Combustion synthesis of (U,Pu)O ₂ solid solution: from parametric study to sintered pellet

This study presents the synthesis of actinide mixed oxides by solution combustion synthesis (SCS) using citric acid as fuel. The approach was chosen because of the promising results on surrogates and both uranium and plutonium pure oxides. The amount of fuel for SCS and the effect of the Pu/(U + Pu) composition were studied to optimize the characteristics of the powders. A solid solution (U,Pu)O_2+<i>x</i> was obtained for all conditions, and the resulting oxides exhibit a homogeneous cationic distribution of uranium and plutonium and nanometric features. A U_0.90Pu_0.10O_2+<i>x</i> powder was selected for pressing tests and sintering due to its industrial interest for the production of MOX fuel for PWR reactors. It was possible to obtain a pellet with a density of 88%TD, characterized by a low-temperature sintering due to the nanometric size of the powder. Despite presenting large macropores, due to the presence of residual carbon in the powder before sintering, the sintered pellet presents the expected round-shaped pores and a very homogeneous plutonium distribution.