Characterisation of Granite Fractures From the In-Situ FEBEX Experiment (Grimsel, Switzerland): Possible Effects on Bentonite Colloid and Radionuclide Transport

摘要

The FEBEX in-situ experiment, installed in 1997 at the Grimsel Test Site (GTS, Switzerland) 400 m depth under the Swiss Alps, simulates a high level radioactive waste repository (HLWR) emplaced in granite. Its initial aim was to study the performance of a bentonite engineered barrier but recently, two new boreholes were drilled in the granite to study the possible bentonite colloid formation and their migration in the granite.This study presents the characterization performed, at the micrometer scale, of the three main water conductive fractures that were identified on the granite cores extracted from the new boreholes. These fractures are possible pathways for bentonite colloid transport (or retention), may be source of natural colloids and may condition colloid stability. The nuclear ion beam techniques μ-Particle X-Ray Emission (μPKE) and Rutherford Backscattering Spectrometry (RBS) were applied for visualizing and quantifying the elemental composition of the fractures surface and of the surrounding micro-fractures, as support of the bentonite colloid analyses.