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Molten salts as heat transfer and storage materials have been used to nuclear energy and concentrated solar power(CSP) applications. In this work, the system of molten salt mixture based on thermodynamic principles was designed as thermal energy storage(TES) materials. The substitutional solution model can be employed to describe the Gibbs energies of all liquid phase. Thermodynamic model parameters for the NaCl-NaNO3-Na2SO4 subsystems were conducted by thermodynamic evaluation and optimization based on experimental phase-equilibria data. Thus, a set of self-consistent thermodynamic database was eventually obtained to reliably calculate the whole phase diagram and thermodynamic properties for the NaCl-NaNO3-Na2SO4 ternary system. The results manifest that the eutectic point of theternary system located at T=280 °C and xNaCl=8.4%, $${x_{NaN{O_3}}}$$ =86.3% and $${x_{N{a_2}S{O_4}}}$$ =5.3%. Moreover, the results predicted were verified experimentally using differential scanning calorimetry(DSC) and the agreement between the measured value[T=(287±2) °C] and predicted value(T=280 °C) was satisfactory. Thus, the thermodynamic calculation method will be used to design and develop novel molten salt mixture as thermal energy storage materials.

The phase diagrams of NaF-BeF2, NaF-ThF4 and NaF-UF4 systems were assessed based on thermodynamic principles, and diverse thermodynamic models were adapted to different systems. Associate solution model (ASM) was used to describe the Gibbs energies of liquid phase of the NaF-BeF2 system, whereas other systems(NaF-ThF4 and NaF-UF4) were treated with the substitutional solution model(SSM) and intermediate compounds were described as stoichiometric compounds according to the Neumann-Kopp rule. All the thermodynamic model parameters were optimized by the least squares procedure until good coincidence was achieved between the calculated results and the experimental data. The derived thermodynamic parameters will be merged into the NaF-BeF2-ThF4-UF4 database to develop the thorium molten salt reactor(TMSR) project.

Phase diagrams for the CsF-UF4 and CsF-ThF4 systems were modeled in the present work through computational thermodynamics. The associate solution model with various complex species(CsMF5, Cs2MF6 and Cs3MF7; M=Th, U) was used to thermodynamically describe the binary molten salts. A total of ten intermediate phases were treated as stoichiometric compounds with their Gibbs energies modeled according to the Neumann-Kopp rule. All these model parameters were optimized by the least squares procedure until good coincidence was achieved between the calculated results and most of the experimental data. The derived thermodynamic parameters will be merged into the multicomponent CsF-LiF-BeF2-ThF4-UF4 database for analyzing physicochemical behavior of CsF in the fuel salt of the molten salt breeder reactor.

Relations of equilibrium phases in the Al-Ca-Li system were calculated by means of the CALPHAD (calculation of phase diagram) method. The reported thermodynamic model parameters for all the constituent binary systems were directly used in the present calculation. A novel thermodynamic description for the three ternary intermetallic compounds(tau (1), tau (2) and tau (3)) was made on the basis of experimental phase equilibria in the Al-Ca-Li system. Comparison between the calculated and experimental phase equilibria shows that we have successfully derived a set of self-consistent thermodynamic parameters for the Al-Ca-Li system. These parameters were then used for the prediction of the selected isothermal and isopleth sections and projected liquidus surface of this ternary system over the entire composition range.