A method for preparing a powder comprising an intimate mixture of U.sub.3O.sub.8 particles and PuO.sub.2 particles and which may further comprise particles of ThO.sub.2 or NpO.sub.2. The method comprises: preparing, via oxalic precipitations, an aqueous suspension S.sub.1 of particles of uranium(IV) oxalate and an aqueous suspension S.sub.2 of particles of plutonium(IV) oxalate; mixing the aqueous suspension S.sub.1 with the aqueous suspension S.sub.2 to obtain an aqueous suspension S.sub.1+2; separating the aqueous suspension S.sub.1+2 into an aqueous phase and a solid phase comprising the particles of uranium(IV) oxalate and the particles of plutonium(IV) oxalate; and calcining the solid phase to convert (1) the particles of uranium(IV) oxalate to particles of triuranium octoxide and (2) the particles of plutonium(IV) oxalate to particles of plutonium(IV) dioxide, whereby the powder is obtained.

The present invention relates to a process for sintering a compacted powder of at least one oxide of a metal selected from an actinide and a lanthanide, this process comprising the following successive steps, carried out in a furnace and under an atmosphere comprising an inert gas, dihydrogen and water: (a) a temperature increase from an initial temperature T.sub.I up to a hold temperature T.sub.P, (b) maintaining the temperature at the hold temperature T.sub.P, and (c) a temperature decrease from the hold temperature T.sub.P down to a final temperature T.sub.F, in which the P(H.sub.2)/P(H.sub.2O) ratio is such that: 500<P(H.sub.2)/P(H.sub.2O)≦50 000, during step (a), from T.sub.I until a first intermediate temperature T.sub.i1 between 1000° C. and T.sub.P is reached, and P(H.sub.2)/P(H.sub.2O)≦500, at least during step (c), from a second intermediate temperature T.sub.i2 between T.sub.P and 1000° C., until T.sub.F is reached.

The present invention relates to a method for preparation of a powder comprising at least one carbide of at least one metal, comprising the steps consisting of: (a) preparing a solution comprising at least one organic gelling agent and at least one inorganic salt of at least one metal in a solvent; (b) modifying the pH of the solution prepared in step (a) in such a way as to precipitate said at least one metal and to obtain a colloidal suspension comprising nanoparticles of oxyhydroxides of said at least one metal; (c) removing the solvent from the colloidal suspension obtained in step (b) by which means a precursor of at least one carbide of at least one metal is obtained; and (d) subjecting the precursor obtained in step (c) to a thermal treatment in order to transform same into a powder comprising at least one carbide of at least one metal. The present invention also relates to the powder thus prepared and the various uses thereof.

A method for treating retained plutonium in a waste organic phase of a plutonium uranium reduction extraction (PUREX) process is provided. The waste organic phase of the PUREX process contains an organic solvent and plutonium, and the method includes contacting the waste organic phase of the PUREX process with an aqueous back extraction solution containing 2,6-pyridinedicarboxylic acid for back extraction to obtain a plutonium back extraction product; and the plutonium in the back extraction solution may be loaded onto the column for adsorption, transformation and desorption by an anion exchange column, ultimately recovering plutonium in the back extraction solution.

A method loading powder into a mold can include immersing the mold comprising one or more microchannels into a suspension comprising the powder and a surfactant suspended in a dispersant, wherein the powder comprises particles having an average particle size of less than 100 μm, wherein the mold is substantially entirely covered by the suspension; heating the suspension having the mold immersed therein under a temperature condition suitable to lower the stability of the particles of the powder in the suspension such that the particles settle out of solution and into the one or more microchannels; and applying an ultrasonic wave to the heated suspension to further settle the particles of the powder into the one or more microchannels thereby filling the one or more microchannels of the mold with the powder.

A method loading powder into a mold can include immersing the mold comprising one or more microchannels into a suspension comprising the powder and a surfactant suspended in a dispersant, wherein the powder comprises particles having an average particle size of less than 100 μm, wherein the mold is substantially entirely covered by the suspension; heating the suspension having the mold immersed therein under a temperature condition suitable to lower the stability of the particles of the powder in the suspension such that the particles settle out of solution and into the one or more microchannels; and applying an ultrasonic wave to the heated suspension to further settle the particles of the powder into the one or more microchannels thereby filling the one or more microchannels of the mold with the powder.

The present invention relates to a method for recovering plutonium from spent radioactive fuel. In one embodiment, the method comprises steps of extracting tetravalent plutonium from an aqueous solution of the spent radioactive fuel using a first organic solvent comprising tributyl phosphate; reducing tetravalent plutonium to trivalent plutonium by adding to an organic phase a second organic solvent comprising dimethylhydroxylamine; and stripping plutonium into the aqueous phase for recycling by adding an aqueous dilute acid solution into an organic phase. The method can significantly improve the efficiency of recovering plutonium from spent radioactive fuel compared with HAN stripping, and at the same time, can avoid the problems resulting from U(IV) reduction and extraction.

A method for preparing a powder comprising an intimate mixture of U.sub.3O.sub.8 particles and PuO.sub.2 particles and which may further comprise particles of ThO.sub.2 or NpO.sub.2. The method comprises: preparing, via oxalic precipitations, an aqueous suspension S.sub.1 of particles of uranium(IV) oxalate and an aqueous suspension S.sub.2 of particles of plutonium(IV) oxalate; mixing the aqueous suspension S.sub.1 with the aqueous suspension S.sub.2 to obtain an aqueous suspension S.sub.1+2, separating the aqueous suspension S.sub.1+2 into an aqueous phase and a solid phase comprising the particles of uranium(IV) oxalate and the particles of plutonium(IV) oxalate; and calcining the solid phase to convert (1) the particles of uranium(IV) oxalate to particles of triuranium octoxide and (2) the particles of plutonium(IV) oxalate to particles of plutonium(IV) dioxide, whereby the powder is obtained.

The present invention relates to a method for recovering plutonium from spent radioactive fuel. In one embodiment, the method comprises steps of extracting tetravalent plutonium from an aqueous solution of the spent radioactive fuel using a first organic solvent comprising tributyl phosphate; reducing tetravalent plutonium to trivalent plutonium by adding to an organic phase a second organic solvent comprising dimethylhydroxylamine; and stripping plutonium into the aqueous phase for recycling by adding an aqueous dilute acid solution into an organic phase. The method can significantly improve the efficiency of recovering plutonium from spent radioactive fuel compared with HAN stripping, and at the same time, can avoid the problems resulting from U(IV) reduction and extraction.

A method loading powder into a mold can include immersing the mold comprising one or more microchannels into a suspension comprising the powder and a surfactant suspended in a dispersant, wherein the powder comprises particles having an average particle size of less than 100 m, wherein the mold is substantially entirely covered by the suspension; heating the suspension having the mold immersed therein under a temperature condition suitable to lower the stability of the particles of the powder in the suspension such that the particles settle out of solution and into the one or more microchannels; and applying an ultrasonic wave to the heated suspension to further settle the particles of the powder into the one or more microchannels thereby filling the one or more microchannels of the mold with the powder.