Experimental investigations and thermodynamic modelling of KCl-LiCl-UCl3 system

Experimental investigations and Gibbs energy modelling of KCl-LiCl-UCl3 system employing CALPHAD method are reported. Gibbs energy modelling of the subsystems KCl-UCl3 and LiCl-UCl3 was carried out primarily using phase diagram data from the literature. For the Gibbs energy modelling of the KCl-LiCl subsystem, new phase boundary data corresponding to four terminal compositions (xLiCl=0.03, 0.05, 0.95 and 0.97) obtained through differential thermal analysis data along with thermochemical and phase diagram data from the literature were used. Thermal analysis was also carried out for KCl-LiCl eutectic mixture containing small amounts of UCl3(xUCl3=9.03×10−3 and 1.79×10−2). The liquidus temperatures for these compositions were found to be 637 K and 674 K. Electromotive force data for dilute solutions of UCl3 in the KCl-LiCl eutectic melt, measured in the temperature range 708-833 K in the present work, were found to be in good agreement with the literature data. These data were also used as input for the Gibbs energy modelling of the KCl-LiCl-UCl3 system. In order to improve the quality of the resulting Gibbs energy functions of the quasibinaries and the quasiternary, enthalpies of mixing of the corresponding melts estimated using an empirical correlation based on surrounded-ion model were also used as input. Finally, the generated Gibbs energy functions were used to compute phase equilibria.