Xenon Diffusivity in Thoria-Urania Fuel

Postirradiation annealing tests were performed to obtain the ¹³³Xe diffusion coefficients in uranium dioxide (UO₂) and mixed thorium-uranium dioxide [(Th-U)O₂] fuels. Specimens were a single-grained UO₂, a polycrystalline UO₂, and a polycrystalline (Th-U)O₂. The (Th-U)O₂ specimen was a mixture of 35% ThO₂ and 65% UO₂. Each 300-mg specimen was irradiated to a burnup of 0.1 MWd/t U. Postirradiation annealing tests were performed at 1400, 1500, and 1600°C, continuously. The xenon diffusion coefficients for the nearly stoichiometric single-grained UO₂ agree well with the data of others. The xenon diffusion coefficients in the polycrystalline (Th-U)O₂ are approximately one order lower than those in the polycrystalline UO₂. The xenon diffusion coefficient in the (Th-U)O₂ increases with the increasing oxygen potential of the ambient gas.