Materials and Chemistry for Molten Salt Systems: Synthesis and Structure
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 2:00 PM
March 22, 2023
Room: 27A
Location: SDCC
Session Chair: Jinsuo Zhang, Virginia Polytechnic Institute and State University
2:00 PM Introductory Comments
2:05 PM Invited
Synthesis of Actinide Fluorides and Chlorides for Molten Salt Reactor Fuels: Pavel Soucek1; O. Beneš2; M. Fucina3; E. Capelli4; P.R. Hania5; E. D'Agata1; A. Rodrigues1; H.J. Uitslag-Doolaard5; R. Konings1; 1European Commission, Joint Research Centre (JRC); 21European Commission, Joint Research Centre (JRC); 3Univ. Lille, CNRS, UMR 8181 - UCCS - Unité de Catalyse et Chimie du Solide, F-59000; 4Orano, 92320 Châtillon; 5Nuclear Research and Consultancy Group
Pure actinide fluorides and chlorides are essential materials for the experimental measurements of thermodynamic and physico-chemical properties of any Molten Salt Reactor (MSR) fuel. This work is focused on synthesis, purification and characterisation of pure ThF4, UF4, UF3, PuF3, UCl4 and PuCl3, as typical fissile or fertile materials for the MSR fuels. The experimental set-up using pure HF, Cl2 and HCl gases is mentioned, as well as the methods and analytical scheme developed for the syntheses. In addition, the fabrication of molten salt fuels in 100g-scale for the irradiation experiments SALIENT-01 and -03 is described. These projects are carried out within collaboration between the Nuclear Research and Consultancy Group (The Netherlands) and Joint Research Centre (European Commission). The main goals of the experiments are to assess the behaviour of the molten fuels containing ThF4, UF4, UF3 and PuF3 during irradiation and the corrosion test of selected Ni-based alloys.
2:35 PM
Reaction Kinetics of the Chlorination of UO2 with ZrCl4: Jarom Chamberlain1; Asmat Taunque1; Michael Simpson1; 1University of Utah
Pyrochemical processing of UO2 nuclear fuel waste can be initiated by chlorination with ZrCl4 to form UCl3. The UCl3 can be used as a fuel for advanced nuclear reactors. Previously, it was reported that complete chlorination of UO2 could be achieved by reacting it with pre-vaporized ZrCl4 contacted with molten LiCl-KCl. This study examines the reaction kinetics and governing reaction mechanism of this chlorination method. It was hypothesized that a diffusion limited shrinking core mechanism governs this process due to a product layer observed around the uranium particles. A series of chlorination experiments using UO2 pellets were conducted to better quantify this product layer. The progress of the reaction was determined from a cross-sectional view of the uranium pellets after chlorination. Images taken using an optical microscope revealed progressive conversion of the UO2. The conversion data taken from these pre-vaporization chlorination experiments was fit to the shrinking core kinetic model.
2:55 PM
Feasibility Study on Aluminum Under Laser Ablation for Corrosion Resistance in Molten Salt: Peggy Milota1; Supathorn Phongikaroon1; 1Virginia Commonwealth University
Laser ablation treatments in other research fields have proven useful in the improvement of corrosion resistance in various materials, but this approach has not been fully explored in molten salt for nuclear applications. This study works to determine the feasibility of using the laser ablation technique on aluminum samples, testing the coupons in a eutectic LiCl-KCl salt at 773 K (simulating a pyroprocessing environment). Data sets were collected to allow electrochemical analysis – 24-hour rounds of open circuit voltage, electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) quantify passivation layer formation and deterioration. Detailed results will be presented and discussed.
3:15 PM
Solvated Electron Dynamics in Molten Salts via Ultrafast Transient Absorption Spectroscopy: Alexander Bataller1; Davis Bryars1; 1North Carolina State University
The extreme radiative environment within molten salt reactors and pyroprocessing units gives rise to electronic excitations that could have significant consequences to the local salt chemistry and reactivity with vessel materials. In particular, the chemically reactive solvated electron known from aqueous solutions is also generated in molten salts and could lead to accelerated material corrosion and nanoparticle formation. However, our understanding of solvated electron chemistry and decay dynamics is in its infancy. An experiment for investigating solvated electrons in molten salts using ultrafast transient absorption spectroscopy will be presented. In this experiment, solvated electrons are generated via photolysis from the third harmonic of a femtosecond Ti:Sapphire laser, and subsequently probed with a time-delayed broadband laser pulse. By varying the delay and measuring the change in absorption, the changing population of solvated electrons, and other species, can be obtained.
3:35 PM Break
3:55 PM
Electrochemical Characterization of Molten Salt Fuel Systems with Boron-Doped Diamond: Hannah Patenaude1; Nastasija Damjanovic1; Charles Lhermitte2; Jason Rakos1; Shirmir Branch3; Marisa Monreal2; Cory Rusinek1; 1University of Nevada, Las Vegas; 2Los Alamos National Laboratory; 3Pacific Northwest National Laboratory
Electrochemical methods can probe fundamental aspects of molten salt matrices so long as the electrodes can withstand the molten salt environment for prolonged periods of time. Boron-doped diamond (BDD) is expected to be resilient against harsh environments, given its sp3-carbon structure. As such, BDD could potentially be used for characterization of dynamic molten salt fuel matrices, and potentially in situ corrosion control and monitoring in the core containment vessels. Characterization of europium(II/III) and uranium (III/IV) in molten LiCl-KCl included formal reduction potential, diffusion coefficients, electron transfer kinetics and stoichiometry, Gibbs free energy, enthalpy, and entropy of molten salt fuel systems using BDD. These measurements provided values comparable to expected literature values and, in general, little corrosion or change to the BDD was observed. Overall, this work advances the understanding of MSR chemistry while simultaneously proving the applicability of BDD as electrode material for harsh environments.
4:15 PM
In-situ XAS and Electrochemistry Measurements on Molten FLiNaK: Sean Fayfar1; Guiqui Zheng1; David Sprouster2; Eli Stavitski3; Denis Leshchev3; Boris Khaykovich1; 1Massachusetts Institute of Technology; 2Stony Brook University; 3Brookhaven National Lab
Molten-salt reactors (MSR) are a proposed advanced nuclear reactor design that have significant benefits over traditional designs. However, the molten salts present new challenges in their corrosive nature, and as such, the reactions that occur between the salts and the metal alloys they interface with need to be studied. We are developing new in-situ analytical techniques to study the physical and chemical interactions that occur at the interface between alloys and molten salts. We have designed a boron nitride (BN) cell that houses a small amount of molten salt with electrodes inserted through the top and is placed in a custom furnace at a synchrotron beamline. We will present our progress in developing techniques to examine the corrosion that occurs between molten LiF-NaF-KF (FLiNaK) salt and a NiCr foil using a combination of x-ray absorption spectroscopy (XAS) and electrochemistry.
4:35 PM
FLiBe Thermodynamic and Physical Properties Validation: Nathanael Gardner1; Raluca Scarlat1; Sven Vogel1; Haley Williams1; Boris Khaykovich1; Sean Fayfar1; 1UC Berkeley
FLiBe, a molten salt composed of eutectic mix of lithium fluoride and beryllium fluoride has the potential to be used as a fuel solvent or coolant in advanced nuclear reactors such as molten salt reactors. However, fission and corrosion products can alter the structure and properties of the salt. Thus using Ab-Initio-Molecular-Dynamics simulations and validating simulation results using neutron and x-ray diffraction, it is possible to observe how the structure of the salt changes as a function of temperature, extract the pair distribution function of the melt, and identify melt species. Neutron diffraction and thermal expansion data gathered on various FLiBe molten salt samples including FLiBe+LiD, FLiBe+Be, and FLiBe gathered from 20℃ to 700℃ will be shown. Significant anisotropy of the thermal expansion along the two crystallographic axes in the hexagonal unit cell was observed and compared for the different compositions to study the influence of these species.