Structure study of new uranium loaded borosilicate glasses

The structure of multi-component borosilicate SiO ₂–B ₂O ₃–Na ₂O–BaO–ZrO ₂ glass loaded with 30 wt.% UO ₃ was investigated by neutron diffraction and high-energy X-ray diffraction. Reverse Monte Carlo modelling was applied to obtain a possible 3-dimensional atomic configuration consistent with the experimental data. It was established that the glassy network consists of tetrahedral SiO ₄ and of mixed tetrahedral BO ₄ and trigonal BO ₃ units. With increasing boron content the relative number of BO ₃/BO ₄ increases and the first neighbour r _{B O} distance decreases. For the U O correlations two distinct first neighbour distances were determined at 1.8 Å with 1.9 oxygen atoms and at 2.2 Å with 3.7 oxygen atoms. Significant second neighbour correlations have been established between uranium and the network former (Si, B), the modifier (Na) and the stabilizer (Zr) atoms. From these observations we may conclude that uranium ions take part in the network forming. This may be the reason of the observed good glassy stability and hydrolytic properties.