In 1995, SCK•CEN and NIRAS/ONDRAF founded the Economic Interest Grouping (EIG) PRACLAY. December 18, 2000 the name of the EIG PRACLAY changed to EIG EURIDICE. The EIG EURIDICE is in charge of the management of the integrated underground research facility (URF) HADES. A User’s Club for the promotion of the URF is in the expansion stage.

Nevertheless, the principal objective of this grouping is to demonstrate the feasibility of the Belgian reference-concept for the deep disposal of heat-emitting high-level vitrified radioactive waste in a geological clay formation, the so-called PRACLAY-project.

In the paper we consider the following items. First an introduction of EURIDICE is given, followed by a brief historic overview of the construction phases of the URF HADES in Mol. This historic overview shows the evolution of the understanding of the hydro-mechanical behaviour of the host-rock. After a brief review of the Belgian reference concept for High Level radioactive Waste (HLW), the objectives and planning of the PRACLAY-project will be discussed. A section also is dedicated to the OPHELIE mock-up, which is a surface simulation of the in situ experiment, and the construction of the connecting gallery, which will be conducted using an industrial technique. As it will be the first time that an industrial technique will be used for the construcionconstruction of a gallery in Boom Clay at a depth of approximately 230 m, the achievement of the gallery is an important milestone in the demonstration programme.

The PRACLAY experiment, which is the most significant part of the demonstration project, is discussed at the end of the paper. It consists of the construction and installation of a pilot gallery (PRACLAY gallery) geometrically identical — except in length — to a disposal gallery, as defined in the reference concept. Due to some recently discovered open questions relative to the actual reference concept, NIRAS-ONDRAF decided to review the reference concept for vitrified HLW. To the extent possible, the PRACLAY experiment must be an in situ verification and confirmation of the present status of scientific and conceptual knowledge. Consequently, the realisation of the PRACLAY-experiment has been delayed.

It is clear that the EIG EURIDICE plays a key role in the iterative process of developing concepts for radioactive waste disposal. Indeed, the preparation of the PRACLAY-experiment gave rise to open questions regarding the Belgian reference-concept, leading to its review. This approach is very important to bring sufficient flexibility into the process of concept development, allowing consideration of new understandings and technical information. This is essential to preserve credibility and confidence in the concept.

The construction of the connecting gallery will provide important information concerning the feasibility of the use of industrial excavation techniques and our understanding of the hydro-mechanical response of the rock during and after its construction.

The PRACLAY experiment aims at demonstrating the feasibility of the Belgian reference concept for the deep disposal of heat-emitting high-level vitrified radioactive waste. It will also allow enhancement of the quality of our assessment capability, and our understanding of safety-relevant phenomena, by better characterising and reducing uncertainties. The computational tools will be verified by comparison of in situ measurements with theoretical model predictions.

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