Dismantling of the EB experiment: Experimental research on the retrieved GBM and bentonite blocks

Abstract

The Engineered Barrier Emplacement Experiment in Opalinus Clay (EB experiment) was a full-scale test for the demonstration of a new concept of high-level waste (HLW) repositories in horizontal drifts in the Opalinus Clay formation. After 10.5 years of hydration, the EB experiment was dismantled in autumn 2012. Samples obtained from the granular bentonite material (GBM), and bentonite blocks were sent to a laboratory for further analysis. The bentonite samples analyzed at the Laboratory of Mechanic of Lille (LML) were obtained from the CMT1, CMT2, CMT3 and RW sections. Their physical states were determined, as were their effective gas permeability and swelling capacity at different relative humidity (RH) levels. The results indicate that the water contents of the GBM determined in the laboratory ranged between 25.63% and 44.88% and that the dry densities ranged between 1.13 and 1.44g/cm3. The blocks had water contents similar to (or slightly higher than) those of the GBM, and their dry densities had decreased from an initial value of 1.69g/cm3 to values close to 1.30g/cm3, which were similar to the average values found in the GBM. The effective gas permeabilities of the GBM samples were within the range of 1.50×10−22m2 and 1.03×10−17m2, whereas, the corresponding values of the samples obtained from the blocks were between 2.20×10−21m2 and 5.12×10−21m2. The permeability values are primarily related to the dry densities and water contents of the samples. Contact with the Opalinus clay (OPA) does not appear to affect the saturation of the GBM, which is not the case for the samples near the concrete plug. The water retention characters of the GBM and blocks were extremely close, which indicates the homogeneity of the materials and a good control in their preparation.