Influence of geochemical variables on long-lived radionuclide migration and risk assessment

The uncertainties associated with predicting long-lived radionuclide migration from geologic repositories are large because of the long times considered and the lack of a geochemical history for the artificial elements. The long-lived radioelements can be categorized according to their inherent chemical properties and geochemical interactions which contribute to varying levels of uncertainty in the predicted risk. The elements Am, Th, and I, although quite different in terms of mobility, have the least uncertainty associated with predictions of their long-term behavior once a reference case is determined. The chemically similar elements Np, Pu, and U represent a second case where the presence of mobile oxycations contributes to complicated solid-solution partitioning evaluations. A third category, created for technetium, considers an element for which one parameter (evaluated with difficulty), redox potential, contributes most to uncertainty, with a small difference in assumed geochemical environment resulting in either a highly retarded or highly mobile chemical form