Characterisation of Granite Fractures From the In-Situ FEBEX Experiment (Grimsel, Switzerland): Possible Effects on Bent
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Characterisation of Granite Fractures From the In-Situ FEBEX Experiment (Grimsel, Switzerland): Possible Effects on Bentonite Colloid and Radionuclide Transport Ursula Alonso1, Tiziana Missana1, Miguel Garcia-Gutierrez1, Alessandro Patelli2, Nairoby Albarran1, Trinidad Lopez-Torrubia3, Daniele Ceccato4,5, Valentino Rigato5 1 CIEMAT, Avda. Complutense, 22 Madrid, 28040 Spain 2 CIVEN, Via delle Industrie 5, Venezia-Marghera, 30175 Italy 3 AITEMIN, Alenza 1, Madrid, Spain 4 Universita di Padova, Dip. di Fisica "G. Galilei", via F. Marzolo 8, Padova 35131, Italy 5 LNL-INFN, Viale dell’Universita 2, Legnaro-Padova, I-35020 Italy ABSTRACT 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 -Particle X-Ray Emission (PIXE) 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. INTRODUCTION Field studies are being carried out since 1997 at the experiment FEBEX (Full Scale Barrier Experiment) emplaced at the Grimsel Test Site (GTS) underground research laboratory 400 m depth under the Swiss Alps. The FEBEX experiment reproduced at a real scale a highlevel radioactive waste repository (HLWR). A compacted bentonite barrier was emplaced in in a granite gallery of 17 m length and 2.28 m diameter to analyze the barrier performance under repository conditions. Full details on the FEBEX experiment can be found elsewhere [1]. After 12 years of operation, the FEBEX experiment is the most realistic long-term experiment installed in the world representing a HLWR emplaced in granite, where different geochemical and physical processes induced by the groundwater (slightly reducing) may occur at the bentonite /granite interface under real conditions. In particular, the possible bentonite colloid generation is an issue because of colloids can affect the migration of radionuclides in the repository [2]. In 2005, within the FUNMIG EU project, two boreholes (FUN01 and FUN02) longer than 17 m where drilled parallel to the FEBEX gallery, close to the bentonite barrier respectively at approximately 30 and 60 cm from the bentonite surface, with the aim of analyzing geochemical gradients induced by the bentonite and bentoni
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