Process for preparing a powder comprising a solid solution of uranium dioxide and of a dioxide of at least one other actinide and/or lanthanide element

1. A method for preparing a powder of a solid solution of dioxide of uranium and of at least one other actinide and/or lanthanide element comprising:

combusting a solution comprising uranyl nitrate and at least one nitrate of the other actinide and/or lanthanide element and glycine, the glycine being used in a predetermined amount in order to form, at the end of combusting, said solid solution, said predetermined amount being an over-stoichiometric amount of glycine relative to the uranyl nitrate obtained by:

a) determining a combustion equation of uranyl nitrate, to which a factor φ U is assigned to the stoichiometric coefficient of glycine;

b) determining an over-stoichiometric amount of glycine, Q U , by multiplying the amount of uranyl nitrate by the stoichiometric coefficient of glycine and by the factor φU, the latter being set to a value greater than 1;

c) determining a combustion equation of the nitrate of the other actinide and/or lanthanide element, to which a factor φ An/Ln is assigned to the stoichiometric coefficient of glycine;

d) determining an amount of the glycine, Q An/Ln , by multiplying the amount of the at least one nitrate of the other actinide and/or lanthanide element by the stoichiometric coefficient of the glycine and by the factor φ An/Ln , the latter being set to a value below 2; and

e) obtaining said predetermined amount by adding at least the amounts of glycine determined in b) (Q U ) and d) (Q An/Ln ), respectively.

2. The method for preparing a powder according to claim 1 , wherein the factor φ U has a value ranging from 1.5 to 1.7.

3. The method for preparing the powder according to claim 1 , wherein the at least one nitrate of the other actinide and/or lanthanide element comprises:

(i) for the nitrate of the other actinide element, a plutonium nitrate, a minor actinide nitrate and/or a thorium (IV) nitrate; and

(ii) for the nitrate of the other lanthanide element, a lanthanide (III) or (IV) nitrate.

4. The method for preparing a powder according to claim 1 , wherein the combusting comprises gradually heating the solution up to an ignition temperature.

5. The method for preparing a powder according to claim 1 , further comprising, before the combusting, preparing the solution comprising uranyl nitrate and at least one nitrate of the other actinide and/or lanthanide element and glycine.

6. The method for preparing a powder according to claim 5 , wherein preparing the solution comprising uranyl nitrate and at least one nitrate of the other actinide and/or lanthanide element and glycine consists of adding, to a first solution only comprising uranyl nitrate and at least one nitrate of the other actinide and/or lanthanide element, the predetermined amount of glycine.