Molten Salt Reactors (MSRs) are the leading candidates out of the six Gen IV advanced nuclear power reactor designs chosen for deployment for nuclear energy in the US. MSR technology is particularly attractive due to better passive safety, operation at atmospheric pressure, high thermal efficiency, lower spent fuel per unit energy and increased solubility of fission products in molten salts. To facilitate robust and economical design of such systems, accurate knowledge of fundamental understanding of the structure and speciation of salts and metals in and near molten salt – cladding interfaces is necessary. Speciation of solutes is important because it determines chemical behavior in solution and the complex speciation from fission and corrosion products impact kinetic, thermodynamic, and transport properties of the molten salt systems.<br/>Molten Salts in Extreme Environments (MSEE) EFRC aims to investigate speciation of metals in molten salt systems by utilizing in situ synchrotron based XAS methods. In our work, Extended X-ray Absorption Fine Structure (EXAFS) and X-Ray Absorption Near Edge Structure (XANES) are used to investigate local coordination environment and chemical structure of metal species such as Nickel in Zinc Chloride based molten salt systems. A combination of XANES, EXAFS and theoretical spectroscopy modeling reveal changes in the local structure around Ni towards distorted NiCl<sub>2</sub> phase as the weight loading of Ni the exceeds solubility limit. In addition, the effect of metal concentration and temperature on changes in local and chemical structure of metal is investigated. XAS studies are complemented by spectroelectrochemical studies of molten salts, enabling a direct correspondence between UV-Vis peak shape and coordination geometry and number, determined by EXAFS. Such knowledge of changes in chemical structure of salts and speciation of metals in molten salt environments will provide critical understanding needed to predict and control the physical and chemical properties of molten salts and corrosion mechanisms in molten salt systems.

Investigating structure and speciation of metals in molten salt system using X-ray absorption fine structure

2019 Fall National Meeting

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