Evaluation of Experimental Studies in the U-Rich Region of the U-Pu Phase Diagram

Abstract

Upon the re-examination of two experimental studies, additional thermophysical data pertaining to the uranium-rich portion of the uranium-plutonium binary phase diagram have been elucidated. The first study involved the analysis of solidification cooling curves following the processing of U-Pu alloys. Two phase transitions (liquidus and bcc) were evaluated and the results agreed very well with the established boundaries. The second study was actually performed over sixty years ago but still warrants recognition due to the paucity of thermodynamic data on the U-Pu system to date. From the investigation, the activity coefficients of plutonium in liquid uranium from 1813 K to 2042 K were derived assuming Henry’s law from which the partial molar excess Gibbs energy change of plutonium was obtained: \( \Delta \bar{G}^{\text{ex}} = R*T*\ln \gamma^{\text{o}}_{\text{Pu}} = - \;76694 + 39.2*T\left( {{\text{J}}/{\text{mol}}} \right). \)