Materials and Chemistry for Molten Salt Systems: Impurity Effects on Molten Salt Properties and Corrosion
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; Michael Short, Massachusetts Institute of Technology; Kumar Sridharan, University of Wisconsin-Madison; Nathaniel Hoyt, Argonne National Laboratory
Wednesday 8:30 AM
March 22, 2023
Room: 27A
Location: SDCC
Session Chair: Michael Short, MIT
8:30 AM Invited
Elucidating the Role of UCl3 in the Corrosion Mechanism of Ni-based Superalloys Exposed to Chloride Molten Salts: Trishelle Copeland-Johnson1; Michael Woods1; Ruchi Gakhar1; Daniel Murray1; Guoping Cao1; Lingfeng He1; 1Idaho National Laboratory
The United States Department of Energy (DOE) aims to diversify the domestic energy portfolio towards more sustainable options, including implementation of molten salt reactor (MSR) technology. Chloride molten salts have been investigated as an appropriate MSR coolant and fuel because their relatively inexpensive, abundant, and exhibit favorable thermophysical properties. However, the corrosivity of chloride molten salts have not been extensively studied, especially with the inclusion of actinide products, such as UCl3. Accordingly, the development of nuclear structural materials with excellent corrosion performance is critical to the successful implementation of MSRs, particularly from a mechanistic perspective. In this investigation, we attempt to elucidate the interfacial corrosion mechanism between Ni-based structural materials, such as Inconel 617, and UCl3-containing salt systems through a multi-modal advanced characterization approach, including electron microscopy techniques. The findings from this investigation will expand the knowledgebase of chloride molten salt corrosion of MSR structural materials for strategic property-to-performance design.
9:00 AM
Ab Initio Molecular Dynamics Study of Thermophysical for High-temperature NaCl-PuCl3 System: Kai Duemmler1; Michael Woods2; Ruchi Gakhar2; Benjamin Beeler1; 1North Carolina State University; 2Idahol National Laboratory
There are several pathways forward to achieving carbon-free power within the US by 2035, however, it will require a combination of renewable sources and baseline sources, such as nuclear. The molten salt reactor (MSR) is an advanced nuclear reactor design, which is more advantageous than light water reactors as they are designed with more inherent safety features. There is a knowledge gap in the properties of molten salts at operational temperatures of MSRs. This study uses ¬ab initio ¬molecular dynamics to study the properties of NaCl-PuCl¬3¬ which is a candidate fuel salt for the fast spectrum MSRs. The thermophysical properties of interest are the density, compressibility, heat capacity, enthalpy of mixing, and the coefficient of thermal expansion along with structural properties including bond length and coordination number.
9:20 AM
Characterization of UCl3, NaCl, and NaCl- 0.352 UCl3 Salts using Neutron Scattering: Sven Vogel1; A. David R. Andersson1; Marisa M. Monreal1; J. Matthew Jackson1; S. Scott Parker1; Gaoxue Wang1; Ping Yang1; 1Los Alamos National Laboratory
Actinide-molten salts are used in next-generation nuclear power plants (molten salt reactors/MSRs), since liquid material is inherently resistant to radiation damage, as well as during metal purification. Experimental data on physical properties is sparse, inaccurate, and rarely includes actinides, especially plutonium. LANL offers the infrastructure and expertise to make and handle samples, including Pu, the modeling expertise for actinide salts as well as neutrons at LANSCE to enable characterization. Here, we report evolution of the crystal structures of NaCl, UCl3, and NaCl- 0.352 UCl3 (eutectic) obtained from in situ high temperature neutron diffraction measurements and compare e.g. lattice parameter changes to density functional theory predictions, thus benchmarking such models against experimental data, as well as providing insight on interactions between the two phases in the eutectic composition.
9:40 AM
Coordination and Thermophysical Properties of Transition Metal Chlorocomplexes and Lanthanides in LiCl-KCl: Qi An1; 1Iowa State University
Eutectic LiCl-KCl molten salt is used in molten salt reactors as the primary coolant due to its high thermal capacity and solubility of fission products. Its thermophysical properties are important parameters for engineering applications of molten salts but may be significantly influenced by metal solute from corrosion of metallic structural materials or fission products such as lanthanides. Here we applied a combination of quantum mechanics molecular dynamics (QM-MD) and deep machine learning force field (DP-FF) molecular dynamics simulations to investigate the structure and thermophysical properties of LiCl-KCl eutectic as well as the influence of dissolved transition metal chlorocomplexes (NiCl2 and CrCl3), as well as lanthanides (Sm, Eu, Ce). We find that the dissolution of Ni, Cr, and lanthanides in the LiCl-KCl system forms the local tetrahedral(NiCl4)2-, octahedral(CrCl6)3-, and octahedral(LnCl3)3- chlorocomplexes, respectively, which do not have a significant impact on the overall liquid salt structures, as well as the thermodynamic properties.
10:00 AM Break
10:20 AM
The Behavior of Oxygen in Molten Fluoride Corrosion Systems: Weiyue Zhou1; Yang Yang2; Michael Short1; 1Massachusetts Institute of Technology; 2Pennsylvania State University
Our knowledge of chemistry and material compatibility in molten salt-cooled energy systems remains outpaced by interest in, and applications of, these salts in generating clean energy. This holds particularly true for molten fluoride salts. Compared to the dominating contribution of oxygen in chloride, sulfide, or nitrate systems, the behavior of oxygen in fluorides and the impact upon corrosion pathways are poorly understood. Though most initial oxygen content in the salt can be removed by purification, the oxygen in the environment can hardly be avoided, calling for understanding the behavior of oxygen in a molten fluoride system. Once present, oxygen can exist as a gas, oxygen anions, or oxyanions. This talk will show experimental results indicating the pathway of oxygen evolution in fluoride systems and the impact on corrosion of metals. Some metals, usually considered corrosion-resistant, are readily attacked in the presence of oxygen, suggesting the importance of understanding oxygen involvement.
10:40 AM
Effect of Impurities on Material Behavior in Molten FLiNaK: Krishna Moorthi Sankar1; Preet Singh1; 1Georgia Institute of Technology
The performance of various materials in MSRs such as structural alloys, graphite moderator, fuel components etc. rely heavily on the redox potential of the molten salt, which in-turn depends on the type and amount of impurities present in the salt. The amount and type of impurities in the salt affects the corrosion behavior of structural materials, chemical stability of graphite, and more. In this study, the effect of various impurities such as oxides, fluorides, and various active elements on the redox potential of molten FLiNaK was systematically studied. The effect of these impurities on the corrosion behavior of selected Ni and Fe based alloys, mechanical properties of some of these alloys, as well as the chemical behavior of nuclear grade graphite were also studied in molten FLiNaK at 700 °C. This presentation will discuss our results to show the impact of impurities on various structural materials in molten FLiNaK.
11:00 AM
Electrochemical Thermodynamic and Kinetic Properties of Ni2+ in Molten FLiNaK Salt: Hojong Kim1; Nathan Smith1; Zi-Kui Liu1; Shunli Shang1; 1Pennsylvania State University
Understanding thermochemical properties of common corrosion products (i.e., Ni2+, Cr3+, Cr2+) from structural materials used in molten salt reactors is important for developing corrosion-resistant alloys and in-situ monitoring of molten salts. Electrochemical techniques including electromotive force (emf) measurements, cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy were utilized to determine thermodynamic and kinetic properties of Ni2+ in eutectic FLiNaK salt. The change in activity of Ni2+ in FLiNaK was determined via emf measurements at T = 475–700 °C for 0.1–20 mol% NiF2 and phase transition temperatures by differential scanning calorimetry. Using 1 mol% NiF2 in the FLiNaK as the reference (Ni/Ni2+), CV and CA were performed to determine the diffusivity and activation energy of Ni2+ in FLiNaK at 475–550 °C in a three-electrode cell. X-ray diffraction at selected NiF2 compositions was measured to determine phase constituents and phase fraction to complement electrochemical measurements.
11:20 AM
Acid/base Effects on Chromium Species in Molten Fluoride Salts: Haley Williams1; Ruben Cho1; Raluca Scarlat1; 1University of California Berkeley
Chromium’s behavior in molten fluoride salts has been characterized by electroanalytical techniques and simulation studies due to its relevance to corrosion in molten salt systems such as solvent, coolant, and/or tritium breeding blanket systems in fission and fusion nuclear reactors. Previous studies have largely investigated LiF-NaF-KF mixtures and the disproportionation of Cr2+ to Cr3+ and Cr0, indicating the effect of solvent composition and solvation mechanism on the degree of stability of chromium species and, therefore, corrosivity. Solvent composition can be characterized by fluoroacidity, a measure of the activity of fluoride and an indicator of the degree of association and polymerization in the melt. Here, we present results of an experimental study to elucidate the relationship between acidity and corrosivity. The diffusivity of Cr2+ and Cr3+ in molten fluoride salts of various fluoroacidities are measured, compared to current literature, and analyzed within the context of solvation pathways and acid/base behavior.