Thermodynamic assessment of the KF-ThF4, LiF-KF-ThF4 and NaF-KF-ThF4 systems

Ocádiz-Flores, J.A.; Carré, E; Griveau, J.‐C.; Colineau, E.; Capelli, E.; Souček, P.; Beneš, O.; Konings, R.J.M.; Smith, Anna

doi:10.1016/j.jct.2020.106069

Cited by 8 publications

(23 citation statements)

References 37 publications

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“…Weighted least square regression was used to obtain a linear trend between specific enthalpies and temperature for each composition. A similar linear trend in specific enthalpies and temperature for short temperature ranges (200 °C-300 °C) at higher temperatures (>T melt ) was noticed in previous literature [13,[39][40][41][42][43], while a nonlinear relationship was obtained when fitting to a wider temperature range [37,38,44,45]. For composition C, a second-order polynomial fit better described the specific enthalpies and temperature trend in temperature range of 700 °C-900 °C (Figure 11C).…”

Section: Specific Heat Capacitysupporting

confidence: 86%

Short- to Intermediate-Range Structure, Transport, and Thermophysical Properties of LiF–NaF–ZrF4 Molten Salts

2022

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LiF–NaF–ZrF4 multicomponent molten salts are identified as promising candidates for coolant salts in molten salt reactors and advanced high-temperature reactors. This study focused on low-melting point salt compositions of interest: 38LiF–51NaF–11ZrF4, 42LiF–29NaF–29ZrF4, and 26LiF–37NaF–37ZrF4. Ab-initio molecular dynamics (AIMD) calculations were performed and compared with available experimental data to assess the ability of rigid ion models (RIM) to reproduce short- to intermediate-range structure, transport, and thermophysical properties of the LiF–NaF–ZrF4 salt mixtures. It is found that as ZrF4 mol% increases, the average cation–anion coordination number (CN) of monovalent cations (Li+, Na+) obtained from RIM calculations decreases, while multivalent Zr4+ CN varied from 15% to 19% in comparison to corresponding AIMD values. In addition, RIM is found to predict the existence of 7, 8, and 9 coordinated fluorozirconate complexes, while AIMD and the available experimental data showed an occurrence of 6, 7, and 8 coordinated complexes in the melt. The intermediate-range structure analysis revealed that while the RIM parameters are able to reproduce a local structure for lower ZrF4 mol% salts such as in 38LiF–51NaF–11ZrF4, an extensive fluorozirconate network formation is observed in RIM simulations for higher ZrF4 mol% compositions. The network generated by RIM parameters is found to be mainly connected by “corner-sharing” fluorozirconate complexes as opposed to both “edge-sharing” and “corner-sharing” connectively portrayed by AIMD. It is found that a close agreement between AIMD and the RIM salt structure for the 11-mol% ZrF4 salt resulted in good agreement in the calculated Zr diffusivities and the viscosity values. However, due to the inaccurate short- to intermediate-range structure prediction by RIM for higher ZrF4 mol% compositions, thermophysical properties such as densities and heat capacity differ by up to 26% and 27%, respectively, upon comparison with AIMD and experimental values. Also, the network-dominated properties such as diffusion coefficients and viscosities differed by up to two and three orders of magnitude, respectively. This study signifies the importance of accurate salt structure generation for an accurate prediction of transport and thermophysical properties of multicomponent molten salts.

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Section: Specific Heat Capacitysupporting

confidence: 86%

Short- to Intermediate-Range Structure, Transport, and Thermophysical Properties of LiF–NaF–ZrF4 Molten Salts

2022

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“…The liquid-liquid mixing enthalpies in AF-ZrF 4 (A = Li, Na, K, Rb) mixtures, are convex curves which become more negative in the order Li, Na, K, Rb. 44 The AF-ThF 4 (A = Li, Na, K) systems 26,45,46 obey the same trend. Moreover, the depth of the curves is greater in ZrF 4 -based systems, due to the strength of the shorter Zr-F bond.…”

Section: View Article Onlinementioning

confidence: 74%

Examination of the short-range structure of molten salts: ThF₄, UF₄, and related alkali actinide fluoride systems

Ocádiz-Flores

Gheribi

Vlieland

et al. 2021

Phys. Chem. Chem. Phys.

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“…The setup was the same as the one used to measure mixing enthalpies in the KF−ThF 4 system, with which the fusion enthalpies of LiF, NaF, KF, and ThF 4 were measured within experimental error. 42 2.3. CALPHAD Modeling.…”

Section: Methodsmentioning

confidence: 99%

“…The uncertainties in the mixing enthalpy Δ mix H m o ( T fus,NaF ) were determined from the standard uncertainty of the calibration process. The setup was the same as the one used to measure mixing enthalpies in the KF–ThF 4 system, with which the fusion enthalpies of LiF, NaF, KF, and ThF 4 were measured within experimental error …”

Section: Methodsmentioning

confidence: 99%

Experimental and Computational Exploration of the NaF–ThF₄ Fuel System: Structure and Thermochemistry

et al. 2021

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The structural, thermochemical, and thermophysical properties of the NaF–ThF 4 fuel system were studied with experimental methods and molecular dynamics (MD) simulations. Equilibrium MD (EMD) simulations using the polarizable ion model were performed to calculate the density, molar volume, thermal expansion, mixing enthalpy, heat capacity, and distribution of [ThF n ] m − complexes in the (Na,Th)F x melt over the full concentration range at various temperatures. The phase equilibria in the 10–50 mol % ThF 4 and 85–95 mol % ThF 4 regions of the NaF–ThF 4 phase diagram were measured using differential scanning calorimetry, as were the mixing enthalpies at 1266 K of (NaF/ThF 4 ) = (0.8:0.2), (0.7:0.3) mixtures. Furthermore, the β-Na 2 ThF 6 and NaTh 2 F 9 compounds were synthesized and subsequently analyzed with the use of X-ray diffraction. The heat capacities of both compounds were measured in the temperature ranges (2–271 K) and (2–294 K), respectively, by thermal relaxation calorimetry. Finally, a CALPHAD model coupling the structural and thermodynamic data was developed using both EMD and experimental data as input and a quasichemical formalism in the quadruplet approximation. Here, 7- and 8-coordinated Th 4+ cations were introduced on the cationic sublattice alongside a 13-coordinated dimeric species to reproduce the chemical speciation, as calculated by EMD simulations and to provide a physical description of the melt.

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Thermodynamic assessment of the KF-ThF4, LiF-KF-ThF4 and NaF-KF-ThF4 systems

Cited by 8 publications

References 37 publications

Short- to Intermediate-Range Structure, Transport, and Thermophysical Properties of LiF–NaF–ZrF4 Molten Salts

Short- to Intermediate-Range Structure, Transport, and Thermophysical Properties of LiF–NaF–ZrF4 Molten Salts

Examination of the short-range structure of molten salts: ThF₄, UF₄, and related alkali actinide fluoride systems

Experimental and Computational Exploration of the NaF–ThF₄ Fuel System: Structure and Thermochemistry

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Thermodynamic assessment of the KF-ThF4, LiF-KF-ThF4 and NaF-KF-ThF4 systems

Cited by 8 publications

References 37 publications

Short- to Intermediate-Range Structure, Transport, and Thermophysical Properties of LiF–NaF–ZrF4 Molten Salts

Short- to Intermediate-Range Structure, Transport, and Thermophysical Properties of LiF–NaF–ZrF4 Molten Salts

Examination of the short-range structure of molten salts: ThF4, UF4, and related alkali actinide fluoride systems

Experimental and Computational Exploration of the NaF–ThF4 Fuel System: Structure and Thermochemistry

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Examination of the short-range structure of molten salts: ThF₄, UF₄, and related alkali actinide fluoride systems

Experimental and Computational Exploration of the NaF–ThF₄ Fuel System: Structure and Thermochemistry