CONTINENTAL-GLACIATION AND NUCLEAR-FUEL WASTE-DISPOSAL - CANADA APPROACH AND ASSESSMENT OF THE IMPACT ON NUCLIDE TRANSPORT THROUGH THE BIOSPHERE

A concept for disposal of immobilized nuclear fuel waste in a vault mi ned deep in stable plutonic rock of the Canadian Shield is being inves tigated in Canada. Far in the future, when man-made and natural protec tive barriers lose their integrity, radionuclides carried by groundwat er may migrate from the vault to the biosphere. During this time, many transitional processes will cause changes to the climate, hydrogeolog y and surface features of the biosphere. Glaciation is the most severe transitional process and its impacts on the disposal concept must be assessed. Using a discrete-state approach, the effects of glaciation w ere evaluated by performing separate time-independent radiological dos e assessments of interglacial and cold interstadial states assuming th at each state persists throughout the entire simulation period of 1000 00 years. We assume that humans will not inhabit a full glacial enviro nment. One of the major glacial processes is increased runoff during m elt. This should decrease nuclide concentrations and doses in the imme diate discharge zone of the vault through flushing and dilution. Tempe rature and moisture fluctuations will have only a minor impact on nucl ide transport in soils and surface waters. Our calculations show that it is unlikely that cold interstadial conditions will lead to substant ially higher doses to humans resulting from radionuclides in the envir onment than the current interglacial state.