EIG EURIDICE contributes to the research on the safety and feasibility of geological disposal and has recorded some tangible achievements over the years.
The extension of HADES from the late 1990s as part of the PRACLAY project has demonstrated that it is technically feasible to construct a waste repository on an industrial scale in poorly indurated clay, as found in the Boom Clay formation. The 80-metre gallery connecting the second shaft with the old section of the laboratory was built using industrial tunnelling techniques, with due attention to speed of execution and cost. A side gallery, i.e. the PRACLAY gallery, was successfully added at right angles to the main gallery. Based on this, we can conclude that it is possible to construct a disposal system with access shafts and main galleries, with disposal galleries lying perpendicular to these main galleries.
Once a repository has been built, it is important to be able to seal off the disposal system, possibly after a transitional period during which it is still accessible. After closure of the repository, the shafts should not provide a pathway for radioactive substances to escape from the clay host rock. The RESEAL experiment demonstrated that bentonite clay forms a tight, impermeable seal at the interface with the Boom Clay and has the same favourable properties as the latter.
Excavation using an industrial tunnelling machine represents significant progress in terms of the safety of a disposal system in clay, because there is much less damage to the clay than with manual excavation. A detailed study of this damage as part of the SELFRAC and CLIPEX projects demonstrated that the fissures caused by excavation extend only over a short distance. The SELFRAC project also found that these fissures close by themselves due to the plastic behaviour of clay, as a result of which it retains its low permeability to water. This is known as "self-sealing".
The heat released by radioactive waste placed in a repository causes thermal disturbance in the surrounding clay and affects its properties and behaviour. The ATLAS experiments have made it possible to determine the clay’s thermal conductivity and to study and model its coupled thermo-hydro-mechanical behaviour. The large-scale PRACLAY experiment is designed to confirm and refine this knowledge and involves heating the PRACLAY gallery for 10 years at a constant temperature of 80°C, measured at the point of contact with the clay.
EURIDICE has more than 30 years’ experience using various measuring instruments and observation methods in the underground research laboratory, and in the Boom Clay formation in particular. These measurements and observations have been part of an extensive set of experiments, some of which have been monitored for the past 25 years and more and are conducted on a scale that is representative of a real disposal facility. The know-how acquired regarding the use of these instruments and methods will ultimately help ONDRAF/NIRAS to develop a monitoring programme for a working radioactive waste repository.