Abstract A full-scale shaft seal was designed and installed in the 5 m-diameter access shaft at Atomic Energy of Canada Limited’s (AECL’s) Underground Research Laboratory at the point where the shaft intersects an ancient water-bearing, low-angle thrust fault at a depth of c. 275 m in granitic rock. The seal consists of a 6 m-thick bentonite-based component sandwiched between 3 m-thick, keyed upper and lower concrete components. This design was adopted in order to limit the mixing of saline groundwater from the deeper regime with the fresher, near-surface groundwater regime. Construction of the shaft seal was done as part of Canada’s Nuclear Legacy Liabilities Program. A jointly funded monitoring project, called the Enhanced Sealing Project (ESP), was developed by AECL (Canada) and jointly funded by NWMO (Canada), SKB (Sweden), Posiva Oy (Finland), and ANDRA (France), and since mid 2009 the thermal, hydraulic and mechanical evolution of the seal has been constantly monitored. The evolution of the type of seal being monitored in the ESP is of relevance to repository closure planning by demonstrating the functionality of shaft seals. Although constructed in a crystalline rock medium, the results of the ESP are relevant to the performance of seals in a variety of host rock types.

Abstract A shaft seal was installed at the intersection of the 5 m-diameter access shaft of the Atomic Energy of Canada Limited’s Underground Research Laboratory with a major, moderately dipping fracture zone (FZ) to limit the mixing of the saline groundwater at the zone below the FZ with freshwater at the zone above the FZ. The shaft seal consists of 6 m-thick clay-based material that is sandwiched between 3 m-thick upper and lower concrete components, and its centre is located at c. 273 m depth below the surface. This paper presents the results of preliminary finite element analyses using 2D-axisymetric and 3D geometries simulating the saturation of the shaft seal. The components in the analyses include the clay, concrete, intact rock and FZ. Of particular interest are the field-observed differences in the hydraulic pressures above and below the shaft seal. The results of the numerical analyses were compared with the 3-year monitoring data. The results of the numerical models showed that the decrease in the pressure difference indicates that there was flow path that connects the zones above and below the shaft seal. A preliminary long-term estimation of the shaft seal hydraulic response (up to 1000 years) was done based on the hydraulic pressure and excavation volume data, combined with the assumptions that that the groundwater level will eventually recover to the initial conditions.