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Isotope Measurements on Air Filters Confirm Civilian Background of Undeclared Nuclear Release

Isotope Measurements on Air Filters Confirm Civilian Background of Undeclared Nuclear Release

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© Dorian Zok/LUH
Air filters

Study of Leibniz University Hannover and University of Münster investigates nuclear background of radioactive cloud

In 2017, a mysterious cloud containing radioactive ruthenium-106 was detected over Europe. Radiation protection entities across Europe are still in the process of clarifying the exact circumstances of the incident. To date, no country has assumed responsibility for the release. A study of Leibniz University Hannover and University of Münster recently published in the scientific journal "Nature Communications" demonstrated that the cloud did not originate from military sources - but rather from civilian nuclear activities.

In autumn 2017, a radioactive cloud containing ruthenium-106 was detected over Europe. Although the activity concentrations were innocuous, they reached up to 100 times the levels of what had been detected over Europe in the aftermath of the Fukushima accident. Since no government has assumed responsibility so far, a military background could not be ruled out.

Moreover, it is impossible to make a clear distinction between civilian and military sources solely based on measurements of radioactive isotopes of ruthenium. For the first time, researchers from Leibniz University Hannover (Institute of Radioecology and Radiation Protection) and University of Münster (Institute of Planetology) succeeded in quantifying stable ruthenium isotopes in air filters that were released with the radioactive ruthenium.

Within the scope of the study, the team left conventional scientific paths: "We usually measure ruthenium isotopes to study the formation history of Earth", says Prof. Dr. Thorsten Kleine from the University of Münster, adding that the methods originally developed to address research questions in planetology were instrumental in solving this mystery. The fact that the airborne ruthenium stemming from nuclear activities occurred in minuscule amounts and were diluted with natural stable ruthenium presented a significant challenge.

Through the clean chemical separation of ruthenium fractions from air filters and subsequent high-precision measurements via mass spectrometry, the researchers determined the ratio of stable ruthenium from the nuclear source. The ruthenium isotopic ratios found in the filter are consistent with the signature of a civilian source, in particular the signature of spent nuclear fuel from a nuclear power plant. Hence, the release of ruthenium from a reprocessing plant for nuclear fuels is the most conclusive scenario for explaining the incident in autumn 2017. A military background (such as the production of weapons-grade plutonium) can be ruled out.

Furthermore, high-precision measurements enabled the researchers to draw further conclusions. "The isotope signature discovered in the air filter exhibits no similarities with nuclear fuels of conventional Western pressurised or boiling water reactors. Instead, it is consistent with the isotope signature of a specific type of Russian pressurised water reactors - the VVER series. Worldwide, approximately 20 reactors of this type of VVER are currently operational", specifies Professor Georg Steinhauser from Leibniz University Hannover.


T. Hopp, D. Zok, T. Kleine, G. Steinhauser. 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

Note to editors:

For further information, please contact Prof. Dr. Georg Steinhauser, Institute of Radioecology and Radiation Protection via email at steinhauser@irs.uni-hannover.de and Prof. Dr. Thorsten Kleine, Institute of Planetary Science via email at thorsten.kleine@uni-muenster.de.