THE GEOCHEMICAL ENVIRONMENT OF NUCLEAR-FUEL WASTE-DISPOSAL

The concept for disposal of Canada's nuclear fuel waste in a geologic environment on the Canadian Shield has recently been presented by Atom ic Energy of Canada Limited (AECL) to governments, scientists, and the public, for review. An important part of this concept concerns the ge ochemical environment of a disposal vault and includes consideration o f rock and groundwater compositions, geochemical interactions between rocks, groundwaters, and emplaced vault materials, and the influences and significance of anthropogenic and microbiological effects followin g closure of the vault. This paper summarizes the disposal concept and examines aspects of the geochemical environment. The presence of sali ne groundwaters and reducing conditions at proposed vault depths (500- 1000 m) in the Canadian Shield has an important bearing on the stabili ty of the used nuclear fuel, its container, and buffer and backfill ma terials. The potential for introduction of anthropogenic contaminants and microbes during site investigations and vault excavation, operatio n, and sealing is described with examples from AECL's research areas o n the Shield and in their underground research laboratory in southeast ern Manitoba.