Experiment on safe disposal of radioactive waste

Trial run in the Mont Terri Rock Laboratory for a deep geological repository.

Following three years of intensive preparation, Nagra’s largest and most complex experiment to date is now entering a key phase. Three heater elements in dummy containers will be emplaced in a test tunnel excavated in the Mont Terri Rock Laboratory and the tunnel will then be backfilled with bentonite granulate. The scale of the experiment and the operating procedures being used are similar to those in a future high-level waste repository. In the coming years, Nagra will monitor the effects of heat on the bentonite backfill and the surrounding rock. The resulting data will provide important input for future repository planning.

Nagra (National Cooperative for the Disposal of Radioactive Waste) has been carrying out a research programme in the Mont Terri Rock Laboratory since 1996. Located close to St-Ursanne in Canton Jura, the Laboratory is an international research platform operated by the Swiss Federal Office of Topography (swisstopo).

For the «Full-Scale Emplacement» (FE) Experiment, a 50-metre long test tunnel with a diameter of around 3 metres was excavated in the Rock Laboratory. These dimensions are scaled 1:1 with a future waste emplacement tunnel in a repository. The test tunnel has been instrumented with hundreds of sensors that will detect the smallest changes in the tunnel environment and the surrounding rock. Emplacement of the three dummy containers is presently underway. Each container is 4.6 metres long and has a diameter of one metre. The void space remaining in the tunnel after emplacement of the containers will be backfilled with bentonite granulate using a specially developed auger machine.

Radioactive waste cannot be used in the experiments in the Rock Laboratory and the heater elements in the dummy containers are therefore used to simulate the heat production of high-level waste. The aim of the FE Experiment is to investigate the effects of heat-producing waste on the bentonite granulate and the surrounding rock, the Opalinus Clay. The Experiment also allows practical experience to be gained with the emplacement techniques that will be used later in a repository. «The results from the FE Experiment provide important input for the planning and design of repositories», explains Herwig Müller, Nagra’s FE Experiment project manager. The data and know-how obtained will allow scientists to check whether the predictions they make today regarding how the repository system will develop in the first decades are accurate.

According to Swiss nuclear energy legislation, the producers of radioactive waste are responsible for its safe management and disposal. In 1972, the nuclear power plant operators and the Federal Government set up the National Cooperative for the Disposal of Radioactive Waste (Nagra) to perform this task. Nagra, which has its headquarters in Wettingen (AG), is the national technical competence centre in the field of deep geological disposal of radioactive waste. Out of a strong sense of responsibility for the long-term protection of man and the environment, 100 employees are involved daily in performing this important work. The high level of competence is secured by targeted research programmes in two Swiss underground rock laboratories and intensive international collaboration.