Patent Number: 050911201
Section: claims

1. Process for obtaining nuclear fuel pellets based on UO.sub.2 from metallic uranium, which does not lead to liquid effluents and gives intermediate, dense, pourable uranium oxide powders without any particular conditioning operation, such as granulation, comprising the steps of: oxidizing metallic uranium in an oxidizing gas at high temperature to obtain an oxide U.sub.3 O.sub.8 ; crushing or milling the U.sub.3 O.sub.8 to obtain a powder with an average grain size of approximately 10 to 30 .mu.m; chemically reducing the U.sub.3 O.sub.8 to UO.sub.2 ; activating the UO.sub.2 with the aid of at least one fine milling operation; and shaping by pressing and fritting. 2. Process according to claim 1, wherein the metallic uranium is oxidized by air or oxygen in the pure state or diluted by a neutral gas at a temperature not exceeding 600.degree. C. 3. Process according to claim 1, wherein the metallic uranium is oxidized in the presence of steam at a temperature not exceeding 800.degree. C. 4. Process according to any one of the claims 1 to 2, wherein the fine milling is a fluidized bed gas jet milling. 5. Process according to any one of the claims 1 to 3, wherein the oxidation phase of an oxidation-reduction cycle is performed with the aid of air or oxygen in the pure state or diluted by a neutral gas at a temperature not exceeding 600.degree. C. 6. Process according to any one of the claims 1 to 3, wherein the activated uranium oxide powder has a specific surface between 1.7 and 3.5 m.sup.2 /g. 7. Process according to any one of the claims 1 to 3, wherein prior to shaping, the activated UO.sub.2 powder is mixed with a metallic oxide in order to obtain mixed oxide fuel pellets. 8. Process according to claim 2, wherein the metallic uranium is oxidized by air or oxygen in the pure state or diluted by a neutral gas at a temperature between 400.degree. and 550.degree. C. 9. Process according to claim 3, wherein the metallic uranium is oxidized in the presence of steam at a temperature between 600.degree. and 750.degree. C. 10. Process according to claim 1, wherein activation of the UO.sub.2 is completed by at least one redox cycle. 11. Process for obtaining nuclear fuel pellets based on UO.sub.2 from metallic uranium, which does not lead to liquid effluents and gives intermediate, dense, pourable uranium oxide powders without any particular conditioning operation, such as granulation, comprising the steps of: oxidizing metallic uranium in an oxidizing gas at high temperature to obtain an oxide U.sub.3 O.sub.8 ; crushing or milling the U.sub.3 O.sub.8 to obtain a powder with an average grain size of approximately 10 to 30 .mu.m; activating the powder with the aid of at least one fine milling operation; chemically reducing the U.sub.3 O.sub.8 to UO.sub.2 ; and shaping by pressing and fritting. 12. Process according to claim 11, wherein the metallic uranium is oxidized by air or oxygen in the pure state or diluted by a neutral gas at a temperature not exceeding 600.degree. C. 13. Process according to claim 11, wherein the metallic uranium is oxidized in the presence of steam at a temperature not exceeding 800.degree. C. 14. Process according to any one of the claims 11 to 13, wherein the fine milling is a fluidized bed gas jet milling. 15. Process according to any one of the claims 11 to 13, wherein the oxidation phase of an oxidation-reduction is performed with the aid of air or oxygen in the pure state or diluted by a neutral gas at a temperature not exceeding 600.degree. C. 16. Process according to any one of the claims 11 to 13, wherein the activated uranium oxide powder has a specific surface between 1.7 and 3.5 m.sup.2 /g. 17. Process according to any one of the claims 11 to 13, wherein prior to shaping, the activated UO.sub.2 powder is mixed with a metallic oxide in order to obtain mixed oxide fuel pellets. 18. Process according to claim 12, wherein the metallic uranium is oxidized by air or oxygen in the pure state or diluted by a neutral gas at a temperature between 400.degree. and 550.degree. C. 19. Process according to claim 11, wherein the metallic uranium is oxidized in the presence of steam at a temperature between 600.degree. and 750.degree. C. 20. Process according to claim 11, wherein the oxidation phase of an oxidation-reduction is performed with the aid of air or oxygen in the pure state or diluted by a neutral gas at a temperature between 400.degree. and 500.degree. C. 21. Process according to claim 11, wherein activation of the UO.sub.2 is completed by at least one oxidation-reduction cycle. 22. Process for obtaining nuclear fuel pellets based on UO.sub.2 from metallic uranium, which does not lead to liquid effluents and gives intermediate, dense, pourable uranium oxide powders without any particular conditioning operation, such as granulation, comprising the steps of: oxidizing metallic uranium in an oxidizing gas at high temperature to obtain an oxide U.sub.3 O.sub.8 ; crushing or milling the U.sub.3 O.sub.8 to obtain a powder with an average grain size of approximately 10 to 30 .mu.m; chemically reducing the U.sub.3 O.sub.8 to UO.sub.2 ; activating the UO.sub.2 with the aid of at least one oxidation-reduction cycle; and shaping by pressing and fritting. 23. Process according to claim 22, wherein the metallic uranium is oxidized by air or oxygen in the pure state or diluted by a neutral gas at a temperature not exceeding 600.degree. C. 24. Process according to claim 22, wherein the metallic uranium is oxidized in the presence of steam at a temperature between 600.degree. and 750.degree. C. 25. Process according to claim 22, wherein the metallic uranium is oxidized in the presence of steam at a temperature not exceeding 800.degree. C. 26. Process according to any one of the claims 22 to 25, wherein the fine milling is a fluidized bed gas jet milling. 27. Process according to any one of the claims 22 to 25 wherein the oxidation phase of an oxidation-reduction cycle is performed with the aid of air or oxygen in the pure state or diluted by a neutral gas at a temperature not exceeding 600.degree. C. 28. Process according to any one of the claims 22 to 25, wherein the activated uranium oxide powder has a specific surface between 1.7 and 3.5 m.sup.2 /g. 29. Process according to any one of the claims 22 to 25, wherein prior to shaping, the activated UO.sub.2 powder is mixed with a metallic oxide in order to obtain mixed oxide fuel pellets. 30. Process according to claim 23, wherein the metallic uranium is oxidized by air or oxygen in the pure state or diluted by a neutral gas at a temperature between 400.degree. and 500.degree. C. 31. Process according to claim 22, wherein the metallic uranium is oxidized in the presence of steam at a temperature between 600.degree. and 750.degree. C. 32. Process according to claim 22, wherein the oxidation phase of an oxidation-reduction cycle is performed with the aid of air or oxygen in the pure state or diluted by a neutral gas at a temperature between 400.degree. and 500.degree. C.