The role of colloids on radionuclide transport in a crystalline medium, still presents large uncertainties despite it has been largely analysed in the past. The scarceness of experimental data obtained under realistic conditions and the difficulties related to the interpretation and modelling of experimental data are amongst the main reasons of the existence of these uncertainties.
The objective of this study is to analyse the possible formation and migration of bentonite colloids from the engineered barrier of a deep geological repository of radioactive waste under in-situ conditions. The study was carried out at the FEBEX gallery at the NAGRA’s Grimsel Test Site (GTS, Switzerland).
In this gallery the FEBEX experiment, which reproduced at a real scale a high-level waste repository in granite was installed in 1996. This offered a unique opportunity of studying the chemical effects produced by the bentonite on the surrounding groundwater, including the formation and release of colloidal particles.
The experimental work described here lasted from the year 2006 (in the frame of the EC-FUNMIG Project) to 2014 (in the frame of the EC-BELBAR Project) and consisted in the analyses of waters, from different intervals of different boreholes at different distances from the bentonite surfaces, to verify the existence of colloidal particles and to identify their nature. Many boreholes already existed, since the construction of the FEBEX experiments and others were specially drilled to the purposes of this study (FUN-1 and FUN-2 boreholes) and all were used for water sampling