In-situ Characterization of Interfaces between Materials and Molten Salts for Molten Salt Reactors

Molten salts are a crucial component in the proposed advanced nuclear reactors called “molten salt reactors” (MSRs). The appealing aspect of an MSR is that a melt-down is virtually impossible, since the fuel is dissolved into the salt. One of the key challenges hindering MSRs is corrosion of structural materials that hold the molten salt due to the interactions between material and molten salt at high temperature, especially within a radioactive environment that accelerates materials degradation. Due to the high temperatures, and corrosive nature of the salt, it is extremely difficult to study corrosion occurring in real time. To address this task, we specifically propose to develop a setup for in situ characterization of the interface between the molten salt and materials by X-ray diffraction, imaging and absorption spectroscopy. X-ray spectroscopy is the most exciting and powerful of these techniques, because it is a powerful way of probing the coordination chemistry and oxidation state of materials at the atomic level. Additionally, we propose to combine XAS with electrochemical measurements to perform spectroelectrochemistry. The goal is to determine the redox speciation and ion coordination environment of Cr ions at different redox potentials. In situ XAS measurements of materials in molten salts are the cornerstone of the Phase II. The Phase I demonstrated the feasibility of using X-rays to probe structural and chemical phenomena in a molten salt in situ, and at high temperature. Graphite and boron nitride analysis cells were designed and tested. High temperature was performed on molten salt in a graphite analysis cell in-situ. Our technical approach is to develop the systems, parts, and procedures necessary for the in situ characterization of molten salt interfaces, and to perform such characterization using the systems and procedures that are developed in the Phase II. In particular, X-ray absorption spectroscopy combined with electrochemical measurements will represent the cornerstone of our approach to understanding corrosion in the molten salt, especially with regard to chromium. Commercial applications and other benefits: While MSRs have been successfully demonstrated, concerns remain regarding the long-term compatibility of currently used alloy materials with the molten salt. Success of these technologies requires new materials that are resistant to corrosion in molten salts. The ability to study the corrosion process in situ at the interface of the salt and the material is expected to accelerate the development of MSRs. More generally, the techniques that we develop in this program are applicable to any corrosive industrial process, which extends the potential public benefit into a wide variety of industrial sectors, and is additionally important to our commercialization efforts.