Evolution of the uranium local environment during alteration of SON68 glass

The speciation of uranium in SON68 glass specimens doped with 0.75-3.5 wt% uranium and in the gels formed by alteration of the specimens was investigated by X-ray absorption spectroscopy. In the glasses, uranium is present at oxidation state VI and coordination number 6 with the same average distances than those found in a UO3 type environment. The U-O distances and uranium coordination numbers are identical throughout the uranium concentration range. During glass alteration the uranium remains at oxidation state VI in the gels, but was found in the uranyl form. An increase in the equatorial distances (from 2.20 and 2.32 Angstrom in the glass to respectively 2.22 and 2.39 Angstrom in the gel) and coordination numbers (to about 7 and 8, respectively) was observed. (C) 2002 Elsevier Science B.V. All rights reserved.