Process for preparing a metal oxide powder, process for manufacturing a metal oxide pellet, powder and pellet as obtained according to these processes and uses thereof

1. A process for preparing a powder of an oxide of at least one metal, each metal having an oxidation number between (III) and (VI), which process comprises successively and in this order:

(a) reacting, with a compound comprising a hydroxide, an aqueous solution comprising, for each metal, at least one salt of the cation of said metal, leading to a precipitate of the hydrated oxide of said at least one metal,

(b) separating the precipitate obtained,

(c) contacting the separated precipitate with an organic protic polar solvent,

(d) removing the organic protic polar solvent by vacuum drying the precipitate, leading to the powder of the hydrated oxide of said at least one metal, said powder being formed of particles the average diameter of which is equal to or lower than 1 μm.

2. The process according to claim 1 , wherein the powder of the hydrated oxide of said at least one metal is formed of particles the average diameter of which is equal to or lower than 100 nm.

3. The process according to claim 1 , wherein the powder of the hydrated oxide of said at least one metal has a specific surface area, measured according to the BET method, equal to or higher than 30 m 2 /g.

4. The process according to claim 1 , wherein the process further comprises, after step (b) and before step (c), a step of washing the separated precipitate, this washing being in particular performed by a protic solvent, optionally in mixture with water.

5. The process according to claim 1 , wherein the process further comprises, after step (d):

(e) heat treating the powder of the hydrated oxide of said at least one metal, leading to the powder of the anhydrous oxide of said at least one metal.

6. The process according to claim 1 , wherein each metal is chosen from the group consisting of actinides, lanthanides and transition metals.

7. The process according to claim 6 , wherein, when the metal is an actinide, it is chosen from a chemical element of the group consisting of U, Th, Pu, Np, Am and Cm.

8. The process according to claim 6 , wherein, when the metal is a lanthanide, it is chosen from a chemical element of the group consisting of Ce, Gd, Nd, Sm and Eu.

9. The process according to claim 6 , wherein, when the metal is a transition metal, it is chosen from a chemical element of the group consisting of Ti, Cr, Zr, Sc, Y and Hf.

10. The process according to claim 1 , wherein when the hydrated oxide of said at least one metal is a single oxide, this oxide is chosen from the group consisting of UO 2+δ , UO 3 , U 3 O 8 , CeO 2−δ , ThO 2 , PuO 2−δ , NpO 2+δ , ZrO 2 and HfO 2 .

11. The process according to claim 1 , wherein when the hydrated oxide of said at least one metal is a mixed oxide, this oxide is chosen from the group consisting of (U,Ce)O 2±δ , (U,Pu)O 2±δ , (U,Am)O 2±δ , (U,Th)O 2+δ , (Ce,Gd)O 2−δ , (U,Gd)O 2±δ , (Th,Pu)O 2−δ , (Th,Y)O 2−δ and (U,Pu,Am)O 2±δ .

12. The process according to claim 1 , wherein, for each metal, the salt of the cation of said at least one metal is chosen from the group consisting of a sulphate, nitrate, and halide.

13. The process according to claim 1 , wherein the compound comprising a hydroxide is ammonium hydroxide or hydrazinium hydroxide.

14. The process according to claim 1 , wherein the molar content of the compound comprising a hydroxide is in excess with respect to the total molar content of cation(s) of said at least one metal, this molar content of the compound comprising a hydroxide being between 150% and 600% with respect to the total molar content of cation(s) of said at least one metal.

15. The process according to claim 1 , wherein the organic protic polar solvent is chosen from the group consisting of an alcohol, a carboxylic acid and a primary amine.

16. The process according to claim 15 , wherein, when the organic protic polar solvent is an alcohol, this alcohol is a monoalcohol or a diol.

17. The process according to claim 1 , wherein the vacuum drying is made by means of a vacuum manifold.

18. A powder of a hydrated oxide of at least one metal, each metal having an oxidation number between (III) and (VI), obtained by the process according to claim 1 , said powder being formed by particles having an average diameter equal to or lower than 1 μm and having a specific surface area, measured according to the BET method, equal to or higher than 100 m 2 /g; and wherein each metal is selected from the group consisting of actinides and lanthanides.

19. A process for manufacturing nuclear fuel comprising providing the powder according to claim 18 and forming a pellet from said powder suitable for utilization as nuclear fuel.

20. A process for manufacturing a pellet of an oxide of at least one metal, each metal having an oxidation number between (III) and (VI), which process comprises successively and in this order:

(1) preparing a powder of an oxide of at least one metal, each metal having an oxidation number between (III) and (VI), by implementing the process according to claim 1 ,

(2) compacting the powder, and

(3) heat treating the compacted powder, leading to the pellet of the oxide of at least one metal.

21. The process according to claim 20 , wherein the pellet of the oxide of at least one metal has a density of at least 90%.

22. The process according to claim 20 , wherein the step (3) of heat treating is made by applying a temperature gradient extending from room temperature to a temperature equal to or lower than 1600° C.