Effect of oxygen defects on thermal conductivity of thorium-cerium dioxide solid solutions

Abstract Thermal conductivity of thorium-cerium dioxide solid solutions has been measured and analyzed using the relaxation time approximation. Despite the presence of oxygen defects, the partially reduced Th 0.8 Ce 0.2 O 1.97 exhibited higher thermal conductivity than the stoichiometric one, Th 0.8 Ce 0.2 O 2.00 , showing the same tendency as that previously reported for Th 0.7 Pu 0.3 O 2-δ . The increase in thermal conductivity with the oxygen defects can be explained by assuming that cerium ions have an average ionic radius of the ionic radii of Ce 3+ and Ce 4+ in the description of phonon–impurity scattering. This result indicates that the small reduction of (Th,Pu)O 2-δ fuel increases the thermal conductivity, especially at high temperatures.