Peculiarities of fuel cycle with advanced composite fuel for thermal reactors

The use of dispersion type fuel elements, with high uranium content such as, U–Mo, U–Nb–Zr, U₃Si, with a Zr alloy matrix ("advanced metmet"), is considered instead of a UO₂ base type fuel for thermal reactors. Such fuels were fabricated and post-preparation analysed. In addition, composite, (U,Th)–PuO₂ fuels were considered based on depleted uranium (or uranium, thorium alloy) and dioxide plutonium powder as the dispersion phases (a "cermet" analogue of heterogeneous MOX). Such fuel elements could be used in thermal reactors as low temperature fuels. Subsequently, a novel reprocessing strategy for composite fuel is proposed. This would allow the separation of uranium from burnt plutonium as well as the newly generated fissile plutonium from the burnt portion without chemical processes, with repeated use in CANDU/RBMK reactors. This would simplify the closure of the nuclear fuel cycle. By sequential use of the composite fuel, the generated Pu in spent fuel could be recycled in a more pragmatic way, reducing drastically the waste flow.