Abstract

Transport of rock salt brine through a vertical multilayer hydraulic sealing system (HTV-1) was examined during the saturation process. The HTV-1 was a semi-technical-scale experiment that simulated a shaft sealing. Multilayer drift and shaft sealings are part of the multibarrier system in geologic repositories for hazardous or radioactive waste. In contrast to the usual sealing constructions, the examined system combines sealing bentonite layers (DS) with equipotential layers (ES) of higher hydraulic conductivity that are expected to prevent inhomogeneous liquid transport in barriers independent of the surrounding host rock and formation water. Rock salt brine (density 1.15 g/mL = 4 mol/L) was chosen to simulate natural brines. It was forced through the column with a solution pressure up to 9.3 MPa. No artificial saturation was applied in advance of brine inflow. The experiment was terminated after 1 yr after the brine passed two DS and two ES and reached the upper DS. A detailed snapshot analysis of water and salt distribution and layer geometry was obtained. The salt/water ratio of the initial brine was 0.26 and was evenly detected within the wet ES as well as the wet DS. Thus, the results revealed the functionality of the sandwich-like sealing system. Natural Ca- and Mg-rich bentonite was partially transformed into its Na-saturated form depending on exposure time to the brine, but high salt concentration did not prevent swelling. Swelling of the lower bentonite layers caused compaction of the upper bentonite layers, as it was confined from the bottom and by jacket friction.

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