(GRS 430) Hydraulic Interaction of Engineered and Natural Barriers – Task 8b-8d and 8f of SKB

K.-P. Kröhn

The Task Force on Groundwater Flow and Transport of Solutes (TF GWFTS) and the Task Force on Engineered Barrier Systems (TF EBS) both established by the Svensk Kärnbränslehantering AB (SKB) have defined the so-called Task 8 to investigate the hydraulic interaction of the granitic host rock at the Hard Rock Laboratory at Äspö and the bentonite clay buffer in a deep geological repository. Task 8 a-d ran parallel to the related BRIE-project (Bentonite Rock Interaction Experiment) at the Äspö Hard Rock Laboratory (HRL). The BRIE-project was concerned with an in-situ test where two boreholes were drilled from a tunnel floor and filled with compacted bentonite.

Task 8 encompassed obviously characterizing the groundwater flow field as well as simulating bentonite re-saturation. Described here is an approach to solve the problem by decoupling both aspects. Groundwater flow was simplified to a steady-state single-phase flow model including discretely described large fractures. Modelling was performed with the code d3f. Outflow data from the rock was then assigned to the inflow boundary of the alternative re-saturation model realized in the experimental code VIPER.

With increasing knowledge about the site the upcoming data and the accompanying flow modelling indicated an inherent problem with predictions for the site and borehole characterization. Specific (deterministic) answers were sought from a flow domain that contains a relevant water-bearing fracture network which is only known in terms of geostatistics. While the overall flow regime could be represented in the final model the results were therefore not detailed below the scale of the boreholes.