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Chalmers University of Technology
UpparbetningUpparbetning
A ä t kä b ä l f ll llAnvänt kärnbränsle – avfall eller resurs?
Gunnar Skarnemark 2012-11-22
Chalmers University of Technology
Nuclear Power back end - Different strategiesNuclear Power back end - Different strategies
1. “The Swedish model” 2. Reprocessing and reuse of uraniumand plutonium
The spent fuel is encapsulated and deposited directly deep into the bedrock.
and plutonium
The spent fuel is dissolved and separated into 3 streams: U Pu and
This method is planned to be used in e.g.Finland and Switzerland.
separated into 3 streams: U, Pu and waste. U and Pu is recycled into fuel production and the waste is vitrified and stored in a geological formation.g g
This method is used in e.g. France, UK, Japan, Russia and India.
3. Separation and transmutation
To be used in combination with recycling , p ,To be used in combination with recycling.
All the long lived fractions of the waste are transmuted into short-lived nuclides thustransmuted into short-lived nuclides, thus shortening the geological storage time considerably.
Research stage only at presentResearch stage only at present.
Chalmers University of Technology
How to choose the best option?
There are (at least) two ways to address the problem:
A i t ti t d th t t l di ti d t ki d- An intention to decrease the total radiation dose to mankind as much as possible
- Sustainability
Chalmers University of Technology
Decrease of total dose:
In this type of calculation the radiotoxicity (”hazard”) of 1 ton of uranium is compared with the radiotoxicity of the same material p y(uranium, TRU elements, fission products) after it has been used as nuclear fuel.
The radiotoxicity is usually plotted as a function of time.
When the radiotoxicity of the waste is equal to that of the original uranium the waste is considered to be ”not harmful”, i.e. it is no ,additional risk any more.
Chalmers University of Technology
Radiotoxicity (“hazard”) of nuclear waste
1E+9
1E+10
Total
Radiotoxicity ( hazard ) of nuclear waste
1E+8
1E+9TW
he)
Plutonium
1E+6
1E+7
xici
ty (S
v/T Minor
actinides
1E+4
1E+5
radi
otox
Uranium
1E+2
1E+3
Fission products
10 100 1000 10000 100000 1000000
time (years)
Chalmers University of Technology
Result:
Once through (the Swedish model): the radiotoxicity of the waste never reaches the uranium level (>106 years needed)
Reprocessing: the curves cross after about 70-80000 years
Partitioning and transmutation: the curves cross after 500-700 years
Chalmers University of Technology
S t i bilitSustainability:
Without reprocessing a LWR utilizes less than 1 % of the energyWithout reprocessing a LWR utilizes less than 1 % of the energy contents of the fuel (if taking into account that the depleted uranium is regarded as waste).
With reprocessing and recycling of Pu as MOX fuel the figure i t 1 2 %increases to 1-2 %.
With fast reactors (breeders) and reprocessing a fuel utilization ofWith fast reactors (breeders) and reprocessing a fuel utilization of about 50 % is possible.
If using an advanced fuel cycle with partitioning and transmutation, i.e. burning also of minor actinides like Np, Am and C 100 % i (th ti ll ) iblCm, 100 % is (theoretically) possible.
Chalmers University of Technology
Thus, sustainable nuclear power requires recycling and P/T.
Th th h ti i l ti l f t i th tThe once-through option is a solution only for countries that regard nuclear power as a ”parenthesis”.
Chalmers University of Technology
In this lecture we will try to distinguish between ”reprocessing” and ”recycling”.
Reprocessing is the old technique they use e.g. at Sellafield , often with unnecessary emissions to air and seaw u ecess y e ss o s o d se
Recycling is the new technology, i.e. emission-free reprocessing combined with a more efficient use of the fuel
Chalmers University of Technology
Reprocessing and reuse of U and PuReprocessing and reuse of U and Pu
Civilian reprocessing
R t d iReuse not used uranium
Recover Pu for use in new mixed oxide fuel (MOX)
Lower the storage time and activity of the spent fuel by removing the bulk actinide activity
Cons:Pros: Cons:
Bad “public acceptance” due to (unnecessary)release of, e.g. 99Tc and 85KrReprocessing in “wrong hands” may lead to
Pros:
Necessary for sustainable use of fissionenergy. (Direct disposal means that only 0.5% ofth t t f th U i d ) Reprocessing in “wrong hands” may lead to
the proliferation of nuclear weaponsShorten the storage time and activity of thespent fuel by removing the bulk actinideactivity
the energy content of the U is used.)
The technique to reprocess with NOenvironmental pollution exists. Not used because
f i l id ti activityVery complicated chemical process
of economical considerations.
Lower dose to man during the disposal time.
Chalmers University of Technology
Nowadays all reprocessing and recycling uses liquid-liquid extraction (solvent extraction, SX)
Definition of SX:
• Transfer of a solute from one liquid phase to another in a h li id li idtwo-phase liquid-liquid system
Chalmers University of Technology
What is needed?
• A soluteT i i ibl l ll d• Two immiscible solvents, usually an aqueous and an organic phase
• The organic phase often consists of an extractant and a• The organic phase often consists of an extractant and a diluent
• Classic example: extraction of iodine (I2) from water into CCl4CCl4
Chalmers University of Technology
Solvent extractionSolvent extraction
NN
NN
NN
N
NN
N
NN
Mixing Separation
N
NN
N
An3+
NO3-
NO3-
NO3-
Organic phase:Extractant + Diluent
N
N N
NNN
Aqueous phase:Lanthanides + FPActinides
(In nitric acid)(In nitric acid)
616AmD
1.0101EuD
606SF 601.0/ EuAmSF
Chalmers University of Technology
PUREXPUREXPlutoniumUraniumRedoxEXtraction
Fuelassemblies Gas
treatment
wastes
unloading
Storagel
off-gastreatment
iodine
Kr-Xe storage
pool
1st cycle
2ndcycle
3rdcycle
oxides
Pu
Oxalateprecipitation
Pu nitrate PuO2
241Am
thermaltreatment
shearing dissolution TBPextraction
2ndcycle
3rdcycle
cladding
U
thermaltreatment
U nitrate
dissolution
HFtreatment
F2combustion
UF6UF4UO3
Cm, FPNp, Am
vitrification
reductionUO2
vitrification
Chalmers University of Technology
I h ld b i d h i i f li i ibl bIt should be pointed out that emission-free recycling is possible but not used due to economical considerations.
The main pollutants are 85Kr, 99Tc and 129I
85Kr can be caught in cooling traps or on zeolites
99Tc can be removed by solvent extraction or ion exchangeTc can be removed by solvent extraction or ion exchange
129I can be reteined in cooling traps or ion-exchange filters
Chalmers University of Technology
”Problems” with the present PUREX processProblems with the present PUREX process Co-extraction of Tc in the U fraction Neptunium distributes between the waste and the U fraction TBP is not inert with respect to radiolysisTBP is not inert with respect to radiolysis.The radiolysis products, e.g. HDBP increase the distribution ratios and makes back-extraction of U and Pu difficult Reduction/oxidation of Pu is necessary. Difficult to get rid of used organic phase (not incinerable)Difficult to get rid of used organic phase (not incinerable) Two possibilities: Modified PUREX N (th t h t fit i th t i l t )New process (that has to fit in the present reprocessing plants)
Chalmers University of Technology
Improvements of PUREX The Tc extraction can be decreased by improved scrubbing after the first extraction Np can be oxidized to Np(VI) by better control of the reaction:Np can be oxidized to Np(VI) by better control of the reaction: 2NpO2
+ + NO3- + 3H+ → 2NpO2
2+ + HNO2 + H2O The reaction is self-catalyzing (HNO2 works as a catalyst) Np(VI) is extracted with U and Pu It can easily be separated in the second U cycle orNp(VI) is extracted with U and Pu. It can easily be separated in the second U cycle or by selective complexation e.g. with butyric aldehyde. The other problematic elements (Pd Se Sn) are beyond the scope of this courseThe other problematic elements (Pd, Se, Sn) are beyond the scope of this course.
Chalmers University of Technology
Still a problem: Radiotoxic Np, Am and Cm still leave the process together with the much less toxic fission products This yields storage times that are almost as long as without reprocessing Desirable: fractions with Np, Am and Cm for nuclear incineration in (fast) reactors or accelerators. Perhaps also fractions with selected fission products.
Chalmers University of Technology
P titi iPartitioning
U Pu Np I Tc
Modified PUREXSpent nuclear fuel
SESAME
Am Cm
Acidic high activity raffinate
DIAMEX
FP
Ln and AnAm, Cm
SANEXCalixarenes
FP
Cs
Oth FP
Vitrification
LnOther FP
An: actinidesLn: lanthanidesFP: fission products
Repository
Chalmers University of Technology
Actinide/lanthanide separations An(III) and Ln(III) are present in the PUREX waste fractionAn(III) and Ln(III) are present in the PUREX waste fraction The separation An(III)/Ln(III) is difficult because
- the chemical properties are very similar - the mass ratio Ln/An is high (about 20 at 47.5 GWd/ton of UO2 fuel)
The separation is a prerequisite for P&T since many lanthanide isotopes have high neutron capture cross sections.
Chalmers University of Technology
Suggested flow sheet
Uranium
Suggested flow sheet
MOX
fabricationEnrichment
Waste
Reactor ReprocessFuel
fabrication Waste
Target
Partitioning
Transmuter
Waste
Target
fabricationWaste
Not yet existing transmutation process
Chalmers University of Technology
Framitidens återvinningsprocesser befinner sig idag i olika utvecklingsstadier
Europa satsar mycket på återvinning, liksom USA och Japan
Chalmers University of Technology
I t ti l t t f th t i t i l t MA tiInternational state of the art… in trivalent MA separation
PUREX,ModifiedPUREX,
UREXSpent Fuel U, Np, Pu
PUREX,Modified PUREX,
UREXFuel U, Np, Pu
UREX,COEXTM
HLLW: FP, Ln(III) + An(III)
UREX,COEXTM
HLLW: FP, Ln(III) + An(III)
TRPO DIDPA TRUEX DIAMEX
Feed acidityadjustment step
FPFP FPFP TODGA FP UNEXTRPO DIDPA TRUEX DIAMEX
acidity
FPFP FPFP TODGA FP FPUNEX FP
SETFICSDIAMEX -SANEX/
HDEHPFP FPSETFICS
ModifiedDIAMEX
FP FPLn(III)
+ An(III)Ln(III)
+ An(III)Ln(III)
+ An(III)Ln(III)
+ An(III)Ln(III)
+ An(III)Ln(III)
+ An(III)
CYANEX N-Donor(BTP)
S-Donor(R2-PSSH)
CYANEX N-Donor(BTP)
S-Donor(R2-PSSH)
DIDPA TALSPEAKDIDPA/DTPA TALSPEAK
Ln(III) An(III)+ Ln(III)
Ln(III) An(III)+ FP
Ln(III) An(III)+ Ln(III)
Ln(III) An(III)+ FP
Ln(III) An(III)+ FP
( )
Ln(III) An(III)
( 2 )
Ln(III) An(III) Ln(III) An(III)
( )
Ln(III) An(III)
( 2 )
Ln(III) An(III) Ln(III) An(III)Ln(III) An(III)Ln(III) An(III) Ln(III) An(III)Ln(III) An(III)
An(III) + Ln(III) co-extractionAn(III) + Ln(III) co -extraction
DIAMEX
SelectiveAn(III) extractionSelective An(III) extraction
SANEXSelective An(III) stripping
INNOVATIVE SANEX
29
Chalmers University of Technology
TERPY
Originally made many years agoDeveloped by Burstall (J. Chem. Soc. 1938, 1662)Evaluated at Chalmers as an americium extractantN N Evaluated at Chalmers as an americium extractant.Lipofilic anion needed for extractionTwo ligand molecules coordinate with each actinideVery narrow useful pH range ~2
NN
Very narrow useful pH range,~2
Chalmers University of Technology
TPTZ
Reported by F.H. Case many years agoJ. Am. Chem Soc., 1959, 81, 905Used greatly in analytical chemistry as a metal binding agent (forms a coloured complex with iron)Better Am/Eu separation factor than TERPY
N
NN This was a useful accademic model compound for determining the influence of number of nitrogensVery instable towards radiolysis
NN
N
NN
Requires lipophilic anionOne ligand molecule binds with each actinide atom
N
Chalmers University of Technology
BODO
O Higher separation factors than TERPY
O ON
TERPYTwo ligand molecules coordinate with each actinidepKa lower than that of pyridineN N pKa lower than that of pyridineMore stable towards radiolysis than TERPY
This molecule was suggested by Chalmers and made by, Dr P. Iveson at Reading by the phosphoric acid catalysed condensation of 2-aminophenol with chelidamic acid
(4-hydroxypyridine-2,6-dicarboxylic acid), followed by O-alkylation of the phenol group.
It was found by Foreman that it was not possible to replace the teratogenic DMF used for the alkylation with the less toxic DMSO, also the phosphoric acid catalysed condensation is not compatable with the presense of alkyl groups such as tert-butyl groups on the aminophenol. This limits our ability to create new analogues of BODO.
Chalmers University of Technology
BTP
Can use nitrate as counter ionCan use nitrate as counter ion-[An(BTP)3]3+ is extracted as a nitrate salt.
Do not protonate (low pKa)High D values for actinides
N N N RRHigh D-values for actinidesStripping can be difficult or impossible Three ligand molecules coordinate with each actinideN
N
N
NN RR
As before F.H. Case reported the first BTPs back in the 1970s as iron binding agents.,During the 1990s at FZK Kolarik and Mullich identified and made these compounds as possible actinide extraction agents.
Sadly these compounds have a series of weaknesses
Normal and isoalkyl side groups are degraded by nitrous/nitric acid mixtures
The DAm value is strongly dependant on the nature of the R groups
fRadiation can inflict grievous reductive damage upon the molecule.
Chalmers University of Technology
BTBP
Can use nitrate as counter ion[An(BTBP)2]3+ is extracted as a nitrate salt.
DAm is largly insenstive to the nature of the side groups
NNRN N R
of the side groups.DAm [BTBP]2 so a change in extractant concentration will have a smaller effect on DAm, than for the
NN
RN
N Rsmaller effect on DAm, than for the BTP systempKa is low, protonation not observed with 3M HNO3.
Chalmers University of Technology
Extractants - BTBPs
N N N
Extractants BTBPs
NN
NN
N
NN
N NN
NN
N
NN
N
C2 BTBPC2-BTBPCyMe4-BTBP
NN
NN
N
NN
N NN
NN
N
NN
N
MF1-BTBP MF2-BTBP
NN
NN
N
NN
N
C6-BTBPC6
Chalmers University of TechnologyDissolved Spent
Nuclear Fuel
Fission Products (Lanthanides),
Corrosion/Activation Products
Chalmers GANEX (Group Actinide Extraction) process
l dl dDissolvedDissolved
SpentSpent NuclearNuclear
FuelFuel
GANEXGANEX ActinidesActinides::
U, U, NpNp, , PuPu, Am, Cm, Am, CmFuelFuel
Fission Fission ProductsProducts ((LanthanidesLanthanides), ),
Corrosion/ActivationCorrosion/Activation ProductsProducts
Chalmers University of Technology
Hur fungerar Chalmers förslag till GANEX-process?
Bränslet löses i ca 4 M HNOBränslet löses i ca 4 M HNO3
Aktiniderna extraheras med CyMe4-BTBP och TBP i y 4cyklohexanon
Ger en aktinidfraktion och en avfallsfraktion
Om så önskas kan man ha ett steg som extraherar huvuddelen avOm så önskas kan man ha ett steg som extraherar huvuddelen av uranet före det steg som extraherar Np, Pu, Am och Cm
Chalmers University of Technology
Varför är Chalmers GANEX-process intressant?
G i P ö i k i k fö kä id iGer ingen ren Pu-ström → minskar risken för kärnvapenspridning
Bra utbyten i testförsökBra utbyten i testförsök
Chalmers University of Technology
Framtiden är kanske:
Snabba reaktorer som även klyver 238U Np Am och CmSnabba reaktorer som även klyver 238U, Np, Am och Cm
Recycling av alla aktinider till dessa snabba reaktorerecyc g v de dess s bb e o e
Allt vårt nuvarande använda kärnbränsle kan då användas som bränsle – i Sverige räcker detta för att producera 10 GW i ca 900 år