Engineering barriers in deep geological disposal: Implications for radioactive nuclide migration and long-term safety

Abstract

The rapid growth of nuclear energy technology, along with the expansion of global nuclear power projects, has led to a significant increase in high-level radioactive wastes (HLWs), particularly spent fuel from nuclear power plants. The disposal of HLWs remains a major challenge due to its high radioactivity, long half-lives, and complex management requirements. Ensuring the long-term safety of HLW disposal is critical for the sustainable development of nuclear energy. Currently, deep geological disposal is considered the most effective and secure method for isolating HLW. This method relies on a multi-barrier system that combines natural geological barriers with artificial engineering barriers to achieve the long-term isolation of radioactive wastes. Engineering barriers, including waste containers, buffering materials, and backfill materials, are essential for preventing radioactive leakage and maintaining isolation in the face of geological and environmental changes. Recent studies have focused on the design and optimization of these barriers, particularly their impact on the migration of key radioactive nuclides. Insights from international practices and technological advancements have highlighted the importance of materials like bentonite, disposal containers, and other engineering barriers in optimizing multi-barrier systems for HLW disposal. Bentonite, a widely used buffering material, is known for its excellent adsorption properties and low permeability. Recent modifications to bentonite have enhanced its ability to adsorb radioactive nuclides such as cesium (Cs) and plutonium (Pu), significantly improving the safety and long-term stability of disposal facilities. Additionally, the migration mechanisms of radioactive nuclides have been examined, with particular attention to the influence of hydrochemical conditions—such as hydration, ion concentration, and pH—on bentonite's adsorption capabilities. This study sheds light on the migration pathways and rates of these nuclides in HLW disposal systems. Another key area of focus is the materials used for disposal containers, particularly cement-based and metal materials, which play a critical role in mitigating corrosion risks during long-term storage. While experimental data show promising corrosion resistance under specific conditions, continued researches are necessary to evaluate the long-term durability of these materials. These findings provide valuable theoretical insights for the engineering design of HLW geological disposal, offering references for the site selection, design, and material optimization of disposal facilities, particularly in China. As experimental data and theoretical models continue to evolve, future safety assessments and long-term behavior predictions will become more accurate. By promoting international collaboration and interdisciplinary research, these efforts contribute to the development of a scientific foundation for the safe and sustainable disposal of HLWs, ensuring environmental safety and the long-term effectiveness of waste management strategies.