On the spatial variability at sedimentary sites examined for suitability as radwaste repositories

The geosphere is an essential part of the barrier system of final repositories for radioactive waste. Therefore, the assessment of its retention potential is of great importance for the post-closure safety analysis of such repositories (long-term safety assessment). In the context of geological and hydrogeological modelling the consideration of heterogeneities (spatial variability) is of special interest. In the present report methods for the consideration of general uncertainties in the frame of performance assessments as well as of spatial variability are presented. The methods are evaluated with regard to their applicability for sedimentary sites. In order to take into account the several types of information available for specific sites, the use of hybrid techniques seems to be preferable. In the case of presence of a large amount of hard information e.g. from borehole logs, geostatistical analyses should be the base of such hybrid methods. Using the example of the distribution of the clay layers at the Gorleben site it has been demonstrated that the performance of such analyses is promising in this special case. Further steps towards the development of an integrated method are proposed. (orig.)