XRD and XAS structural characterization of mixed-valence plutonium(III,IV) oxalate hydrates used to obtain controlled particle shape of plutonium oxide

The oxalic conversion of plutonium into oxide is one of the most important steps of the present fuel cycle dealing with the recycling of plutonium contained in the used fuel. This operation, which occurs at the end of the PUREX process, includes two steps, oxalic precipitation followed by calcination in air, and permits to elaborate one of the main starting materials for the MOX fuel fabrication. Coordination chemistry of plutonium with oxalic acid is rich and several plutonium oxalate hydrates, the quite well-known PuIV(C2O4)2.6H2O1 and PuIII2(C2O4)3.10H2O2 and the other novel structures described here, can lead to PuO2. Considering the morphology of the plutonium oxalate particles, it is interesting to notice that there is a strong correlation between the shape of these particles and the crystal structure of the plutonium oxalate.