Underground laboratories are set up in rock formations that are fundamentally suitable for the final disposal of radioactive waste. They are important for investigating the complex behaviour of repository systems under controlled and at the same time natural boundary conditions. One example of this is the Mont Terri Rock Laboratory, which has been in operation since 1996 under the management of the Swiss Federal Office of Topography (swisstopo). It is located in the canton of Jura, near the small town of Saint-Ursanne. Around 1200 metres of tunnels and niches were excavated for the rock laboratory to provide a research platform for various experiments in the Opalinus Clay.

The key question is: can radioactive waste be safely stored in Opalinus Clay? The Mont Terri rock laboratory is all about research. It offers ideal conditions for various types of experiments. These are focussed on three main areas: (i) One group of experiments involves the development of new investigation and measurement methods tailored to the Opalinus Clay. (ii) The Opalinus Clay is investigated in detail as a host rock for the deep geological disposal of radioactive waste. (iii) Demonstration experiments show the feasibility of future deep geological disposal of radioactive waste and the thermal-hydraulic-mechanical behaviour of the Opalinus Clay.

In addition to final disposal, experiments on other geoscientific topics, such as geological CO2 storage, are part of an international research project. The Mont Terri project consists of 22 members from nine nations and is coordinated by swisstopo. The partners are responsible for financing and carrying out the scientific experiments in the rock laboratory. The Helmholtz Association, represented by GFZ, UFZ, KIT, FZ Jülich and HZDR, has been a member of the project since 1 July 2018. In addition to geophysical exploration, the Helmholtz Association centres are involved in various experiments on the hydrogeology, microbiology and geochemistry of a repository complex.