Recent status of xafs work on molten salt systems in the spring-G8

The local structure and structural change of trivalent metal chlorides RECl3 (RE=Gd, Tb and Dy) and UCl3 by mixing with LiCl-KCl eutectic were investigated by a high-temperature XAFS and a molecular dynamics (MD) techniques. In both of molten pure DyCl3 and its mixture with LiCl-KCl, the local structure was predominantly the octahedral 6-fold coordination (DyCl6)3-. Coordination numbers (CN) of the 1. neighbour correlation in molten pure GdCl3 and TbCl3 were slightly larger than 6. By the mixing, however, they decreased to 6. It seems that the local structure of molten RECl3 diluted in LiCl-KCl solvent is commonly the octahedral coordination. On the other hand, the local structure of molten pure UCl3, which has a larger cation than Gd3+ ion, was an 8-fold and its mixture with LiCl-KCl was not a stable 6-fold coordination. The molecular dynamics simulation of the mixture systems clarified that the mixing behaviour is completely different between with LiCl and with KCl. It is estimated that a stable octahedral 6-fold coordination structure is not formed in 'a binary mixture of MCl3 having a large metal ion with LiCl' like UCl3-LiCl system. (authors)