Sodium-cooled fast reactors utilize metallic fuels that include bond-sodium within the fuel element. Molten salt electrolysis at 773 K with eutectic KCl-LiCl mixed with UCl3 as an electrolyte can recover the actinides from spent fuel. The critical factor affecting the useful life of the electrolyte is the increase in liquidus temperature from the accumulation of lanthanides, actinides, and sodium. Therefore, thermodynamic modeling of the KCl-LiCl-NaCl-UCl3 system was carried out by considering experimental data from the present work and literature as input. The liquidus and solidus temperatures for the two ternary systems, KCl-NaCl-UCl3 and LiCl-NaCl-UCl3, were determined using differential scanning calorimetry. The thermodynamic parameters for pure UCl3 were optimized for liquid and solid states over a wide temperature range. Several constituent binary (AkCl-UCl3; Ak: K, Li, Na) and ternary (KCl-LiCl-UCl3, KCl-NaCl-UCl3 and LiCl-NaCl-UCl3) systems were assessed or reassessed in this work. A new intermediate phase (K3UCl6) was included in the reassessment for the KCl-UCl3 system. There is good agreement between the experimental and calculated thermochemical and phase diagram data for all the systems optimized in the present work. This work is beneficial to determine the effect of NaCl on the liquidus temperature and other thermodynamic properties of KCl-LiCl electrolyte mixed with UCl3 for improving the efficiency of molten salt electrolysis.
