NMR Insights into Wasteforms for the Vitrification of High-Level Nuclear Waste

Abstract

Magic-angle spinning nuclear magnetic resonance of B-11, Si-29 and Al-27 has been used to study the distribution of nonbridging oxygen atoms (NBO) in an alkali borosilicate glass to which surrogate oxides for high-level radioactive waste have been added. The properties of such glasses are shown to depend on the fraction N (4) of four-coordinated boron atoms (B4) and on the fraction of silicate tetrahedra possessing one NBO, Q(3). The aqueous corrosion rate increases with Q(3) content, as does weight loss due to evaporation from the melt. The activation energy for direct current conduction scales with N-4. Values of N-4 obtained for these glasses deviate from those predicted by the currently accepted model and are strongly affected by the modifier or intermediate nature of the surrogate oxide and also by its effect on the distribution of NBO between the silicate and borate polyhedra.