Long-term Performance of Engineered Barrier Systems, PEBS
Country / Region: Europe
Begin of project: March 1, 2010
End of project: February 28, 2014
Status of project: February 28, 2014
In connection with investigations into the suitability of host rocks for the final disposal of heat-generating waste, the BGR maintains a close network with comparable organisations in neighbouring European countries. This has led to a broad scientific exchange in recent years, which has also resulted in joint bilateral and multilateral research projects.
EU projects in which the BGR was involved were included in the 7th Framework Programme of EURATOM. With the ‘Long-term Performance of Engineered Barrier Systems (PEBS)’ project, the BGR took over the coordination of such an EU project for the first time.
The aim of this project was to produce improved short-, medium- and long-term prognoses on the behaviour of geotechnical barriers in a repository for heat-generating waste. To this end, laboratory experiments and underground investigations on a scale of 1:2 were observed over 3 to 10 years, the results were compared with calculations based on existing models and the calculation models were optimised. The project was started in spring 2010. Results were presented after four years. The 17 partners came from seven nations. A special feature since the establishment of the EURATOM programme was the first participation of a Chinese organisation as an equal consortium partner.
The laboratory experiments included infiltration tests in which a special clay material, in this case bentonite, is filled into cells and subjected to thermal and hydraulic loads. The swelling behaviour of bentonite was determined. Of interest was whether the saturation is influenced by the hydraulic gradient, by thermo-osmosis effects or by microstructural changes in the material. The two main underground experiments were carried out in the Mont Terri laboratory in Switzerland. In the first experiment, a heater simulating a 1:2 model of a waste container with a surface temperature of up to 140° C was placed in a horizontal borehole and backfilled with bentonite. Various measurements, e.g. of moisture or temperature, were carried out in the backfilled cavity and in the near field of the host rock using more than 200 sensors and a small ultrasonic measuring system. In the second test, the condition of the bentonite backfill material after a hydration phase of approx. 10 years was investigated and the development over time and the condition of the host rock after opening and removal of the backfill material was characterised. Among other things, ultrasonic methods were used to determine how the host rock, pressurised by the originally swelling bentonite, behaves during unloading.
Project results
The research leading to these results has received funding from the European Atomic Energy Community's Seventh Framework Programme (FP7/2007-2011) under grant agreement n° 249681.
The project was rounded off with knowledge transfer measures. For example, the relevant European, Japanese and Chinese ministries and authorities were invited to an event to find out about the current state of science and technology in the field of engineered barriers. At a further event, the BGR reported in detail on the production, processes and various quality characteristics of bentonite as well as on its behaviour under repository-relevant stresses.
Project contributions:
