Fabrication and Thermal Conductivity of (Th,U)O₂ Pellets

Techniques to fabricate thorium-uranium dioxide fuel [(Th,U)O₂] have been developed, and the thermal conductivity of (Th,U)O₂ pellets has been measured. Mixtures of thorium dioxide (ThO₂) and uranium dioxide (UO₂) powders were successfully wet-milled, compacted, and sintered at 1700°C to fabricate (Th,U)O₂ pellets. The wet-milling process results in a fuel density of 96 to 98% of theoretical density and a uniform distribution of the uranium and thorium in the (Th,U)O₂ pellet. The laser flash method was used to measure the thermal diffusivity of the ThO₂ and (Th,U)O₂ pellets, and the thermal conductivities of (Th_0.655U_0.345)O₂ and (Th_0.355U_0.645)O₂ fuel were found to be lower than that of ThO₂ or UO₂ fuel. The degradation of the thermal conductivity by the UO₂ substitution is great at low temperatures but decreases as the temperature increases.