Solubility studies and thermal expansion coefficient of uranium–lanthanum mixed oxide system

Abstract

Uranium–lanthanum mixed oxides (U 1− y La y ) O 2± x ( y = 0.1–0.9) of 13 different compositions were prepared by combustion synthesis using citric acid as the fuel. Sintering of the solid solutions was carried out at 1873 K. The solubility limit of La 2O 3 in UO 2 at 1873 K was determined to be ∼82% from the room temperature XRD patterns of the sintered samples. However, the solubility limit of La 2O 3 in the mixed oxides prepared by solid-state route and sintered under identical conditions was found to be ∼70%. The coefficients of thermal expansion for (U 1− y La y ) O 2± x ( y = 0.2, 0.4, 0.6, 0.8) in the temperature range 298–1973 K determined by high temperature X-ray diffraction (HTXRD) method are 17.7, 18.5, 19.2 and 20.0 × 10 −6 K −1, respectively.