Secret Russian Nuclear Accident Caused a Huge Radiation Cloud to Blanket Europe, Scientists Claim

New research has suggested the huge radioactive cloud that blanketed parts of Europe in 2017 was produced by an accident at a nuclear facility in central Russia, despite Moscow denying responsibility at the time.

The study, published on Monday in the Proceedings of the National Academy of Sciences, said there is no doubt that the cloud of radiation came from the Mayak nuclear reprocessing plant, located in Russia's Chelyabinsk region near its border with Kazakhstan.

Austrian scientists were the first to raise the alarm on October 3, 2017, after detecting abnormally high levels of local radiation. German researchers reported similar findings at around the same time. Both nations are thousands of miles from Mayak, and investigators soon realized that a large swathe of the continent had been affected.

Later readings showed the radiation was detected across Europe and even as far as Asia, the Arabian Peninsula and the Caribbean.

The cloud—of radioactive ruthenium-106—sat above parts of Europe for weeks with levels of radiation fluctuating. It eventually cleared and radiation levels returned to normal. French and German authorities quickly determined that Russia was the most likely source. Though Russian officials acknowledged the heightened radiation, they dismissed any suggestion that the source was within the country.

State-owned Russian nuclear energy corporation Rosatom said the data collected in 2017 was "not sufficient to establish the location of the pollution source." Other Russian officials proposed alternative explanations, such as the re-entry of a burning satellite.

But the new research—conducted jointly by the Institut de Radioprotection et de Sûreté Nucléaire in France and Leibniz University Hannover in Germany—pinpointed Mayak as the source by analyzing 1,300 data points. The study reported that the leak had occurred sometime between 12 p.m. on September 26 and 12 p.m. on September 27.

The cloud was made up of ruthenium-106—a byproduct of nuclear fission with a half-life of 374 days. During spent nuclear fuel reprocessing, these isotopes are usually separated from the radioactive plutonium and uranium taken from nuclear power reactors, and kept in long-term storage with other radioactive waste byproducts, Live Science explained.

The ruthenium-106 in the cloud meant the radioactivity must be the result of a nuclear reprocessing accident. Nuclear chemist Georg Steinhauser of Leibniz University in Hanover—co-lead author of the paper alongside with IRSN's Olivier Masson—told Newsweek this suggests that the Mayak facility was the source.

"We are very certain that the source is in the Eurasian border region, and—to the best of our knowledge—there is only one facility that is capable of handling such amounts of radioactivity in this area, and this is Mayak," Steinhauser explained.

The radioactive cloud was diluted enough that it did not pose a threat to those living under it, though Steinhauser noted they were unable to fully assess the impact in close vicinity of Mayak itself. "If anybody was exposed to the cloud directly, there is a risk of harmful doses," he noted.

Masson explained that if a similar release had occurred in France "it would have led to the evacuation of workers to avoid any additional over exposure."

Regardless, the release of the cloud and the denials and silence from Russia are cause for concern. "We certainly hope that the Russian authorities will handle this incident with more transparency," Steinhauser told Newsweek.

"For the nuclear scientific community, we do not want to blame Russia for the incident, but we would like to learn our lessons from it, just like after Fukushima when safety standards were revised."

The suspected accident at Mayak registered between 30 and 100 times the level of total radiation released after the Fukushima accident in Japan in 2011, Steinhauser told Live Science.

However, he noted that the damage from this incident does not compare to Fukushima or a worse incident like Chernobyl. However, the Mayak accident is "probably the most significant release from civilian nuclear fuel reprocessing," Steinhauser added, larger than the Three Mile Island incident in the U.S. in 1979.

But in a statement sent to Newsweek, Rosatom maintained there had been no accident at any of its facilities. A spokesperson said that national regulators and international inspectors visited Mayak in 2017 and found "nothing to suggest that the ruthenium-106 isotope originated from this site, nor found any traces of an alleged accident, nor found any evidence of local staff exposure to elevated levels of radioactivity."

The statement said that the new study does not contain any new data or facts that differ from those reviewed by the inspectors in 2017. "The independent international inquiry has found the accidental release scenario to be inconsistent with the established facts," the spokesperson said.

Rosatom noted that any radioactive release of the alleged magnitude would have been recorded by Mayak's monitoring systems and would have triggered alarms and evacuation procedures. Its statement said that 250 Mayak workers—including those working in its radiochemistry plant—were examined at an independent lab "and none of them were found to have any traces of excess exposure."

"Contrary to a speculative theory in the PNAS report, the cerium-144 project activities conducted at the Mayak facility from August to November 2017 were related only to rare-earth concentrate which would only contain barely detectable traces of ruthenium-106 isotope," Rosatom added.

Mayak, used for both nuclear and civilian purposes, has a history of nuclear accidents. In 1957, a storage tank at the facility exploded, contaminating tens of thousands of people, The Washington Post noted. And in 2004, it was revealed that plant officials were dumping nuclear waste into a local river.

This article has been updated to include comments from Olivier Masson and a statement from Rosatom.

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This file photo shows a worker labeling yellow barrels containing potentially radioactive material at a former nuclear power plant on June 6, 2011 in Rheinsberg, Germany. Sean Gallup/Getty