Dissymmetric n,n-dialkylamides used particularly for separating uranium(vi) from plutonium(iv), synthesis thereof and uses of same

An N,N-dialkylamide of formula (I):

• wherein:
• R1 is a linear alkyl group having 1 to 4 carbon atoms;
• R2 is a linear alkyl group having 1 to 10 carbon atoms;
• R3 is a linear or branched alkyl group having 6 to 15 carbon atoms;
• provided that R3 differs from an n-octyl, n-decyl, n-dodecyl, 2-ethylhexyl and 2-ethyloctyl group when R1 is an n-butyl and R2 is an ethyl group.

A method for synthesizing an N,N-dialkylamide of formula (I):

• wherein:
• R1 is a linear alkyl group having 1 to 4 carbon atoms;
• R2 is a linear alkyl group having 1 to 10 carbon atoms;
• R3 is a linear or branched alkyl group having 6 to 15 carbon atoms;
• provided that R3 differs from an n-octyl, n-decyl, n-dodecyl, 2-ethylhexyl and 2-ethyloctyl group when R1 is an n-butyl and R2 is an ethyl group;
• comprising reacting a carboxylic acid of formula (II):
• wherein R1 is a linear alkyl group having 1 to 4 carbon atoms and R2 is a linear alkyl group having 1 to 10 carbon atoms, with an amine of formula HN(CH3)R3 wherein R3 is a linear or branched alkyl group having 6 to 15 carbon atoms, in an organic solvent and with a coupling agent;
• provided that R3 differs from an n-octyl, n-decyl, n-dodecyl, 2-ethylhexyl or 2-ethyloctyl group when R1 is an n-butyl group and R2 is an ethyl group.

A method for extracting uranium(VI) and/or plutonium(IV) from an acid aqueous solution, comprising at least one contacting of the aqueous solution with an organic solution comprising a N,N-dialkylamide or a mixture of N,N-dialkylamides of formula (I):

• wherein:
• R1 is a linear alkyl group having 1 to 4 carbon atoms;
• R2 is a linear alkyl group having 1 to 10 carbon atoms;
• R3 is a linear or branched alkyl group having 6 to 15 carbon atoms;
• provided that R3 differs from an n-octyl, n-decyl, n-dodecyl, 2-ethylhexyl and 2-ethyloctyl group when R1 is an n-butyl and R2 is an ethyl group;
• in an organic diluent, followed by a separation of the aqueous solution from the organic solution.

A method for separating totally or partially uranium(VI) from plutonium(IV) from an acid aqueous solution A1, comprising:

• a) a co-extraction of uranium and plutonium from the aqueous solution A1, the co-extraction comprising at least one contacting of the aqueous solution A1 with an organic solution S1 comprising an N,N-dialkylamide or a mixture of N,N-dialkylamides of formula (I):
• wherein:
• R1 is a linear alkyl group having 1 to 4 carbon atoms;
• R2 is a linear alkyl group having 1 to 10 carbon atoms;
• R3 is a linear or branched alkyl group having 6 to 15 carbon atoms;
• provided that R3 differs from an n-octyl, n-decyl, n-dodecyl, 2-ethylhexyl and 2-ethyloctyl group when R1 is an n-butyl and R2 is an ethyl group;
• in an organic diluent, followed by a separation of the aqueous solution A1 from the organic solution S1;
• b) a stripping of plutonium, in oxidation state +IV, and of a fraction of uranium from the organic solution S1 resulting from a), the stripping comprising at least one contacting of the organic solution S1 with an aqueous solution A2 comprising from 0.1 mol/L to 0.5 mol/L of nitric acid, followed by a separation of the organic solution S1 from the aqueous solution A2;
• and
• c) an extraction of all or part of the uranium fraction contained in the aqueous solution A2 resulting from b), the extraction comprising at least one contacting of the aqueous solution A2 with an organic solution S2 identical to the organic solution S1 of a), followed by a separation of the aqueous solution A2 from the organic solution S2;
• whereby there are obtained an aqueous solution comprising plutonium without uranium, or a mixture of plutonium and uranium, and an organic solution comprising uranium without plutonium.

A single-cycle method for processing an aqueous solution A1 resulting from a dissolution of a spent nuclear fuel in nitric acid, the aqueous solution A1 comprising uranium, plutonium, americium, curium and fission products including technetium, the cycle comprising:

• a) a co-extraction of uranium and plutonium from the aqueous solution A1, the co-extraction comprising at least one contacting, in an extractor, of the aqueous solution A1 with an organic solution S1 comprising an N,N-dialkylamide or a mixture of N,N-dialkylamides of formula (I):
• wherein:
• R1 is a linear alkyl group having 1 to 4 carbon atoms;
• R2 is a linear alkyl group having 1 to 10 carbon atoms;
• R3 is a linear or branched alkyl group having 6 to 15 carbon atoms;
• provided that R3 differs from an n-octyl, n-decyl, n-dodecyl, 2-ethylhexyl and 2-ethyloctyl group when R1 is an n-butyl and R2 is an ethyl group;
• in an organic diluent, followed by a separation of the aqueous solution A1 from the organic solution S1;
• b) a decontamination of the organic solution S1 resulting from a) with respect to americium, curium and fission products, the decontamination comprising at least one contacting, in an extractor, of the organic solution S1 with an aqueous solution A2 comprising from 1 mol/L to 6 mol/L of nitric acid, followed by a separation of the organic solution S1 from the aqueous solution A2;
• c) a partitioning of the uranium and plutonium contained in the organic solution S1 resulting from b) into an aqueous solution comprising either plutonium without uranium, or a mixture of plutonium and uranium, and an organic solution comprising uranium without plutonium, the partitioning comprising:
• c1) a stripping of plutonium, in oxidation state +IV, and of a fraction of uranium from the organic solution S1 resulting from b), the stripping comprising at least one contacting, in an extractor, of the organic solution S1 with an aqueous solution A3 comprising from 0.1 mol/L to 0.5 mol/L of nitric acid, followed by a separation of the organic solution S1 from the aqueous solution A3;
• c2) an extraction of all or part of the uranium fraction contained in the aqueous solution A3 resulting from c1), the extraction comprising at least one contacting, in an extractor, of the aqueous solution A3 with an organic solution S2 identical to the organic solution S1 of a), followed by a separation of the aqueous solution A3 from the organic solution S2;
• d) a decontamination of the organic solution S2 resulting from c1) with respect to technetium, the decontamination comprising:
• d1) a stripping of technetium, in oxidation state +IV, from the organic solution S2 resulting from c1), the stripping comprising at least one contacting, in an extractor, of the organic solution S2 with an aqueous solution A4 comprising from 0.1 mol/L to 3 mol/L of nitric acid and at least one reducing agent capable of reducing technetium from oxidation state +VII to oxidation state +IV, followed by a separation of the organic solution S2 from the aqueous solution A4;
• d2) an extraction of the uranium fraction contained in the aqueous solution A4 resulting from d1), the extraction comprising at least one contacting, in an extractor, of the aqueous solution A4 with an organic solution S3 identical to the organic solution S1 of a), followed by a separation of the aqueous solution A4 from the organic solution S3;
• e) a stripping of the uranium from the organic solution S3 resulting from d1), the stripping comprising at least one contacting, in an extractor, of the organic solution S3 with an aqueous solution A5 comprising no more than 0.5 mol/L of nitric acid, followed by a separation of the organic solution S3 from the aqueous solution A5;
• and
• f) a regeneration of the organic solution S3 resulting from e);
• whereby a first and a second aqueous solution are obtained, decontaminated with respect to americium, curium and fission products including technetium, the first aqueous solution comprising plutonium without uranium, or a mixture of plutonium and uranium, and the second aqueous solution comprising uranium without plutonium.