Thermal conductivity of gadolinia-chromia doped UO2 fuel

Abstract

UO2-Gd2O3 burnable absorber fuel has been utilized in the nuclear industry with the purpose to increase fuel burn up. However, gadolinium decreases the thermal conductivity and grain size of the UO2, both effects contribute to premature fuel degradation. The addition of oxides in UO2 is one of the alternatives to minimize these effects. In this work, UO2 pellets were obtained with Cr2O3 additions in the range of 0.05–0.24 wt% together with 6 wt% Gd2O3 to investigate effects on density and thermal conductivity. The thermal diffusivity of the fuel pellets was determined at room temperature by a laser flash method. The density of the pellets was determined by the immersion technique. Thermal conductivity was determined by the product of density, thermal diffusivity and specific heat capacity. The results showed that the presence of gadolinia decreased fuel pellets densities and the chromium oxide tended to increase them. The thermal conductivity of UO2-Gd2O3 pellets was about 22% and 25% lower than that of UO2. On the other hand, the effect of Cr2O3 on the thermal conductivity of the UO2 pellets had a minor effect.