Safe disposal of high-level waste in deep clay layers
High-level and/or long-lived waste originates mainly from nuclear power plant fuel and demolition material from nuclear installations. Until a final destination can be found, the waste is stored safely on the premises of Belgoprocess, a subsidiary of ONDRAF/NIRAS, the National institute for radioactive waste and enriched fissile materials.
SCK•CEN started investigating the possibility of safely storing high-level and/or long-lived waste deep underground as early as the 1970's. Other European countries were also considering deep burial as a possible long-term solution at the time. Several countries have now opted to go down this route.
Underground laboratory: HADES
In 1980, SCK•CEN started the construction of a laboratory in a deep clay layer at 225 meter below the site of the Research Centre in Mol. Belgium was one of the first countries in the world with an underground laboratory in soft clay. It was named HADES, after the God of the underworld in Greek mythology. Many of the experiments conducted subsequently in HADES were given names derived from Greek mythology.
Nowadays the HADES laboratory is managed by ESV EURIDICE, an economic partnership between SCK•CEN and ONDRAF/NIRAS. The clay layer which houses HADES is called the ‘Boom clay layer'. The name refers to the municipality of Boom where this clay layer reaches the surface and is mined for the production of bricks.
HADES enables us to conduct unique experiments in the clay layer deep underground, where SCK•CEN scientists investigate the chemical and microbiological properties of clay, how slow radioactive elements disperse in it and the speed at which potential waste packaging materials degrade. Combined with surface laboratory analyses we managed to chart the properties and behaviour of the clay.
Pictures of HADES
The excavation of HADES resulted in a continual improvement in excavation techniques. Since 1995 the operations have been carried out using an actual tunnelling machine, which enabled us to demonstrate that it is possible to create underground galleries by industrial means.
These more recent excavation techniques disturb the clay far less meaning that radioactive substances are better contained in a disposal installation.
Natural and artificial barriers
Our current disposal concept has been developed on the basis of more than 30 years' research. The stainless steel walled vessels currently containing the waste will, in turn, be packed into a specially designed storage container, consisting of a number of artificial barriers designed to protect personnel from radioactivity. They also guarantee that the waste remains completely encapsulated for the first few millennia.
After this initial phase, when the level of radioactivity should already have reduced considerably, the surrounding clay will act as the main, natural barrier. The clay ensures that the radioactive substances remain isolated from man and the environment for thousands of years. Clay allows very little water to permeate through it and clay particles bind with radioactive substances so that they can only move very slowly. Finally, because of its plastic properties, any small tears or cracks in the clay created during excavation will close up again naturally. Once stored, the waste will be totally isolated from the layers above and below.
Safe and technically feasible
With more than 30 years' experience, we can safely say that the disposal of high-level and/or long-lived radioactive waste in a deep clay layer is technically feasible and safe. We produced various computer models and simulations on the basis of the research results. They demonstrate that the small quantities of radioactivity released at very dilute concentrations from the clay layer after thousands of years will no longer be hazardous to man and the environment.