Thermodynamics of Materials in Extreme Environments: Thermodynamics of Molten Salts
Sponsored by: ACerS Basic Science Division, ACerS Energy Materials and Systems Division
Program Organizers: Xiaofeng Guo, Washington State University; Kristina Lilova, Arizona State University; Kyle Brinkman, Clemson University; Alexandra Navrotsky, Arizona State University; Jake Amoroso, Savannah River National Laboratory; Xingbo Liu, West Virginia University; Gustavo Costa, NASA Glenn Research Center

Monday 8:00 AM
October 10, 2022
Room: 415
Location: David L. Lawrence Convention Center

Session Chair: Xiaofeng Guo, Washington State University


8:00 AM Introductory Comments

8:10 AM  Invited
Thermodynamic Database Development with a Focus on Corrosion in Potential Nuclear Reactor Molten Salt Systems: Theodore Besmann1; Juliano Schorne-Pinto1; Jacob Yingling1; Johnathan Ard1; Mina Aziziha1; Amir Mofrad1; 1University of South Carolina
    The continuing effort to expand the successful Molten Salt Thermal Properties Database – Thermochemical, has driven efforts to improve the accuracy of database values and the efficiency of required assessments. Fundamental studies of salts have made it clear that they experience short-range ordering, and the effect on the resulting coordination numbers on salt thermodynamic properties is captured in the current modified quasi-chemical model in the quadruplet approximation. The accuracy of these models is being improved through the use of multiple system endmembers, better capturing phenomenological behavior with varying temperature and composition. Optimization of systems using experimental and computational information to fit model parameters in such complex systems is problematic, and thus methodologies to more efficiently effect the fits have been developed. These approaches have been used to develop system models of consequence to corrosion in MSRs and will be described along with the current state of the database.

8:40 AM  Invited
Predictive Modeling of Complex Liquids with Uncertainty Quantification by Open-Source Tools: Illustrated with Thermodynamic Properties of Molten Salts: Shun-Li Shang1; Rushi Gong1; Jorge Paz Soldan Palma1; Brandon Bocklund2; Nathan Smith1; Yi Wang1; Hojong Kim1; Zi-Kui Liu1; 1Pennsylvania State University; 2Lawrence Livermore National Laboratory
    Design and development of molten salts depend on understanding and predictive modeling of critical salt properties such as melting points, heat capacities, and solubility of fission products, hence appealing for accurate models and especially modeling tools. Using a model system of NiF2-FLiNaK, the present work demonstrates the recent development of our open-source tools PyCalphad (https://pycalphad.org) and ESPEI (https://espei.org) to perform CALPHAD modeling using the modified quasichemical model in quadruplet approximation (MQMQA), which were recently implemented in the PyCalphad/ESPEI framework. The modelled results are compared with experimental results in the literature, the present measurements using electromotive force and differential scanning calorimetry, and the present ab initio molecular dynamics (AIMD) simulations; demonstrating a new approach to perform CALPHAD modeling with uncertainty quantification for complex liquids using the MQMQA.

9:10 AM  
Addressing the Thermodynamic Behavior of Volatile Fission Products in Fluoride Salt-Fueled Molten Salt Reactors: Behavior of Cesium and Iodine: Clara Dixon1; Mina Aziziha1; Juliano Schorne-Pinto1; Jacob Yingling1; Amir Mofrad1; Theodore Besmann1; 1University of South Carolina
    Developing accurate thermochemical models to predict the behavior of the volatile fission products cesium and iodine under simulated accident conditions is integral to the development and licensing of any MSR. We are thus developing thermochemical models and values for cesium and iodine in the molten fuel salts which is key to simulating their species formation and transport in a potential MSR accident. We analyzed the pseudo-binary systems of cesium and iodine with LiF-NaF-KF (FLiNaK) through data mining and DSC thermal analysis. We used the Computer CALculation of PHAse Diagrams (CALPHAD) methodology to model the various pseudo-binary systems and interpolated the pseudo-binary systems to generate pseudo-ternary models of cesium with the fluorides of Li-Na-K, and similarly create the first pseudo-quaternary model for cesium with FLiNaK.

9:30 AM  
Melting Point, Enthalpy of Fusion, and Excess Heat Capacity of a FLiNaK Determined by the CALPHAD Method: Juliano Schorne Pinto1; Johnathon Ard1; Mina Aziziha1; Kyle Foster1; Jacob Yingling1; Amir Mofrad1; Matthew Christian1; Theodore Besmann1; 1University of South Carolina
    We have of necessity revisited the thermodynamic models and values for the molten salt coolant FLiNaK (46.5 LiF–11.5 NaF–42 KF mol%) as part of the Molten Salt Thermal Properties Database − Thermochemical (MSTDB−TC) development effort, using additional excess Gibbs energy terms to allow the capture of any excess heat capacity (ΔCp) from mixing of the salt components and obtain an accurate enthalpy of fusion (ΔHfus). This required using the CALPHAD method to reevaluate the heat capacity and heat content, and vapor pressures over, solely LiF, NaF, and KF, as well as for their constituent pseudo-binary systems. Finally, internally consistent values were determined using observed phase equilibria, enthalpies of mixing (ΔmixH), ΔHfus, and ΔCp, producing a thermodynamic model for the pseudo-ternary system that predicts a eutectic composition of 46.7 LiF–11.4 NaF–41.9 KF mol% and melt temperature of 735.2 K, and computed Cp, and ΔHfus in good agreement with measured values.

9:50 AM Break

10:00 AM  
Thermodynamic Modelling and Experimental Investigation of LiCl-NaCl-UCl3 and KCl-NaCl-UCl3 Systems: Liangyan Hao1; Soumya Sridar1; Thomas Kirtley2; Elizabeth Sooby2; Wei Xiong1; 1University of Pittsburgh; 2University of Texas at San Antonio
    During the electrorefining process, the fuel component uranium and bond sodium will dissolve in the LiCl-KCl electrolyte. Therefore, with the increase of time and weight of processed spent fuel, the composition of the electrolyte changes greatly, which in turn influences its liquidus temperature and other physical properties. To have a better control of the electrorefining process, the CALPHAD method was used in this work to optimize the LiCl-NaCl-UCl3 and KCl-NaCl-UCl3 systems. To fill knowledge gap of phase equilibria in literature, DSC measurements were performed to obtain solidus and liquidus. Whenever experimental information is lacking, the empirical rule is applied to estimate the enthalpy of mixing and provide guidance to the optimization. The calculated phase diagram and thermochemical properties agree well with experimental results. It is expected that this work will contribute to efficiency of the pyroprocessing technology.

10:20 AM  
Enthalpy of Mixing of LaCl3 − LiCl:KCl Pseudo Binary Molten Salt System: Vitaliy Goncharov1; Jeffrey Eakin1; Jiahong Li1; Qiang Zhang1; Cornelius Ivory1; James Boncella1; Jason Lonergan2; Hongwu Xu3; Xiaofeng Guo1; 1Washington State University; 2Pacific Northwest National Laboratory; 3Los Alamos National Laboratory
    LiCl:KCl molten salt eutectic (58 mol. % LiCl − 42 mol. % LiCl) has emerged as an effective medium for pyrochemical processing of spent metallic nuclear fuels. However, the thermodynamic effects of fission by-products (e.g., trivalent La) and tetravalent U within the molten LiCl-KCl eutectic systems remain unclear. In this work we report experimentally measured molar enthalpies of mixing (ΔHmix) for the LaCl3 − LiCl:KCl and UCl4 − LiCl:KCl pseudobinary systems. The mixing energetics for both systems demonstrate irregular mixing behavior with minimums occurring within the alkali rich regions (< 50 mol. % Ln/An). The results of this work suggest that the magnitudes of mixing interactions stemming from dispersion forces and polarizabilities dominate the energetic landscape, while the formation of associate Ln/An-Clx polyhedra contributes to the observed nonlinearity of the interaction parameter (λ) curve within the LiCl-KCl compositionally dominant region.

10:40 AM  
Calorimetric Determination of Melting Point Temperatures, Heat Capacities, and Heats of Fusion of Binary NaCl−UCl3 and MgCl2 − UCl3 Systems: Vitaliy Goncharov1; Xiaofeng Guo1; Jason Lonergan2; Kyle Makovsky2; Bruce McNamara2; 1Washington State University; 2Pacific Northwest National Laboratory
    NaCl−UCl3 and MgCl2 − UCl3 binary molten salt systems have been proposed as major components for Generation IV (Gen IV) chloride molten salt reactor (MSR) fuels. However, uncertainty remains in several key thermophysical and thermochemical properties of these systems due to limited number of measurements and concerns over purities of the examined samples. In this work, we report calorimetric efforts aimed in examining the melting point temperatures (Mp), isobaric heat capacities (Cp, 25 °C to 800 °C), and heats of fusion (ΔHfus) of high purity ultra-dry NaCl− UCl3 and MgCl2 − UCl3 binary systems with compositions of UCl3 = 0, 20, 40, 60, 80, 100 mol. %. Mp, Cp, and ΔHfus, are assessed in context of previously published data and updated thermophysical parameters are proposed for optimizations of NaCl − MgCl2 − UCl3 phase diagram.

11:00 AM  
Density, Volatility, and Viscosity of Molten Sodium and Potassium Chloride Salts: Michaella Swinhart1; Jordan Barr2; Ralf Sudowe3; Scott Beckman2; Kyle Makovsky4; Bruce McNamara4; Charmayne Lonergan4; Jason Lonergan4; 1Colorado State University/Pacific Northwest National Lab; 2Washington State University; 3Colorado State University; 4Pacific Northwest National Lab
    Thermophysical properties are of critical importance to the successful demonstration of a molten salt reactor (MSR) as they establish some critical design constraints. This study focuses on the sodium and potassium-chloride (ClNaK) salt system. Many of these properties need to be understood to optimize models and for successful reactor operations. Volatility experiments are underway using thermal gravimetric analysis (TGA) that will elucidate the thermal stability of ClNaK salts. Viscosity is being developed by method of parallel plate utilizing a thermomechanical analyzer (TMA). Current density experiments performed using a modified geometric method, align well with literature values. For instance, initial measurements give a density of pure KCl and NaCl at 800°C of 1.41 and 1.44 g/cm3 which are within 5% of previously reported values. This talk will detail the development of the molten salt characterization techniques and the results found in the ClNaK system.