Method for preparing a powder comprising particles of triuranium octoxide and particles of plutonium dioxide

1. A method for preparing a powder comprising particles of triuranium octoxide and particles of plutonium dioxide, comprising the steps of:

a) preparing, by oxalic precipitations, an aqueous suspension S 1 of particles of uranium(IV) oxalate and an aqueous suspension S 2 of particles of plutonium(IV) oxalate;

b) mixing the aqueous suspension S 1 with the aqueous suspension S 2 to obtain an aqueous suspension S 1+2 comprising particles of uranium(IV) oxalate and particles of plutonium(IV) oxalate;

c) separating the aqueous suspension S 1+2 into an aqueous phase and a solid phase, the solid phase comprising the particles of uranium(IV) oxalate and the particles of plutonium(IV) oxalate; and

d) calcining the solid phase to convert (1) the particles of uranium(IV) oxalate to particles of triuranium octoxide and (2) the particles of plutonium(IV) oxalate to the particles of plutonium(IV) dioxide, whereby the powder is obtained;

and wherein steps b) and c) are performed simultaneously or successively.

2. The method of claim 1 , wherein step a) comprises:

placing an aqueous solution A 1 comprising nitric acid and uranium(IV) nitrate in contact with an aqueous solution A 2 comprising a first precipitating agent to form a first reaction medium in which uranium(IV) is precipitated in a form of uranium(IV) oxalate, the first precipitating agent being oxalic acid, a salt or an alkylated derivative thereof; and

placing an aqueous solution A′ 1 comprising nitric acid and plutonium(IV) nitrate in contact with an aqueous solution A′ 2 comprising a second precipitating agent to form a second reaction medium in which plutonium(IV) is precipitated in a form of plutonium(IV) oxalate, the second precipitating agent being oxalic acid, a salt or an alkylated derivative thereof.

3. The method of claim 2 , wherein a concentration of nitric acid in the aqueous solutions A 1 and A′ 1 is between 0.5 mol/L and 5 mol/L.

4. The method of claim 2 , wherein a concentration of the uranium(IV) nitrate in the aqueous solution A 1 and a concentration of plutonium(IV) nitrate in the aqueous solution A′ 1 are between 0.001 mol/L and 1 mol/L.

5. The method of claim 2 , wherein a concentration of the first precipitating agent in the aqueous solutions A 2 and a concentration of the second precipitating agent A′ 2 are between 0.05 mol/L and 1 mol/L.

6. The method of claim 2 , wherein the first precipitating agent is present in the first reaction medium in excess with regard to stoichiometric conditions for an oxalic precipitation of uranium(IV) and the second precipitating agent is present in the second reaction medium in excess with regard to stoichiometric conditions for an oxalic precipitation of plutonium(IV).

7. The method of claim 2 , wherein the aqueous solution A′1 further comprises uranium(VI) nitrate.

8. The method of claim 1 , wherein step c) comprises a vacuum or pressure filtration of the aqueous suspension S 1+2 .

9. The method of claim 1 , wherein steps b) and c) are performed simultaneously.

10. The method of claim 1 , wherein step d) comprises a treatment of the solid phase at a temperature of at least 550° C. and in an oxidizing atmosphere.

11. The method of claim 1 , wherein the powder further comprises particles of an actinide(IV) dioxide, the actinide(IV) dioxide being thorium dioxide or neptunium dioxide, and wherein the method further comprises the steps of:

a′) preparing, by oxalic precipitations, the aqueous suspension S 1 of particles of uranium(IV) oxalate, the aqueous suspension S 2 of particles of plutonium(IV) oxalate and an aqueous suspension S 3 of particles of actinide(IV) oxalate;

b′) mixing the aqueous suspensions S 1 , S 2 and S 3 with each other to obtain an aqueous suspension S 1+2+3 comprising the particles of uranium(IV) oxalate, the particles of plutonium(IV) oxalate and the particles of actinide(IV) oxalate;

c′) separating the aqueous suspension S 1+2+3 into an aqueous phase and a solid phase, the solid phase being formed by the particles of uranium(IV) oxalate, the particles of plutonium(IV) oxalate and the particles of actinide(IV) oxalate; and

d′) calcining the solid phase to convert (1) the particles of uranium(IV) oxalate to the particles of triuranium octoxide, (2) the particles of plutonium(IV) oxalate to the particles of plutonium dioxide, and (3) the particles of actinide(IV) oxalate to the particles of actinide(IV) dioxide, whereby the powder is obtained;

and wherein steps b′) and c′) are performed simultaneously or successively.

12. The method of claim 1 , wherein the powder further comprises particles of an actinide(IV) dioxide, the actinide(IV) dioxide being thorium dioxide or neptunium dioxide, and the method comprises the steps of:

a″) preparing, by oxalic precipitations, an aqueous suspension S 1 of particles of uranium(IV) and actinide(IV) double oxalate, and the aqueous suspension S 2 of particles of plutonium(IV) oxalate;

b″) mixing the aqueous suspension S 1 with the aqueous suspension S 2 to obtain an aqueous suspension S 1+2 comprising particles of uranium(IV) and actinide(IV) double oxalate and particles of plutonium(IV) oxalate;

c″) separating the aqueous suspension S 1+2 into an aqueous phase and a solid phase, the solid phase being formed by the particles of uranium(IV) and actinide(IV) double oxalate and the particles of plutonium(IV) oxalate; and

d″) calcining the solid phase to convert (1) the particles of uranium(IV) and actinide(IV) double oxalate to the particles of triuranium octoxide and actinide(IV) dioxide, and (2) the particles of plutonium(IV) oxalate to the particles of plutonium dioxide, whereby the powder is obtained;

and wherein steps b″) and c″) are performed simultaneously or successively.