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A ä t kä b ä l f ll llAnvänt kärnbränsle – avfall eller resurs?

Gunnar Skarnemark 2012-11-22


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.



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


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.


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)


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


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.


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”.


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


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.


Recycling and reuse of U and Pu


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


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


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


PUREXPUREX


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


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


PUREX, emissions from SellafieldPUREX, emissions from Sellafield


”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)


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.


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.


Wh b d ???What can be done???


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


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.


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


Framitidens återvinningsprocesser befinner sig idag i olika utvecklingsstadier

Europa satsar mycket på återvinning, liksom USA och Japan


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


På Chalmers går vi delvis egna vägar:


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


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


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.


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.


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.


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


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


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


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