Materials and Chemistry for Molten Salt Systems: Salt Properties and Chemistry
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee, TMS: Nuclear Materials Committee
Program Organizers: Stephen Raiman, University of Michigan; Raluca Scarlat, University of California, Berkeley; Jinsuo Zhang, Virginia Polytechnic Institute and State University; Kumar Sridharan, University of Wisconsin-Madison; Nathaniel Hoyt, Argonne National Laboratory; Michael Short, Massachusetts Institute of Technology

Tuesday 2:30 PM
March 1, 2022
Room: 203B
Location: Anaheim Convention Center

Session Chair: Raluca Scarlat, University of California, Berkeley

2:30 PM  
Determination of Fluoride Molten Salt Thermal Diffusivity and Sound Speed via Transient Grating Spectroscopy: Sean Robertson1; Michael Short1; 1Massachusetts Institute of Technology
    Accurate knowledge of molten salt thermophysical properties is critical to optimize the safety and efficiency of molten salt-based energy applications. For molten fluorides, currently of high interest for fission and fusion reactors, data regarding these properties are either non-existent or poor. Thermal diffusivity and sound speed in particular play important roles in the modeling of a reactor’s steady-state and transient scenarios. Transient Grating Spectroscopy offers a potential means of determining both thermal diffusivity and sound speed to a high degree of accuracy. To facilitate this technique, an optically transparent fluoride salt-compatible setup has been designed and tested. Demonstration of system capabilities has been achieved through the acquisition of sound speed and thermal diffusivity in lithium chloride, showing excellent agreement with literature data. Initial measurements in fluorides stand in contrast to thermal diffusivity values obtained from other techniques, highlighting potential uncertainty in both the temperature coefficient and magnitude of the property.

2:50 PM  
Understanding the Structure of Complexes in Molten Salts Using Absorption Spectroscopy: Jeremy Moon1; Dev Chidambaram1; 1University of Nevada, Reno
     The detection and prediction of the speciation and structure of lanthanide and actinide complexes in molten salts is vital to advanced molten salt nuclear technologies as the chemical form of dissolved actinide fuel and lanthanide fission products will affect solubility, thermophysical properties, and degradation of system components. Electronic and vibrational spectroscopy can yield information about the structure and speciation of these elements by probing electronic and vibrational transitions governed by quantum selection rules. We have fabricated a system to conduct absorption spectroscopy and Raman spectroscopy at high temperatures in an inert atmosphere glovebox. While most electronic and vibrational transitions in lanthanides are commonly considered to be relatively insensitive to the surrounding chemical environment, we will share our observation that some transitions are affected by temperature or the anion field surrounding the lanthanide cation and may yield information about the distortion of the complex.Acknowledgments: DOE-NE, NRC, and NSF

3:10 PM  
Ab Initio Molecular Dynamics Study of Thermophysical and Transport Properties for High Temperature LiCl-KCl and NaCl-MgCl2 System: Kai Duemmler1; Yuxiao Lin2; Michael Woods2; Toni Karlsson2; Ruchi Gahkar2; Benjamin Beeler1; 1North Carolina State University; 2Idaho National Laboratory
    Molten Salt Reactors (MSRs) are considered one pathway towards the carbon free future. MSRs are a safer and more economical method of nuclear electricity generation. The two main designs for MSRs use either a chloride or fluoride salt as a moderator and/or fuel salt. There exists a significant knowledge gap in the fundamental properties of some of these salts at the relevant temperatures and conditions for the MSRs. Through the use of ab initio molecular dynamics, it is possible to investigate the atomic interaction. In this work, the thermophysical properties of LiCl-KCl and NaCl-MgCl¬2 are studied including density, compressibility, heat capacity, enthalpy of mixing, and Gibbs free energy of mixing. Additionally, several transport properties are also studied including self-diffusion coefficient, viscosity, and the thermal conductivity. Results are compared with recent state-of-the-art experimental investigations.

3:30 PM  
Chlorination of UO2 to UCl3 in a Molten LiCl-KCl Using ZrCl4: Jarom Chamberlain1; Michael Simpson1; 1University of Utah
    Direct chlorination of UO2 to UCl3 is being developed to enable synthesis of fuel salt for molten chloride fast reactors from commercial spent nuclear fuel. In the reported experiments, NiCl2 was reacted with a metallic Zr rod in molten LiCl-KCl to produce dissolved ZrCl4. A stable concentration of 1 wt.% ZrCl4 in the molten salt was achieved over the course of a two-hour experiment when an initial 5 wt.% of NiCl2 was added to the salt. UO2 particles were then immersed in the salt along with a Zr metal rod. Concentration of U in the salt versus time as measured with ICP-MS was recorded as 0.15 wt.% after four hours. A layer of zirconium oxide surrounding an unreacted core of UO2 was also observed. This preliminary work is a first step towards studying the direct introduction of ZrCl4 in the salt via sparging ZrCl4 vapor into the salt.

3:50 PM Break

4:10 PM  
Molten Uranium Chloride Salts Investigated by Ab Initio Molecular Dynamics Simulations: David Andersson1; 1Los Alamos National Laboratory
    Thermodynamic and thermophysical properties of uranium-bearing molten salts are important input to design of molten salt reactors and selection of the fuel salt. In parallel with new experiments performed by the community, ab initio molecular dynamics (AIMD) simulations have been carried out for select uranium chloride molten salts, e.g. NaCl-UCl3, KCl-UCl3 and AlCl3-UCl3. The VASP code was used for the simulations, which relied on the PBE exchange correlation potential with a Hubbard U term added for the actinide elements and also included models for dispersion interactions. The modelling approach was first benchmarked for the density of binary salts, followed by the ternaries. Next, a larger set of thermodynamic and thermophysical properties were calculated. The predicted properties were correlated to the evolution of the radial pair distribution function in the mixed salts. Finally, the role of the predicted data in development thermodynamic and thermophysical databases will be discussed.

4:30 PM  
First-principles Molecular Dynamics of CaF2-MgF2 Molten Salt System: Yifan Zhang1; Abu Miraz2; Uday Pal3; Adam Powell1; Michael Gao4; Yu Zhong1; 1Worcester Polytechnic Institute; 2Louisiana Tech University; 3Boston University; 4National Energy Technology Laboratory
    To study the transport properties of ions and phase transformations in the CaF2-MgF2 molten salt system, this work provides extensive simulations from molecular dynamics approaches. The local structures, ionic self-diffusion coefficients, and viscosity of this system are investigated by classical interatomic potential molecular dynamics (IPMD) and first-principles molecular dynamics (FPMD). Since there are no suitable potential parameters for IPMD simulation of the CaF2-MgF2 system currently, a genetic algorithm built by Python was used to fit the parameters to the physical properties of the salt. The fitted parameters will be more accurate in the MD simulation to obtain the properties of the material through thousands of high-throughput calculations in the genetic algorithm and comparison with experimental data and DFT results. All calculated properties are compared with experimental data from existing literature.