Materials and Chemistry for Molten Salt Systems: Corrosion and Speciation
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
Monday 2:00 PM
March 20, 2023
Room: 27A
Location: SDCC
Session Chair: Nathaniel Hoyt, Argonne National Laboratory
2:00 PM Invited
Flibe Chemistry Control for Fluoride Salt-Cooled High-Temperature Reactors: Francesco Carotti1; Augustus Merwin1; Kaitlin Johnson1; Sam Mossadeghian1; Jacob McMurray1; Michael Hanson1; Alan Kruizenga1; 1Kairos Power
Kairos Power (KP) is focused on development of the fluoride-salt-cooled, high-temperature reactor (KP-FHR), which uses 2LiF-BeF2 (known as Flibe) as the reactor primary loop coolant. Monitoring and control of Flibe chemistry is necessary for efficient long-term operations of KP-FHR. Oxidizing impurities (e.g. H2O, O2), from cover gas contamination or maintenance cycles, may drive corrosion and limit component lifetime, while accumulation of corrosion products (CrF2, FeF2, MnF2) in the salt can lead to undesired solubility-driven material deposition in the system. KP chemistry control focuses on addressing those phenomena by leveraging fundamental Flibe thermochemistry principles combined to an iterative testing approach for laboratory and engineering-scale Flibe systems. This talk presents KP approach to Flibe chemistry technology development and chemistry control in KP-FHR, with specific case-studies on fundamentals and applications of redox control, online and offline chemistry monitoring strategies, and chemistry of impurity ingress and removal from the salt.
2:30 PM
Fundamental Aspects of Chromium Corrosion in Molten Fluoride Salts: Ho Lun Chan1; Elena Romanovskaia1; Minsung Hong2; Valentin Romanovski1; Peter Hosemann2; John Scully1; 1University of Virginia; 2University of California Berkeley
An existing knowledge gap in the field of molten salt corrosion is the lack of in-situ, diagnostic and instantaneous corrosion measurements of corroding metallic system. Electrochemical techniques, such as linear polarization resistance and impedance spectroscopy (EIS), on molten salt systems have been extensively utilized by numerous investigators to bridge this gap; however, interpretation and discussion that address fundamental principles of electrode reactions and properties of the electrode-salt interface are underdeveloped. The objective of this work is to revisit the electrochemical corrosion behavior of pure Cr in molten FLiNaK salts at 600oC. A variety of electrochemical and materials characterization based measurements, including linear/cyclic voltammetry, EIS, potentiostatic polarization and high-temperature rotating disk electrode experiments were performed to gain insights on their rate-limiting steps and potential-dependent interfacial vs mass transport regimes. These results were coupled with examination of the post-corrosion interface and also consider the phase stability of fluoride salt species predicted using thermodynamic approach.
2:50 PM
Thermodynamics and Kinetics of Extrinsic Corrosion Impurities in Molten Salts: Jicheng Guo1; Amber Polke1; Timothy Lichtenstein1; Sumit Bhattacharya1; Nathaniel Hoyt1; 1Argonne National Laboratory
Molten salts play important roles in applications such as molten salt reactors (MSR) and concentrating solar power (CSP) systems. The presence of extrinsic impurities such as hydroxides and oxides can lead to the corrosion of high temperature alloys that are exposed to molten salt environments. In this work, we will present the thermodynamic and kinetic properties of these corrosive impurities along with the properties of the high temperature alloys that they attack. Specific results include chromium oxidation potentials and activity coefficients in various alloys, along with the diffusion coefficients of alloy constituents. We will also show results describing a test vessel where decay constants for species such as hydroxides and hydroxyhalides can be determined. When combined, these fundamental values provide key insights and enable predictions of component lifetimes for molten salt systems.
3:10 PM
Modeling the Evolution of Structural Alloy Microstructure Due to Molten Salt Corrosion: Chaitanya Bhave1; Michael Tonks1; Kumar Sridharan2; Adrien Couet2; 1University of Florida; 2University of Wisconsin-Madison
Corrosion of structural alloys by molten salts can pose a significant engineering challenge for developing molten salt reactors (MSRs). Alloys can experience grain boundary depletion of major structural components such as Cr, Fe, Ni, void formation, and salt infiltration. We have previously developed an electrochemical phase-field model for capturing the depletion of structural alloy components during corrosion by molten salts. This work expands on the mesoscale corrosion model to capture the evolution of the grain structure and void phase evolution driven by corrosion. We study the impact of salt chemistry, grain boundary energy, and the alloy-salt interfacial energy on the formation of voids in the alloy and salt infiltration. Uncertainty quantification is performed on the model to investigate the impact of experimental uncertainty on predictions.
3:30 PM Break
3:50 PM
Exploring the Effect of Radiation and Temperature on the Local Structure of Metal Ions in Molten Salt Environments using X-ray Absorption Spectroscopy: Nirmalendu Patra1; Kazuhiro Iwamatsu1; Mehmet Topsakal1; Alejandro Ballesteros2; Ruchi Gakhar3; Michael Woods3; Simon Pimblott3; Jay LaVerne2; James Wishart1; Anatoly Frenkel4; Simerjeet Gill1; 1Brookhaven National Laboratory; 2University of Notre Dame; 3Idaho National Laboratory; 4Stony Brook University
Understanding the effect of solvent chemistry and radiation on the speciation and local structure of metals is crucial for predicting the stability and reactivity of molten salts for successful deployment of molten salt reactors. Due to the effects of radiation, such as generation of solvated electrons, metal ions can be reduced to a variety of species, including metal nanoparticles. In present work, we investigate the speciation of Ni2+ ion and radiation-induced Ni metal nanoparticle formation in three molten salt systems (ZnCl2, ZnCl2-KCl, MgCl2-KCl) using synchrotron-based X-ray absorption spectroscopy, optical absorption spectroscopy and electron paramagnetic resonance studies. The evolution of local structure of these metal ions as a function of solvent composition, temperature, and radiation dose will be discussed. 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.
4:10 PM
High Temperature X-ray Scattering and MD Simulation of Molten Fluoride Salts: Anubhav Wadehra1; Yifan Zhang2; Haoxuan Yan1; Alexander Levy1; Jicheng Guo3; Daniel Olds4; Karl Ludwig1; Uday Pal1; Yu Zhong2; Adam Powell2; 1Boston University; 2Worcester Polytechnic Institute; 3Argonne National Laboratory; 4Brookhaven National Laboratory
Molten salt reactors (MSRs) potentially provide many unique benefits. LiF-NaF-KF (m% 46.5-11.5-42 - FLiNaK) and NaF-ZrF4 (m% 53-47) are model MSR salts - the former salt is used as a heat transfer coolant and for thermal solar energy storage applications while the latter salt has been used as a fuel carrier and primary coolant. Knowledge of the atomic structure of the liquid salt is important for understanding the origin of the material’s physical and chemical properties. This study will discuss the molten salt structure data of both the fluoride salts as a function of temperature using high-energy x-ray scattering experiments that were conducted at Beamline 28-ID-D at NSLS-II, Brookhaven National Lab. Interatomic potentials molecular dynamics (IPMD) simulation results will also be presented and compared with experiments through the predicted pair distribution functions and coordination numbers at multiple temperatures by using LAMMPS.
4:30 PM
Operando Synchrotron X-ray Nano-tomography and Multimodal Studies on the Evolution of Metals in Molten Chloride Salts: Yu-chen Karen Chen-Wiegart1; 1Stony Brook University / Brookhaven National Laboratory
Operando synchrotron X-ray characterization enables investigation of the evolution of metals in molten salts under reaction conditions. In this talk we will present our latest studies using operando synchrotron X-ray nano-tomography by transmission X-ray microscopy, coupled with transmission electron microscopy. Temperature-dependent 3D morphological evolution pathways for Ni-20Cr in molten MgCl2-KCl were investigated to reveal the complex interplay between different processes concerning molten salt corrosion. The effects of different metal chloride additives will also be discussed. Furthermore, the reaction of pure Cr immersed in MgCl2-KCl will also be presented. By combining the imaging techniques with operando X-ray diffraction and spectroscopy, as well as atomic simulations, we probed how the morphological, chemical, and structural evolution of Cr proceed in molten salt. Overall, the work furthers our understanding of how metals interact with molten chloride salts, revealing underlying mechanisms in the demonstrated model systems.
4:50 PM Cancelled
Evaluation of the Lanthanide Electrolytic Extraction on Li-Bi Liquid
in Molten Fluorides
: Pierre Chamelot1; Mathieu Gibilaro1; Laurent Massot1; 1Laboratoire de Génie Chimique UMR5503
In the development of GEN IV reactor system, nuclear fuel reprocessing for each concept appears to be one key point. However, the reprocessing scheme for MSR was not fully demonstrated, particularly the lanthanide fission product extraction. This study is dedicated to the reprocessing step concerning Lanthanide extraction from the molten fluoride by electrolysis using Bi pool. At start, only Li+ is reduced into Bi and the corresponding potential decrease with the increase of Li activity in Bi during the electrolysis until the lanthanide potential extraction was reached. To evaluate the lanthanide extraction efficiency on Bi with different Li contents, the electrochemical behaviour of NdF3 and SmF3 on Bi and Mo electrodes were first studied followed by electrolytic extractions on Bi pool.The results evidence that SmF3 was not extracted and NdF3 extraction needed a reduction potential corresponding to a minimum Li content in the Bi pool.
5:10 PM
Keep It Lewis-Basic: Stability of NaSICON Separators in AlCl3-NaI Catholytes for Molten Sodium Batteries: Adam Maraschky1; Melissa Meyerson1; Stephen Percival1; Amanda Peretti1; Erik Spoerke1; Leo Small1; 1Sandia National Laboratories
We examined sodium batteries with NaI-AlCl3-based molten salt catholytes of differing Lewis acidities. Batteries with AlCl3-rich (acidic) catholytes experienced a linear decline in energy efficiency during cycling, whereas NaI-rich (basic) catholytes maintained a steady > 95% energy efficiency for > 50 cycles. We developed a 3-electrode cell, which enabled identification of the NaSICON-catholyte interface as the source of increased battery impedance. XPS revealed a decrease in Na content in the NaSICON exposed to the acidic catholyte. Raman spectroscopy indicated that basic catholytes lack the dimer species found in acidic catholytes. The relative reactivity of chloroaluminate species with NaSICON’s constituent metal oxides was correlated based on thermodynamics. The mechanistic causes for NaSICON’s susceptibility to Lewis-acidic degradation will be discussed. Recent progress towards achieving high current densities through NaSICON in these molten salt systems will also be shared.