Thermodynamic Properties of Non-Stoichiometric UO<SUB>2</SUB>-ThO<SUB>2</SUB> Solid Solution by Electro-Motive Force Measurements

Abstract

The thermodynamic properties of UO2-ThO2 solid solution of compositions (UyTh1−y)O2+x with y values of 0.295 to 0.048 and x values below 0.029 were determined by emf measurements. The oxygen concentration cells were of the type(This article is not displayable. Please see full text pdf.) and operated in the temperature range 900 to 1050°C.From the emf values and these temperature dependence, partial molar free energies, enthalpies and entropies of solution of oxygen in the solid solutions were calculated.Between these partial molar quantities and the mean valence of U ion in the solid solutions, there exist correlations which are nearly independent of the values of y. These results suggest that the non-stoichiometry of UO2-ThO2 solid solution is similar to that of UO2+x.