Abstract: A process is described for synthesizing a mixed peroxide or hydroxo-peroxide of an actinyl and at least one cation X1, wherein the actinyl is a uranyl or neptunyl and the at least one cation X1 is a di-, tri- or tetra-charged metal cation. This process includes the reaction in a solvent of a salt of the at least one cation X1 with a compound C2 selected from mixed peroxides and hydroxo-peroxides of the actinyl and of at least one singly charged cation X2, whereby compound C2 is converted to the peroxide or hydroxo-peroxide by replacement of the at least one cation X2 by said at least one cation X1. Also disclosed is a process for synthesizing a mixed oxide of an actinide selected from uranium and neptunium, and of at least one metal able to form a di-, tri- or tetra-charged cation, which implements the preceding synthesis process.

Abstract: A method for preparing a powder of a solid solution of dioxide of uranium and of at least one other actinide and/or lanthanide element comprising combusting a solution that comprises uranyl nitrate and at least one nitrate of the other actinide and/or lanthanide element and glycine, with the glycine being used in a predetermined amount so as to form, at the end of the combustion, the solid solution.

Abstract: A process is described for synthesizing a mixed peroxide or hydroxo-peroxide of an actinyl and at least one cation X1, wherein the actinyl is a uranyl or neptunyl and the at least one cation X1 is a di-, tri- or tetra-charged metal cation. This process includes the reaction in a solvent of a salt of the at least one cation X1 with a compound C2 selected from mixed peroxides and hydroxo-peroxides of the actinyl and of at least one singly charged cation X2, whereby compound C2 is converted to the peroxide or hydroxo-peroxide by replacement of the at least one cation X2 by said at least one cation X1. Also disclosed is a process for synthesizing a mixed oxide of an actinide selected from uranium and neptunium, and of at least one metal able to form a di-, tri- or tetra-charged cation, which implements the preceding synthesis process.

Abstract: The invention relates to a method for preparing a powder of a solid solution of dioxide of uranium and of at least one other actinide and/or lanthanide element comprising a step for combustion of a solution comprising uranyl nitrate and at least one nitrate of the other actinide and/or lanthanide element and nitrogen-containing fuel used according to a specific predetermined amount so as to form at the end of this step, said solid solution.

Abstract: A method for preparing an oxalate of one or more actinides for processing and recycling nuclear fuel, comprising: the precipitation of said actinide or the coprecipitation of said actinides in the form of oxalate particles by bringing into contact an aqueous solution containing the actinide(s) with an aqueous solution of oxalic acid or of an oxalic acid salt; and the collection of the resulting oxalate particles; characterized in that the precipitation or coprecipitation is carried out in fluidized bed.

Abstract: A method for preparing an oxalate of one or more actinides for processing and recycling nuclear fuel, comprising: the precipitation of said actinide or the coprecipitation of said actinides in the form of oxalate particles by bringing into contact an aqueous solution containing the actinide(s) with an aqueous solution of oxalic acid or of an oxalic acid salt; and the collection of the resulting oxalate particles; characterized in that the precipitation or coprecipitation is carried out in fluidized bed.

Abstract: Method for coprecipitation (or simultaneous precipitation) of at least one actinide in oxidation state (IV) with at least one actinide in oxidation state (III), wherein: a solution i.e. mixture of actinide(s) in oxidation state (IV) and actinide(s) in oxidation state (III) is prepared by adding to it a singly charged cation whose presence makes it possible to stabilize the aforementioned oxidation states in the mixture, or a singly charged cation which does not act to stabilize the aforementioned oxidation states in the mixture; a solution containing oxalate ions is mixed with the said mixture of actinides in order to carry out coprecipitation, i.e. simultaneous precipitation, of the said actinides in oxidation states (IV) and (III) and a fraction of the singly charged cation. According to another embodiment, a solution i.e.

Abstract: Method for coprecipitation (or simultaneous precipitation) of at least one actinide in oxidation state (IV) with at least one actinide in oxidation state (III), wherein: a solution i.e. mixture of actinide(s) in oxidation state (IV) and actinide(s) in oxidation state (III) is prepared by adding to it a singly charged cation whose presence makes it possible to stabilize the aforementioned oxidation states in the mixture, or a singly charged cation which does not act to stabilize the aforementioned oxidation states in the mixture; a solution containing oxalate ions is mixed with the said mixture of actinides in order to carry out coprecipitation, i.e. simultaneous precipitation, of the said actinides in oxidation states (IV) and (III) and a fraction of the singly charged cation. According to another embodiment, a solution i.e.