Thermodynamic assessments of the U-Ni and Th-Ni systems

The thermodynamic assessments of the U-Ni and Th-Ni binary systems were carried out by using the CALPHAD (Calculation of Phase Diagrams) method on the basis of the experimental data including the thermodynamic properties and phase equilibria. The Gibbs free energies of the liquid, bcc, fcc, αU and βU phases were described by the subregular solution model with the Redlich-Kister equation, and those of the intermetallic compounds (U₆Ni, U₇Ni₉, U₅Ni₇, UNi₂, δ, ε, UNi₅, Th₇Ni₃, ThNi, Th₄Ni₇, ThNi₂, αTh₂Ni₇, βTh₂Ni₇, ThNi₅, Th₂Ni₁₉) in the U-Ni and Th-Ni binary systems were described by the sublattice model. The thermodynamic parameters of the U-Ni and Th-Ni binary systems were optimized for reproducing the experimental data, respectively, and an agreement between the calculated results and experimental data was obtained in each binary system.