Swiss repository experiment enters monitoring phase

The underground tunnel in which the Full-scale Emplacement Experiment will be carried out at the Mont Terri Rock Laboratory in Switzerland has been sealed and monitoring has begun. The experiment aims to simulate the conditions within a repository containing high-level radioactive waste.

The underground tunnel in which the Full-scale Emplacement Experiment (FE Experiment) will be carried out at the Mont Terri Rock Laboratory in Switzerland has been sealed and monitoring has begun. The experiment aims to simulate the conditions within a repository containing high-level radioactive waste.

The test tunnel has been sealed with a concrete plug (Image: Nagra)

The aim is to determine how temperatures, humidity, pressure, deformation, gas composition, permeability, etc., will evolve in the granular bentonite mixture and the surrounding rock in the coming years. The results, it said, will provide important input for future repository planning.

For the experiment, a 50-metre long tunnel with a diameter of some 3 metres has been excavated in the Mont Terri Rock Laboratory. Hundreds of sensors have been installed within the test tunnel to detect the smallest changes in the tunnel environment and the surrounding rock. Three dummy containers - each 4.6 metres long and about 1 metre in diameter and containing a heater element - have been emplaced in the tunnel. The voids in the tunnel after emplacement of the containers have been backfilled with bentonite granulate.

Actual radioactive waste could not be used in the experiment, so the heating elements are being used to simulate the heat production of high-level waste.

Switzerland's national radioactive waste disposal cooperative Nagra announced yesterday that the heating elements had been switched on and the tunnel has now been sealed using a concrete plug. The first measurements have now been analysed, it said.

Nagra will monitor the tunnel over at least the next ten years.

The scale of the experiment and the operating procedures being used are similar to those in a future high-level waste repository, Nagra said. The experiment has also given it practical experience with the waste emplacement technologies to be used in future repositories.

Nagra's FE Experiment project manager Herwig Müller said, "Experiments like this are very important as they allow computer simulations to be compared with real data; the results obtained are then used at a later stage to make calculations for the geological repository."

The FE Experiment is an international partner project and is supported financially by the European Union. The total cost of the project - started in 2011 - is expected to be greater than CHF3 million ($3 million).

Nagra has been carrying out a research program in the Mont Terri Rock Laboratory since 1996. The laboratory is an international research platform operated by the Swiss Federal Office of Topography.

Up until 2006, much of Switzerland's used nuclear fuel was sent overseas for reprocessing. High level waste, and used fuel from 2006 onwards, is mostly stored at a central interim storage at Wurenlingen.

Six Swiss sites were proposed in November 2011 to host deep geological repositories during the first stage of the selection process. In January, Nagra selected two regions - Zürich Nordost and Jura Ost - for further investigation.

Researched and written
by World Nuclear News