Résumé
Within the U and Pu recycling process from nuclear spent fuels, the conversion of purified U and Pu solution into 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"). This study deals with the development of a new "direct" conversion route based on advanced thermal denitration to synthetize mixed actinide oxide (U1-xPuxO2±δ). This new synthetize method consists in the gelation of an actinide nitrate solution within a crosslinked polymer, followed by dehydration and calcination under controlled conditions to obtain the targeted mixed actinide oxide. On the basis of 0.5 g batch productions, the feasibility of the synthesis of all the solid solution U1-xPuxO2±δ with x ranging from 0 to 1 was demonstrated without any redox adjustment of the actinide feeding solutions and whatever nitric acidity (up to 7 M) or total actinide concentrations. Moreover, a first scale up was operated on the basis of a 15 g U0.80Pu0.20O2±δ batch, also dedicated to study the pellet fabrication using the powder as synthetized (i.e. without any grinding step). 94 percent of the theoretical density pellet was obtained with oxygen to metal ratio of 2.00. Therefore, such a conversion route allows fabrication of any kind of MOx fuels (PWR or SFR) offering several advantages: no redox adjustments, no solid/liquid partitioning required and reduction of actinide dissemination risks.