Thermodynamic modeling of the Pb-U and Pb-Pu systems

The thermodynamic assessments of the Pb-U and Pb-Pu binary systems were carried out using the CALPHAD (calculation of phase diagrams) method based on experimental data for thermodynamic properties and phase equilibria. The Gibbs free energies of the liquid, bcc, fcc, (αU), (βU), (δ′Pu), (γPu), (βPu) and (αPu) phases were described by a subregular solution model with the Redlich-Kister equation, and those of the intermetallic compounds (Pb3U, PbU, PbPu3, Pb3Pu5, Pb4Pu5, Pb5Pu4, αPb2Pu, βPb2Pu and Pb3Pu) by a two-sublattice model. The thermodynamic parameters for the two binary systems were optimized to consistently reproduce the available experimental data with satisfactory agreement.