Prix Schläfli 2018 in Geosciences: Alexandre Bagnoud
Not far from St. Ursanne, the idyllic medieval village on the Doubs, there is another, quite different visitor attraction: swisstopo's Mont Terri rock laboratory. The microbiologist Alexandre Bagnoud often visited this laboratory between 2012 and 2016, not as a layman curious about optimum conditions for storing radioactive waste, but as an active researcher.
"Yes, I spent a lot of time in the tunnels there," recalls Bagnoud. It felt a little like babysitting, because his experiment needed a lot of attention. But he enjoyed the unique atmosphere deep inside the Jura rocks, the absence of day and night and the even temperatures, whether in summer or in winter. "When you're inside, you sort of lose your awareness of time."
But what is the link between an expert in bacteria and the issue of the permanent storage of radioactive waste? Experts think on a geological time scale when it comes to reducing the radioactivity of used fuel rods, and so research on nuclear waste also focuses on correspondingly slow processes. Researchers mainly analyse the physical properties of suitable rock formations and geodynamic processes that could threaten the hermeticity of deep geological repositories. But biological processes also play an important role, because there are micro-organisms almost everywhere, even thousands of metres below the earth's surface.
He has always been interested in the diversity of these simple life forms that look so similar under a microscope. "But when you look at their metabolism, these organisms have a much wider spectrum of variation than animals or plants." At the beginning of his research career, Bagnoud quickly realised that he wanted to investigate the role of these smallest - but far from unimportant - players in ecological systems.
In the course of his research for his doctoral thesis, he did in fact discover a microbial community consisting of seven kinds of bacteria with surprising properties. These bacteria do not pose a threat to a deep geological repository — quite the opposite in fact: if the design of the repository is adapted slightly, they can be used to bind the hydrogen that inevitably builds up when the steel containers start rusting. This development of gas is a factor of uncertainty in the storage of radioactive waste. The gas pressure could become so great that even a perfectly suited rock formation can become permeable.
After he solved the countless technical problems – in many respects, he entered new territory with his experimental design and his main challenge in the initial years lay in overcoming opposition – for two years Bagnoud followed the development of "his" family of microbes, which he exposed to large quantities of hydrogen, deep inside the Opalinus Clay rock formation at Mont Terri.
Once the bacteria had used up all the available oxygen and iron, there was a noticeable change in the composition of the community and the metabolism of the various bacteria species. They began to use hydrogen as their source of energy and in this way controlled the amount of gas. As a result of his doctoral thesis, the researchers involved in the project recommended constructing a niche for the bacteria in the repositories, a fourth "biological" barrier consisting of porous material. This would allow Bagnoud's darlings to set themselves up in an environment that would be downright hostile to us, but to them is actually very hospitable.
Alexandre Bagnoud was awarded the Prix Schläfli 2018 in Geosciences by the Swiss Academy of Sciences for his article "Reconstructing a hydrogen-driven microbial metabolic network in Opalinus Clay rock", which he published during his doctoral studies at the EPF Lausanne. He is now researching at the University of Vienna.
Those who wish to learn more about the research into the permanent storage of radioactive materials can also visit the Mont Terri rock laboratory. More information is provided at: www.mont-terri.ch