CIEMAT Publications

Abstract

Some deep geological nuclear waste disposal concepts are considering the installation around the waste canisters of bentonite barriers made up of two components: highly compacted blocks to support the canister and a granular buffer material consisting of bentonite pellets to fill the rest of the disposal gallery. The combined use of pellets and blocks in the same section of the barrier introduces difficulties in the understanding and modelling of the system performance. With the aim of obtaining information about the hydro-mechanical evolution of initially inhomogeneous bentonite samples (pellets/blocks) upon hydration under isothermal conditions, a series of laboratory tests in decimetre-scale cells was carried out. In most tests axial stress and water intake were measured over time; in others, performed in transparent cells, it was possible to visually follow the bentonite macroscopic changes upon hydration. Finally, in one of the tests, relative humidity and radial pressure were measured. Except for the latter, which was performed with MX-80 bentonite, all the other tests used the Spanish FEBEX bentonite. Upon dismantling the final physical state and microstructure of the samples were analysed.