Continental glaciation and nuclear fuel waste disposal: Canadaʹs approach and assessment of the impact on nuclide transport through the biosphere

A concept for disposal of immobilized nuclear fuel waste in a vault mined deep in stable plutonic rock of the Canadian Shield is being investigated in Canada. Far in the future, when man-made and natural protective barriers lose their integrity, radionuclides carried by groundwater may migrate from the vault to the biosphere. During this time, many transitional processes will cause changes to the climate, hydrogeology 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 were evaluated by performing separate time-independent radiological dose assessments of interglacial and cold interstadial states assuming that each state persists throughout the entire simulation period of 100 000 years. We assume that humans will not inhabit a full glacial environment. One of the major glacial processes is increased runoff during melt. This should decrease nuclide concentrations and doses in the immediate discharge zone of the vault through flushing and dilution. Temperature and moisture fluctuations will have only a minor impact on nuclide transport in soils and surface waters. Our calculations show that it is unlikely that cold interstadial conditions will lead to substantially higher doses to humans resulting from radionuclides in the environment than the current interglacial state.