Variation of the thermal conductivity of (U,Dy)O_2 solid solutions as a function of the Dy content

摘要

The relationship between the lattice parameter (a) and the Dy content (y) in (U_(1-y)Dy_y)O_2, 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 U~(5+) existed in preference to U~(6+) in (U,Dy)O_2 solid solutions. The thermal conductivities of UO_2 and (U,Dy)O_2 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 UO_2 and (U,Dy)O_2 could be expressed as K(SS) = K_(UO_2)/(l + K_(UO_2)(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 U~(4+) and U~(5+) ions rather than that between the U~(4+) and Dy~(3+) played a dominant role in the reduction of the thermal conductivity of (U,Dy)O_2.