Variation of the thermal conductivity of (U,Dy)O2 solid solutions as a function of the Dy content

The relationship between the lattice parameter (a) and the Dy content (y) in (U1−yDyy)O2, 0 ≤ y ≤ 0.2, is expressed as a = 0.5470 − 0.0215y in this study. When the above relation was applied to the Ohmichi's rule, it was suggested that U5+ existed in preference to U6+ in (U,Dy)O2 solid solutions. The thermal conductivities of UO2 and (U,Dy)O2 gradually decreased with the temperature, which showed that the temperature dependency of the thermal conductivity up to 1473 K followed the phonon conduction model, K = (A + BT)−1. The relationship between the thermal conductivity of UO2 and (U,Dy)O2 could be expressed as K(SS)=KUO2/(1+KUO2(0.9704y−0.0006yT))K(SS)=KUO2/(1+KUO2(0.9704y−0.0006yT)). It was also found that the size effect had a greater influence on the lattice defect thermal resistivity than the mass effect and especially, the size difference between the U4+ and U5+ ions rather than that between the U4+ and Dy3+ played a dominant role in the reduction of the thermal conductivity of (U,Dy)O2.