State of the bentonite barrier and THM effects observed after five years of operation

The work presented here has been performed in the framework of FEBEX, which is a research project for the study of the near field of a high level radioactive waste (HLW) repository. A part of this project is a large-scale in-situ experiment performed at the Grimsel Test Site (GTS, Switzerland) that reproduces a gallery for HLW disposal according to the Spanish concept, with two heaters simulating the containers and a bentonite barrier around them. The system was thoroughly instrumented to follow its evolution, particularly with respect to humidity and temperature changes. After five years of operation, heater 1 was switched off in February 2002. Following cooling of the system during four months, the bentonite barrier was dismantled and the heater extracted. During dismantling many bentonite samples in the form of cores or of complete blocks were taken. Several determinations have been carried out in these samples with the aim of: characterize the actual state of the bentonite and determine the possible changes in its thermo-hydro-mechanical (THM) and geochemical properties that occurred during the experiment, due to the combined effect of temperature, water content, joints and solutes. The results of the characterisation performed concerning physical and THM properties are reported and analysed in this paper. (authors)