Characterization and Radiation Resistance of a Mixed-Alkali Borosilicate Glass for High-Level Waste Vitrification

Abstract

Glasses related to those used for the vitrification of high-level waste (HLW) have been produced from the sodium-lithium borosilicate system. Their thermal and structural characteristics have been measured for a wide range of boron oxide contents (NBS series) and for a range of alkali oxide to boron oxide ratios, R, for several fixed silica to boron oxide ratios, K (ABS series). The NBS series of glasses was seen to exhibit a maximum in the glass transition temperature, T_g, and a minimum in the fraction of 4-coordinated borons, N₄, at 22 mol% and 29 mol% boron oxide, respectively. With variation of K and R, initial results indicate an increase in T_g to a maximum before a gradual decrease. Density measurements show a general increase before remaining within experimental error at larger R. Initial α-particle irradiation tests have been carried out on several base glass samples and show evidence of B(α,n) reactions, the occurrence of which could have important consequences for the future viability of wasteforms designed for reprocessing of higher burn-up fuel.