Materials and Chemistry for Molten Salt Systems: On-Demand Oral Presentations
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
Monday 8:00 AM
March 14, 2022
Room: Nuclear Materials
Location: On-Demand Room
Thermochemistry of Iodine-containing Molten Reciprocal Salts: Mina Aziziha1; Juliano Pinto1; Clara Dixon1; Jacob Yingling1; Johnathon Ard1; Amir Mofrad1; Matthew Christian1; Theodore Besmann1; 1University of South Carolina
To make our Molten Salt Thermal Properties Database-Thermochemical (MSTDB-TC) relevant for molten salt reactor safety analysis, it is important to include the reciprocal iodide salt systems. The iodide salts are volatile and radiologically hazardous, and thus their behavior under accident conditions are important to understand. As necessary, we reassessed iodide with chloride or fluoride reciprocal system thermodynamic models using a self-consistent methodology within the CALPHAD approach. In this presentation, we present the results of the analyses and the thermochemical properties of the various pseudo-binary systems including but not limited to LiI-LiF, BeI2-BeF2, UI3,UI4-UF3,UF4, LiI-LiCl, NaI-NaCl, MgI2-MgCl2, and UI3,UI4-UCl3,UCl4. Using these pseudo-binary models, we were able to extrapolate to related pseudo-ternary and pseudo-quaternary systems.
Wetting Properties of Molten Salts at Material Interface for Reactor Applications: Michael Woods1; Christopher Wolfe2; Toni Karlsson1; Ruchi Gakhar1; 1Idaho National Laboratory; 2University of New Mexico
The development of emerging molten salt-based technologies requires a fundamental understanding of the complex chemistry at the high temperature salt-alloy interface. Determination of the interfacial behavior will enable the estimation of mechanistic details pertaining to the corrosion of structural materials by molten salts. Contact angle is a key piece of information for understanding interfacial behavior (foaming, intrusion into pores, and wetting surfaces) and measurements performed at Oak Ridge National Lab during the Molten Salt Reactor Experiment demonstrate that the contact angle fluctuates with the redox chemistry of salt and presence of moisture. This study has used the sessile drop method to measure the contact angle at a three-phase interface of a liquid droplet on various substrates relevant to molten salt applications. This data and its implications to molten salt applications will be discussed.
Electrochemical Determination of Thermodynamic and Kinetic Properties of Ni2+ in FLiNaK Molten Salt: Nathan Smith1; Stephen Lombardo1; Hojong Kim1; Shunli Shang1; Zi-Kui Liu1; 1Pennsylvania State University
Electrochemical techniques including electromotive force measurements (EMF), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were utilized to determine thermodynamic and kinetic properties of Ni2+ in FLiNaK at T = 500–700 °C. A concentration cell with a Ni wire in a fixed composition of NiF2 in FLiNaK as a reference electrode and Ni wires in varying compositions of NiF2 in FLiNaK as working electrodes was used for EMF measurements, which provided activity values of Ni2+ in FLiNaK as well as valuable information about the solubility of Ni2+ and phase behavior. Cyclic voltammetry was also performed using a three-electrode cell to determine the diffusivity of Ni2+ in FLiNaK as a function of temperature as well as corresponding activation energies. Complementary characterization including X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and differential scanning calorimetry (DSC) were employed to confirm and supplement electrochemical results.
Research Progress in the Development of a Molten-salt Forced-circulation Loop: Guiqiu Zheng1; Guanyu Su1; Nesrin Cetiner1; David Carpenter1; 1Massachusetts Institute of Technology
It is critically important to develop molten-salt forced-circulation loop facilities with advanced technologies for the investigation of materials corrosion, components performance, tritium and fission products transport, heat transfer and so on. A team at the Nuclear Reactor Laboratory at the Massachusetts Institute of Technology (MIT) is building molten salt loop systems that can pump high-temperature fluoride salts at various velocities in circulating loops. We start with inert gas-filled loop for testing key components and control system at high temperatures, and then fluoride salt-filled loops with and without neutron irradiation. One of the primary targets is to irradiate the test section of FLiBe salt-filled loop using a neutron beam source at MIT Nuclear Reactor to study the dynamic behavior of tritium and activation products in flowing salt. We will present our progress on the molten salt loop design and development of other associated facilities at our laboratory along with preliminary results.
Generation of Corrosion-related Component Thermodynamic Values for a Molten Salt Reactor Thermodynamic Database (MSTDB-TC) and Example Applications: Theodore Besmann1; Jacob Yingling1; Juliano Schorne-Pinto1; Johnathan Ard1; Mina Aziziha1; Matthew Christian1; Amir Mofrad1; Mahmut Aslani1; Clara Dixon1; Kyle Foster1; Jake McMurray2; Ruchi Gakhar3; 1University of South Carolina; 2Oak Ridge National Laboratory; 3Idaho National Laboratory
This presentation focuses on using the CALPHAD method to create Gibbs energy models and functions for corrosion-related components for inclusion in the Molten Salt Thermal Properties Database-Thermochemical (MSTDB-TC). These include envisioned reactor fluoride- and chloride-base systems together with the likely important corrosion products chromium, nickel, and iron. The role of thermodynamics in understanding corrosion mechanisms will be described and examples will be explored for utilizing the database in modeling corrosion in reactor performance codes. The current content of the MSTDB-TC and the means for obtaining a no-cost license for use of the database will be provided.
Electrochemical Studies of Structural Alloy Corrosion in LiF-NaF-KF (FLiNaK) at 700 ˚C: William Doniger1; Adrien Couet1; Kumar Sridharan1; 1University of Wisconsin-Madison
The potentiodynamic polarization method has been used to measure the corrosion behavior of metals and alloys in FLiNaK salt at 700 ˚C. Ni, Fe, Cr, 316L stainless steel, and Ni-20Cr alloys are polarized to different overpotentials to induce varying degrees of corrosion attack. Results indicate the materials have i) characteristic equilibrium potentials with respect to the K/K+ redox couple and ii) unique corrosion currents and Tafel slopes that describe their corrosion behavior. The polarized electrodes have been characterized in detail using SEM-EDS, profilometry, and atomic force microscopy. A combination of electrochemical data and characterization results of the polarized electrodes provides a promising basis for evaluating new advanced alloy concepts.
Development of Corrosion Resistant Metallic Coatings for Molten Salt Nuclear Reactors: Elizabeth Trillo1; Ronghua Wei1; Xihua He1; 1Southwest Research Institute
Current material options for construction of high-temperature components of nuclear reactors are limited in terms of those that may provide adequate corrosion resistance for the desired operating life. Materials such as austenitic stainless steel possesses excellent high temperature strength and lower cost, but exhibits poor corrosion resistance in molten fluoride salts. In this research, bi-layer and tri-layer coatings (including Ni, Mo, W, and Ta) on Alloy 617 substrates were fabricated using plasma enhanced magnetron sputtering (PEMS) and electrodeposition. High temperature fluoride molten salt testing was conducted at temperatures between 610 C to 850 C. Delamination and intergranular corrosion was assessed on the samples after exposure by optical microscopy.
Data-driven Models for Corrosion of Structural Alloys in Molten Chloride Salts: Christopher Taylor1; Brett Tossey1; 1DNV
Increasing effort is being put into testing materials performance in high temperature, molten salt environments. To facilitate future data collection efforts and materials selection decision-making, a schema has been developed for corrosion data collected on alloys in molten salts. The schema provides the basis for a data-driven effort to characterize corrosion of alloys in molten salts using features such as composition, microstructure, and environmental parameters. In this talk, we will present the structure of the database, initial data visualization efforts and the results of predictor evaluation. Pathways towards combining science-based models for materials degradation with data-driven methods (such as machine learning algorithms like decision trees, random forest, and linear/non-linear regression methods) will be presented and discussed. Knowledge gaps identified as a result of the data collection and visualization efforts will also be presented, along with original data collected for alloy corrosion metrics in our laboratory.
Development of Novel Methods for Purification of Fluoride Salts: Dino Sulejmanovic1; Bruce Pint1; 1Oak Ridge National Laboratory
Because of their high thermal stability and low vapor pressure, molten fluoride salts are considered as coolants for use in Gen IV nuclear reactors. One of the challenges of using molten salts as coolants is their corrosivity to structural alloys due to the presence of impurities which directly/indirectly drive corrosion. To minimize the corrosion issues in molten fluoride environments, salt purification is extremely important. To date, the most common purification method has been the use of a mixture of hydrogen and hydrogen fluoride (HF). However, due to safety concerns involving the use of HF, other purification approaches are being investigated. In this talk, several salt purification methods will be evaluated and compared. As an ultimate test of salt purity, 316H stainless steel specimens were exposed to molten fluorides purified by nonconventional approaches. This research was funded by The U.S. Department of Energy Office of Nuclear Energy, Molten Salt Reactor Campaign
Stainless Steel Compatibility in Flowing Fluoride Salts: Bruce Pint1; Yi-Feng Su1; Cory Parker1; Dino Sulejmanovic1; Stephen Raiman1; 1Oak Ridge National Laboratory
There is considerable interest in molten salts for several applications including next generation nuclear reactors. Moving beyond static, isothermal experiments that cannot assess mass transfer, thermal convection loops (TCLs) have been used for decades to provide more representative compatibility data. Two similar monometallic type 316H stainless steel TCL experiments have been conducted for 1000 h with a peak temperature of 650°C in order to compare the behavior of FLiNaK and FLiBe salts. The initial FLiNaK TCL showed Cr dissolution on the hot and cold legs and a small amount of Fe transfer to the cold leg. Comparison results from the FLiBe TCL experiment will be presented.This research is sponsored by the U.S. Department of Energy, Office of Nuclear Energy, Molten Salt Reactor Campaign
Molecular Structure of Molten Fluoride Salts for Nuclear Energy by Diffraction Measurements
and Ab–initio Simulations: David Sprouster1; G Zheng2; D Olds3; S-C Lee4; Y Zhang4; B Khaykovich2; 1Stony Brook University; 2Massachusetts Institute of Technology; 3Brookhaven National Laboratory; 4University of Illinois Urbana-Champaign
There has been a resurgence of Molten–Salt Nuclear Reactor (MSR) concepts. Designers of MSR’s need detailed knowledge of the molten salt properties and predictive models. Properties of interest include molecular structure and speciation for the salt components and impurities. In this work, we discuss our coupled experiment and modelling efforts aimed at validating fast–acting models that can handle molten salts with a large number of chemical elements to predict properties as a function of composition and temperature. In particular, the molecular structure as described by Pair–Distribution Functions (PDF) underlines the solubility, thermodynamic, and transport properties of the melts. Here, we report on our recent PDF measurements of FLiNaK with added fission product (CsF) or redox control agent (ZrF4). We find that ZrF4 and CsF additions lead to complex phases and non-trivial melting behavior. Our approach has been crucial in verifying and validating high–quality numerical models of molten salts.
Temperature-dependent Dealloying Mechanisms and Morphology Evolutions in Eutectic Molten Chloride Salts: Touraj Ghaznavi1; Roger Newman1; 1University of Toronto
Dealloying of electrochemically reactive elements (e.g., Cr, Fe) is the dominant and detrimental form of corrosion in high temperature molten salts. This work studies alloying effects by use of Fe-(Cr)-Ni model alloys in model molten chloride salts at different homologous temperatures. We have developed a reliable Mg|Mg2+ reference electrode for these media, including in-situ electrochemical measurement of residual impurity content. We have discovered that at low homologous temperature, a microporous Ni layer evolves, and the dealloying mechanism is controlled by surface diffusion of more-noble element; compared with aqueous systems, the parting limit (55-60 at.% of less-noble element) is reduced by several percent due to increased surface mobility of Ni in molten Cl salts. We will also talk about changing criteria for dealloying at high homologous temperature where the operative mass transport is mediated by vacancy diffusion, porosity changes its appearance to negative dendrites, and the parting limit becomes meaningless.
High-throughput Measurements of Alloy Properties to Enable Long-term Corrosion Simulations: Nathaniel Hoyt1; Jicheng Guo1; 1Argonne National Laboratory
Long term simulations of the material performance of nickel alloys in molten salt reactors and concentrating solar power systems require accurate fundamental measurements of the alloy properties. Key properties that control the corrosion behavior in nonisothermal loops include thermogalvanic coefficients and the effective diffusion coefficients of alloy constituents. At present, measurements of effective diffusion coefficients for species such as Cr within relevant alloys are limited to only a few candidate materials. In order to close this gap, Argonne National Laboratory has been conducting an extensive campaign of fundamental property measurements using electrochemical techniques applied to a range of metal alloys. The extracted properties are in turn used to enable multiphysics simulations of the interactions between alloys and complex salts in full-scale systems over extended durations.