Structure study of new uranium loaded borosilicate glasses

The structure of multi-component borosilicate SiO2–B2O3–Na2O–BaO–ZrO2 glass loaded with 30 wt.% UO3 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 SiO4 and of mixed tetrahedral BO4 and trigonal BO3 units. With increasing boron content the relative number of BO3/BO4 increases and the first neighbour rBO distance decreases. For the UO 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.