Advanced nuclear fuel cycles employing molten salts incorporate online pyroprocessing methods for molten fuels and coolants, but lack the chemical knowledge required to manage chemical and neutronic melt properties as well as ensure nuclear security of the systems. Prior to implementation of these online processing techniques, a thorough understanding of salt phase diagrams and coordination environments must be developed. The capability of experimental investigations are limited by the corrosive nature of halide salts, the high temperatures of systems (&gt; 450 °C), and access to relevant radioisotopes. Such challenges necessitate the development of models for predicting salt properties and behavior, especially in the presence of multiple solutes and other contaminants. This work presents the implementation of both rigid and polarizable force fields for modeling lanthanide and actinide chloride salts. The polarizable force field adapts a previously parameterized point dipole model to a core-shell polarization scheme. The trivalent f-elements cerium and uranium are studied in chloride media at 1100 - 1200 K. Evaluation of structural and transport properties is completed with classical molecular dynamics. Simulation data is supplemented by ab initio calculations and experimental data. Preliminary results of the rigid ion model suggest strong ionic interactions resulting in reduced values for diffusion coefficients and enhanced long-range ordering of ion clusters, potentially leading to the development of polymeric networks in the salt. These networks may include point, edge, and face sharing structures. Rigid model simulations predict M3+-Cl- coordination numbers of 7.8 and 8.2 for U3+ and Ce3+, respectively. The strength of ionic interactions is reduced by the introduction of polarizability to the system.

Characterization of thermophysical and structural properties of trivalent f-element chloride salts with a polarizable ion model

ACS Fall 2021

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