Clay models for radioactive barriers
Subterranean storage tunnels or repositories for radioactive wastes are required to be highly advanced engineered structures. Due to changes in storage concepts, the approach has been to move away from permanently sealed facilities to manageable ones. In this light they must involve protecting barriers to prevent leakage of radioactive material that could result from damage and corrosion. Likewise, they must also act as suitable insulation barriers to prevent humidity and water entering the system and accelerating storage decay. The bentonite blocks that this technology proposes as an insulation barrier consist of pre-compacted bentonite that has been specially prepared to afford the maximum protection qualities. The intended barrier is made by compacted bentonite blocks at the bottom part and a granular bentonite backfill material in the rest of the tunnel. To do so they first had to design a method that would guarantee that bentonite blocks had the most favourable grain density and size distributions. This is affected in order to offer the best packing and density values when the clay is installed. The bentonite raw material is dried to a specific water content in order to guarantee as high dry density as is possible to impart emplacement values approaching 1.5g/cm3. Aside from clay density and dryness, the project also investigated several other factors that would have a bearing on the overall effectiveness of the process. Since the surrounding rock will have an important interaction with the barrier, hydro-mechanical performance had to be understood. Studies involving barrier design such as water pathways, had to account for water salinity and its corrosive impact. It also had to consider geophysical properties as buffer swelling at injection point areas and the component material used in the hydration system. As attitudes towards subterranean storage change from "permanent" storage to "sustainable" storage, the role of insulation becomes vital as longevity of storage drums and containers becomes questionable. Due to the various threats to storage systems and the inherent shortcomings of storage devices, they need to be modulated, maintained and repaired as needed. Clays therefore become an important means in providing suitable answers to the very difficult solution of radioactive waste storage.
