A one-dimensional heating test was performed to investigate the coupled THM response of MX80 bentonite in unconstrained conditions during basal heating. Measurements include the transient temperature/volumetric water content redistribution at different vertical distances from the flat heater under high temperature gradients and global volumetric strains. The main implication is that the heater surface area in contact with the surrounding bentonite plays a major role in the temperature distribution and the associated coupled water flow. This critical finding may help guide the geometric design of small-scale laboratory mock-up experiments used to study THM processes in controlled laboratory conditions.

Numerical models and experimental results have not yet reached accurate predictions of how long it takes for bentonite mixtures to hydrate until complete saturation or how the unsaturated hydraulic permeability evolves. Thus, an experimental campaign based on Magnetic Resonance Imaging (MRI) and 3D X-Ray micro computed tomography (µCT) is proposed to capture, image and quantify water infiltration in bentonite/sand blocks. X-Ray radiography analysis enable quantifiable observations of absorption increase associated to an augmentation of water content. Additionally, Single Point Imaging (SPI) MRI’s sequence quantifies the water content along bentonite/sand specimens based on linear correlation with its signal intensity.

• The work aims to assess numerically the phenomenology underlying the response and performance of large diameter sealing structures under real disposal conditions. • The simulations address the complexity of the problem by considering large scale 3D geometries, advanced constitutive models, complex hydro mechanical coupled formulation, and key geometric details at decimeter scale. • Results evidence a progressive hydration and swelling of the sealing core during more than 2000 years after repository closure. The concrete plugs placed at both ends of the core move longitudinally, but the central part of it maintains a swelling pressure within the admissible design range.

A fully instrumented vertical infiltration column has been recently developed using independent fast infiltration systems on top and slow infiltration rates at the lateral boundaries to mimic the peculiar saturation of the Vertical Sealing Systems VSS. A binary mixture of high-density MX80 bentonite pellets (80% mass) and powder is proposed as engineered barrier for these VSS. A 2D plane-strain numerical model based on the discretisation of pellets and powder using Code_Bright FEM has been used to gain insight into the coupled hydro-mechanical response of this multi-porosity material upon hydration.