Time-dependent biosphere processes in nuclear fuel waste disposal assessments

This paper identifies time-dependent processes that, operating over very long periods of time, could affect the rate or pattern of radionuclide migration through the biosphere from an underground nuclear fuel waste vault, and suggests ways of dealing with these processes in an assessment model. Glaciation (including glacially induced faulting and succession) is identified as the only process requiring explicit time-dependent modelling. Glaciation will be modelled by defining a small number of discrete biosphere states, performing a separate, time-dependent assessment of each state in turn, and basing the final assessment on the state for which the most severe consequences are predicted. This approach provides a manageable and credible first step in evaluating the effects of glaciation on radionuclide migration through the biosphere