Demonstration of high-level radioactive waste disposal on the basis of the Opalinus clay project

Deep borings allow determining the position and the extent of the geologic layers which constitute the ground until the granite basement. The intermediate layers are formed principally of clay; in particular through the borehole in Benken (Zuercher Weinland), Switzerland a layer of Opalinus clay of 113 m thickness was detected. For the construction of a repository for deep underground disposal of radioactive waste, Opalinus clay is especially interesting because it is perfectly watertight. The information given by the boring corroborates the results of seismic studies. Seismic measurements were carried out between the Aare River and the Lake of Constance; they delivered an accurate profile of the geological layers over a domain of 50 km2. The method of seismic optics allows bringing to light small irregularities of the geologic structures. It was established that the studied layers are very little deformed. In the course of 180 million years the mud at the bottom of the former sea was solidified into a perfectly watertight sediment rock. This characteristic is used for the safe storage of radioactive wastes. Besides the technical barriers, it contributes to isolate the wastes from the vital space for a long-time period. Opalinus clay has been comprehensively studied in underground laboratories by international teams of scientists