Carbamides for separating uranium(VI) and plutonium(IV) without reducing the plutonium(IV)

A method for totally or partially separating uranium(VI) from plutonium(IV), without reducing plutonium(IV) to plutonium(III), from an aqueous solution A1 issued from the dissolution of a spent nuclear fuel in nitric acid, comprising:

• a) a co-extraction of uranium(VI) and plutonium(IV) from the aqueous solution A1, the co-extraction comprising at least one contacting, in an extractor, of the aqueous solution with an organic solution S1 comprising a carbamide as an extractant in an organic diluent, followed by separating the aqueous solution from the organic solution, the carbamide being of formula(I):
• wherein:
• R1, R2 and R3, identical or different, represent a linear or branched alkyl group, comprising from 1 to 12 carbon atoms, a cycloalkyl group comprising from 3 to 12 carbon atoms or a cycloalkylalkyl group comprising from 4 to 13 carbon atoms;
• R4 represents a hydrogen atom, a linear or branched alkyl group, comprising from 1 to 12 carbon atoms, a cycloalkyl group comprising from 3 to 12 carbon atoms or a cycloalkylalkyl group comprising from 4 to 13 carbon atoms;
• b) a stripping of plutonium(IV) and a fraction of uranium(VI) from the organic solution issued from a), the stripping comprising at least one contacting, in an extractor, of the organic solution with an aqueous solution A2 comprising from 0.1 mol/L to 0.5 mol/L of nitric acid, followed by separating the organic solution from the aqueous solution;
• and
• c) an extraction of all or part of the uranium(VI) fraction present in the aqueous solution issued from b), the extraction comprising at least one contacting, in an extractor, of the aqueous solution with an organic solution S2 comprising the carbamide in an organic diluent, followed by separating the aqueous solution from the organic solution;
• whereby an aqueous solution comprising plutonium(IV) without uranium(VI) or a mixture of plutonium(IV) and uranium(VI), and an organic solution comprising uranium(VI) without plutonium(IV) are obtained.