Patent Number: 
Section: claims

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 U3O8, the other portion being in a form of uranium dioxide UO2; andb) reducing at least one portion of the triuranium octaoxide U3O8 into uranium dioxide UO2. 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 U3O8 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 UO2, 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 U3O8, 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 U3O8, 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 UO2, optionally a powder of plutonium oxide, and at least one powder of a minor actinide oxide; andoptionally 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 U3O8, 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 P1;a crushing operation; andat 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 U3O8, 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 UO2 into triuranium octaoxide U3O8, 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.