PNNL

Abstract

Batches designed to simulate nuclear high-level waste glass were compressed into pellets that were heated at a rate of 5°C/min and photographed to obtain the profile area as a function of temperature. Three types of batches were prepared with different nitrate-carbonate ratios. To determine the impact of the heat supply by an exothermic reaction and the batch expansion, the nitrated batches were prepared with varying addition of sucrose. To obtain the impact of the grain size of the quartz component, the mixed nitrate-carbonate batches were prepared with silica particles ranging in size from 5 µm to 195 µm. One batch containing only carbonates was also tested. Sucrose addition had little effect on the batch expansion, while the size of silica was very influential. The 5-?m grains had a strongest effect, causing the generation of both primary and secondary foam, whereas only secondary foam was produced in batches with grains of 45 µm and larger. The retention of gases evolved as the batch melts creates primary foam. Gases evolved from oxidation-reduction reactions once the batch has melted produce secondary foam. We suggest that the viscosity of the melt and the amount of gas evolved are the main influences on foam production. As more gas is produced in the melt and as the glass becomes less viscous, the bubbles of gas coalesce into larger and larger cavities, until the glass can no longer contain the bubbles and they burst, causing the foam to collapse.