Examining Actinide-Molten Salts Across Length Scales: Local Structure, Thermal Properties

Actinide-molten salts are complex systems central to pyroprocessing for actinide metal purification and recovery, to molten salt reactors (MSRs)--a next-generation nuclear reactor concept currently in rapid growth, and also to a growing number of new energy-related applications. There are gaps in the literature concerning the chemistry and thermal properties of these systems, especially in data collected with well-documented methodology and experimental detail, using salts with analytical data confirming purity, and reported with thorough error analysis and quantified uncertainty. With the overarching goal to contribute to a better understanding of these complex systems, enabling prediction of their behavior, a suite of advanced characterization techniques is being developed at Los Alamos National Laboratory for the accurate and precise measurement of actinide-molten salt thermochemical and thermophysical properties, and for the study of their local structure. The high-quality empirical data collected using these capabilities supports the optimization of pyroprocesses, the development of MSRs, and the validation and refinement of models. Efforts to examine actinide-molten salts across length scales will be described, including recent results from studies both on local structure and on thermal properties of uranium- and plutonium-bearing chloride salts. A selection of techniques and results will be detailed, with a focus on pulsed neutron characterization at the Los Alamos Neutron Science Center (LANSCE), including progress using pair distribution function (PDF) analysis to gain insight into uranium-molten salt local structure, and recent results from measurements of the liquid density of uranium- and plutonium-molten chloride salts as a function of temperature and composition using neutron radiography.