THERMAL-EXPANSION AND THERMAL-CONDUCTIVITY OF CESIUM URANATES

Two kinds of cesium uranates: which are often predicted by thermochemi cal calculations to be formed in irradiated oxide fuels with high oxyg en potentials, were prepared from U3O8 and Cs2CO3 to determine the the rmal expansions and the thermal conductivities. The lattice parameters of tetragonal Cs2UO4 and monoclinic Cs2U2O7 were measured by the high -temperature X-ray diffraction method as a function of temperature. Th e linear thermal expansions of Cs2UO4 and Cs2U2O7 Obtained from the te mperature dependencies of the lattice parameters were 1.2% and 1.1% fr om room temperature to 973 and 1,073 K; respectively. The thermal diff usivities of Cs2UO4 and Cs2U2O7 were measured on the disk-shaped sampl es by the laser flash method as a function of temperature. The thermal conductivities were evaluated from the measured thermal diffusivities and the bulk densities; and the specific heat capacity available in l iterature. The thermal conductivity of Cs2UO4 corrected for 100%TD was 1.2 W/m . K at 980 K and that of Cs2U2O7 was 0.94 W/m . K at 1,093 K, which are about 30% and 27% of that of UO2, respectively.