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

Uranium–lanthanum mixed oxides (U1−y Lay) O2±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 La2O3 in UO2 at 1873 K was determined to be ∼82% from the room temperature XRD patterns of the sintered samples. However, the solubility limit of La2O3 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 (U1−y Lay) O2±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.