Physical properties of KCl-UCl3 molten salts as potential fuels for molten salt reactors

Abstract

Passive molten salt reactors are receiving a significant amount of research attention for their inherent safety. While KCl-UCl3 exhibit high UCl3 loading of 53 mol% at the eutectic composition, their physical properties remain largely unexplored for both forced and natural circulation. Here, we employ classical molecular dynamics simulations to calculate the physicochemical properties of KCl-UCl3 molten salts at various temperatures and compositions. The computed density, heat capacity, and viscosity show that only viscosity exhibits temperature dependence while the others rarely change between 600 °C to 800 °C. The computed ionic structures reveal the formation of polymer-like uranium network structures at compositions above 40% UCl3, a distinct feature of KCl-UCl3 compared to NaCl-33%UCl3 eutectic mixture. We rationalize that the U network structure increases the absolute viscosity, yet also provides the temperature-dependent viscosity via allotropic U3+-Cl− polyhedral coordination. The molten salts are also assessed for both forced and natural convection with the computed physicochemical properties.