UxTh1-x(C2O4)2 Solid Characterisation Studies

Many advanced reprocessing schemes under development are aimed at co-processing and co-conversion of actinides, unlike current reprocessing plants that produce separate uranium and plutonium products. The most well developed option for the co-conversion stage is probably oxalate co-precipitation, followed by the thermal co-conversion to a mixed oxide product. It is thus envisaged that future processes will avoid separation of plutonium from uranium and instead allow part of the uranium to flow with the plutonium, resulting in co-precipitation as the oxalate, and finally co-conversion to a mixed uranium-plutonium oxide (MOX), which can be fabricated into recycled nuclear fuel for further energy generation.The co-crystallisation of uranium (IV) and plutonium (III) into a single oxalate structure ensures the homogenous distribution of the two actinides at the molecular scale. The joint conversion of uranium and plutonium to the oxide form makes it possible to remove the complicated step of blending and grinding the two distinct oxide powders, as currently employed for the purposes of MOX fuel fabrication. This concept can also be extended to other actinides, including minor actinides from partitioning processes such as SANEX (Selective Actinide Extraction) and GANEX (Grouped Actinide Extraction) processes or even a thorium containing product from recycle of thorium based fuels.A selection of U_xTh_1-x(C₂O₄)₂ solids at varying concentrations of uranium and thorium were prepared by oxalate co-precipitation. Uranium (VI) was conditioned electrochemically at -0.7 V to uranium (IV), in the presence of hydrazine. The reduced uranium (IV) in nitric acid was mixed with thorium nitrate solutions at different concentration ratios with oxalic acid. The mixed tetravalent uranium-thorium oxalate solid products have been characterised by Raman and IR spectroscopies. The influence of thorium substituted into the uranium oxalate structure was evaluated. Several vibrational modes were found to be affected by the variation in ionic radius appearing to be metal sensitive and therefore, provide the initial indication in the evaluation of the chemical composition.