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Mechanisms of oxygen bubble formation in a glass melt in the nuclear waste vitrification context

Abstract : This doctorate takes place in the framework of nuclear waste vitrification and it deals with gas production occurring during the high-temperature process. We are focused on molecular oxygen produced by redox reactions of multivalent elements. Indeed, these elements can be found in different contexts, including natural and industrial systems. This thesis aims to understand, fundamentally, the mechanisms of oxygen bubble formation and growth and how they are linked to redox reactions taking place in this context. We have chosen a simplified nuclear glass system composed of a borosilicate glass doped with cerium oxide. To support the understanding of bubble formation and growth in this given context, we characterized the simplified system in terms of physical and thermochemical properties. First, we studied the mass transfer between an oxygen bubble and the melt, for varying cerium contents (% Ce2O3) and oxygen fugacities (fO2). This study was carried out by both experimental and numerical means. The results confirm that cerium redox reaction significantly enhances the mass transfer, mainly in reduced states and high cerium oxide contents. A theoretical model assuming instantaneous redox reaction and a diffusion dominated by molecular oxygen allows, globally, to explain the experimental results. Afterward, we expanded the study to a bubble population scenario. This part of the work has also been investigated by both experimental and numerical means. The melting of a granular medium, composed of glass beads, leads to a bubble population nucleated mainly due to air trapping. Assuming that the bubble dynamics is driven by their residence time in the crucible, the overall dynamics at various temperatures is the same. A numerical model based only on mass transfer does not estimate bubble behavior, and consequently coalescence should be taken into account.Finally, we proposed a novel in-situ method to infer bubble volume fraction. We demonstrated the theoretical and technical viability of this novel method by comparing the results with other well-established approaches from the literature.
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Submitted on : Tuesday, January 5, 2021 - 12:22:24 PM
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  • HAL Id : tel-03097356, version 1

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Luiz de Paula Pereira. Mechanisms of oxygen bubble formation in a glass melt in the nuclear waste vitrification context. Material chemistry. Université Paris sciences et lettres, 2020. English. ⟨NNT : 2020UPSLM033⟩. ⟨tel-03097356⟩

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