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

Wednesday 8:30 AM
March 17, 2021
Room: RM 49
Location: TMS2021 Virtual

Session Chair: Raluca Scarlat, UC Berkeley


8:30 AM  
Development of Higher Order Systems for the Molten Salt Thermodynamic Database and their Application: Theodore Besmann1; Kaitlin Johnson1; Johnathan Ard1; Jacob Yingling1; Matthew Christian1; Juliano Schorne-Pinto1; Mahmut Aslani1; Jake McMurray2; Max Poschmann3; Markus Piro3; 1University of South Carolina; 2Oak Ridge National Laboratory; 3Ontario Tech
    The fuel or coolant salt in a molten salt reactor after significant time/burnup undergoes compositional changes due to generation of fission products, ingress of contaminants, and formation of corrosion products. The understanding of the equilibrium state of this complex salt is a key issue for reactor control, management of corrosion, and assessment of safety as it provides chemical potentials, phase equilibria, and vapor pressures. Their determination requires a set of Gibbs energy models for the multicomponent systems, including how the components interact in the salt. That need is being addressed in the development of the Molten Salt Thermochemical Database (MSTDB). As the MSTDB component library is expanding it is also including developed representations of many element systems. The presentation will cover how these higher order systems are generated, the current status of the MSTDB, and newly developed higher order systems together with potential implementation through the THERMOCHIMICA thermochemical solver.

8:50 AM  
Ab Initio Molecular Dynamics Simulations of Actinide Molten Chloride Salts: David Andersson1; 1Los Alamos National Laboratory
    Design of molten salt reactors and selection of the fuel salt require knowledge of thermodynamic and thermophysical properties of the salt. Some information is available in the literature and additional data is being generated in new experiments. To supplement experimental efforts and enable investigation of a larger composition space, including harsh elements such as Pu, ab initio molecular dynamics (AIMD) simulations have been carried out. In this study, NaCl-UCl3-UCl4-PuCl3 were simulated using the VASP code. The PBE exchange correlation potential were used with a Hubbard U term added for the actinide elements. Different models for the Van der Waals interactions were tested. The modelling approach is first benchmarked for the density of binary salts, followed by the ternaries and quaternaries. Next, a larger set of thermodynamic and thermophysical properties are calculated. Finally, we discuss limitations of the AIMD approach and alternative approaches to address the problem.

9:10 AM  
Extracting Salt Properties from Visualization of Molten Salt Sessile Droplets: Sara Mastromarino1; Malachi Nelson1; Raluca Scarlat1; Ryan Hayes2; 1University of California Berkeley; 2University of California, Berkeley
    Imaging of sessile droplets of FLiBe and FLiNaK has generated a few different types of data sets of thermo-physical properties of the salts. The experimental setup consists of a furnace to melt salt samples on the plates observed with a digital camera. The wetting behavior of FLiBe and FLiNaK on graphite plates has been investigated by quantifying the contact angle. The surface tension of the salts has been estimated from drop shape analysis. The transient volumetric change through freezing was quantified from drop volume analysis. The solidification and melting phenomena were visualized, observing homogeneous in FLiNaK and heterogeneous nucleation in FLiBe; from DSC, FLiBe was observed to exhibit deep supercooling. This talk will provide a summary of thermo-physical properties that can be derived from high-resolution images of sessile molten salt droplets and from high-resolution videos of thermal transients experienced by sessile droplets.

9:30 AM  
Liquid-vapor Equilibrium and Transport Phenomena in Molten Salt Systems: Jacob Mcmurray1; Joanna McFarlane1; Scott Greenwood1; Abbey McAlister1; Matt Kurley1; 1Oak Ridge National Laboratory
    Molten salt reactors (MSRs) operate at high temperatures but near atmospheric pressures. Depending on the design, unit operations that remove and/or process the cover gas will be necessary. The chemical potential of a species is a thermodynamic property and chemical potential gradients, among others, are dominate driving forces for mass transport. Therefore, it is important to understand the liquid-vapor equilibrium in an MSR system since that information, combined with kinetic considerations, must be known to properly model mass accountancy and the unit operations that are needed for off-gas system design and operation. Reported here are the results of mass loss Knudsen effusion coupled mass spectrometry measurements. The results are used to develop thermodynamic models that are coupled to liquid-vapor mass accountancy simulations using the Modelica based Transform code. Research sponsored by the U. S. Department of Energy and the Office of Nuclear Energy Advanced Reactor Technology Program.

9:50 AM  
Optimization of the Phase Equilibria and Thermodynamics for Rare-earth Fluoride Systems Relevant to Molten Salt Reactors: Kaitlin Johnson1; Juliano Schorne Pinto1; Theodore Besmann1; 1University Of South Carolina
    Accurate thermodynamic models are necessary for advancement and licensing of molten salt reactor designs. In the investigation of the impact of fission products on fuel phase behavior, the Nd-Li-F, Nd-Na-F, Nd-U-F, and Ce-U-F systems have been evaluated and optimized for inclusion in the database. Historical phase change data and thermochemical values were used to assess the NdF3-LiF and NdF3-NaF pseudo-binary phase diagrams using the modified quasichemical model to describe the behavior of the melt. In the absence of existing experimental data, initial phase diagrams of the CeF3-UF4 and NdF3-UF4 were based on analogous systems and differential scanning calorimetry was used to determine phase change behavior to allow optimization of the developed thermodynamic models. Approximations of associated higher order systems were then developed based on the pseudo-binary systems.

10:10 AM  
Molten Salt Reactor: Fluoride/Chloride Salt Comparison: Sylvie Delpech1; Céline Cannes1; Davide Rodrigues1; 1IJCLAB-CNRS
     The molten salt reactor is one concept selected by the Generation IV forum in 2001. This concept, based on the use of a liquid fuel, consists of salts mixture melted at high temperature. The first concepts were based on the U/Th fuel cycle. Recently, researches have been carried out in order to adapt this concept to the U/Pu fuel cycle which is the French reference cycle. Neutronic studies evidenced the requirement to replace the fluoride salt with a chloride salt because the fluorides thermalize the neutron spectrum.Fluoride salts were the subject of studies for many years. The use of chloride salts necessitates academic research, in particular on their reactivity towards water and oxygen and on the behavior of actinides (or their simulant) in these solvents. This talk presents the preliminary studies realized on this topic and comparison between chloride and fluoride salts from the viewpoint of chemical safety issues.

10:40 AM  
X-ray Absorption Studies Investigating Solute-solvent Interactions in Molten Salt Environments: Elaine Dias1; Simerjeet Gill1; Ruchi Gakhar2; Santanu Roy3; Mehmet Topsakal1; William Phillips2; Bobby Layne1; Shannon Mahurin3; Phillip Halstenberg3; James Wishart1; Vyacheslav Bryantsev3; Anatoly Frenkel1; 1Brookhaven National Laboratory; 2Idaho National Laboratory; 3Oak Ridge National Laboratory
    Facilitation of robust and economical design of molten salt reactor systems requires fundamental understanding of the structure and speciation of salts and metals in and near molten salt environments. We use X-ray absorption spectroscopy (XAS) to investigate the effect of metal concentration and temperature on local coordination environments and chemical structures of metal species (Nickel) in Zinc chloride based molten salt systems. XAS studies complemented by optical studies enable a direct correspondence between UV-Vis peak shape and coordination geometry and number, determined by EXAFS. Such knowledge of speciation of metals and radiation-induced nanoparticles in molten salt environments provides a critical understanding necessary to predict and control physical and chemical properties of molten salts and corrosion mechanisms in molten salt systems. This work was supported as part of the Molten Salts in Extreme Environments, Energy Frontier Research Center, funded by the U.S. Department of Energy Office of Science.

11:00 AM  
Imaging Nanostructural Heterogeneities Induced by Molten Salt Corrosion in Ni-Cr Alloy: Yang Yang1; Weiyue Zhou2; Sheng Yin1; Sarah Wang3; Qin Yu1; Robert Ritchie1; Mark Asta1; Ju Li2; Michael Short2; Andrew Minor1; 1Lawrence Berkeley National Laboratory; 2Massachusetts Institute of Technology; 3University of California, Berkeley
    Nanostructural heterogeneities, such as chemical precipitation and porosity, can be introduced during corrosion, compromising materials performance. A prominent challenge to decipher how heterogeneity develops is the pre- and post-mortem characterization of the defect evolution, which involves the localization of excess free volumes and elastic strains. Here, using a combination of advanced electron microscopy techniques including focused-ion-beam lift out, three-dimensional (3D) electron tomography and four-dimensional scanning transmission electron microscopy (4D-STEM), we report on the characterization of the nanostructural heterogeneity in a Ni-Cr alloy induced by molten-salt corrosion. In this presentation, we attempt to address several fundamental questions regarding the detailed mechanisms of defect transport near the grain boundaries and how they are affected by nonequilibrium point-defect concentrations, strain, microstructure and chemical reactions.