THE TREATMENT OF CLIMATE-DRIVEN ENVIRONMENTAL-CHANGE AND ASSOCIATED UNCERTAINTY IN POST-CLOSURE ASSESSMENTS

The post-closure performance of radioactive waste repositories is influenced by a range of processes such as groundwater flow and fracture movement which are in turn affected by conditions in the surface environment. For deep repositories the period for which an assessment must be performed is in the order of 10(6) years. The geological record of the last 10(6) years shows that surface environmental conditions have varied considerably over such timescales and it is thus pertinent to examine the influence of such changes on the potential performance of a repository in detail. A model of surface environmental change, known as TIME4, has been developed on behalf of the UK Department of the Environment for use with the probabilistic risk assessment code VANDAL. This paper describes the extent of surface environmental change, discusses possible driving mechanisms for such changes and summarises the processes which have been incorporated within the TIME4 model. The underlying cause of change in surface environment sub-systems is inferred to be climate change but considerable uncertainty remains over the mechanisms of such change. Methods for treating these uncertainties are described.