Test casules for nuclear waste repository

More secure repository with denser clay

Almost a decade ago, the Swedish Nuclear Fuel and Waste Management Company (SKB) buried test capsules 450 metres underground. The purpose was to analyse how bentonite clay affected microbes in the repository. Researchers have now started unearthing the capsules.

SKB is responsible for managing Swedish nuclear waste and spent nuclear fuel. They have employed the KBS-3 method for a long time, which entails disposing of spent fuel in copper capsules in Swedish bedrock at a depth of 500 metres. The capsules are encased in bentonite clay.

Trials 450 metres below ground

A great deal of research has been conducted to analyse and prove that the repositories will be preserved for at least 100,000 years. An experiment has been in progress for ten years involving five miniature capsules at a depth of 450 metres in the Äspö Hard Rock Laboratory. Four of the five capsules were encased in packages containing bentonite clay. Three of these have low-density clay, while the fourth has high density. One capsule was encased without clay.

"After a visual inspection, we can see that sulphate-reducing bacteria were most active in the package without clay. Iron components in this package were also extremely corroded," says Johannes Johansson from SKB, project manager for the experiment.

Compact clay slows down corrosion

Iron in the package containing high-density clay had not corroded as much. Even the copper underwent slower corrosion in the compacted clay than in the absence of clay. The results provide greater understanding of the significance of bentonite density to microbial activity and, ultimately, for safe storage. 

The microbes can be identified via DNA analysis and researchers can determine the corrosion process through chemical surface analysis and microscopy.