Abstract
Binary mixtures of high-density MX-80 bentonite pellets (80%) and bentonite powder (20%) at hygroscopic water content have been recently considered as an alternative engineered barrier system for the long-term disposal of radioactive wastes. These mixtures display a dry density of around 1.49 Mg/m3 on pouring and present components with multi-modal pore size distributions that significantly evolve during the hydro-mechanical paths. To better understand the hydro-mechanical behaviour of this multiple porosity mixture, the contribution initially focuses on describing the initial state, as well as the main microstructural features determined by mercury intrusion porosimetry tests for the mix and each of the components (pellets and powder). Afterwards, hydro-mechanical results of both components and the mixture are presented. The hydraulic results focus on the water retention and water permeability, while the mechanical tests concentrate on the compressibility properties on loading.
Highlights
Introduction and backgroundBentonite-based mixtures have been recently proposed as candidate sealing materials for high-level radioactive wastes deep geological disposal for high-level radioactive wastes [1,2,3]
In the VSEAL project, the mixture, constituted by high-density bentonite pellets (80% dry mass ratio) and bentonite powder obtained from crushed pellets, displays an emplacement dry density of 1.49 Mg/m3 on pouring
A microstructural characterisation focused on the pore size distribution with mercury intrusion porosimetry MIP (Micrometrics Auto Pore IV 9500) was performed on freeze-dried pellet and powder at two hydraulic states
Summary
Bentonite-based mixtures have been recently proposed as candidate sealing materials for high-level radioactive wastes deep geological disposal for high-level radioactive wastes [1,2,3]. The French Institute for Radiological Protection and Nuclear Safety (IRSN) has been recently involved in the ‘Vertical Sealing System’ (VSEAL) project that studies the long-term hydration process of an engineered barrier based on granulated/powder MX-80 bentonite and the impact of gas migration at different hydraulic states. In the VSEAL project, the mixture, constituted by high-density bentonite pellets (80% dry mass ratio) and bentonite powder obtained from crushed pellets, displays an emplacement dry density of 1.49 Mg/m3 on pouring. This heterogeneous mixture will undergo important pore size distribution changes on hydration, which will have consequences on the short-term HM behaviour of the material and its long-term response to gas migration. Afterwards, the main hydraulic properties (water permeability and water retention curves) and mechanical properties (compressibility on loading at constant water content) are described for the components and the mixture
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