The Nuclear Waste Management Organization (NWMO) is responsible for the implementation of Adaptive Phased Management, the federally-approved plan for the safe long-term management of Canada’s used nuclear fuel. Under this plan, used nuclear fuel will ultimately be placed within a deep geological repository in a suitable host rock formation.

The NWMO completed an assessment of postclosure safety for a conceptual repository constructed at a depth of 500 m below ground surface (mBGS) in a hypothetical sedimentary rock setting in Southern Ontario, Canada. The Normal Evolution Scenario considered in that assessment postulates the release of radionuclides from defective containers and subsequent transport to the biosphere via a water supply well. Transport simulations were performed using constant climate conditions and a steady-state groundwater flow geosphere. Results indicate that doses from these postulated releases would be many orders of magnitude below the regulatory limit.

This paper presents results from a follow-up study which considers the impact of glaciation on transport, evaluating a large number of sensitivity cases for geosphere parameters, processes, and boundary conditions. Sensitivity cases are compared using transient system performance over a 1 million-year simulation period. A “snapshot” Mean Life Expectancy (MLE) approach is developed where MLE calculations are performed at 500-year intervals by assuming the flow system is constant at those times. MLE statistics from across the repository footprint are presented. Time-series results from minimum “snapshot” MLE calculations provide a useful data set for effective comparisons of temporal effects over the 1 million-year simulation period. Summary statistics provide useful comparisons of sensitivity cases.