New method for studying underground storage of nuclear waste

The Swedish model for handling nuclear waste is based on storage in deep geological repositories. The method being developed involves encapsulating the waste in copper containers. Copper is a perfect material for the job since it barely corrodes at all in the oxygen-poor environments that exist at 500 metres below ground.

The requirements are extreme. The waste must be enclosed in the containers for at least 100,000 years, an almost incomprehensible amount of time. The Swedish Nuclear Fuel and Waste Management Company’s research shows that the corrosion is so slow that the containers actually can be expected to remain intact for the full amount of time. These results have, though, been questioned giving rise to a lively debate with political undertones.

‘Naturally this is not a question that can be settled with political arguments. Instead, scientific experiments and careful observations are necessary. This is a great challenge since the underlying processes are exceptionally unlikely. The measuring methods must be sensitive to the minimal changes in the material that can lead to significant corrosion on a time scale of 100,000 years’, says Sergei Butorin, researcher at the Department of Physics and Astronomy.

The Uppsala researchers have developed a method that makes it possible to follow the decisive processes on a molecular level. Using X-ray scattering techniques with a synchrotron radiation source it is possible to study in detail how copper reacts in different environments simulating different scenarios in the bedrock.

In an oxygen-free environment, corrosion through reactions with sulphur compounds is the most important process. The Uppsala researchers have identified which copper sulphides that are formed. One important question is how quickly the oxygen atoms that exist in water could react with the copper.

‘Such a process would have to happen in the very outer atomic layers of the metal, giving rise to copper hydroxide. We can see this directly in our spectra’, says Sergei Butorin.

‘We still haven’t seen any traces of that reaction, but the results are still preliminary. The methods are being tweaked and the research continues. With a deep understanding of the processes at atomic level we will be able to make predictions over large time scales that are certain enough to make all debate superfluous.’

The results have recently been published in Journal of Physical Cheimstry and in Journal of Analytical Atomic Spectroscopy, where the study has been published on the front page.