Abstract
Within the U and Pu recycling process from spent nuclear fuels, the conversion of purified U and Pu solution onto oxide powder is a key step at the interface between the separation / purification processes and the fabrication of uranium-plutonium oxide fuels called MOx ("Mixed Oxides"). In order to simplify the industrial process, conversion must be able to integrate fluxes with the minimum of adjustments while leading to oxides or mixtures of oxides adapted to a direct shaping of fuel pellets. This work deals with the development of a new conversion route without any precipitation and solid/liquid separation, the Advance thermal Denitration in presence of Organic Additives (ADOA). This new synthesis route consists in the addition of an organic additive (monomer, crosslinking and an organic agent) to the purified actinide solution. The resulting fully homogeneous solution is heated up to 100°C and supplemented with initiator to quickly allow complete polymerization into a gel. The xerogel is then formed by dehydration of the polymeric gel. A calcination permits obtaining the targeted mixed actinide oxide. Using a large panel of characterization technics, elucidation of the mechanism of this synthesis route was achieved allowing its optimisation. Oxides produced using this conversion route are U1-xPuxO2 pure solid solutions with x = 0 to 1. They are suitable for a direct pellitizing without any grinding/shieving step. Radiolysis have only little effect on the process. Thus, this new route meets the main requirements for conversion process dedicaded to Pu multirecycling implementation.