In Situ Determination of Speciation and Local Structure of NaCl-SrCl2 and LiF-ZrF4 Molten Salts

Identification and Decomposition of Uranium Oxychloride Phases in Oxygen-Exposed UCl3 Salt Compositions

Complementary X-ray absorption fine structure (XAFS) spectroscopy and Raman spectroscopy studies were conducted on several UCl₃ concentrations in several chloride salt compositions. The samples were 5% UCl₃ in LiCl (S1), 5% UCl₃ in KCl (S2), 5% UCl₃ in LiCl-KCl eutectic (S3), 5% UCl₃ in LiCl-KCl eutectic (S4), 50% UCl₃ in KCl (S5), and 20% UCl₃ in KCl (S6) molar concentrations. Sample S3 had UCl₃ sourced from Idaho National Laboratory (INL), and all other samples were UCl₃ sourced from TerraPower. The initial compositions were prepared in an inert and oxygen-free atmosphere. XAFS measurements were performed in the atmosphere at a beamline, and Raman spectroscopy was conducted inside a glovebox. Raman spectra were able to confirm initial UCl₃. XAFS and later Raman spectra measured, however, did not correctly match the literature and computational spectra for the prepared UCl₃ salt. Rather, the data shows some complex uranium oxychloride phases at room temperature that transition into uranium oxides upon heating. Oxygen pollution due to failure of the sealing mechanism can result in oxidation of the UCl₃ salts. The oxychlorides present may be both a function of the unknown O₂ exposure concentration, depending on the source of the leak and the salt composition. Evidence of this oxychloride claim and its subsequent decomposition is justified in this work.

Molecular Dynamics and Experimental Study of the Effect of CeF3 and NdF3 Additives on the Physical Properties of FLiNaK

The paper presents the results, which are consistent within 2%, obtained both in the simulation of molecular dynamics and in the experiment on the study of the kinetic properties of molten FLiNaK with addition of lanthanide fluorides. The parameters of the Born-Huggins-Meier potential for the interaction of CeF₃ or NdF₃ with FLiNaK components are first calculated using the ab initio approach. The enthalpy of the system with dissolved CeF₃ or NdF₃ calculated in the model increases by ∼4.4% over the entire temperature range studied (800 ≤ T ≤ 1020 K). The self-diffusion coefficients of the molten salt components are calculated from the Einstein relation and also estimated from the shear viscosity data. The temperature dependences of the shear viscosity of molten FLiNaK as well as FLiNaK with additions of 15 mol % CeF₃ or NdF₃ are determined experimentally and by calculation. In addition, the dependence of shear viscosity on the concentration of CeF₃ and NdF₃ in FLiNaK is measured and calculated. The linear growth of the shear viscosity with the CeF₃ and NdF₃ concentrations is obtained. Experimental dependence is in good agreement with the simulated results in the case of NdF₃, and there is the discrepancy while CeF₃ addition. An analytical approximation of the temperature and concentration dependences for the viscosity of molten FliNaK and for the calculated self-diffusion coefficients of constituent elements is proposed. Linear approximation of temperature dependence of the self-diffusion coefficients of similar components in the corresponding extended systems is presented.