Thermal conductivity analysis of UO2-based fuel by relaxation-time approximation method

The effects of solute elements and oxygen vacancies on the thermal conductivity of UO 2 were quantitatively evaluated using the relaxation-time approximation method. In UO 2 fuel, all solute elements—including various FP, burnable poisons such as Gd, Pu in MOX fuel, and added MA—reduce the thermal conductivity. The magnitude of this reduction depends on the specific element and the effects overlap, making quantitative evaluation challenging. In this study, these effects were analyzed using the relaxation-time approximation method by determining the relevant phonon scattering parameters. Single-crystalline and polycrystalline UO 2 samples, as well as polycrystalline UO 2 solid solutions, were fabricated, and their thermal conductivities were measured. The thermal conductivity was found to decrease with increasing differences in atomic mass and ionic radius between the solute elements and uranium ions, as well as with increasing oxygen vacancy concentration. Based on these results, phonon scattering parameters, including the Grüneisen constant, were determined. The determined parameters successfully reproduced the thermal conductivities of the fabricated samples and accurately represented previously reported data for MA-containing UO 2 . These parameters can therefore be used to predict the thermal conductivity of a wide range of UO 2 -based fuels.