The valence state and the local environment of uranium ions in borosilicate glasses intended for immobilizing high-level wastes with high concentrations of iron and aluminum ions are investigated using X-ray absorption (XANES, EXAFS) spectroscopy. It is demonstrated that, in glasses predominantly containing iron oxides, at least 80% of the total uranium exists in a hexavalent form as uranyl ions. In high-alumina glasses, uranium is in hexavalent and pentavalent states; in this case, the fraction of the latter form increases with an increase of the uranium concentration and its local environment is similar to the configuration of an axially distorted tetrahedron.
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