Method for preparing a porous nuclear fuel based on at least one minor actinide

1. A method for manufacturing a porous fuel comprising uranium, optionally plutonium and at least one minor actinide successively comprising:

a) compacting as pellets a mixture of powders comprising uranium oxide, optionally plutonium oxide and at least one oxide of a minor actinide, at least one portion of the uranium oxide being in a form of triuranium octaoxide U 3 O 8 , the other portion being in a form of uranium dioxide UO 2 ; and

b) reducing at least one portion of the triuranium octaoxide U 3 O 8 into uranium dioxide UO 2 .

2. The manufacturing method according to claim 1 , wherein the oxide of a minor actinide is selected from the group consisting of an americium oxide, a curium oxide, a neptunium oxide and mixtures thereof.

3. The manufacturing method according to claim 1 , wherein the uranium oxide in the form of triuranium octaoxide U 3 O 8 is associated within the same grains with an oxide of a minor actinide and optionally with plutonium oxide, said grains having a grain size of more than 100 μm.

4. The method according to claim 1 , further comprising before the compacting a), preparing said mixture of powders as defined in a).

5. The method according to claim 4 , wherein said preparing the mixture of powders consists of putting into contact a first mixture comprising a powder of uranium oxide in the form of uranium dioxide UO 2 , optionally a powder of plutonium oxide, and at least one powder of an oxide of a minor actinide and a second mixture of powders comprising uranium oxide in the form of triuranium octaoxide U 3 O 8 , optionally plutonium oxide and an oxide of a minor actinide.

6. The method according to claim 5 , wherein the second mixture of powders appears as grains comprising the association within a same grain of uranium oxide in the form of triuranium octaoxide U 3 O 8 , of optionally plutonium oxide, and of an oxide of a minor actinide, said grains having a grain size of more than 100 μm.

7. The method according to claim 5 , wherein the first mixture stems from the following operations:

an operation for putting into contact a powder of uranium oxide in a form of uranium dioxide UO 2 , optionally a powder of plutonium oxide, and at least one powder of a minor actinide oxide; and

optionally an operation for co-milling the resulting mixture in order to obtain an intimate mixture of powders.

8. The method according to claim 6 , wherein the second mixture of powders stems from the following operations:

an operation for putting into contact a powder of uranium oxide in a form triuranium octaoxide U 3 O 8 , optionally a powder of plutonium oxide, and at least one powder of an oxide of a minor actinide;

an operation for co-milling said powders;

a pressing operation at a predetermined pressure P 1 ;

a crushing operation; and

at least one sifting operation so as to isolate the grains having a grain size of more than 100 μm.

9. The method according to claim 4 , wherein said preparing the mixture of powders consists of putting into contact a first co-precipitated powder of an oxide of uranium optionally plutonium, and of a minor actinide with a second mixture of powders comprising uranium oxide in the form of triuranium octaoxide U 3 O 8 , optionally plutonium oxide and at least one oxide of a minor actinide.

10. The method according to claim 9 , wherein the second mixture of powders is obtained from a fraction of the first co-precipitated powder, said fraction is subject to a calcination step in air so as to transform the uranium oxide UO 2 into triuranium octaoxide U 3 O 8 , the resulting product being then optionally subject to a pressing operation, followed by a crushing operation and a sifting operation so as to isolate the powders having a grain size of more than 100 μm.

11. The method according to claim 8 , wherein the powders stemming from the sifting operations having a grain size of less than 100 μm are recovered and subject to the following successive operations:

a pressing operation at a pressure advantageously greater than 300 MPa;

a crushing operation;

at least one sifting operation so as to isolate the powder having a grain size of more than 100 μm,

said powders being intended to enter the composition of the second mixture of powders.

12. The method according to claim 1 , wherein the reduction is applied by having a reducing gas stream pass at a temperature ranging from 600 to 1,000° C. for a period which may range from 1 to 10 hours.

13. The method according to claim 1 , further comprising after the reduction, sintering fuel pellets.

14. The method according to claim 13 , wherein the sintering is applied by heating the aforementioned pellets to a temperature ranging from 1,000 to 1,800° C., for a period which may range from 1 to 8 hours.

15. The method according to claim 14 , wherein the sintering is carried out in a neutral gas atmosphere, optionally in the presence of hydrogen and water.

16. The manufacturing method according to claim 3 , wherein said grains have a grain size ranging from 100 to 250 μm.

17. The method according to claim 6 , wherein said grains have a grain size ranging from 100 to 250 μm.

18. The method according to claim 8 , wherein in said at least one sifting operation, the isolated power has a grain size ranging from 100 to 250 μm.

19. The method according to claim 10 , wherein said grains have a grain size ranging from 100 to 250 μm.

20. The method according to claim 11 , wherein in said at least one sifting operation, the isolated power has a grain size ranging from 100 to 250 μm.