Effect of MCl3 (M=La, U or Sc) component on the local structures and transport properties of LiCl-KCl-MCl3 eutectic: A molecular dynamics study

LiCl-KCl eutectic material is a crucial waste reprocessing candidate for use in molten salt reactors and the major component of spent nuclear fuel. Investigating the structure and thermodynamic transport properties of this eutectic mixed with fission waste cations will provide a better understanding of the reprocessing progress. In this study, molecular dynamic simulations were performed on the molten salts of a LiCl-KCl eutectic mixed with La3+, U3+, or Sc3+ cations, and the mole fractions of the trivalent cations ranged from 0% to 50% at 773 K, 873 K, and 973 K. The local structures (in nearest neighbor distance and coordination numbers) and macroscopic transport properties (self-diffusion, electrical conductivity, and viscosity coefficients) of the three systems have been studied. When the trivalent cation concentration varied from 0 mol% to 50 mol%, the mean nearest neighbor distance of La3+-Cl- and U3+-Cl- increased and the mean nearest neighbor distance of Sc3+-Cl- decreased, and the coordination numbers of La3+ and U3+ increased while the coordination numbers of Sc3+ decreased as the trivalent cation concentrations increased. The trivalent cations were primarily present in the form of [MClx](3-x) in diluted mixtures, and they linked to form a network in the viscous regions. The viscosity was primarily affected by the network and followed by a nearly linear increase with the degree of the network in the arbitrary trivalent mixtures. Additional investigation predicted the electrical conductivity and self-diffusion over a broader range; the results indicated that the electrical conductivities were hardly affected by the radius of the given trivalent cation. (c) 2019 Elsevier Ltd. All rights reserved.