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Etude des mécanismes à l’origine des reprises d’altération : Modélisation et impact sur les verres de confinement

Maxime Fournier 1
1 LCLT - Laboratoire d'Etudes du Comportement à Long Terme des matériaux de conditionnement
DE2D - Département de recherche sur les technologies pour l'enrichissement, le démantèlement et les déchets : DEN/DE2D
Abstract : A sudden and still poorly understood phenomenon, the resumption of alteration results in a sudden acceleration of the glass alteration rate due to the destabilization of the amorphous passivating layer formed on the glass surface. Understanding the origin and the consequences of this phenomenon is a major issue for the prediction of nuclear glass long-term behavior.This study quantitatively links the alteration degree of a six-oxide reference glass and the formation mechanisms of zeolites and C-S-H that control the solution chemistry. The role played by the decrease in aluminum concentration as an indicator of resumption is highlighted. It appears that the resumption occurrence and rate are correlated to the couple (T, pH), but even in the most adverse situations the resumption rate is lower than the initial alteration rate, which remains the fastest kinetic regime. Previously limited to alkaline pH, the characterization of alteration resumptions was extended to conditions more representative of those found in a geological repository. This approach required the development of a new tool: seeding, that reduces or eliminates the latency period preceding a resumption. The results obtained demonstrate its usefulness in understanding the role of zeolites in amorphous layer destabilization and for modeling alteration resumptions.A geochemical modeling approach to alteration resumption is proposed, based on the formalism of the GRAAL glass alteration model. It is based on the calculation of zeolite thermodynamic constants, on the implementation of their nucleation and growth kinetics, and on assumptions related to the solubility of the amorphous layer. When zeolite precipitation consumes alkali, glass alteration—driven by zeolite precipitation—releases alkali. The model highlights the importance of such chemical couplings and shows that, in the stoichiometry of French nuclear reference glass, their cumulative effects are the cause of a pH decrease which limits zeolite precipitation.
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Maxime Fournier. Etude des mécanismes à l’origine des reprises d’altération : Modélisation et impact sur les verres de confinement. Chimie inorganique. Université Montpellier, 2015. Français. ⟨NNT : 2015MONTS194⟩. ⟨tel-02025749⟩

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