A characterisation and radiation resistance study of a mixed-modifier borosilicate glass for HLW vitrification
The short-range structural order, in glasses from the technologically important Na20-LhO-B203-Si02 system, is investigated using NMR and thermophysical techniques. The change in the populations of tetrahedrally coordinated borate units and various trigonal borate units is deduced from llB NMR and compared with the most widely accepted, NMR based, structural model of Dell, Bray and Xiao 1. Differences from the model are discussed and substantiated with results obtained from 29Si NMR. Structure sensitive properties such as density, glass transition temperature and thermal expansion coefficient are reported across a wide range of modifier concentrations. This information is then related to and compared with the structural arrangements obtained from NMR studies of less complex systems. An empirical density modee·3 designed for the single-modifier borosilicate systems has been used to gain information regarding the structural arrangements in the current system. Investigation of specific, carefully controlled, compositional changes to the current HL W vitrification glass, MW, has been carried out. The effect of 8 20 3 concentration on the chemical durability of glasses from this system has been studied using dynamic leach tests. In addition, the role of La203, a waste simulant, has been investigated using similar analytical methods, and suggestions as to its primary function in the glass have been discussed. Finally, a preliminary study of the interaction of several compositions, related to MW, with high-energy a-particles and UV -radiation, has been pursued. The presence of radiation induced structural and physical changes has been probed using ESR and 'Y-ray spectroscopy, enabling suggestions for the types of defects produced and nuclear reactions taking place to be made.