Materials and Chemistry for Molten Salt Systems: Poster Session
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
Tuesday 5:30 PM
March 21, 2023
Room: Exhibit Hall G
Location: SDCC
Session Chair: Stephen Raiman, University of Michigan
O-2: Corrosion of 316H Stainless Steel and Graphite in Static Molten FLiNaK Salt: Sarah Mcquaid1; Stephen Raiman2; 1Texas A&M University; 2University of Michigan
The use of molten salt in molten salt reactors (MSR) introduces a new set of design requirements because of its interaction with the structural alloys. Graphite, the most common moderator material in thermal spectrum MSRs, is believed to interact with salt-facing structural stainless steel, but debate exists regarding the nature and extent of the interactions.For this work, the corrosion of 316H SS in molten FLiNaK salt with and without graphite was examined to study the effects of the molten salt and graphite moderator on the alloy’s corrosion behavior and mechanical properties. Tests were run at 650 °C for 100 hours in sealed nickel crucibles. Samples exposed in the same crucible with graphite were characterized to look for formation of chromium carbides that may affect mechanical behavior. This poster will present new insights into the interaction of stainless steel and graphite in molten fluoride salt.
O-3: Detection of Transition Metals in Solid and Molten Salts Using UV-Vis Spectra: Diego Macias1; Stephen Raiman1; Dino Sulejmanovic2; 1The University of Michigan; 2Oak Ridge National Laboratory
Molten salt reactors (MSRs) require materials that can withstand molten salt environments. During salt exposure, the corrosion of alloys proceeds by extraction of the alloying elements from the alloy surface into the liquid salt. Being able to detect and monitor the alloying elements in molten salts could be used as an in-situ measure of corrosion. Fluoride and chloride-based molten salts are transparent in the visible spectrum which allows for the detection of light-absorbing species such as transition metal impurities using UV-Vis spectroscopy. Our preliminary work compared the difference between absorbance spectra of pure salts and the salts with various concentrations of either Fe2+, Cr2+ or Ni2+ cations as a baseline. These baseline spectra allowed for quantification of Fe2+, Cr2+ and Ni2+ in molten chloride salt after a 316H specimen exposure. In addition, the correlation between the concentrations in the salt and the extent of corrosion of 316H specimens was determined.
O-4: High-Throughput Ex-situ Quantification of Corrosion Products from Molten Salt Corrosion Experiments of High Entropy Alloys by Laser Induced Breakdown Spectroscopy (LIBS): Bonita Goh1; Isabelle Baggenstoss1; Adrien Couet1; 1University of Wisconsin Madison
It is imperative to comprehensively understand the chemistry of molten salts for designing robustly engineered systems in the next generation in solar and nuclear power applications. To this end, significant strides have been made in the molten salt research community to develop electrochemical sensors to monitor online various chemical species of impurities and corrosion products. However, independent verification of dissolved analyte quantities in the molten salt by conventional techniques such as Inductively Coupled Plasma mass spectrometry and optical emissions spectroscopy severely limits the turnaround time for sensor calibration due to the necessity of intermediate gravimetry and acid digestion analytical preparation steps. Acid digestion is also highly specific to analyte and chemical species, further encumbering the analysis of multiple chemical species within the same salt sample. We present a solution to these problems by a batch-sampling LIBS process to simultaneously quantify multiple dissolved analytes in salts at room temperature per sample.
Optimization of Phase Equilibria and Thermodynamics for Actinide Chloride Systems Relevant for Molten Salt Reactors: Juliano Schorne Pinto1; Jacob Yingling1; Johnathon Ard1; Theodore Besmann1; 1University of South Carolina
A crucial issue for the development of molten salt reactors (MSRs) is the lack of thermodynamic information for its main constituents, i.e., fuel and/or coolant. For example, enthalpies of liquid-liquid mixing for uranium and plutonium trichloride with alkali metal chloride systems are limited. However, they are important to reliably model thermodynamic properties required for calculating the state of complex systems present in MSRs. The work reported here supports the development of thermodynamic functions through empirical correlations coupled with numerical modeling to predict the enthalpy of mixing for unexplored AkCl-UCl3 and AkCl-PuCl3 (Ak=alkali element) systems. Additionally, we assessed the historical phase equilibria data and thermochemical values together with original differential scanning calorimetry measurements. The results provide a consistent, reliable set of values that have been integrated into the Molten Salt Thermal Properties Database-Thermochemical (MSTDB-TC), an open-source compendium for MSR applications.
O-6: Purification of Lithium, Sodium, and Potassium-based Chloride Salts via Hydrochlorination with Real-time Monitoring: Mario Alberto Gonzalez1; Jarom Chamberlain1; Jacob Yankee1; Suhee Choi1; Matthew Newton1; Ethan Hamilton1; Michael Simpson1; 1University of Utah
Incomplete water removal from halide salts can lead to hydrolysis at temperatures required to melt them. This can lead to the formation of volatile HCl and salt-soluble oxide and/or hydroxide impurities, which increase the corrosivity of the salt towards metals. In electrolytic processes, oxides and hydroxides can contribute to low cell efficiencies. Anhydrous HCl bubbled into molten salts can react with these impurities and remove them as volatile water. A system has thus been designed, built, and extensively tested for hydrochlorinating molten salts at temperatures up to 550oC using 5% HCl in argon. The off-gas is bubbled through an auto-titrator to determine when reaction of HCl has ceased. In-process and ex-process titration data will be presented for purification performed on a variety of salts including eutectic LiCl-KCl, NaCl-CaCl2, NaCl-MgCl2, and NaCl-KCl-MgCl2. The procedure, techniques, and parameters for salt purification via hydrochlorination will be reported in this presentation.
Reducing Graphite Interactions with Structural Corrosion Products: Cody Falconer1; Hongliang Zhang1; Kumar Sridharan1; Adrien Couet1; 1University of Wisconsin Madison
With the development of the FHR, understanding and eliminating material/salt interactions with components such as the graphite-based fuel and moderator may be critical for the longevity of the reactor. In the FHR concept, salt-facing graphite is anticipated to be present as the FHR utilizes graphite as a moderator as well as a salt-facing coating on the fuel compact. The challenge for this large surface area of graphite is its interactions with the corrosion products created from the corrosion of the structural alloy used in the reactor. It has been previously demonstrated through corrosion tests that the presence of graphite accelerates the corrosion of alloys due to activity gradients that result in the deposition of a carbide onto graphite surfaces. In this work, it is demonstrated that this carbide formation will occur. Furthermore, a novel coating design is demonstrated and shown to greatly reduce graphite interactions during static salt exposure tests.
O-7:The Reduction of Solid Uranium Dioxide in Calcium Salt: Nagihan Karakaya1; Jinsuo Zhang1; 1Virginia Tech
Reprocessing the spent nuclear fuel has excessive attention due to reducing the radiotoxicity and increasing the efficiency of fuel utilization all around the world. The widely used nuclear fuel which is UO2 needs to be treated to convert into the metal form to further processing to obtain a new form of nuclear fuel. In this study, the oxide reduction mechanisms of solid UO2 were investigated in two separate categories; -Chemical reduction and -Electrochemical reduction in calcium salts. In chemical reduction, the concentration effect of active metal (Ca) was determined under various applications. In electrochemical experiments, the temperature effects were determined on the reduced uranium metal. And the clear comparisons between the two methods have been determined by examining the samples under SEM-EDS and XRD analyses.