2014/11/14 by Till Popp, Christopher Rölke, Klaus Salzer
paper · doi:10.1144/sp415.1
Abstract Deep underground repositories for radioactive waste generally rely on a multibarrier system to isolate the waste from the biosphere. It consists of the natural geological barrier provided by the repository host rock and its surroundings, the waste container and an engineered barrier system (EBS): that is, the backfilling and sealing of shafts and galleries to block any preferential path for radioactive contaminants. Bentonite emplaced in compacted block form is the preferred option for the clay buffer for most waste management organizations. In assessing the performance of bentonite block masonries, conductive discrete interfaces inside the sealing elements (i.e. contacts between blocks) and to the host rock may act not only as mechanical weakness planes but also as preferential fluid pathways. We performed hydraulic tests on prefabricated bentonite–sand block assemblies (60:40). The results document that despite existing interfaces, the investigated bentonite block assembly behaves no different to that of the homogenous matrix during the saturation of the buffer. This has been confirmed by gas-injection tests on the former interface, as well by shear tests. The outstanding observation is that our results convincingly demonstrate that interfaces between bentonite bricks may ‘heal’ (not only seal), as was physically verified by confirmation of cohesion after presaturation.