Effect of grain boundary scattering on the thermal conductivity of uranium dioxide

Uranium dioxide (UO₂) is a primary nuclear fuel used in the light water reactors. The thermal conductivity of the fuel material is an important physical parameter that governs the conversion of heat generated via nuclear fission events into electricity. UO₂ is a Mott-Hubbard insulator with an energy gap of ≈2 eV and its thermal and magneto-vibrational properties are still under debate. The thermal conductivity of an insulating material depends on various scattering mechanisms such as defects, phonon-phonon, or grain boundaries. In this talk, we will present the effect of grain size and grain boundary scattering on the thermal conductivity of UO₂. It is observed that the grain boundary scattering is prominent at low temperatures (below 30 K) where thermal conductivity decreases systematically with lowering the grain-size. We have estimated various physical parameters contributing to the thermal conductivity using the Callaway-model and their relation with the grain-size will be discussed.