In autumn 2017, a slightly radioactive ruthenium-106 cloud covered the sky over parts of Europe and Asia , with this element even being detected at measuring stations in the Caribbean. Although it was a release of radiation harmless to human health, the values were up to one hundred times higher than the total concentrations measured in Europe after the Fukushima accident. In addition, as no government has so far assumed responsibility for said escape, the radiological protection entities do not rule out that it had a military origin.
However, a study that has just been published in the journal Nature Communications concludes that the cloud would have formed as a result of civil nuclear activities, specifically in a nuclear fuel reprocessing plant.
Ruthenium in air filters
The researchers, from the Institute for Radioecology and Radiation Protection at the University of Leibniz in Hannover and the Institute for Planetology at the University of Münster, quantified stable ruthenium isotopes captured in air filters before, during and after nuclear release. The results revealed that the ruthenium collected during the 2017 period in which the cloud was detected had an unnatural isotopic composition.
The researchers compared their data with the ruthenium isotopic compositions of spent nuclear fuels, showing that the release corresponds to the isotopic fingerprint of the fuel, at the end of its useful life, of a type of pressurized water nuclear reactors used in Russia. Therefore, this radioactive cloud is not related to the production of plutonium for nuclear weapons. “The isotope signature discovered in the air filter does not bear similarities to nuclear fuels from conventional western pressurized or boiled water reactors. Instead, it is consistent with the isotope signature from a specific type of pressurized water reactors. Russians: the VVER series. Around the world, approximately 20 VVER reactors of this type are in operation “, specifies Professor Georg Steinhauser from Leibniz University in Hannover.
Techniques used to study the history of planet Earth
“Ruthenium isotopes are usually measured to study the history of the formation of the Earth,” explained Thorsten Kleine, a researcher at the University of Münster, adding that these methods developed for research in other disciplines have been essential to solve the problem. mystery. ” The fact that ruthenium from nuclear activities was released in minute amounts and diluted with the stable ruthenium naturally present in the air was a major challenge.”
Previously, another research work published in the journal PNAS analyzed more than 1,300 measurements throughout Europe and different parts of the world, concluding that, although it is difficult to pinpoint the exact origin of the release of radioactivity, everything points to an area to the south. of the Urals, coinciding with the Majak nuclear facility.
Referencia: T. Hopp et al. (2020): Non-natural ruthenium isotope ratios of the undeclared 2017 atmospheric release consistent with civilian nuclear activities. Nature Communications; DOI: 10.1038/s41467-020-16316-3