Synthesis route for the safe production of targets for transmutation of plutonium and minor actinides

Composites of actinide oxides dispersed in a Mo metal matrix is a recent inert matrix fuel (IMF) concept for the transmutation of Pu and the minor actinides (MA = Np, Am, Cm). These elements are present in spent nuclear fuel, and their long term radiotoxicity can be minimised if they are recovered from the fuel and irradiated in dedicated targets nuclear reactors. The synthesis of such highly radioactive fuels is not simple and given the high radiotoxicity of Am, the safety of operation of such a process must be examined for production of small scale analytical batches. Infiltration of Am nitrate infiltration into porous PuO2 beads has potential safety bonuses. The beads are produced by sol-gel external gelation route. Tests have been made here with CeO2, as a surrogate for PuO2 and have been optimised for both bead production and pelletisation of a blend of calcined beads and Mo powder. Addition of carbon to the sol gel feed solution, and its subsequent pyrolysis provides a means to optimise the porosity of the oxide beads. It acts as a pore former. The highest quality product meeting typical fuel specifications required addition of 20 g/litre carbon in the sol-gel feed and calcination of the CeO2 beads at 800˚C. Subsequent Mo cermet composites with 20 or 40 % by volume of ceramic reached densities in excess of 90 % of the theoretical value as is required for nuclear reactor applications. Finally, the step from CeO2 surrogates to (Pu,Am)O2 targets has been made.JRC.E.4-Nuclear fuel