A Review on Gas Tightness of Bentonite Barrier in Geological Repositories for High-Level Nuclear Waste

The geological disposal of high-level radioactive waste (HLW) is one of the key challenges facing the sustainable development of nuclear energy. As the core material of the engineered barrier system (EBS), the gas tightness performance of bentonite directly affects the long-term safety of the repository. This paper systematically reviews the research progress on gas migration laws in bentonite barrier systems, with a focus on two aspects: gas permeability under multi-field coupling conditions, and the effects of interface behavior as well as cracking-healing behavior of the soil on gas tightness. The review indicates that significant progress has been made in the breakthrough pressure, gas permeability, and multi-field coupling behavior of saturated/unsaturated bentonite. However, there remain notable deficiencies in understanding the cracking-healing mechanism under drying paths, the quantitative description of gas breakthrough paths under interface effects, and the dynamic evolution of gas tightness during cyclic drying-wetting processes. This paper points out that future research should focus on the above-mentioned knowledge gaps, establish a quantitative model linking breakthrough pressure and soil swelling performance, and reveal the coupling mechanism between cracking-healing behavior and gas tightness, thereby providing theoretical support for the long-term safety assessment of HLW geological repositories.