THE DEVELOPMENT OF A SAFETY ASSESSMENT MODEL OF THE GEOSPHERE FOR A REPOSITORY SITED IN THE CRYSTALLINE BASEMENT OF NORTHERN SWITZERLAND

A modelling study of groundwater flow and radionuclide transport in th e geosphere surrounding a repository for vitrified high-level waste si ted in the crystalline basement of northern Switzerland has been carri ed out as part of the recently completed Kristallin-I project. The stu dy derives information from an analysis of seven deep boreholes, along with seismic surveys, regional surface geological mapping and hydroch emical and hydrogeological analysis. This paper describes the transpor t model itself and how, by means of a suite of supporting models, fiel d data are translated into input parameters. Supporting models include : (i), a conceptual model of the proposed siting region; (ii) a set of hydrogeological models, the formulation of which is guided by the con ceptual model and by hydrochemical and isotopic data. Sources of uncer tainty in the conceptual model are described and a parameter sensitivi ty study is presented that illustrates the resultant uncertainty in ra diological consequences. A particular source of uncertainty is the het erogeneous nature of the geosphere, giving rise to a complex and incom plete dataset from which ranges of input parameter values must be deri ved. (C) 1997 Elsevier Science B.V.