Abstract
There has been a renewed interest over the past decade in the use of molten salts as coolants and fuels in next-generation nuclear reactors that are used for electricity generation and to supply high-temperature, low-pressure heat. For solid-fuel salt-cooled reactors, molten salts are used as the coolant for solid-fueled reactors that operate at high temperatures (>500 °C) while for liquid salt fueled reactors, fissile, fertile, and fission products are dissolved in a homogeneous molten salt which serves as both the fuel matrix and the primary coolant. Two key challenges with a liquid salt fueled reactor is to manage the solubility and oxidation state of the materials dissolved in the molten salt and to manage the interfacial interactions of the molten salt with the reactor materials to limit corrosion. To understand how the structure and dynamics of molten salts impact their physical and chemical properties, such as viscosity, solubility, and thermal conductivity, as well as chemical reactivity, it is necessary to determine the structure and speciation of the molten salt at the atomic/molecular scale. The Molten Salts in Extreme Environments (MSEE) Energy Frontier Research Center is addressing these challenges through a coordinated experimental and theoretical effort to elucidate the atomic and molecular basis of molten salt behavior, including interactions with solutes and interfaces and under coupled extremes of temperature and radiation. The structure of bulk salt mixtures, such as MgCl2/KCl, and solute speciation in molten salts has been studied to better understand behavior in these complex environments using combined X-ray scattering and spectroscopy, neutron scattering, optical spectroscopy and computational modeling. The chemical and morphological evolution of metal/molten salt interfaces has been examined using X-ray tomography and electron microscopy to better understand corrosion processes in molten salt systems. This presentation will discuss the challenges in molten salt chemistry for nuclear energy applications and highlight recent results in understanding the structure, properties and reactivity of high temperature molten salts.