Investigation of the local structure of molten ThF4–LiF and ThF4–LiF–BeF2 mixtures by high‐temperature X‐ray absorption spectroscopy and molecular‐dynamics simulation

The microscopic structures of ThF4–LiF and ThF4–LiF–BeF2 molten salts have been systematically investigated by in situ high‐temperature X‐ray absorption fine‐structure (XAFS) spectroscopy combined with molecular‐dynamics (MD) simulations. The results reveal that the local structure of thorium ions was much more disordered in the molten state of the ThF4–LiF–BeF2 salt than that in ThF4–LiF, implying that the Th and F ions were exchanged more frequently in the presence of Be ions. The structures of medium‐range‐ordered coordination shells (such as Th–F2nd and Th–Th) have been emphasized by experimental and theoretical XAFS analysis, and they play a significant role in transport properties. Using MD simulations, the bonding properties in the molten ThF4–LiF and ThF4–LiF–BeF2 mixtures were evaluated, confirming the above conclusion. This research is, to the best of our knowledge, the first systematic study on the ThF4–LiF–BeF2 molten salt via quantitative in situ XAFS analysis and MD simulations. X‐ray absorption fine‐structure (XAFS) spectra of ThF4–LiF–BeF2 at room temperature, 600°C, 700°C and 800°C were obtained for the first time. The structural differences between ThF4–LiF and ThF4–LiF–BeF2 mixtures in the molten and solid phases were compared to understand the behaviors of thorium ions and the transport properties in the fluoride media through experimental and theoretical XAFS analysis combined with molecular‐dynamics simulations.