In France, vitrified waste from nuclear fuel processing is to be disposed deep underground in clay geological strata. In this confined, low-porosity environment, the chemical interaction between the glass, the corrosion products of the metal containers and the site clay should control the weathering of the glass once the medium is again saturated with water. Predicting the long-term weathering of vitrified packages requires a thorough understanding of the many interrelated reaction mechanisms involved. In practice, these mechanisms are classified according to their importance on weathering kinetics, and then integrated within models adapted to the relevant time and space scales.
This thesis focuses on the geochemical modeling of glass weathering, which is carried out using a reactive transport code (CHESS/HYTEC), a thermodynamic database and a kinetic law for glasses (GRAAL2 model, derived from the GRAAL model (Frugier et al. 2018)). This model takes into account the role of the composition of the glass weathering layer on its protective character, enabling GRAAL2 to simulate variations in weathering rate as a function of glass composition and environmental conditions.