For the past few decades, scientists in many countries have been researching whether the concept of disposing of high-level and/or long-lived radioactive waste in deep, stable strata would be a responsible option. Possible host formations would be clay, granite or salt.
Some deep clay layers in the Belgian bedrock appear to be highly suitable. Clay absorbs and holds radioactive substances for a very long time, preventing them from spreading quickly. A deep clay layer is also plastic, like modelling clay. Any cracks that form will reseal themselves. Moreover, the clay formation under investigation is already tens of millions of years old and is stable.
Belgium has two main clay formations: Boom Clay and Ypresian Clay. The name of the clay refers to the area where the layer rises to the surface.
The Boom Clay formation was deposited around 30 million years ago in a calm sea, when a large part of Belgium was below sea level. Today, it runs partly under the Campine region. Borehole drilling has shown that its composition is fairly homogeneous throughout. Geologists believe that the Boom Clay will remain stable at depth for at least a million years.
The distribution of land and sea 30 million years ago
The present-day occurrence of the Boom Clay formation in the Campine Basin