Hydroxide coprecipitation in nitric acid was used to synthesize U0.86Pu0.14O2±x solid solutions for the fabrication of model mixed nuclear fuels, one of the main objectives of this study being to evaluate the cationic homogeneity. Three precipitation methods were compared: simultaneous precipitation of U(IV) and Pu(IV), simultaneous precipitation of U(IV) and Pu(III), and precipitation of a premixed solution containing U(IV)-Pu(III). In order to obtain dense pellets, oxide precipitates were calcined and sintered at 1700 °C under Ar-4.3 vol H2 %. Despite an apparent similarity on a macroscopic scale, the pellets produced by the different methods reveal distinct microstructures, indicating differences in the sintering capability of the powders. These differences in microstructure and density have a low impact on the cationic homogeneity of the pellets after sintering. Regardless of the precipitation method used, the distribution of U and Pu elements remains uniform, with a higher level of homogeneity than that measured on MOX fuel obtained by other wet or dry chemistry routes. Finally, the most efficient coprecipitation route was applied to mixed oxides with 11 and 17 mol % Pu, in a range typical of PWR and FNR fuels, revealing a clear influence of Pu content on the physicochemical and sintering behavior of the powders.
Chmali et al. (Wed,) studied this question.