Surface analysis of simulant UK high level waste glass

Abstract

Simulated waste glasses which were 25 wt% Magnox glass, 36 wt% Magnox glass and International Simple Glass (ISG) were subjected to aqueous corrosion in static mode with deionised water at 90 °C for 7 to 28 days. Magnox glass is Mg- and Al- rich while ISG has only 6 components but no Mg in the composition. These glasses were assessed before and after corrosion using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) with Energy X-Ray Dispersive Spectrocopy (EDX), Transmission Electron Microscopy (TEM), Ion-ToF Secondary Ion Mass Spectrometry (ToF-SIMS) and Inductively Coupled Plasma – Optical Electron Spectroscopy (ICP-OES) in particular a novel wedge technique was developed for ToF-SIMS enabling accurate assessment of corrosion. Characterisation reveals changes in the morphology and elemental distributions from the surface to the bulk. Depletion of alkali ions i.e Na and Li was observed indicating the interdiffusion (ion exchange) process occurs after leaching. Formation of a gel layer which was Si-rich was also observed which forms due to the hydrolysis process. Formation of alteration layers were also observed on the glass due to leachates saturation which enables released ions to be sorbed and precipitate on the glass surface. It is found that high waste loading glass (36 wt% Magnox) has higher durability compared to the other glasses as it has a lower leaching rate that is 0.7 gm-2d-1 compared to 2.1 gm-2d-1 and 22 gm-2d-1 for 25 wt% Magnox glass and ISG glass respectively. The level of each element was determined and its role in the glass structure, either acting as modifier or intermediate, was identified.