Materials and Chemistry for Molten Salt Systems: Corrosion, Wear and Corrosion Products
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 8:30 AM
March 20, 2023
Room: 27A
Location: SDCC

Session Chair: Stephen Raiman, University of Michigan


8:30 AM  
In-situ Corrosion Monitoring of 316 SS L Natural Convection Loop by Radioactive Isotope Tracking: Yafei Wang1; Cody Falconer1; Aeli Olson1; Ivan Mitchell1; Brian Kelleher1; Jonathan Engle1; Kumar Sridharan1; Adrien1; 1University of Wisconsin-Madison
    Molten salt corrosion studies under flow conditions is not well understood mostly because of the challenges to quantify corrosion kinetics (dissolution/deposition) in these systems. This study explores the in-situ corrosion monitoring of a 316 SS L molten salt natural convection loop through the radioisotope tracking technique. Radioactive isotope tracers including Cr-52, Mn-51, and Co-56 were generated by 12 MeV proton irradiation of a thinned down tube section on the hot leg. Using HPGE gamma-ray detectors located at different locations, the dissolution of the irradiated 316 SS L was in-situ monitored through the activity measurement of the radioactive isotope tracers. At the same time, the flow of the dissolved isotope tracers was also in-situ monitored at different loop locations. A mass transport model is then developed and validated by the in-situ activity measurements and post-corrosion SEM/EDS tube characterizations.

8:50 AM  
Long-Term Corrosion Behavior of 316SS and Alloy 601 in Elevated Temperature Molten Nitrate Salt: Andrew Dong1; Camilla Stitt2; Peter Hosemann1; George Young2; 1University of California Berkeley; 2Kairos Power
    Nitrate salt is being investigated for use as a high temperature heat transfer fluid in concentrated solar power and advanced nuclear designs. At temperatures around and above 600°C, elevated corrosion rates in structural alloys have been observed, associated with thermal decomposition of the nitrate salt. However, limited data exists at these temperatures and especially for long exposure times (>2000 hours). This presentation will discuss examination into the long-term corrosion behavior of 316SS and Alloy 601 exposed to static molten Solar Salt (60%NaNO3-40%KNO3). Results from five parallel studies involving over 250 corrosion samples will be presented with temperatures of exposure ranging from 590°C to 650°C and exposure times up to 5000 hours. Trends from weight change corrosion rates and observed corrosion scales will be compared and discussed.

9:10 AM  
Salt Impurities: Measuring Them, Getting Them Out, and Learning to Live with Them: Stephen Raiman1; Kyle Williams2; 1The University of Michigan; 2Texas A&M University
    To minimize degradation of salt-facing components, it is important to understand the material and chemical factors that affect corrosion. Dating back to the MSRE, efforts toward controlling corrosion in molten fluoride salts focused on careful alloy selection, thorough salt purification, and additives for redox control. This work highlights recent work on controlling salt chemistry to mitigate corrosion in fluoride and chloride salts. Specifically, new work on fluoride salt purification will be shown. Additionally, we will report on new techniques to measure salt oxygen and hydrogen content with combustion analysis. This work presents new progress toward measuring and understanding salt chemistry effects on corrosion

9:30 AM  
Diffusion Dynamics of Molten FLiNaK Quantified with Quasi-elastic Neutron Scattering: Brent Heuser1; Golam Rakib1; Yang Zhang1; Shao-Chun Lee1; 1University of Illinois
    The Cold Neutron Chopper Spectrometer at the Spallation Neutron Source was used to measure the incoherent quasi-elastic neutron scattering response of molten FLiNaK, a potential coolant and fuel for molten salt reactors. The element weighted self diffusion coefficient was measured by fitting the 3 meV QENS broadening as a function of temperature from 500 C to 800 C. Enriched Li-7 was used to reduce the strong absorption from Li-6. We determine the activation energy associated with self diffusion from the temperature dependence of the diffusivity, Ea=0.46 eV. Discussion will focus on the comparison of our measured diffusivities and advanced computations of the same system. In addition the effect of Ce dopant on the system dynamics will be presented. Finally, the effect of Ce on the melting temperature and specific heat will be presented.

9:50 AM  
Effects of Impurities on Corrosion of 316H Stainless-Steel in Molten FLiNaK Salt: Dino Sulejmanovic1; Timothy Hall2; Holly Garich2; Bruce Pint1; 1Oak Ridge National Laboratory; 2Faraday Technology
    Halide molten salts are being considered as coolants and solvents of fissile materials for next generation nuclear concepts. One of the main challenges of using molten salts in nuclear reactor applications is their corrosivity to structural alloys, largely due to the presence of impurities which directly or indirectly drive corrosion. Impurities such as water can react with halide salt constituents and form corrosive compounds such as HCl and HF. Understanding the effects of impurities on corrosivity of halide salts to structural alloys is a key step in advancing molten salt reactors (MSRs). To test the effects of impurities on corrosion of alloy coupons, we exposed 316H stainless-steel in molten FLiNaK salt with impurities at 700°C for 500h. Effects of water, transition metal cations and corrosion inhibitors as added impurities in FLiNaK salt were evaluated. This work focuses on mass change, coupon cross-sections, SEM-EDS and salt chemistry analysis.

10:10 AM Break

10:30 AM  
Chromium Solution in Molten Uranium-Sodium Chloride Salts Investigated by Ab Initio Molecular Dynamics Simulations: David Andersson1; Gaoxue Wang1; Bo Li1; Ping Yang1; 1Los Alamos National Laboratory
    Thermodynamic, thermophysical and corrosion properties of uranium-bearing molten salts are important input to design of molten salt reactors and selection of the fuel salt. Thermodynamic and thermophysical properties have been calculated for NaCl-UCl3 based on ab initio molecular dynamics (AIMD) simulations and the predictions were validated against experimental data. 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 next step is to investigate corrosion properties, which was performed by adding Cr ions in the 2+ and 3+ charge states to NaCl-UCl3 at the eutectic composition. Simulations were performed to extract the impact on energy, density, diffusion and local structure. Finally, the influence of the predictions on modeling corrosion from structural materials in molten salt reactor environments will be discussed.

10:50 AM  
Determination of Instantaneous Corrosion Current Densities of Materials in Molten FLiNaK Salts: Elena Romanovskaia1; Ho Lun Chan1; Francisco Garfias1; Sara Mastromarino2; Raluca Scarlat2; John Scully1; 1University of Virginia; 2University of California, Berkeley
    Abstract: In this work, a variety of corroborating methods including (1) electrochemical impedance spectroscopy, (2) static immersion exposure, (3) in-situ electrochemical diagnostic techniques were utilized to study the corrosion behavior of pure Cr metal in a LiF-NaF-KF eutectic salt at 600°C. The in-situ electrochemical diagnostic technique involves capturing the CrF3- and CrF63- ions produced from Cr oxidation/corrosion on a platinum working electrode using cyclic voltammetry throughout 50 hours of molten salt static exposure. The concentration of Cr cations was determined as a function of exposure time and compared with the mass loss of Cr coupon in a static immersion exposure test. A particular focus was spent on calculating and comparing the corrosion current densities (icorr) calculated from each method. The results, challenges, and limitation of each method are discussed.

11:10 AM  
Friction and Wear Measurements of Candidate Metal Alloys for Fluoride Salt Pump Bearing and Shaft Materials: Michael Borrello1; Lorenzo Vergari1; Raluca Scarlat1; Lewis Handy-Cardena2; Mark Anderson2; 1UC Berkeley; 2University of Wisconsin, Madison
    Molten Salt Reactors (MSRs) and Concentrated Solar Power (CSP) plants require the development of pumps that can withstand the high temperature environment (between 500C to 800C), maintain resistance to corrosion occurring in the salt, and mitigate wear occurring at the material interfaces. New candidate materials are being examined for their corrosion resistance and tribological performance in fluoride salts like FLiBe and FLiNaK. Example materials being investigated include Cermet nickel-tungsten-carbide, Haynes 242, Haynes 282, and silicon nitride. This talk will present tribological data for friction coefficient and wear of the candidate materials while exposed in fluoride salts at prototypical temperatures in a Ball on Plate tribometer and Pin on Disk tribometer. This data will serve to provide a preliminary ranking of material performance in molten fluoride salt pump systems.

11:30 AM  
Speciation of Metal Ion Solutes in Molten Salt Matrices for Reactor Applications using Advanced Spectroscopy Techniques: Ruchi Gakhar1; Kaustubh Bawane1; William Phillips1; Michael Woods1; 1Idaho National Laboratory
    Due to their large liquid temperature range and high actinide solubility, molten salts have regained attention for application in advanced nuclear fuel cycles and next generation nuclear reactors. A critical requirement for advancing molten salt technology is the fundamental understanding of the complex interplay between structure and dynamics of solutes (impurities, and corrosion and fission products) in the high-temperature media. The structure and speciation of salt components relate to the solute reactivity and is driven by the inherent radiation-induced processes, which in turn can degrade reactor performance. The team seeks to understand the speciation of metal ions in molten chloride salts and its variation with temperature and melt composition using advanced spectroscopy techniques.