(GRS 208) Geoelectric Investigation of Bentonite Barrier Saturation

Tilmann Rothfuchs, Rüdiger Miehe et al.

Within the framework of the Swedish nuclear programme, SKB has constructed a fullscale replica of the deep repository planned for the disposal of spent nuclear fuel. This Prototype Repository has been constructed at the Äspö Hard Rock Laboratory at a
depth of 450 m below ground. The Prototype includes six deposition holes in which fullsize canisters with electrical heaters have been placed and surrounded by a bentonite buffer. The deposition tunnel has been backfilled with a mixture of bentonite and
crushed granitic rock. Water uptake of the bentonite buffer in the deposition holes and of the bentonite/crushed rock backfill in the disposal gallery is one of the central issues to be investigated in the frame of the Prototype Repository Project performed at the Äspö URL. GRS uses the geoelectric method to monitor changes in water content, as the electric resistivity of the materials is etermined by the solution content. Several electrode arrays in the buffer, the backfill, and the rock serve for determining the
resistivity distributions in cross sections of the different materials. From the resistivity the solution content can be derived using the results of calibration measurements on samples at defined conditions.