The construction design of deep geological repositories for high-level radioactive waste (HLW) consist of the construction of a barrier system around the waste containers produced by a sealing hard stiffness material. In this paper, thermal-hydraulic-mechanical-chemical properties of bentonite-sand were presented for geological and engineered barrier through Na-type bentonite. Unconfined compressive strengths were measured, and compared under unsaturated/saturated condition, with/without heating effect and/or chemical exposure due to salt components. Saturated specimens were swelled both distilled water and salt water with salt component of 3.5 %. Also, heating effort leaded decreasing of unconfined compressive strength for saturated bentonite-sand samples.

A multi-physics simulator, with geochemical reactions that depend on the pH condition, was proposed. The simulator was validated by replicating the measurements of the evolving permeability and the solute concentrations in a single rock fracture obtained from flow-through experiments under different pH conditions. Then, the changes in fracture permeability during the virtual long-term flow-through tests were predicted by assuming the permeant under various pH, stress, and temperature conditions. The predicted results show that the rate of permeability reduction under a pH of 11 was about 10 times faster than that under a pH of 7.0, and the impact of the pH condition was confirmed.

Hydro-chemical interactions at the interface between host rock and clay buffer in geological disposal facility for nuclear waste can lead to buffer erosion. The erosion of clay buffer can induce loss of a critical component of the engineered barrier system and migration of highly hazardous radionuclides into the environment. Classical local formulations for modelling the hydro-mechanical behavior of soils are not suitable for analysis of this discontinuous physical phenomenon, while non-local formulations offered by Peridynamics (PD) provide clear advantages. A bond-based PD formulation of coupled clay extrusion and sol transport in a fracture is presented. The PD model, named Pyramid, of clay extrusion accounts for the van der Waals forces, repulsive electrostatic double layer forces and friction forces between the particles. A 2D case study of clay extrusion and erosion under water flow in a fracture is presented. The case study is compared with experimental results of erosion of compacted MX-80 bentonite reported in the literature to demonstrate the accuracy of formulations and the Pyramid model. This validation shows the potential applications and prediction capability of the Pyramid model for evaluating the erosion of clay buffer under geological disposal conditions.

Gaomiaozi (GMZ) bentonite is a suitable buffer material for underground repository barrier of high-level waste (HLW) in China. Strong alkaline cementitious material formed from the corroded lining concrete by groundwater will penetrate into bentonite buffer, meanwhile, the temperature of the barrier will rise under the radiant heat from the decay of the radionuclide. The laboratory tests were conducted to simulate the diffusion of KOH solution into bentonite under elevated temperature conditions and investigate the changes in mineral composition and microstructure of GMZ bentonite by X-ray diffraction (XRD), nitrogen adsorption and scanning electron microscopy (SEM). The results confirmed that alkaline dissolution of montmorillonite minerals in GMZ bentonite is increased with both pH value of the alkaline solution and the temperature. For example, montmorillonite content decreased from initial 44.4% to 25.9% in severe situation. The degree of alkaline corrosion of bentonite is inversely proportional to the distance between the contact interface of bentonite and alkaline solution and visible macro fissures were observed by naked eyes at the interface. Within 2mm of the surface, the wing-like gels produced by montmorillonite hydration were dissolved apparently; and beyond 4mm, the bentonite retained its original microstructure. The results reveal the adverse effects of alkaline corrosion of GMZ bentonite on the long-term performance of buffer barriers should be paid great attention.

Bentonite is a material considered to be used as a component of a barrier in deep geological repositories for nuclear waste. Its behaviour is affected by temperature, humidity and chemical composition of water saturating its pores. Reproduction of bentonite behaviour in such thermo-hydro-mechanical (THM) conditions involves extensive use of empirical and physical coupled relationships. This paper investigates parameters, which influence the bentonite behaviour in THM experiments relevant to the conditions in the repositories. For the study, a numerical investigation is performed based on test simulation computed with the finite element code Thebes (Abed and Sołowski 2017). A numerical simulation by Abed and Sołowski (2017) of a non-isothermal infiltration experiment (Villar and Gomez-Espina 2009) has been taken as a basis for the investigation. The results of this simulation were compared with a series of 7 other simulations that are set up by inactivating the selected thermally coupled variables, one at a time. Presented results identify the key parameters the simulation is sensitive to and provide insights on the relevance of the underlying coupled processes.