Uncertainties in predicting long-term environmental impacts from geologic repositories

The assessment of environmental impacts of construction and operation of a deep geologic repository for high-level radioactive waste can be carried out using methods well-established for conventional radioactive waste management and production facilities. Uncertainties of assessments in impacts of repositories increase with time after closure and are related to predicting long-term conditions of the accessible human environment (e.g., population trends and distributions, water use, land use, diets, and habits), and long-term changes in ecosystems, and geologic and hydrologic regimes surrounding and above the repository. Primary concerns are related to the thermal and fission product decay period which is in the order of several hundred years. Thermal changes in the immediate vicinity of the repository could have a direct effect on root systems and indirect effects on ground water regimes, possibly contributing to long-term changes in ecosystems. Releases of radionuclides to the accessible environment are not expected to occur under predicted conditions and would not occur for thousands to tens of thousands of years under extraordinary circumstances. The characteristics of the human environment at that time cannot readily be predicted and therefore uncertainties in consequence results may be large