Chemical state analysis of simulated corium debris by EXAFS

The chemical state of uranium, zirconium, iron and lanthanide elements in simulated corium debris samples prepared in lab-scale were investigated by synchrotron radiation based extended X-ray absorption fine structure (EXFAS) technique. According to the EXAFS analysis of uranium, their most likely local structure was cubic like fluorite UO2. Exceptionally, pentavalent uranium was observed in the UO2-ZrO2-Fe2O3-CaO sample, in which the nearest U-O distance was clearly shorter than those of other samples containing tetravalent uranium. The local structure around zirconium could be classified into cubic, tetragonal and calcia stabilized zirconia with CaO. The oxidation state of iron was divalent for the most samples and a metallic phase was also detected in some of them. The small amount lanthanide elements (Nd and Gd) in the simulated debris seem to exist as a solid solution with UO2.