XPS study of Th, U, Np and Pu containing murataite ceramics

Immobilisation of the long-lived radioactive high-level wastes (HLW) requires high-stability and high-capacity matrices. The synthesized analogues of the natural murataite are promising matrices for the actinide-containing HLW disposal. To understand the chemical processes inside these matrices it is necessary to know the physical and chemical states of the included radionuclides. X-Ray photoelectron spectroscopy proved to be the most adequate method for this purpose. The present work carried out an XPS study of the murataite titanate ceramic samples (Ti-Mn-Ca-An-Zr-Al-Fe-O, where An Th, U, Np, Pu) containing 10 mass % of An. The X-ray diffraction data show that the studied ceramics was formed by the dominating murataite phase with thrice-, octo- and penta-repeated fluorite cell. The quantitative elemental and ionic analysis of the studied ceramics was done on the basis of the XPS parameters from the all available binding energy range 0 to 1000 eV. The oxidation states of the included metal ions were determined to be: Ca2+, Ti4+, Mn2+, Fe3+, Zr4+, Al3+, An4+. Average metal-oxygen interatomic distances in the studied ceramics were evaluated on the basis of the oxygen binding energies. The XPS data were compared to the SEM DS results. (authors)