(608c) Thermophysical Property Measurement of Uranium Containing Fluoride and Chloride Salts

Actinide-containing fluoride and chloride molten salts are utilized as fuel salts in molten salt reactors (MSR’s) and have applications in pyrochemical-processing for fuel recovery. However, the thermophysical property data of these salts such as melting point, viscosity, and density and the effects on these properties of varying levels of actinide content are relatively unknown. This presentation will present novel data on the viscosity, density, and melting point of two candidate salts for use in MSR’s, NaCl-UCl₃ and NaF-BeF₂-UF₄. Additionally, to model the effects of plutonium produced by fission on the fuel salts’ thermophysical properties, the effects of cerium added as CeCl₂ and CeF₃­ as a surrogate for plutonium will be shown. Salt viscosity is fit Arrheniusly against temperature to extract the activation energy of viscous flow. Similarly, the measured salts are fit according to their concentration of network-forming species to show how oligomer formation drives viscosity. Salts are tested for Newtonian behavior by measuring the viscosity at shear rates ranging from 0.1 to 100 s^-1.

Melting point is measured using a ThermysONE DSC & TGA with platinum crucibles. Viscosity is measured using a Modular Compact Rheometer 702e (MCR702e) with parallel plate and cup and bobber rotational methods. Density is measured using the hydrostatic method: a metal bobber is suspended by wire from a scale, lowered into the salt, and the change in mass measured. To account for uncertainty in bobber thermal expansion, three different materials are used: stainless steel, brass, and 80Ni-20Cr alloy. All measurements take place inside an inert argon glovebox.

Salts utilized in the research were provided by the Nuclear Materials and Fuel Cycle Center at Virginia Tech and from TerraPower through Los Alamos National Laboratory.