Measurement of the oxygen partial pressure and thermodynamic modeling of the U–Nd–O system

Abstract

Fission products greatly impact the properties of fuel necessitating a thorough understanding of the thermochemical properties of oxide fuels with fission products. However, thermochemical data for the U–Nd–O system is insufficient even though neodymium is a major fission product. As neodymium will likely be present as a solute in UO2, this research focuses on the study of (U1−yNdy)O2±x. Experimental measurements and analyses of the oxygen partial pressure (pO2)-temperature-oxygen to metal ratio (O/M ratio) relationships were performed using a thermogravimetric analyzer (TGA) and an oxygen analyzer. Thermodynamic computational modeling was performed using the CALPHAD (CALculation of PHAse Diagrams) method with the FactSage software. The Gibbs energy of the (U1−yNdy)O2±x solid solution was described by the compound energy formalism (CEF), which is based on earlier thermodynamic modeling data of the binary U–O system from Guéneau et al.. The thermodynamic and phase diagram data of the U–Nd–O system produced in this work show good agreement with the experimental data.