Identification and Decomposition of Uranium Oxychloride Phases in Oxygen-Exposed UCl 3 Salt Compositions.

Complementary X-ray absorption fine structure (XAFS) spectroscopy and Raman spectroscopy studies were conducted on several UCl ₃ concentrations in several chloride salt compositions. The samples were 5% UCl ₃ in LiCl (S1), 5% UCl ₃ in KCl (S2), 5% UCl ₃ in LiCl-KCl eutectic (S3), 5% UCl ₃ in LiCl-KCl eutectic (S4), 50% UCl ₃ in KCl (S5), and 20% UCl ₃ in KCl (S6) molar concentrations. Sample S3 had UCl ₃ sourced from Idaho National Laboratory (INL), and all other samples were UCl ₃ 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 UCl ₃ . XAFS and later Raman spectra measured, however, did not correctly match the literature and computational spectra for the prepared UCl ₃ 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 UCl ₃ salts. The oxychlorides present may be both a function of the unknown O ₂ 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.