Fabrication of mixed uranium–plutonium carbide fuel pellets with a low oxygen content and an open-pore microstructure

Mixed uranium–plutonium carbides are considered as potential fuels for Generation IV fast reactors. Compared to that of oxide fuels, their fabrication with regard to required specifications is more difficult. Carbides are obtained by a two-step procedure from the mixture of UO2, PuO2 and graphite powders. Due to their extreme reactivity with oxygen and moisture, fabrication and handling of carbide fuels are performed in glove boxes maintained under a dynamic flow of nitrogen providing operational safety. Nevertheless, oxygen pickup during processing of the material seems unavoidable and thus must be limited by suitable procedures. The oxygen content in the carbides can vary over a wide range of values, which can affect the green density and hence the sintered density. The addition of zinc stearate in a suitable amount to the fuel powder leads to an open-pore microstructure. A high open porosity contributes to minimizing the residual oxygen content in the sintered pellets.