectrical Ways for significantly reducing the volumes and
energyrequirementsintheEuropeanUnion. radiotoxicities of the waste and to shorten the
very long times for which the waste must be stored
safely are being investigated. This is the motivation
*Anyfootnoterequired.
behind the partitioning and transmutation (P&T)
??
?? activities worldwide. Partitioning refers to aqueous
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Magilletal.
orpyroprocessingmethodswhichareusedtoseparate 234Uand79Se,theirorderofimportancedependingon
(partition) the various components of the used fuel: the repository concept (see Fig. 1).3,4 The dose from
uranium, plutonium, minor actinides, fission prod- the US base case repository is from 99Tc and 129I for
ucts. Transmutation refers to the conversion of a about the first 50000 years, after which the dose is
nuclideintooneorseveralothernuclidesinanuclear primarily from 237Np, an order of magnitude higher
reactor as a result of neutron-induced fission or than the other contributors.4 This shows that even if
capturereactions. fissionproductsaremoremobileingeologicalreposi-
This paper addresses the potential impact of P&T tory than actinides, some of them such as 237Np, are
on the long-term disposal of nuclear waste. In par- alsomaincontributorstothedoserate.
ticular, it evaluates how realistic P&T scenarios can Actinidetransmutationstrategiesaddressprimarily
leadto areduction inthe time requiredfor thewaste the radiotoxicity (hazard) of the high-level waste
to be stored safely. The calculations have been done (HLW). To reduce the long-term risk (dose to the
independently by three research groups, namely ITU population), the long-lived fission products would
andFZKinGermany,andbytheCEAinFrance. also have to be transmuted or specially transmuted.
In addition, the reprocessing of spent nuclear fuel
inevitably results in the production of secondary
Risk andsafety
waste(resins,fuelhullsandendpieces,etc.)contami-
What is meant by risk in connection with the nated with long-lived radionuclides. The long-term
disposalofnuclearwaste?Thisquestionwasrecently managementofsuchwasteishighlyproblematic,and
addressedbyaNationalAcademyofSciencepublica- theimpactondisposalrequiresdetailedstudy.
tion.2 The analysis of safety involves assessing the
likelihood and the severity of harmful events to
humans, property, or to the environment. Such a Will P&Tmake nuclear waste disposal
‘risk’ analysis involves estimating the harm in terms
publicly acceptable?
oftheprobabilityofoccurrenceandtheseverityofthe
consequences. Nuclear waste disposal is a problem of radioactive
From the viewpoint of the radiotoxicity, which material ‘packaging’ in the extreme. One of the
plays a role mainly in accidental intrusion scenarios, challenges facing the nuclear industry is to demon-
P&T must first be concerned with the actinides, par- strate that an underground repository can contain
ticularlytheminoractinides,thetoxicityofthefission nuclear waste for very long periods of time and that
product lying at least two orders of magnitude lower any releases that might take place in the future will
afterafewhundredyears. pose no significant health or environmental risk. It
The long-term risk of a geologic repository is, must be taken into account that the engineered bar-
however, usually dominated by fission products riers which initially contain the wastes will degrade,
which are generally more mobile than the actinides. and that some residual radionuclides may return to
In the case of nuclear waste disposal, the risk con- the surface in low concentrations at some time in the
cerned is that of the radionuclides entering the bio- future due to groundwater movement and environ-
sphere, for example by groundwater transport. The mentalchange.
probability of occurrence of such events is based on One way of building confidence in engineered
computer models which can be very complex. Dose barriersisbystudyingtheprocesseswhichoperatein
contributions arise primarily from 129I, 99Tc, 237Np, natural and archaeological systems and by making
101
Total
100 14C
m/year 1100&&12 122233971INPap
mre 10&3 239Pu
e: 10&4 242Pu
at 79Se
e r 10&5 99Tc
s
Do 10&6 234U
10&7
10&8
10&9
0 20 000 40 000 60 000 80 000 100 000 120 000 140 000
Time: years
Fig.1.Expectedvaluedosehistoryover100000yearstoanindividualusingwaterfromawell20kmfromtherepository4
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Partitioningandtransmutationscenarios
appropriate parallels witharepository.Thesestudies The Inchtuthil Roman nails.6 The most northerly
arecallednaturalanalogues.Intheeventthat P&T is fortress in the Roman Empire at Inchtuthil in Perth-
introduced, thetimescales overwhichthewastemust shire,Scotlandhadtobeabandonedhastilyin87ad.
beisolatedfromthebiospherearemuchreducedand In an attempt to hide metal objects which could be
one can have much greater confidence in the engi- used for weapons, the Romans buried over one
neered barriers by studying societal analogues—that millionnailsina5mdeeppitandcoveredthemwith
is, society-built structures which have withstood the 3m of compacted earth. These nails were discovered
testoftimeoveracoupleofthousandyears. in the 1950s. It was found that the outermost nails
were badly corroded and had formed a solid iron
oxide crust. The innermost nails, however, showed
Naturalandsocietalanalogues5
onlyverylimitedcorrosion.Thiswasattributedtothe
There are many radioactive materials which occur factthattheouternailsremovedtheoxygenfromthe
naturallyandcanbefoundinrocks,sediments,etc.In infiltrating groundwaters such that by the time they
particular, uranium, which isthe main component in cameintocontactwiththeinnerlyingnailsthewaters
nuclear fuel, occurs in nature. By studying the distri- were less corrosive. In the same way, the large
butioninnature,informationcanbeobtainedonthe volumes of iron in waste canisters are expected to
movementofuraniuminrocksandgroundwaters. maintain chemically reducing conditions in an envir-
Natural analogues provide a way of informing the onment which might otherwise become oxygen-rich
wider public on the principles on which repositories duetotheradiolyticdecompositionofwater.
are built, without using complex mathematical
demonstrationsofsafetyandrisk.Oneoftheconcepts The Kronan cannon.7 The Kronan was a Swedish
which can be presented using analogues is the very warship built in 1668 and which sank in 1676 during
slow degradation of materials over thousands of the Battle of O¨ land. One of the bronze cannons on
years. Some notable analogues are discussed below. board the Kronan had remained partly buried in a
(SeealsoFig.2.) verticalposition,muzzledowninclaysedimentssince
Dunarobba forest Natural and societal analogues
109 Inchtuthil
Roman nails
108
Used fuel
before P&T
uel 107
nt f The Kronan cannon
e
p
s
n
o
Oklo natural fission reactors er t 106
p
v
NrzeouancceltesoarrSandstone oxicity: S 105 Uranium ore
ot
Sandstone Ore layer adi
Granite on r
sti 104
e Used fuel
g
In Fission after P&T Hadrian's Wall
products
The Needle's Eye
103
102
101 102 103 104 105 106
Time: years
Fig.2.WillP&Tmakenuclearwastedisposalpubliclyacceptable?
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Magilletal.
the ship sank. This cannon is a good analogue for partoftheRepublicofGaboninWestAfrica.Further
canisterstobeusedintheSwedishandFinnishspent investigations revealed that nuclear fission had taken
fuelrepositorieswhichhaveacopperoutershell,since place. The uranium ore bodies at Oklo are the only
the cannon had a very high copper content (96.3%). known examples of natural fission reactors. The
From an analysis of the cannon surface, a corrosion criticality took place approximately 2 billion years
rate of 0.15mm/year was established. At this rate of ago as a result of dissolution, mobilisation and accu-
corrosion,itwouldtakesome70000yearstocorrode mulation of uranium in sufficient mass to achieve
1cm thickness of copper. This provides evidence for criticality. The chemistry of the uranium is such that
theverylonglifeofcopperspent fuelcanisters inthe it is insoluble in water under oxygen-free conditions,
repository. butreadilysolubleinwaterinthepresenceofoxygen.
The fission reactions operated intermittently for
Hadrian’s Wall. In ad 122 Emperor Hadrian
between105and106years.
ordered construction of a wall to separate the lands
The naturalfission reactorsatOklocanbeconsid-
of the Britons from that of the Picts to the north.
ered as analogues for very old radioactive waste
Hadrian’s Wall was over 100km long and 5m high
repositories and can be used to study the transport
and was built from stone blocks cemented together.
behaviour of transuranic nuclides and stability of
The Wall is of interest as an analogue due to the
uraniummineralswhichhaveundergonecriticality.
longevity of Roman cement used to bind the stones
together. Modern Portland cement is very similar
chemically and mineralogically. From these studies, The P&T efficiency
conclusionscanbedrawnwithregard tothestability
andlongevityofmoderncementsinrepositories. Before addressing the potential impact that P&T
canhaveonthelong-termdisposalofnuclearwaste,it
The Dunarobba forest. In the Dunarobba forest
is useful to introduce the concept of P&T efficiency.
near Todi in Italy, dead tree trunks approximately 2
Intuitively, if the efficiency of the P&T processing
million years old have been found in their original
were 100%, all of the harmful products would be
upright position. Remarkably, in contrast to typical
separated from thenuclear wasteand transformedin
fossilised trees, the Dunarobba trees are still com-
short-lived or stable products, thereby avoiding the
posed of wood. The wood has been preserved due to
requirement for a nuclear waste repository. In prac-
the surrounding clay. This clay stopped oxygenated
tice,however,anefficiencyof100%cannotbereached
waters from reaching the wood, thereby limiting
and arepository will be required,albeitforconsider-
the aerobic decomposition. The Dunarobba trees are
ableshorterperiodsoftime.Buthowshortisshort?
of relevance in repository concepts for low- and
TheefficiencyoftheP&Tprocessisdenotedbye
PT
intermediate-levelwastessincethewoodisconsidered
(0(cid:1)e (cid:1)1) and clearly this is a function of the
PT
to be analogous to the organic/cellulosic materials
individual partitioning efficiency e and the transmu-
P
whichcomprisealargepartofthewaste.
tation efficiency e . This transmutation efficiency e
T T
The Needle’s Eye.8 This site in south-west Scot- corresponds to the burnup B of the fuel which is the
land, close to a natural rock arch known as the fractionofthematerialwhichhasfissioned.
Needle’sEye,comprisesasea-cliffinwhichtheminer- Nuclearwastemayhavetoberecycledmanytimes
alised veins of uranium and other metals are partly before it is completely fissioned. In each recycle the
exposed. Uranium is present as pitchblende (UO2) partitioning losses are (1(cid:2)eP). The number of
associatedwithsecondaryminerals. recyclesNisinverselyproportionaltothetransmuta-
The pitchblende has undergone dissolution by two tion efficiency—that is, N (cid:3)1=eT. (If the transmuta-
processes. In the first, slow leaching results in a tion efficiency were 1, only one partitioning step
preferential loss of 234U relative to 238U. The second wouldberequired.)
is dissolution by oxidising waters. The mobilised Morerealistically,thetransmutationefficiencymay
uranium is redeposited in close proximity to the vein betypically0.2(suchthatapproximatelyfiverecycles
as stable oxidised uranium minerals. In contrast to are required for transmutation). It follows that the
uranium, the dissolution and transport of thorium is totallosses(1(cid:2)eT)areequaltothepartitioninglosses
negligible. inonestepmultipliedbythenumberofrecycles,that
The Needle’s Eye is ideal for investigating radio- is
nuclidemigrationbehaviourandfortestinggeochem-
Totallosses=partitioninglossesinasinglecycle
icalcodesinsimulationexercises.
(cid:4)thenumberofrecycles,or
The Oklo natural fission reactors. In 1972 scien-
ð1(cid:2)e Þ
tists in France found that the 235U content of ore ð1(cid:2)ePTÞ’ e P ð1Þ
beingprocessedtomakenuclearfuelpelletshadbeen T
depleted from the normal 0.72% to 0.62%. The ore As an example,consider theefficiencyof theparti-
had been obtained from Oklo in the south-eastern tioning process to be e ¼0(cid:5)999 (or 99.9%). If the
P
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Partitioningandtransmutationscenarios

M
Partitioning Losses M (1 & εP) The P&T efficiency
P&T (1) M ε P

Transmutation
M ε (1 & ε )
P T The overall P&T efficiency:
Partitioning Losses M ε (1 & ε ) (1 & ε ) ε ε
P&T (2) MεP2 (1 & εT) P T P εPT= 1 & (1T & εP) ε
T P
Transmutation
M ε2(1 & ε)2
P T
Partitioning Losses M ε 2(1 & ε )2 (1 & ε )
P&T (3) M ε 3 (1 & ε )2 P T P
P T
Transmutation
M εP3 (1 & εT)3
...

Fig.3.Multiplerecyclingofnuclearwastethroughpartitioningandtransmutation
efficiency of the transmutation process is e ¼0(cid:5)20 burnups,reprocessingsandrecyclingsandsumsupall
T
(meaningthat20%oftheactinidesarefissionedinthe thelossesthatoccurateachofthereprocessings.
cycle),thentheoverallefficiencyoftheP&Tprocessis
ð1(cid:2)e Þ
e ’1(cid:2) P ¼0(cid:5)995ðor99(cid:5)5%Þ ð2Þ Standardised burnupcalculations
PT e
T
Radiotoxicityandeffectivedosecoefficients
Inamoredetailedanalysis,asshowninFig.3,the
A measure of the potential hazard of nuclear
effect of multiple recycling can be investigated. Con-
material is provided by the toxicity and in particular
siderareactorloadedinitiallywithamassMoffresh
its radiotoxicity arising from its radioactive quality
fuel. In a first step, the separation of the different
ratherthanthechemicaltoxicity.Theradiotoxicityof
waste streams is done, and a fraction (Me ) is irra-
P anuclideisdeterminedbyitseffectivedosecoefficient
diatedwhiletheremainingfraction[Mð1(cid:2)e Þ]leaves
P eðTÞ,whichaccountsforradiationandtissue weight-
for processing. Following the irradiation, a fraction
ing factors, metabolic and biokinetic information.
[Me ð1(cid:2)e Þ] is reprocessed, and the fraction
P T ThequantityTistheintegrationtimeinyearsfollow-
[Me ð1(cid:2)e Þð1(cid:2)e Þ] goes to the waste and the
P T P ingintake.Foradults,theintegrationtimeis50years,
remainingfraction[Mð1(cid:2)e Þe2]isrecycledforanew
T P such that the radiotoxicity (in sievert, Sv) resulting
irradiation. Thisprocess can be repeatedindefinitely.
from intake of a particular nuclide is the product of
Itfollowsthatthetotallossesaregivenby
the effective dose coefficient (units Sv/Bq) and the
ð1(cid:2)e ÞM activity(inBq)ofthatnuclide,thatis
PT
¼Mð1(cid:2)e ÞþMe ð1(cid:2)e Þð1(cid:2)e Þ Radiotoxicity¼Activity(cid:4)eð50Þ ð5Þ
P P T P
þMð1(cid:2)e Þ2ð1(cid:2)e Þe2 þ(cid:5)(cid:5)(cid:5) In many computer codes the older values of effective
T P P dose coefficients from ICRP689 are in use. In 1996
¼Mð1(cid:2)ePÞ½1þePð1(cid:2)eTÞþe2Pð1(cid:2)eTÞ2þ(cid:5)(cid:5)(cid:5)(cid:6) these values were updated in a new publication,
ICRP72.10
Mð1(cid:2)e Þ
¼ P ð3Þ Whereas most of the differences between the
½1(cid:2)e ð1(cid:2)e Þ(cid:6)
P T ICRP68 and ICRP72 values are small, there are two
or exceptions.For210Po,thereisaverybigincreasefrom
2(cid:5)4(cid:4)10(cid:2)7 in ICRP68 to 1(cid:5)2(cid:4)10(cid:2)6 in ICRP72. For
e e
e ¼ P T ð4Þ 93Zr there is an increase from 2(cid:5)8(cid:4)10(cid:2)10 Sv in
PT 1(cid:2)ð1(cid:2)e Þe
T P ICRP68 to 1(cid:5)1(cid:4)10(cid:2)9 Sv in ICRP72. The different
As an example consider the case: e ¼0(cid:5)999 (99.9% values for 210Po lead to a significant change in the
P
separationefficiency),e ¼0(cid:5)20(meaningthat20%of reference radiotoxicity since 210Po is a daughter
T
the actinides are fissioned in the cycle), hence productof238U.
e ¼0.995(99.5%effectiveseparationefficiency).
PT
Burn-upcalculations
Using the infinite summation method, one follows
aninitialbatchofactinidesthroughallthesuccessive Standardisedburnupcalculationshavebeencarried
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Table1.Standardisedburnupcalculations(4.2%enrichment,50GWd/t,6yearscoolingtime):actinidemass(g)inventoryper
tonofspentfuel
FZK(F) ITU(I) CEA(C) (F(cid:2)I)/F: (C(cid:2)I)/C: (F(cid:2)C)/F:
Nuclide Freshfuel KORIGEN ORIGEN2 APOLLO2 % % %
(Biblis) (PWRUS50) (JEF2.2)
235U 4.20(cid:4)104 6.96(cid:4)103 6.86(cid:4)103 7.60(cid:4)103 1.5 9.8 (cid:2)9.2
236U 5.59(cid:4)103 5.65(cid:4)103 5.46(cid:4)103 (cid:2)1.1 (cid:2)3.5 2.3
238U 9.58(cid:4)105 9.24(cid:4)105 9.24(cid:4)105 9.22(cid:4)105 0.0 (cid:2)0.2 0.2
237Np 7.27(cid:4)102 7.61(cid:4)102 7.00(cid:4)102 (cid:2)4.6 (cid:2)8.7 3.8
238Pu 3.35(cid:4)102 3.12(cid:4)102 3.39(cid:4)102 7.1 8.1 (cid:2)1.1
239Pu 5.66(cid:4)103 5.86(cid:4)103 6.09(cid:4)103 (cid:2)3.6 3.7 (cid:2)7.6
240Pu 2.73(cid:4)103 2.73(cid:4)103 2.84(cid:4)103 0.0 3.9 (cid:2)4.1
241Pu 1.22(cid:4)103 1.30(cid:4)103 1.33(cid:4)103 (cid:2)6.0 2.5 (cid:2)8.7
242Pu 8.42(cid:4)102 8.52(cid:4)102 8.59(cid:4)102 (cid:2)1.2 0.8 (cid:2)2.0
241Am 4.64(cid:4)102 4.87(cid:4)102 5.02(cid:4)102 (cid:2)4.8 3.1 (cid:2)8.1
242mAm 8.42(cid:4)10(cid:2)1 1.16(cid:4)100 9.02(cid:4)10(cid:2)1 (cid:2)37.8 (cid:2)28.6 (cid:2)7.2
243Am 1.92(cid:4)102 2.11(cid:4)102 2.05(cid:4)102 (cid:2)9.8 (cid:2)3.1 (cid:2)6.5
242Cm 4.38(cid:4)10(cid:2)3 4.98(cid:4)10(cid:2)3 4.64(cid:4)10(cid:2)3 (cid:2)13.7 (cid:2)7.2 (cid:2)6.0
243Cm 5.60(cid:4)10(cid:2)1 8.21(cid:4)10(cid:2)1 6.56(cid:4)10(cid:2)1 (cid:2)46.5 (cid:2)25.1 (cid:2)17.1
244Cm 6.22(cid:4)101 7.08(cid:4)101 7.15(cid:4)101 (cid:2)13.8 1.0 (cid:2)14.9
245Cm 2.86(cid:4)100 4.30(cid:4)100 6.11(cid:4)100 (cid:2)50.5 29.6 (cid:2)113.8
246Cm 3.61(cid:4)100 6.78(cid:4)10(cid:2)1 7.62(cid:4)10(cid:2)1 81.2 11.1 78.9
Total 1.00(cid:4)106 9.49(cid:4)105 9.49(cid:4)105 9.48(cid:4)105
out by three different organisations: ITU, FZK and Actinide decay andradiotoxicity calculations
CEA.Theresultsfortheactinidemassinventoriesare
Actinideingestionradiotoxicityplottedagainsttime
given in Tables 1 and 2 for the actinides and fission
products respectively. The burnup calculations were Based on the ICRP72 values for the effective dose
basedona4.2%enrichmentof235Uin238U,aburnup coefficients, the total actinide ingestion radiotoxicity
of50GWd/tMandsixyearscoolingtime.Thecodes/ plotted against time is shown in Fig. 6. The ITU
libraries used (KORIGEN/Biblis, ORIGEN2/ results, obtained with Nuclides.net,11 are compared
PWRUS50, and APOLLO2/JEF2.2) are standard totheFZKandCEAresults.Theresultsareingood
codesandcross-sectionlibrariesforsuchcalculations. agreement(seeinsetinFig.6).Onthelogarithmicplot
thesmalldifferences between the results do notshow
up.
Actinides. The actinide mass inventory resulting
Itisalsoofinteresttoseehowthemaincomponents
from burnup and cooling is given in Table 1. In the
contributetothetotalingestionradiotoxicity.Thisis
lastthreecolumns,acomparisonoftheresultsismade
showninFig.7fortheITUdata,wheretheresultsare
of the ITU, FZK, and CEA results. There is good
grouped according to chemical element present after
agreement on the actinide mass inventories from the
sixyearscooling(thedataaregiveninTable3ofthe
various codes used by ITU, FZK and CEA for the
appendix). Notice that ‘U’ refers to the sum of all
standard calculation (4.2% enrichment, 50GWd/t,
uranium isotopes at time six years. At later times the
6yearscoolingtime).
uranium isotopes decay to other chemical elements
which are also accounted for in the ‘U’ curve. The
. For U and Pu isotopes, agreement is better than advantage of grouping in this manner is that it is
(cid:7)10%. easiertoseetheeffectsofpartitioning.
. ForAmisotopes,agreementisbetterthan(cid:7)20%. As can be seen from Fig. 7, the total ingestion
. For 242Cm and 244Cm, agreement is reasonable radiotoxicity arises from the plutonium isotopes
((cid:7)25%), but less good for 245Cm and 246Cm (present after six years cooling!). Around 200 years,
((cid:7)70%). the Pu radiotoxicity is 4.3(cid:4)107Sv (from Table 3)—
that is, a factor 180 (4.3(cid:4)107/2.4(cid:4)105) above the
referencevalueindicatedbythedashedline(discussed
TheresultsarealsocomparedinFigs4and5.
in detail in the following section). Conversely, to
reduce the waste toxicity to reference levels in this
Fission products. The results for the fission timescale,theeffectivePuremovalefficiencyneedsto
product inventories are given in Table 2. Very short- be 0.994 (i.e. 1(cid:2)1/180). Similarly at 200 years, the
and long-lived products have been omitted. The americium radiotoxicity is 9.4(cid:4)106Sv—that is, a
results of the decay calculations are given in the next factor 40 higher than the reference level. Hence an
section. effectiveremovalefficiencyneedstobeapproximately
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Partitioningandtransmutationscenarios
Table2.Standardisedburnupcalculations(4.2%enrichment,50GWd/t,6yearscoolingtime):mass(g)inventorypertonof
spentfueloffissionproductswithhalf-livesintherange0.5–1015years
Fissionproduct Half-life FZK ITU CEA
3H 12.34y 4.91(cid:4)10(cid:2)2 6.07(cid:4)10(cid:2)2 5.08(cid:4)10(cid:2)2
10Be 1.5(cid:4)106y 1.41(cid:4)10(cid:2)2 1.96(cid:4)10(cid:2)4 —
14C 5.7(cid:4)103y 4.37(cid:4)10(cid:2)3 3.96(cid:4)10(cid:2)5 4.37(cid:4)10(cid:2)3
79Se 6.5(cid:4)105y 3.20(cid:4)100 8.75(cid:4)100 7.16(cid:4)100
81Kr 2.3(cid:4)105y 1.46(cid:4)10(cid:2)5 4.26(cid:4)10(cid:2)5 1.57(cid:4)10(cid:2)5
85Kr 10.76y 2.45(cid:4)101 2.33(cid:4)101 2.39(cid:4)101
87Rb 4.8(cid:4)1010y 3.49(cid:4)102 3.59(cid:4)102 3.47(cid:4)102
90Sr 28.86y 6.79(cid:4)102 6.73(cid:4)102 6.62(cid:4)102
93Zr 1.5(cid:4)106y 1.05(cid:4)103 1.06(cid:4)103 1.03(cid:4)103
93mNb 16.1y 3.02(cid:4)10(cid:2)3 2.96(cid:4)10(cid:2)3 3.16(cid:4)10(cid:2)3
94Nb 2.0(cid:4)104y 6.86(cid:4)10(cid:2)4 1.15(cid:4)10(cid:2)3 6.64(cid:4)10(cid:2)4
97Tc 2.6(cid:4)106y 2.19(cid:4)10(cid:2)7 — —
98Tc 4.2(cid:4)106y 1.61(cid:4)10(cid:2)3 1.37(cid:4)10(cid:2)2 1.50(cid:4)10(cid:2)5
99Tc 2.1(cid:4)105y 1.18(cid:4)103 1.09(cid:4)103 1.15(cid:4)103
106Ru 1.02y 3.25(cid:4)100 3.72(cid:4)100 3.60(cid:4)100
107Pd 6.5(cid:4)106y 3.35(cid:4)102 3.53(cid:4)102 3.53(cid:4)102
108mAg 4.2(cid:4)102y 3.03(cid:4)10(cid:2)6 1.81(cid:4)10(cid:2)6 3.39(cid:4)10(cid:2)6
110mAg 2.5(cid:4)102d 1.39(cid:4)10(cid:2)3 3.82(cid:4)10(cid:2)3 3.78(cid:4)10(cid:2)3
109Cd 1.27y 3.67(cid:4)10 5.20(cid:4)10(cid:2)8 4.40(cid:4)10(cid:2)13
113mCd 14.11y 2.48(cid:4)10(cid:2)1 3.31(cid:4)10(cid:2)1 1.35(cid:4)10(cid:2)1
115In 4.4(cid:4)1014y 2.59(cid:4)100 2.56(cid:4)100 2.44(cid:4)100
119mSn 2.9(cid:4)102d 8.38(cid:4)10(cid:2)5 1.43(cid:4)10(cid:2)4 9.62(cid:4)10(cid:2)5
121mSn 55.04y 6.85(cid:4)10(cid:2)2 5.05(cid:4)10(cid:2)3 7.48(cid:4)10(cid:2)1
126Sn 2.1(cid:4)105y 3.58(cid:4)101 4.14(cid:4)101 4.54(cid:4)101
125Sb 2.76y 4.21(cid:4)100 4.36(cid:4)100 4.47(cid:4)100
123Te 6(cid:4)1014y 4.89(cid:4)10(cid:2)3 2.07(cid:4)10(cid:2)2 9.11(cid:4)10(cid:2)3
129I 1.6(cid:4)107y 2.37(cid:4)102 2.67(cid:4)102 2.72(cid:4)102
134Cs 2.07y 2.71(cid:4)101 3.09(cid:4)101 2.97(cid:4)101
135Cs 2.3(cid:4)106y 5.75(cid:4)102 5.39(cid:4)102 5.94(cid:4)102
137Cs 30.09y 1.57(cid:4)103 1.56(cid:4)103 1.57(cid:4)103
133Ba 10.52y 3.08(cid:4)10(cid:2)8 0.00(cid:4)100 —
138La 1.1(cid:4)1011 3.43(cid:4)10(cid:2)3 1.41(cid:4)10(cid:2)1 —
144Ce 2.8(cid:4)102d 1.77(cid:4)100 2.06(cid:4)100 1.97(cid:4)100
147Pm 2.63y 4.41(cid:4)101 3.06(cid:4)101 4.45(cid:4)101
145Sm 340d 2.31(cid:4)10 0.00(cid:4)100 —
146Sm 1.0(cid:4)108y 9.58(cid:4)10(cid:2)3 1.42(cid:4)10(cid:2)2 —
147Sm 1.1(cid:4)1011y — 2.00(cid:4)102 2.78(cid:4)102
151Sm 90y — 1.82(cid:4)101 1.71(cid:4)101
Totalmass(g) — 6.12(cid:4)103 6.27(cid:4)103 6.44(cid:4)103
0.975 (1(cid:2)1/40). The ‘Np’ and ‘U’ curves fall far the total radiotoxicity of the three waste streams
belowthereferencelevels. would still be more than 3(cid:4)105Sv, a value which is
For curium, it can be seen that the radiotoxicity above the reference level. In this case a separation of
around 200 years is actually below the reference the curium from the waste would be a necessity in
level—indication that it may not be necessary to ordertoreducethetotalradiotoxicitytothereference
remove it from the waste. Nevertheless, this depends level.
on the P&T strategy followed for the other waste
streams. The Cm radiotoxicity follows, from 200 Theradiotoxicityreferencelevel
years until 5000 years, a plateau around the value of To produce 1t of fresh fuel with an enrichment of
105Sv. If the separation and transmutation of the 4.2% 235U, 7.83t of natural uranium are required.
plutoniumandamericiumisefficientenoughtoreduce This amount is determined from the enrichment
significantly the total radiotoxicity of the waste then balanceconditions
the curium could be left in the waste (its own radio-
U ¼U þU ;
toxicity is then below the reference level). But it Feed Product Tails
ð6Þ
should be borne in mind that even if, after the 235U ¼235U þ235U
Feed Product Tails
separation and transmutation of plutonium and
americium, the radiotoxicity of each of the waste Leadingto
streams such as Pu, Am and Cm reaches a value e (cid:2)e
U ¼ Product TailsU ð7Þ
of 105Sv, a value which is below the reference level, Feed e (cid:2)e Product
Feed Tails
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Magilletal.
103
4.2% enriched, 50 GWd/t, 6 years' cooling
102
el
u
ent f 101 ITU
p
s FZK
e
n th 100 CEA
y i
ntor 10&1
e
v
n
kg) i 10&2
s (
s
ma 10&3
e
d
ni
cti 10&4
A
10&5
10&6
235U 236U 238U 237Np 238Pu 239Pu 240Pu 241Pu 242Pu 241Am 242Am 243Am 242Cm 243Cm 244Cm 245Cm 246Cm
Nuclide
Fig.4.ActinidemassinventoriespertonofspentPWRfuelaftersixyearscooling—acomparisonofITU,FZKandCEA
results
Total (g)
151Sm
147Sm
146Sm
145Sm
147Pm
144Ce
138La
133Ba
137Cs
135Cs
150y 1 3 4 1C2s9I
τ5y < <1 1 2 1111222m563SSSTnbne
.0 119mSn ITU
s: 115In
duct 1 1 130m9CCdd FZK
on pro 11 1100087mmPAAdgg
Fissi 1 0 99698RTTucc
97Tc
94Nb
93mNb
93Zr
90Sr
87Rb
85Kr
81Kr
79Se
14C
10Be
3H
0.001 0.01 0.1 1 10 100 1000 10 000
Mass: g
Fig.5.Comparisonoffissionproductsafterburnup(atsixyearscooling)
where e ¼235U =U is the enrichment Forthisreasontheingestionradiotoxicityof7.83t
Product Product Product
of the product uranium, e ¼235U =U is the of natural uranium, in equilibrium with its daughter
Feed Feed Feed
enrichment of the feed uranium, e ¼ products, is considered as the reference level in the
Tails
235U =U istheenrichmentofthetailsuranium. calculations. The resulting ingestion radiotoxicity is
Tails Tails
The enrichments e ¼4(cid:5)2%, e ¼0(cid:5)711%, then 2.41(cid:4)105Sv based on the ICRP7210 values for
Product Feed
e ¼0(cid:5)2% and the desired amount of enriched theeffectivedosecoefficient.HadtheICRP689values
Tails
uranium of U ¼1t result in U ¼7.83t beentaken,alowervalueof1.47(cid:4)105Svwouldhave
Product Feed
naturaluranium. resulted.Themainreasonforthisdifferenceisdueto
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Partitioningandtransmutationscenarios
108
el ITU
u
nt f 107 FZK
e CEA
p
s
n
o
per t 106
v
S
y:
cit
xi
oto 105
di Time:years ITU FZK CEA
n ra 1166110012 17..12666110078 17..11103966110087 17..25525566110087
estio 104 1166110034 14..885266110076 14..77704666110076 14..89985866110076
ng 16105 3.396105 3.0156105 3.1836105
I 16106 8.726104 7.0026104 7.1786104
103
101 102 103 104 105 106 107
Time: years
Fig.6.ActinideingestionradiotoxicityofspentPWRfuel—acomparisonofITU,FZKandCEAresults
109
'U'
108 'Np'
el
u 'Pu'
nt f 'Am'
pe 107 'Cm'
s
n Total
o
er t 106
p
v
S
city: 105
xi Reference radiotoxicity:
oto 7.83 t uranium
adi 104 in equilibrium
n r
o
esti 103
g
n
I
102
101
101 102 103 104 105 106
Time: years
Fig.7.ActinidemassinventoriesinspentPWRfuelplottedagainsttime(ITUdata).Resultsaregroupedbyelement,present
aftersixyearscooling.(ResultsbasedonICRP7210)
the much higher effective dose coefficient for 210Po consideredinthisstudy,aswellastheopencycle.The
giveninICRP72. resulting radiotoxicity curves are shown in Fig. 8, in
BasedontheICRP7210values,thetimetoreachthe whichthecrossoverpointindicatesthetimeatwhich
reference toxicity level is 130000 years. Using the the radiotoxicity of the waste reaches the reference
ICRP689 values this time would increase to 170000 level.Thefollowingobservationscanbemade.
years.
(a) The open cycle: the spent fuel is directly sent to
long-term storage with no P&T. It takes 130000
Radiotoxicityreduction indifferentP&T years before the radiotoxicity reaches the refer-
encelevel.
strategies
(b) The full multi-recycling of Pu as well as Am and
ToinvestigatetheeffectsofdifferentP&Tstrategies Cmwithhigh overallefficiencyofP&T processes
on the radiotoxicity reduction, three cases have been (99.5% for Pu and 99% for AmþCm). The
271
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Magilletal.
109
Total
Actinides
108 Fission products
el Ref. 7.83 t U in equilibrium
nt fu With P&T
pe 107
s
n
o
er t
v p 106 130 000 years
S
y:
cit
otoxi 105 270 years
di
a
n r
o
sti 104
e
g
n
I 1500 years [partial Pu 99.5% Am + Cm 90%]
103
500 years [full Pu 99.5% Am + Cm 99%]
1000 years [full Pu 99.5% Am + Cm 95%]
102
101 102 103 104 105 106
Time: years
Fig.8.IngestionradiotoxicityofonetonusednuclearfuelbasedonICRP72effectivedosecoefficients
crossoverpointis500years.IftheCmisleftinthe Cm. Targets containing small amounts of Am (and
waste,thistimeisextendedto1000years. maybe Cm) would be placed in the fast reactor and
(c) The full multi-recycling of Pu as well as Am and irradiatedduringalongperiodoftime.
Cm with less overall efficiency of P&T processes This strategy requires the knowledge and demon-
(99.5% for Pu and 95% for AmþCm). The stration of advanced aqueous reprocessing of spent
crossoverpointis1000years. oxide fuel, to recover Pu, Np, Am and Cm. The
(d) Thepartialmulti-recycling:multi-recyclingofthe reprocessing in current (but modified) installation
Pu (99.5% of P&T efficiency), and one single requireshighseparationrates(99.9%forPuandNp,
recyclingoftheAmandCm.InthiscasetheAm and99%forAmandCm),whichseemsfeasiblefrom
andCmaretransmutedintargetsinafastreactor, presentresearchresults.13Theseparationefficiencyof
and then 90% of P&T overall efficiency is fore- severalactinidesdemonstratesthat99.9%ofrecovery
seen. Thus the crossover point is around 1500 is achievable for Pu, Np and Am with the DIAMEX
years. In this strategy, we can also consider process.13 One open question is the treatment of the
leaving theCm inthe waste, and then 3000years Cm.IftheCmisnottransmutedwhiletheAmis,then
arerequired. the separation of the Cm from Am has to be done,
which needs further experimental demonstration. In
BasedontheseresultsitcanbeconcludedthatP&T
this case Cm must be conditioned and decay to Pu,
can help reduce the radiotoxicity of the spent fuel by
whichcouldbefurthertransmutedifnecessary.
morethantwoordersofmagnitudeafter500to1500
After separation, the minor actinides have to be
years. The fission products radiotoxicity curve gives
conditioned preferably in stable U-free targets for
the theoretical limit to the total radiotoxicity reduc-
their irradiation in fast reactors for their transmuta-
tion in the case that all the actinides are partitioned
tion by fission. The development of the facilities and
andtransmuted—thatis,nolosses.Thistimeisabout
fabricationprocessesaregoingonmainlyatITUand
270yearstoreachthesameorderofmagnitudeinthe
CEA for Europe, and the feasibility of their fabrica-
radiotoxicityreduction.
tion, transmutation and good irradiation behaviour
has been partially demonstrated.14 New experiments
P&Tstrategy technical feasibility12 planned in Phenix and HFR will further increase the
present database15 and more experiments will still be
Feasibilityofthepartialmulti-recyclingstrategy
requiredbeforeconsideringthesenewcompoundsfor
Thepartialmulti-recyclingstrategy(Fig.9)consists licensing in commercial installations and for large-
ofthemulti-recyclingofthePuandNpinfastreactors scaleutilisation.Thiscanbeachievedwithinacouple
associatedwithonesinglerecycleofAmandperhaps of decades taking into account the long lead-time
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