Thermophysical Properties of NaCl–UCl₃–PuCl₃ Molten Salts: A Combined Computational and Experimental Study

Actinide-bearing molten salts for use as fuels are an essential part of next generation molten salt reactors. Yet, numerous multicomponent salt mixtures are underdeveloped or have not been investigated. This study, based on a combination of experimental and modeling techniques, is dedicated to determining and understanding a variety of properties of the ternary system of NaCl–UCl3–PuCl3, which represents a scenario for burnup of NaCl–UCl3 fuel, at two compositions (∼10 and 5 mol % PuCl3 in eutectic NaCl–UCl3 pseudobinary) and a range of temperatures. Evaluation of the heat flow and mass loss data showed the 0.61NaCl–0.30UCl3–0.09PuCl3 salt had a melting temperature of 551 ± 5 °C. Two additional thermal effects were observed occurring at approximately 410 and 494 °C. The transition occurring at 410 °C may be due to the presence of oxide in the salt. Extrapolation of thermodynamic data indicates the transition occurring at 494 °C is due to the formation of a liquid phase. Experimental testing determined the density of this system is a linear function of temperature and can be represented by the equation ρ = 4.014–0.0010T(°C), R2 = 0.992. Additionally, by using atomistic modeling, we found that increasing the PuCl3 content from 5 to 10 mol % led to the formation of larger Pu3+ clusters and slower transport of ions.