Abstract: Ontario Power Generation (OPG) is proposing a Deep Geologic Repository (DGR) for the long-term management of low and intermediate level radioactive waste generated at OPG owned or operated nuclear facilities. As envisioned, the DGR would be excavated within an 840 m thick, Paleozoic age, sedimentary sequence underlying the Bruce nuclear site in the Municipality of Kincardine, Ontario, Canada. Lateral development of the DGR would occur in the Cobourg Formation, an argilla-ceous limestone that is overlain by 200 m of Ordovician shale. As part of investi-gations conducted to assess the safety of the DGR, geomechanical analyses were carried out to evaluate rock-mass barrier integrity over a timeframe of 1Ma. The primary concern regarding long-term performance of the emplacement rooms is their degradation over time when subjected to different loading conditions, include-ing time-dependent strength degradation, seismicity, gas generation within the repo-sitory and multiple glacial loading/unloading cycles. This paper describes a series of analyses performed to explore rock mass stability and barrier integrity surrounding the waste emplacement rooms. Results indicate that while damage in the near field may arise over time, the capacity of the enclosing formation barrier to contain and isolate the waste is not affected.
1 INTRODUCTION Nuclear Waste Management Organization (NWMO), on behalf of Ontario Power Generation (OPG), is managing the development of a Deep Geologic Repository (DGR) for Low and Intermediate Level Waste (L&ILW) at the Bruce nuclear site, located in the municipality of Kincardine in Ontario, Canada. The site-specific, long-term geomechanical stability study was conducted as a part of the DGR site character-rization activities. The analy-ses included assessments of DGR cavern, pillar and shaft stability, and the evolution of damage and deformation of the surrounding rock mass in response to excavation activities and the long-term dynamic geological conditions expected at the site.