Efficiency of a borehole seal by means of pre-compacted bentonite blocks

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Abstract

The backfilling and sealing of shafts and galleries is an essential part of the design of underground repositories for high-level radioactive waste. Part of the EC funded project RESEAL studied the feasibility of sealing off a borehole in plastic Boom Clay by means of pre-compacted bentonite blocks. Two bentonites, FoCa and Serrata, have been used. Based on laboratory tests, the bentonite blocks had an initial dry density of about 1.8 g/cm3 to obtain a swelling pressure of about 4.4 MPa, corresponding to the in situ lithostatic stress, at full saturation. The set-up was equipped with several sensors to follow-up the behaviour of the seal and the surrounding host rock during hydration. Full saturation was reached after five months and was mainly reached by natural hydration. Swelling pressure was lower than originally foreseen due to the slow reconsolidation of the host rock. Later on, the efficiency of the seal with respect to water, gas and radionuclide migration was tested. The in situ measured permeability of the seals was about 5•10_13 m/s. A gas breakthrough experiment did not show any preferential gas migration through the seal. No evidences of a preferential pathway could be detected from 125I tracer test results.

Details

Original languageEnglish
Pages (from-to)123-134
JournalPhysics and Chemistry of the Earth
Volume32
Issue number1-7
DOIs
Publication statusPublished - Oct 2006
EventClays in Natural & Engineered Barriers for Radioactive Waste Confinement - ANDRA, Tours, France
Duration: 14 Mar 200518 Mar 2005

Keywords

  • seal, bentonite, migration, diffusion, radwaste

ID: 80581