Advances in gas permeation problems of buffer/backfill materials in high-level radioactive waste geological repository

A brief introduction is given to the findings and the latest advances in the mechanism of gas generation and migration, the testing equipments and methodologies as well as the properties of gas migration. The results show that the hydrogen based multi-component is generated during the operation of the repository, mainly resulting from the anaerobic corrosion of iron. There are four mechanisms for describing the gas migration in the buffer/backfill materials, including the advection-diffusion of gases dissolved in ground-water, visco-capillary two-phase flow, local dilated pathway flow and macroscopic fracture flow. Therefore, gas permeation devices for tests under the constant volume, K₀ confined, isotropic stress and triaxial conditions are successively developed. Numerous gas injection tests are conducted using the gas flow-rate control or injection pressure control methods. It is shown that the gas permeability and characteristic pressures are influenced by many factors, including the physical properties and boundary conditions of the samples tested. Considering the complexity of the operation conditions for the buffer/backfill materials in a deep geological repository, investigations on the gas permeation under multi-field (thermo-hydro-chemical-mechanical) and multi-phase (solid-liquid-gas) coupled conditions should be a very important work to be conducted.