Please activate JavaScript!
Please install Adobe Flash Player, click here for download


WWW.HZDR.DE 20 21 TITLE // THE HZDR RESEARCH MAGAZINE Scheinost explains. "Will they be captured by microorganisms, thus becoming mobile? How do the radioactive compounds interact with the host rock and with technical barriers? What happens when the steel barrels rust?" Such questions are decisive for the long-term safety of a repository site, which is expected to be capable of storing waste from nuclear power plants for one million years. X-rayed for atomic precision In order to answer these questions, researchers have to decode the chemistry of radioactive elements and their compounds. ROBL provides a valuable tool for this task: X-ray absorption spectroscopy. During the experiments, the samples are exposed to the intense light produced by the synchrotron. Scientists measure to what extent the X-rays interact with the atoms in the sample. "We can derive very important information from the energy-dependent absorption spectra," Scheinost explains. "For example, what is the predominant oxidation state of the atoms, where exactly are they located on surfaces of minerals, for instance, and which type of bonding they form." These properties determine the mobility of the radioactive compounds – if they will be retained in the repository or released into the ground water that may occur in the host rock. "These are questions of detail," Scheinost summarizes. "But often with significant effects." And anyone who takes a closer look will discover new relationships. Experiments at ROBL have thus already disproved assumptions made by experts, as the French facility offers another big advantage. "Unlike in most experiments, we can simulate environmentally relevant conditions very well. One example is the exclusion of oxygen from the air, which will of course be the case in a repository." The smallest details yield new discoveries Scheinost and several international colleagues were able to demonstrate that, under conditions prevailing in a repository, the radioactive and highly toxic heavy metal selenium-79 – a fission product found in burnt-up nuclear fuel – is less mobile than previously thought. "By conducting experiments on samples in the absence of oxygen, we were able to ascertain that selenium-79 remains bound to steel containers, even if they have rusted through due to the possible contact with water," Andreas Scheinost explains. "The minerals that encase the future repository will offer further protection. They will ensure that radionuclides do not pose an increased risk to the safety of a repository." Scheinost and his colleagues achieved a similar result in experiments with the radioactive element plutonium. Actually, researchers had expected that reactions occurring in the absence of oxygen reveal increased mobility of the heavy metal. As measurements taken at the Rossendorf Beamline have shown, the plutonium will remain firmly sorbed at the DEEP INSIGHTS: Andreas Scheinost exposes radioactive samples to intense X-rays at the European Synchrotron Radiation Facility ESRF in Grenoble. Photo: AVANGA