SYNTHESIS OF GEOCHEMICAL AND FRACTURE MINERAL STUDIES RELEVANT TO A DEEP GEOLOGICAL REPOSITORY FOR NONFUEL WASTES AT CHALK RIVER

Abstract

As part of a feasibility study under the Nuclear Legacy Liabilities Program, the geochemistry of the crystalline bedrock at the Chalk River Laboratories site has been investigated to examine the suitability of the bedrock to host a potential deep geologic repository, termed a Geologic Waste Management Facility, for the long-term management of intermediate-level radioactive wastes for Canadian Nuclear Laboratories, formerly Atomic Energy of Canada Limited. Characterization of the groundwater and fracture-filling minerals are important considerations in assessing how the geochemical environment would affect the performance and safety of such a facility. Regional groundwater chemistry at the site has evolved over time by groundwater mixing and by rock-water interactions. Collaborative studies with the University of Waterloo and the United States Geological Survey have provided data for whole-rock, fracture minerals, and groundwater isotope systematics. The sampled groundwaters appear in general to be geologically recent in age (i.e., similar to 10 000 years) and tend to be more dilute than Canadian Shield groundwaters at similar depths from other locations. Models of groundwater evolution at the site are suggestive of mixing relationships that include significant contributions from geologically recent meteoric and postglacial melt waters.