Thermodynamic investigations of ThO2–UO2 solid solutions

Abstract Heat capacities and enthalpy increments of solid solutions Th 1− y U y O 2 (s) ( y  = 0.0196, 0.0392, 0.0588, 0.098, 0.1964) and Simfuel ( y  = 0.0196) were measured by using a differential scanning calorimeter and a high temperature drop calorimeter. The heat capacities were measured in two temperature ranges: 127–305 K and 305–845 K and enthalpy increments were determined in the temperature range 891–1698 K. A heat capacity expression as a function of uranium content y and temperature and a set of self-consistent thermodynamic functions for Th 1− y U y O 2 (s) were computed from present work and the literature data. The oxygen potentials of Th 1− y U y O 2+ x (s) have been calculated and expressed as a polynomial functions of uranium content y , excess oxygen x and temperature T . The phase diagram, oxygen potential diagram of thorium–uranium–oxygen system and major vapour species over urania thoria mixed oxide have been computed using FactSage code.