In situ Experiments in Granite for the Underground Disposal of Radioative Wastes. Executive Summary of Phase 1

摘要

The first phase of the Stripa Project concerned the development of methods and techniques or repository site investigations as well as verification of previosly obtained laboratory results by in situ experiments. The hydrogeological and hydrogeochemical investigations resulted in a recommendation on hydraulic testing at repository depth and the conclusion that detailed hydrogeochemical processes cannot be understood without the integrated use of several investigation techniques. Increased knowledge on the detailed flow of water and migration of nuclides in single fractures have strengthend our confidence in predicted retardation. The diffusion of the radionuclides into the rock matrix and sorption onto fracture surfaces have proven to be active in situ processes. The major conclusion from the investigation of bentonite as a buffer and backfilling material is that the main physical processes are understood and can be predicted for various repository geometries. The major process is water uptake from the rock since it governs the build-up of temperatures and swelling pressures. This uptake is primarily related to the water-bearing capacity of the surrounding rock and yields a fast maturation of the clay if the deposition holes are intersected by hydraulically active fractures. It was also concluded from the experiment that the techniques required for preparation and application of bentonite-based buffer materials are available. (ERA citation 14:000270)