Patent Number: 
Section: claims

1. A method for preparing a nuclear fuel consisting of an oxide of uranium and at least one minor actinide selected from the group consisting of americurium, curium, neptunium and mixtures thereof comprising the following steps:preparing a nitric acid load solution comprising said at least one minor actinide in the form of a minor actinide nitrate with said minor actinide nitrate comprising a minor actinide cation and a nitrate anion and with said uranium being in the form of a complex of hydroxylated uranyl nitrate of formula UO2(NO3)2-x(OH)x with x≦1;passing said nitric acid load solution over a cation exchange resin comprising carboxylic groups —COOH, such that the complex of hydroxylated uranyl nitrate of said load solution causes concomitant ion exchange to occur between the uranyl cations of said complex and the minor actinide cations with protons of said carboxylic groups —COOH in the cation exchange resin whereby the uranyl cations and said minor actinide cations remain bound to the resin; andheat treating by carbonization of said cation exchange resin thus loaded whereby the nuclear fuel so obtained will consist of an oxide of uranium and at least one minor actinide selected from the group consisting of americurium, curium, neptunium and mixtures thereof. 2. The method according to claim 1, wherein the minor actinide elements stem from a flow for reprocessing used fuel. 3. The method according to claim 1, wherein the step for preparing the load solution comprises:preparation of a first nitric solution comprising nitrate of said minor actinide element;introduction of a pre-determined amount of uranium oxide UO3 or optionally U3O8, into said first solution, to form a hydroxylated uranyl nitrate complex of formula UO2(NO3)2-x(OH)x with x≦1;a step for mixing the resulting solution. 4. The method according to claim 1, wherein the step for preparing the load solution consists of introducing a predetermined amount of uranium trioxide into a first solution comprising nitrate of said minor actinide element and already uranyl nitrate, so as to form a hydroxylated uranyl nitrate complex of formula UO2(NO3)2-x(OH)x with x≦1. 5. The method according to claim 3, wherein the predetermined amount of uranium trioxide to be introduced into the first solution is determined so that the molar ratio between the number of moles of nitrate ions and the number of moles of uranium is less than 2. 6. The method according to claim 1, wherein the resin is a resin resulting from (co)polymerization of (meth)acrylic acid or acrylonitrile with a cross-linking agent. 7. The method according to claim 1, wherein the resin, before the step for passing the load solution over it, undergoes one or more of the following steps:a wet calibration step, so as to isolate the desired grain size fraction;at least one washing step by applying a basic and acid treatment cycle with ammonia and nitric acid followed by a rinsing step with demineralized water;a drying step after the rinsing step;a shape-sorting step so as to remove broken or non-spherical particles. 8. The method according to claim 1, wherein the step for passing the load solution is carried out by percolation of the latter over the resin. 9. The method according to claim 1, wherein the step for passing the load solution over the resin is carried out until an eluate is obtained, having a concentration identical with that of the load solution. 10. The method according to claim 1, wherein the heat treatment step comprises a carbonization step at a temperature which may range up to 1000° C. 11. The method according to claim 10, wherein the heat treatment step comprises a step for reducing the material obtained after the carbonization step, so as to obtain a mixed carbide and/or oxycarbide comprising uranium and at least one minor actinide element selected from americurium, curium, neptunium and mixtures thereof. 12. A method for preparing a nuclear fuel consisting of an oxycarbide or a carbide of uranium and at least one minor actinide selected from the group consisting of americurium, curium, neptunium and mixtures thereof comprising the following steps:preparing a nitric acid load solution comprising said at least one minor actinide in the form of a minor actinide nitrate with said minor actinide nitrate comprising a minor actinide cation and a nitrate anion and with said uranium being in the form of a complex of hydroxylated uranyl nitrate of formula UO2(NO3)2-x(OH)x with x≦1;passing said nitric acid load solution over a cation exchange resin comprising carboxylic groups —COOH, the complex of hydroxylated uranyl nitrate of said load solution causing concomitant ion exchange to occur between the uranyl cations of said complex and the minor actinide cations with protons of said carboxylic groups —COOH in the cation exchange resin, whereby the uranyl cations and said minor actinide cations remain bound to the resin;heat treating by carbonization of said cation exchange resin thus loaded whereby said nuclear-fuel is so obtained and reducing said oxide of uranium and at least one minor actinide whereby the nuclear fuel obtained consists of an oxycarbide or a carbide of uranium and at least one minor actinide selected from the group consisting of americurium, curium, neptunium and mixtures thereof.