Irradiation Performance of (Th,U)O2 Fuel Designed for Advanced Cycle Applications

Abstract

Our reference fabrication route for Advanced Cycle thoria-based fuel is conventional in that it produces cold-pressed and sintered pellets. However we are also evaluating alternative fuels which offer the potential for simpler fabrication in a remote facility, and in some cases improved high burnup performance. These alternatives are impregnated, spherepac, and extruded thoria-based fuels. Spherepac fuel has been irradiated at a linear power of 50-60 kW/m to about 180 MW.h/kg H.E. There have been unexplained defects in fuel with both freestanding and collapsible cladding. Impregnated fuel has operated to 650 MW.h/kg H.E. at 50-60 kW/m. An experiment examining fuel from the sol-gel extrusion process has reached 450 MW.h/kg H.E. at a maximum linear power of 60 kW/m. The latter two experiments have operated without defects and with fission gas release less than that for UO₂ under identical conditions. The extruded fuel has a pellet geometry similar to that for conventional fuel and is AECL's first practical demonstration of thoria-based fuel with the fissile component distributed homogeneously on an atomic scale. We will continue monitoring the extruded fuel to a burnup approaching 1000 MW.h/kg H.E., as an indicator for the performance expected from co-precipitated (Th,U)O₂ or mechanically-mixed (Th,U)O₂ with good fissile homogeneity.