Thermodynamic properties of ZrCl4 with LiCl, NaCl, KCl, CsCl, MgCl2, and UCl3 for molten salt reactor applications

A set of self-consistent Gibbs energy functions has been developed to describe the thermochemical behavior of the major reactive fission product ZrCl₄ with key components in chloride molten salt reactors (MSRs): LiCl–ZrCl₄, NaCl–ZrCl₄, KCl–ZrCl₄, CsCl–ZrCl₄, MgCl₂–ZrCl₄ and UCl₃–ZrCl₄. Low ZrCl₄ concentration phase equilibria most relevant to MSR applications have been confirmed via differential scanning calorimetry for NaCl–ZrCl₄, and X-ray diffraction analysis performed on equilibrated samples of NaCl–ZrCl₄, KCl–ZrCl₄, MgCl₂–ZrCl₄, and UCl₃–ZrCl₄. Within the framework of the modified quasi-chemical model in the quadruplet approximation, extrapolations of pseudo-binary models were generated to represent KCl–MgCl₂–ZrCl₄, KCl–NaCl–ZrCl₄, and MgCl₂–NaCl–ZrCl₄, which show agreement with phase equilibria data where available without the use of ternary interaction parameters. The optimized thermodynamic descriptions for these systems and others are available in the open-source compendium Molten Salt Thermal Properties Database – Thermochemical (MSTDB–TC).