Abstract: The invention relates to a powder of an alloy based on uranium and molybdenum in a metastable ? phase, which is formed of particles which have an elongation index at least equal to 1.1, a non-zero closed porosity value and which are composed of grains having a molybdenum content, for which the variations within the same grain are of at most 1% by mass. It also relates to a method allowing preparation of this alloy powder as well as to the use of said powder for manufacturing nuclear fuels and targets for producing radioisotopes. Applications: Manufacturing of nuclear fuels, notably for experiment nuclear reactors; manufacturing of targets for producing radioisotopes, notably for the medical industry.

Abstract: A method for preparing a powder of an alloy based on uranium and molybdenum in a metastable ? phase is provided, which comprises: a) putting at least one first reagent selected from uranium oxides and mixtures thereof, uranium fluorides and mixtures thereof, into contact with a second reagent consisting in molybdenum and a third reagent consisting in a reducing metal, the first, second and third reagents being in a divided form; b) reacting the reagents at a temperature?the melting temperature of the third reagent and under an inert atmosphere, whereby this reaction leads to the formation of the alloy comprising uranium and molybdenum in the form of a powder, for which the particles are covered with a reducing metal oxide or fluoride layer; c) cooling the so formed powder at a rate at least equal to 450° C./hour; and d) removing the reducing metal oxide or fluoride layer which covers the particles of the powder of the alloy comprising uranium and molybdenum.

Abstract: The invention relates to a powder of an alloy comprising uranium and molybdenum in ?-metastable phase, a composition of powders comprising this powder, and the uses of said alloy powder and of said composition of powders. The alloy powder comprising uranium and molybdenum in ?-metastable phase according to the invention is formed of particles comprising a nucleus which consists of said alloy, and which is covered with a layer of alumina positioned in contact with this nucleus. Applications: manufacture of nuclear fuel elements and, in particular, of fuel elements for experimental nuclear reactors; manufacture of targets intended for production of radioelements, which are useful in particular for medical imaging, such as technetium 99m.

Abstract: The invention relates to a powder of an alloy based on uranium and molybdenum in a metastable ? phase, which is formed of particles which have an elongation index at least equal to 1.1, a non-zero closed porosity value and which are composed of grains having a molybdenum content, for which the variations within the same grain are of at most 1% by mass. It also relates to a method allowing preparation of this alloy powder as well as to the use of said powder for manufacturing nuclear fuels and targets for producing radioisotopes. Applications: Manufacturing of nuclear fuels, notably for experimental nuclear reactors; manufacturing of targets for producing radioisotopes, notably for the medical industry.

Abstract: The invention relates to a method for preparing a powder of an alloy based on uranium and molybdenum in a metastable ? phase, which comprises: a) putting at least one first reagent selected from uranium oxides and mixtures thereof, uranium fluorides and mixtures thereof, into contact with a second reagent consisting in molybdenum and a third reagent consisting in a reducing metal, the first, second and third reagents being in a divided form; b) reacting the reagents at a temperature?the melting temperature of the third reagent and under an inert atmosphere, whereby this reaction leads to the formation of the alloy comprising uranium and molybdenum in the form of a powder, for which the particles are covered with a reducing metal oxide or fluoride layer; c) cooling the so formed powder at a rate at least equal to 450° C./hour; and d) removing the reducing metal oxide or fluoride layer which covers the particles of the powder of the alloy comprising uranium and molybdenum.

Abstract: A method for producing mixed oxide nuclear fuel pellets comprises the steps of preparing an U-Pu oxide blend powder having a Pu content in excess of the finally desired value, preparing uranium oxide powder, mixing adequate quantities of both powders in order to achieve the desired plutonium content and compacting and sintering the mixture for obtaining the pellets. The step of preparing the uranium oxide powder involves the following sequence of substeps: a) preparing an aqueous solution of uranyl nitrate to which between 0.5 and 2 wt % of organic thickeners are added such that the viscosity of the solution is adjusted to values between 20 and 100 centipoise, b) dispersing of the solution into droplets, c) introducing the droplets into a hydroxide bath, d) washing the resulting beads, e) drying the beads by azeotropic distillation using an immiscible organic solvent, f) thermally treating the beads in an oxidizing atmosphere and g) thermally treating in a reducing atmosphere.

Abstract: The invention relates to a process for thermal etching under oxidizing conditions of a ceramic, more particularly with the aim of revealing its grain boundaries and for the study of its granular microstructure. The invention applies to technical and nuclear ceramics and in particular UO2 and to (U, Pu) O2 mixtures. The thermal etching is performed in a furnace or kiln under a controlled atmosphere constituted by an oxidizing gas supplying a chemical oxygen potential of −75 to −125 kJ/mole and comprises the following successive stages: rapid rise in the temperature of the furnace to a rate of 900 to 1500° C./h from the initial temperature to a temperature plateau, maintaining the temperature at said plateau at a value of 1250 to 1450° C. for between 30 and 15 minutes, lowering the temperature to the final temperature.