U environment in leached SON68 type glass: a coupled XPS and time-resolved photoluminescence spectroscopy study

X-ray photoelectron spectroscopy (XPS) and time-resolved photoluminescence measurements have been performed on SON68 type nuclear glass and its leached product (gel) in order to characterize uranium environment in both materials. XPS measurements allow to detect two oxidation states in glass: about 20% of tetravalent uranium and 80% of hexavalent uranium, present under two types of environment. Comparison of XPS and time-resolved photoluminescence data allow to identify these U(VI) environments. In glass, they are respectively attributed to an uranate and an uranyl-type environment. In gels, U(IV) is oxidized in U(VI), the uranyl type environment is conserved whereas some amorphous uranyl hydroxides are formed. The U environment depends strongly on the leaching mode, in particular the leaching duration and water renewal rate.