UNDERSTANDING THE IMPACT OF FUTURE GLACIATION ON THE PERFORMANCE OF A CANADIAN DEEP GEOLOGICAL REPOSITORY FOR USED NUCLEAR FUEL

The Nuclear Waste Management Organization was established by the nuclear electricity generators in Canada and is responsible for implementing Adaptive Phased Management, the approach selected by the Government of Canada for long-term management of used nuclear fuel generated by Canadian nuclear reactors. In support of this objective, NWMO is pursuing an active technical research and development program in the area of used fuel storage and repository engineering, geoscience, safety assessment, and technical support to the development of a collaborative siting process.

The NWMO reference time frame for the safety assessment of a deep geological repository (DGR) is one million years, roughly equivalent to the time scale for the radioactivity in used fuel to decrease to that due to its natural uranium content. Given that the North American continent has been re-glaciated approximately every 100,000 years over the past million years, it is expected that a DGR site within the northern latitudes of North America will be subject to glaciation events associated with long-term climate change. Since glacial cycles are likely the most intense of plausible natural perturbations to a site, their potential impacts on the key safety functions of a DGR have been investigated within the Canadian program for several years.

Work programs are being directed to improve the understanding of geosphere responses to past and future glaciation cycles, acquire insight into the resilience of the geosphere at repository depths and provide a reasoned basis to support the treatment of long-term climate change in a DGR safety case. Some of the elements of the multidisciplinary approach include:

· Physical and temporal boundary conditions related to future glaciation by simulating the magnitude and time rate of change of ice sheet thickness, ground surface temperature and permafrost occurrence, amongst other attributes;

· Impacts on redox stability based on numerical simulations and paleohydrogeological investigations;

· Deep groundwater flow system evolution and impacts of Thermo-Hydro-Mechanical effects imposed by glacial cycles;

· Seismicity and faulting induced by glacial rebound; and

· Natural analogue studies to assess the impact of permafrost (eg Lupin Mine) and ice sheets (Greenland Project) on groundwater flow.