Postclosure safety assessment of a used fuel repository in crystalline rock

For decades Canadians have been using electricity generated by nuclear power reactors in Ontario, Quebec and New Brunswick. The used nuclear fuel removed from these reactors is a highly radioactive waste product requiring careful short and long-term management. Although its radioactivity decreases with time, the used fuel will remain a potential health risk for many hundreds of thousands of years. Canada's used nuclear fuel is now safely stored on an interim basis at licensed facilities located where it is produced. The Nuclear Waste Management Organization (NWMO) is responsible for the implementation of Adaptive Phased Management (APM), the federally-approved plan for safe long-term management of Canada's used nuclear fuel. Under the APM plan, used nuclear fuel will ultimately be placed within a deep geological repository in a suitable rock formation. A deep geological repository is a multi-barrier system designed to protect people and the environment in the long term. The barriers are the durable wasteform, long-lived corrosion resistant containers, engineered sealing materials and the surrounding geosphere. A site selection process is currently underway to identify a safe site for a deep geological repository in an informed and willing host community. The process of site selection will take several years. As potentially suitable sites are identified with interested communities, detailed field studies and geoscientific site characterization activities will be conducted to assess whether the APM multi-barrier repository concept could be safely implemented to meet rigorous regulatory requirements. At this early stage in the process, before specific sites have been identified for detailed examination, NWMO has been conducting generic studies to understand and illustrate the long-term performance and safety of the multi-barrier repository system within various geological settings. This report provides an illustrative case study of postclosure safety for a deep geological repository in a hypothetical crystalline Canadian Shield setting. Its purpose is to illustrate a postclosure safety assessment consistent with the Canadian Nuclear Safety Commission (CNSC) Guide G-320 on Assessing the Long Term Safety of Radioactive Waste Management. For a licence application for an actual candidate site, a full safety case would be prepared that would include the results of site-specific geoscience investigations, a site specific deep geological repository design, and a more comprehensive safety assessment than described in this document. (author)