HADES - Underground laboratory

The underground laboratory HADES is the most important research infrastructure in Belgium for experimental research on the deep geological disposal of radioactive waste. In 1980, the Belgian Nuclear Research Centre, SCK•CEN, started the construction of the underground laboratory. HADES is situated in Boom clay at a depth of 224 meters and was extended in different phases: recently, the construction of a second access shaft (1997-1999) and the building of the connexion gallery (2001-2002) were completed.

The Belgian Nuclear Research Centre and HADES

Soon after its foundation, SCK•CEN played a prominent role in the research on safe management and treatment of radioactive waste in Belgium. Since the beginning of the '70, several experts have been recognising that the storage of medium- and high-level radioactive waste caused a problem that could mortgage the future of nuclear energy. Furthermore, there was a growing broad international consensus on the fact that deep disposal is a safe and durable solution for the long-term management of radioactive waste. From this moment on, research was concentrated on the deep (geological) disposal of highly active and long-lived waste.

In 1974, SCK•CEN initiated the Belgian research programme regarding the geological disposal of radioactive waste. In the initial phase, SCK•CEN made an inventory of the possible host formations for deep disposal of radioactive waste, in close collaboration with the Geological Survey of Belgium.

Furthermore, exploratory analyses on rock samples and test drillings were carried out. From the end of the '70, research was concentrated on deep disposal in clay formations. This led to the construction of the underground laboratory HADES on the premises of SCK•CEN. The major phases in the development of HADES comprised, among other things, the construction of the first access shaft (1980-1982), the building of the Underground Research Laboratory (URL) (1982-1983) and the experimental shaft (1983-1984), the extension of the lab with the Test drift (1987), the construction of the second access shaft (1997-1999) and the realisation of the connexion gallery (2001-2002).

The building of the underground laboratory demonstrated that it is technically feasible to dig out shafts and galleries in a plastic clay layer. Moreover, the excavation techniques have continuously been improved during the successive phases and methods have been developed to minimise the disruption of the clay formation. Since 1997, the underground laboratory HADES is managed by EIG EURIDICE, the Economic Interest Group between SCK•CEN and the Belgian Agency for Radioactive Waste and Enriched Fissile Materials, ONDRAF/NIRAS.

The Boom clay formation

The underground laboratory HADES is situated in a Boom clay formation at a depth of about 224 meters. Within the Belgian research programme, the Boom clay is studied as a reference formation for the geological disposal of radioactive waste. However, the site where the future disposal facility will be built has not been chosen yet.

The Boom clay is found on the site in Mol at a depth between 161 and 264 meters. It reaches a total thickness of more than 100 meters. Safety assessments confirm that the Boom clay possesses good qualities, also thanks to its low hydraulic conductivity and good sorption properties regarding radioelements. Therefore, it is a potentially interesting host rock for the disposal of radioactive waste.

HADES and the Belgian research programme in the field of geological disposal

During the past decades, several aspects that could influence the long-term safety of geological disposal have been examined. Next to the extensive research on the properties of Boom clay, numerous on-site experiments were carried out in HADES.
This experimental work has led to a better insight into the processes that determine the long-term behaviour of radioactive waste in real disposal conditions. Research is especially concentrated on the direct disposal of used fuel coming from nuclear power plants and the disposal of vitrified highly active waste that is produced after the retreatment of used fuel.

Furthermore, an important part of the on-site research addresses the study of the barriers placed around the waste to isolate it from the Boom clay. The multiple barriers around the radioactive waste play an important role in the field of the long-term safety of disposal. These barriers comprise among other things the metal containers in which the waste is situated, the filling materials (based on clay or cement) and the overpack or gallery wall. The knowledge acquired in this field is used to optimise and, if necessary, to adapt the multibarrier system.

For more than twenty years, the Belgian Nuclear Research Centre has been carrying out research in HADES on the migration of radioisotopes. Migration data coming from experiments in HADES are incorporated in geochemical and/or transport models and in safety calculations. The latter allow predicting the long-term evolution of the disposal system. Results of this research indicate that geological disposal in a clay formation that has been stable for millions of years and, what's more, possesses good sorption properties, can be considered as a safe and durable solution.

In a next phase of the Belgian research programme, the possibility of geological disposal will be demonstrated on true operation scale. Thereto, a demonstration test (PRACLAY) is planned, in which the behaviour of the disposal system is examined on true scale and at temperatures that are equal to those applied for the disposal of vitrified highly active waste.

HADES in an international context

HADES still is the reference laboratory for research on geological disposal of radioactive waste in clay formations. The expertise developed by SCK•CEN concerning geological disposal in clay is recognised all over the world. Consequently, SCK•CEN plays an international, scientific role in assignments that exceed its dimension.

SCK•CEN participates in numerous international research programmes that are financed by the European Commission within the 6th Framework Programme EURATOM. Within this Framework Programme, SCK•CEN is in charge of an integrated project (NF-PRO), in which all processes able to influence the immediate environment of the disposal system are integrated. This integrated project has a total budget of 17 million euros and consists of a consortium of 40 organisations.

The underground laboratory HADES is internationally recognised as a centre of expertise for disposal in clay, within the framework of the 'Network of Centres of Excellence for the Demonstration of and the Training in Radioactive Waste Disposal Technologies in Underground Research Facilities'. This network, in which SCK•CEN plays a central role, is supported by the International Atomic Energy Agency (IAEA) in Vienna.

Furthermore, in order to maintain the internationally recognised lead of SCK•CEN regarding research on geological disposal in clay and to put it at the disposal of the international community, the Belgian Nuclear Research Centre strives for a durable integration of its research activities in a broader context. To this end, SCK•CEN develops for example structural collaboration forms on large research infrastructures like HADES with other countries that consider disposal in clay.

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