It is proposed to develop a multi scale model to numerically investigate the gas transport processes at play in clay barriers, and improve their mechanistic understanding. Motivated by the experimental evidences that such processes are governed by the rock structure at a micro level, the model integrates a representative element volume which contains a detailed reproduction of the microstructure constituents, like the pore network or the bedding planes. From this local description of the material, the macroscopic response to loading can be derived using homogeneisation techniques. Applying this model to an injection test helps reproducing the creation of preferential pathways.

An in situ experiment, which will measure diffusion of dissolved gas (neon) at larger scale is presented. The existing MEGAS setup will be re-used for this purpose. Results of a first in-diffusion experiment with helium are shown, and compared with a predictive model.

Understanding the processes and mechanisms involved in the creation and accumulation of discrete gas phases by nuclear waste disposals buried in clay formations is essential. In this work, the D-23 MAGIC and LASGIT (gas test 1) are studied based on the same methodology, modeling strategy, and material properties applied in the previous work for DECOVALEX 2019 Task A stage 1A (ENGINEER) for evaluating multiphase flow in porous media incorporating permeability heterogeneity. A coupled hydro gas 3D FEM numerical model is developed for each case by the UPC/Andra team to simulate the gas flow tests using the CODE BRIGHT software.

The self-sealing capacity of Boom Clay after gas transport is experimentally analysed from a multi-scale perspective. The macroscopic results show a recovery of the initial water permeability after gas transport upon re-saturation, demonstrating a good self-sealing capacity. The self-sealing is also observed with microstructural techniques after the tests. The fissures detected after the gas injection are not visible anymore.

- Several thermal modelling exercises of a bentonite laboratory test are conducted to inspect the relevance of different model aspects, especially vapour loss. - The case is a thermo-hydraulic test in which a temperature gradient is applied to a bentonite specimen. The steady-state temperatures are well captured. However, the transient values are not. - Vapour loss is a possible heat sink missing in the model. Nevertheless, the vapour mass that would make the model match the experimental values is 100 times the estimated vapour leakage. This makes it unlikely that vapour loss is the main cause of the mismatch.