Evaluating the Performance of the Composite Seals at Canada's Underground Research Laboratory (2008–2024)

Established in 2008 as a joint research project, the Enhanced Sealing Project (ESP) investigated the performance and Thermal-Hydraulic-Mechanical (THM) evolution of a full-scale composite seal at Canada's Underground Research Laboratory (URL). The seal was highly instrumented and comprised of a ∼6-m-thick bentonite clay component sandwiched between ∼3-m-thick concrete components, installed in a ∼5-m-diameter vertical circular shaft at the depth of ∼270 meters below the ground surface. This study utilized the ESP results up to 2024 and URL's historical data from the 1980s, to assess the performance and behaviour of the composite seal at the URL and the maturity of sealing technology for a Deep Geological Repository (DGR). The findings suggest that: (a) groundwater level perturbation can be minimized after the URL closure, (b) the preliminary swelling pressure of the composite seal can meet the required design specifications, and (c) full-scale composite seals can be constructed using existing techniques - demonstrating maturity of DGR sealing technologies. Finally, the ESP and URL have created a comprehensive dataset spanning over 46 years, covering the entire lifecycle of an underground facility – from siting, construction, operation, closure, and post-closure stages, which supports the development of a DGR's design and safety case.