EXAFS and XANES Investigation of the Coordination of Technetium in Borosilicate Glass

Abstract

Among the various radionuclides contained in glasses storing high level nuclear waste, ⁹⁹Tc is of particular interest because it is not fixed on geological materials and has the highest initial leaching rate. Since these properties depend on the valence state and the local atomic coordination of Tc in the glass, we decided to investigate them by using EXAFS and XANES spectroscopy at the K edge of Tc. The samples were thin films of TcO₂ and NaTcO₄, and a borosilicate glass containing 2% Tc by weight. The analysis of the spectra indicates a major contribution of a single shell of neighbours and seems to exclude the possibility that these neighbours are oxygen atoms in the Tc glass. A good agreement was obtained by assuming that atoms surrounding Tc are also Tc. The first-neighbour distance was in accord with the value obtained for the crystalline structure of metallic technetium.