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Host rock

In the long term, safety has to be ensured through the use of multiple technical (artificial) and natural barriers. The host rock itself constitutes a natural barrier that will encapsulate radioactive substances below the ground. Opalinus is a clay with good retention qualities and for this reason it has been selected as the only host rock suitable for high-level waste. Opalinus clay, "Brauner Dogger", Helvetic marl, and Effingen Member are host rocks suitable for disposal of low and intermediate level waste (L+ILW).
Properties of the host rock
Properties of the host rock ENSI evaluates the siting areas in particular on the basis of the criteria group "properties of the host rock".
Because of their high clay content, Opalinus, "Brauner Dogger", Effingen Member and Helvetic marl are in principle suitable types of host rock for an L+ILW repository. This high content of clay leads to rock good self-sealing characteristics, which protect against fissures, and offer a large surface area to bind up radioactive substances; the vicinity of such a deep geological repository would be almost impermeable by water. With the exception of Helvetic marl, all the host rock formations are located in potential sites in northern Switzerland. In the Alps, large accumulations of Helvetic marl occur in only a few places; the only site with the necessary area for a L+ILW repository is found at Wellenberg.

Opalinus is a clay formation that was formed from marine material deposited approximately 175 million years ago. Its distinctive features are the high clay content and its homogeneity. The opalinus clay layer is more than 100 meters deep, and above and below it there are sediment layers rich in clay and marl with good retention qualities for radioactive substances justifying the selection of this rock as the host a high-level waste (HLW) repository.

Related documents

Fact sheet: Opalinus clay project
Fact sheet: Opalinus clay
Contact: Seraina Branschi
Last update: 30.11.2011

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