Deep geological repositories (DGRs) for isolating nuclear waste must be designed to last hundreds of thousands of years. Relevant processes needing consideration over such time scales include density-dependent flow, glacial loading, permafrost formation and thaw, and heat and brine transport. Host geological media can be complex and heterogeneous, including discrete fractures or fracture zones and depth-dependent hydraulic conductivity. Numerical modelling can provide much needed insight into the behavior of these non-linear systems.
In this context, the finite element model HEATFLOW/SMOKER has been further developed and applied to predict the effect of glacial cycles and permafrost freeze/thaw on deep groundwater flow systems relevant to a DGR. Simulations are based on a 2D conceptual model of the recently-approved Revell storage site in northern Ontario, Canada.
Driven by future projections of historic air temperatures, glacier base temperatures and glacier thickness, the 120,000-year simulations show how permafrost can extend hundreds of metres deep, potentially isolating deep flow systems. Unfrozen zones (or taliks) potentially forming in discharge zones, remain a concern as pathways to surface.