Scientists Find Source Of Mysterious Radioactive Cloud That Drifted Over Europe In 2017


Tom Hale


Tom Hale

Senior Journalist

Tom is a writer in London with a Master's degree in Journalism whose editorial work covers anything from health and the environment to technology and archaeology.

Senior Journalist


A warning sign near the Mayak nuclear reprocessing plant in the Chelyabinsk area. Kiselev Alexey/Shutterstock

In September 2017, a cloud of radioactive contamination sneaked across Europe, marking the most serious release of radioactive material since Fukushima in 2011. However, until recently, the source of this radioactive material had remained a point of contention.

In a new study, an international team of scientists has now concluded that the freak radioactive spike can be traced back to southern Russia and was most likely the result of an accident at a nuclear reprocessing plant in the Ural Mountains.


As reported in the Proceedings of the National Academy of Sciencesa team of 70 experts from across Europe looked at 1,300 measurements of radioactive isotope ruthenium-106 from sites across the Eurasian continent. By their workings, between 250 and 400 terabecquerels of ruthenium-106 were released from somewhere in the southern Urals near the Russian border to Kazakhstan, just as earlier reports had speculated. 

It’s noteworthy that this pocket of the Urals is home to one of the biggest nuclear facilities in Russia – Mayak – which specializes in reprocessing spent nuclear fuel from nuclear reactors and plutonium from weapons. While there is still no official word from Mayak or Russian authorities on the new findings, the nature of the incident has become much clearer with this study, the researchers say. 

Map of ruthenium-106 average concentrations across Europe between September and October 2017. Note the red one over southern Russia. O Masson et al/PNAS 2019

"It was a pulsed release that was over very quickly," Professor Georg Steinhauser, a radiation expert from the University of Hanover, said in a statement. "We were able to show that the accident occurred in the reprocessing of spent fuel elements, at a very advanced stage, shortly before the end of the process chain.

"Even though there is currently no official statement, we have a very good idea of what might have happened." 


The Mayak plant has been linked to a number of incidents in the past, most notably the Kyshtym disaster in September 1957, almost exactly 50 years before this recent incident. The catastrophic accident occurred when a cooling system for one of the waste storage tanks failed, causing the combustion of 70 to 80 tons of radioactive waste. At least 10,000 people were evacuated from their homes and hundreds are believed to have died from the effects of the radioactivity, making the incident the world’s third most serious nuclear accident.

Fortunately, the radiation from the 2017 incident never posed any risk to public health.

Russian authorities, by no surprise, have previously denied responsibility for the radiation. Moscow insisted that its air monitoring systems only found negligible amounts of ruthenium-106 in Russian territory, but detected high radiation levels over Romania, Italy, and Ukraine. 

Nevertheless, this new study isn’t the first to point the finger at Russia. In February 2018, a report by the French Institute of Radioprotective and Nuclear Security also tracked the radioactive cloud back to the Urals using radiation readings from various institutions and data on air currents.


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