The origin of the mysterious radioactive cloud that covered Europe in 2017 finally determined

During the year 2017, several measuring stations spread around the world detect a radioactive cloud of ruthenium-106 over Europe. If until now, hypotheses about the Russian origin of this peak of radioactivity had been formulated, there was no evidence to confirm them. This is now done with a new international study pointing the finger at the Russian nuclear complex Mayak.

The radioactivity peak - in the form of an extremely high concentration in the air of ruthenium-106 radioactive isotope - was detected by scientists in October 2017, but the source of this radiation (almost 1000 times higher than normal) had never been definitively confirmed.

At the time, many had speculated that nuclear facilities in Russia were responsible for what was perceived as an accidental release of ruthenium-106, despite the denials of the time by the Russian authorities.

But new research, published in the journal PNAS , aims to confirm and detail the hypothesis of Russian origin, according to an international team of nearly 70 scientists led by Olivier Masson, researcher in radionuclides, the Institute of Radiation Protection and nuclear safety (IRSN) in France.

Massive radioactive release: Russian nuclear plant Mayak

" Based on the dispersion of concentration in the air and chemical considerations, it is possible to assume that the rejection took place in the southern region of the Urals (Russian Federation) " explain the researchers in their new article . Based on what they claim to be the most comprehensive assessment of the incident to date, Masson and his team have analyzed more than 1,300 radioactive cloud measurements, recorded by 176 measurement stations in nearly 30 countries.

Map showing the different radioactivity measurements made by several European stations in 2017. The values ​​are given in mBq · m -3 . Credits: O. Masson et al. 2019

Although the radioactive material released into the air is not harmful to human health, it nevertheless constituted the most serious release of radioactive material since the Fukushima accident in 2011, with maximum values ​​of 176 millibecquerels of isotope per cubic meter of air.

Shortly after the release, Russian officials have hinted that the radioactive peak may have been caused by the crash of a satellite, the isotope being released by the battery of the machine when it enters the Earth's atmosphere. . However, this is not what this new study concludes.

Map showing atmospheric concentrations of ruthenium-106 in Europe. Credits: O. Masson et al. 2019

The measurements indicate the largest single release of radioactivity from a civilian reprocessing plant, " says one of the researchers, radioecologist Georg Steinhauser of the University of Hanover. More specifically, the new evidence - based on the modeling of air mass movements at the time of the accident - indicates that the Mayak Russian nuclear complex in the southern Urals " should be considered a likely candidate for release Conclude the researchers.

Ruthenium-106, cesium-144 and neutrinos

This corresponds exactly to the first suspicions dating back to November 2017, although the Russian nuclear company Rosatom has since insisted that the normal measurements in the ground around the plant show that the Mayak plant could not be responsible for it because the ruthenium-106 concentration would have been thousands of times higher.

The new findings, however, cast doubt on the veracity of these claims, as the team speculated that the accident could have occurred in Mayak, while scientists were trying to produce the cerium-144 isotope for later use. in neutrino experiments at the Gran Sasso National Laboratory in Italy, as has already been speculated.

Simulation estimating the half-life of radioruthenium for different types of reactors, based on the ratio 103 Ru / 106 Ru. The results are in agreement with an origin pointing towards the Russian nuclear power station. Credits: O. Masson et al. 2019

We were able to show that the accident occurred during the reprocessing of spent fuel elements, at a very advanced stage, shortly before the end of the treatment chain, " explains Steinhauser. " Even though there is currently no official statement, we have a very good idea of ​​what may have happened ."

A concordant cluster of indices 

If the modeling of the researchers is correct, the accident occurred at the end of September 2017, on the 25th or the 26th of the month, almost exactly 60 years after one of the worst nuclear accidents in history on the same site: the disaster of Kyshtym, ranked as the third most serious nuclear accident in the history of international nuclear events.

Although there is no evidence in the new research to definitively prove that an accident at the Mayak site was at the origin of the radioactive plume, there is more evidence to support this.

The neutrino research to be conducted in Italy - called SOX (Short-Range Oscillations with BoronXino) - was canceled only several months after the release of the radioactive cloud at the end of 2017, after the cerium-144 required for the experiments were not obtained. Information about the cancellation of the project explained that " during the purification of the equipment, unexpected problems occurred, resulting in a loss of activity and an increase in the level of impurities ".


Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017
O. Masson, G. Steinhauser, D. Zok, O. Saunier, H. Angelov, D. Babić, V. Bečková, J. Bieringer, M. Bruggeman, C. I. Burbidge, S. Conil, A. Dalheimer, L.-E. De Geer, A. de Vismes Ott, K. Eleftheriadis, S. Estier, H. Fischer, M. G. Garavaglia, C. Gasco Leonarte, K. Gorzkiewicz, D. Hainz, I. Hoffman, M. Hýža, K. Isajenko, T. Karhunen, J. Kastlander, C. Katzlberger, R. Kierepko, G.-J. Knetsch, J. Kövendiné Kónyi, M. Lecomte, J. W. Mietelski, P. Min, B. Møller, S. P. Nielsen, J. Nikolic, L. Nikolovska, I. Penev, B. Petrinec, P. P. Povinec, R. Querfeld, O. Raimondi, D. Ransby, W. Ringer, O. Romanenko, R. Rusconi, P. R. J. Saey, V. Samsonov, B. Šilobritienė, E. Simion, C. Söderström, M. Šoštarić, T. Steinkopff, P. Steinmann, I. Sýkora, L. Tabachnyi, D. Todorovic, E. Tomankiewicz, J. Tschiersch, R. Tsibranski, M. Tzortzis, K. Ungar, A. Vidic, A. Weller, H. Wershofen, P. Zagyvai, T. Zalewska, D. Zapata García, and B. Zorko

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