Thermal conductivities of irradiated UO2 and (U,Gd)O2

The evaluation of thermal conductivity of irradiated fuel is very important since it directly affects the fuel operating temperature. The disk-shaped UO2 and UO2–10 wt%Gd2O3 samples were prepared and irradiated to about 4%FIMA to measure the thermal diffusivities by the laser flash method. The burnup was almost uniform within each sample. The irradiation temperature was almost constant and uniform within each sample except the temperature escalation that occurred during the irradiation. The thermal conductivity, determined from the thermal diffusivity, density and specific heat capacity, decreased by irradiation, while it partly recovered after the thermal diffusivity measurement at temperatures up to about 1800 K. The thermal conductivity reduction attributable to the irradiation-induced point defects was small in the samples which experienced higher temperature than 1273 K during the temperature escalation. The present results were compared with the reported models.