FEBEX till mind

The FEBEX experiment at the Grimsel Test Site

Recently the Full-scale Engineered Barrier Experiment (FEBEX), which is intended among other things to provide greater knowledge of different processes in clay buffers, was dismantled. The purpose with the FEBEX was to increase the knowledge about the near-field of a repository for high-level radioactive waste.

The Swiss hard-rock laboratory is located at the Grimsel Test Site about 2,000 kilometres south of Forsmark at an altitude of just over 1,700 metres above sea level. Here, as at SKB’s underground laboratory at Äspö north of Oskarshamn, research on the final disposal of spent nuclear fuel is taking place. The Grimsel Test Site is operated by Nagra, the Swiss counterpart to SKB.

In 1997 two steel canisters with electric heaters were installed horizontally in the rock. The canisters were surrounded by a perforated steel cage encased in bentonite clay and the gallery was sealed with a concrete plug. A grand total of 632 sensors were installed to make it possible to make direct measurements of the clay, the rock and the heaters during the course of the experiment. These included temperature, humidity, total pressure, movements and portal pressure. The heaters in the canisters maintained a temperature of about 100 degrees Celsius to simulate the heat that will be generated by the canisters with spent fuel in the final repository.

Focus on microbial processes in clay

Buffer materials from the FEBEX in situ test will be used in WP2 in order to study if there are viable microbes after almost two decades in the clay and also to develop methods to extract DNA from clay particles. Of particular interest are microorganisms that can accelerate canister corrosion in the near-field either by hydrogen scavenging or by sulphide and/or acetate production. We also hope to get a better understanding of if there are microbes that accelerate degradation of bentonite based buffers and influence the long-term behaviour of plug systems and seals.

 

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For further information about the FEBEX experimetn please visit:

http://www.skb.com/news/skb-learns-about-clay-in-switzerland/