Oxygen Bubble Formation in a Glass Melt in the context of Nuclear Waste Vitrification

This work takes place in the framework of nuclear waste vitrification and it deals with gas production occurring during the high-temperature process. We have focused on molecular oxygen (O-2) produced by redox reactions of multivalent elements. This phenomenon is also relevant to further natural and industrial systems. Our aim is to understand the mechanisms of oxygen bubble formation and growth, and how they are linked to redox reactions that occur during nuclear waste vitrification. We have performed different physico-chemical characterizations to support the understanding of bubble formation in the mentioned context. Experimental and numerical results of mass transfer between an isolated oxygen bubble and the melt, at varying content of the multivalent oxide (% Ce2O3) and varying oxygen fugacity (fO(2)) are firstly presented. The results indicate that the presence of the multivalent element significantly enhances mass transfer from bubbles to melt, most acutely at reduced conditions and high contents. We further investigated a bubble population in a simplified nuclear waste glass melt. The melting of a granular starting glass, composed of glass beads, leads to a bubble population formed mainly due to air trapping. By assuming that the bubble dynamics is driven by their residence time in the crucible, the overall dynamics at various temperatures can be rationalized, scaled, and generalized.