Thermodynamic Assessment of Reciprocal Salt Systems Involving Cesium, Rubidium and Iodine for Molten Salt Reactor (MSR) Safety Analysis

Gibbs energy models necessary to describe the thermochemical behavior of rubidium, cesium and iodine in molten FLiNaK (46.5LiF-11.5NaF-42KF mol%) and compositions of NaCl-KCl-MgCl2, which are proposed molten salt reactor coolant and fuel solvents, have been developed. The alkali elements and iodine fission products are of particular concern due to their high radiotoxicity and volatility. Initially, to generate models for the systems it was necessary to obtain more accurate Gibbs energy functions for CsF and RbCl, which required fitting model parameters to reported vapor pressures over the condensed phases. These values together with reported phase equilibria, mixing enthalpy (ΔmixH), enthalpy of fusion (ΔfusH), thermodynamic activity, and vapor pressure measurements allowed evaluation of thirty-two pseudo-binary systems, LiF-RbF, LiF-CsF, LiI-NaI, LiI-KI, LiI-RbI, LiI-CsI, NaF-RbF, NaF-CsF, NaCl-RbCl, NaCl-CsCl, NaI-KI, NaI-RbI, NaI-CsI, KF-RbF, KF-CsF, KCl-RbCl, KCl-CsCl, KI-RbI, KI-CsI, RbF-CsF, RbI-CsI, NaCl-NaI, KCl-KI, RbF-RbI, RbCl-RbI, CsCl-CsI, MgCl2-RbCl, MgCl2-CsCl, MgI2-NaI, MgI2-KI, MgI2-RbI and MgI2-CsI. were evaluated using Original differential scanning calorimetry (DSC) measurements for the LiF-CsF, LiI-NaI, LiI-RbI, LiI-CsI, NaCl-CsCl, NaI-RbI and RbI-CsI systems were necessary to accurately complete their evaluation. Ternary reciprocal system representations for the Li,Cs|F,I, Li,K|F,I, Li,Na|F,I, Li,Rb|F,I, Na,K|F,I, Na,Rb|F,I, Na,Cs|F,I, K,Rb|F,I, K,Cs|F,I and Rb,Cs|F,I, Na,K|Cl,I, Na,Rb|Cl,I, Na,Cs|Cl,I, K,Rb|Cl,I, K,Cs|Cl,I, Rb,Cs|Cl,I, Mg,Na|Cl,I, Mg,K|Cl,I and Mg,Rb|Cl,I systems were obtained by interpolation of the optimized pseudo-binary systems with additional parameters determined based on reported behavior., Original DSC measurements were found to be necessary to fully represent the Na,Mg|Cl,I and K,Mg|Cl,I systems.