Back in September 2017, unbeknownst to the general public, a slightly radioactive cloud moved across Europe. It was the most serious release of radioactive material since Fukushima 2011 but it caused no health risk for the population and therefore went unnoticed.
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Now, a new study has been published that attempts to locate the source of the release. The research consists of more than 1300 measurements from all over Europe and other regions of the world. 176 measuring stations from 29 countries were involved in the work.
Russian nuclear facility Majak
What the researchers uncovered was that the radiation did not come from a reactor accident, but an accident in a nuclear reprocessing plant. Although the exact origin of the radioactivity is difficult to pinpoint, the scientists suspect a release site in the southern Urals where the Russian nuclear facility Majak is located.
"We measured radioactive ruthenium-106," said Prof. Georg Steinhauser from the University of Hanover (who is closely associated with the Atomic Institute). "The measurements indicate the largest singular release of radioactivity from a civilian reprocessing plant."
The release was spotted in autumn of 2017. It consisted of a cloud of ruthenium-106 with maximum values of 176 millibecquerels per cubic meter of air, values up to 100 times higher than the total concentrations measured in Europe after the Fukushima incident.
It was the fact that no radioactive substances other than ruthenium were measured that led the researchers to believe that the source must have been a nuclear reprocessing plant. However, to this day, no one has assumed responsibility for this incident.
The second-largest nuclear release in history
The Russian nuclear facility Majak had already been the scene of the second-largest nuclear release in history after Chernobyl. The accident happened back in September 1957 and resulted from the explosion of a tank containing liquid waste from plutonium production.
Dr. Olivier Masson from the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) in France and Steinhauser can date the 2017 release to the time between 25 September 2017, 6 p.m., and 26 September 2017 at noon. This date is almost exactly 60 years after the 1957 accident.
"This time, however, it was a pulsed release that was over very quickly," said Steinhauser. "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 study is published in the journal Proceedings of the National Academy of Sciences (PNAS).