When a radioactive cloud drifted over parts of Europe in September 2017, Russia denied being the source. Maybe it was caused by a satellite burning up at re-entry, Russian officials said. And again Tuesday, Russia's government-owned nuclear energy corporation said in a statement obtained by the Washington Post, "We maintain that there have been no reportable events at any Rosatom-operated plants or facilities." But new research disagrees. An international team of scientists in France and Germany has found the release was the result of a nuclear fuel-reprocessing accident at a nuclear facility in the Chelyabinsk region of the Ural Mountains, close to the Kazakhstan border. It happened between noon Sept. 26 and noon Sept. 27 at the Mayak facility, according to the report in the Proceedings of the National Academy of Sciences, per Live Science.
Scientists thought the radiation came from Russia at the time, but from a different source. The cloud of radioactive ruthenium-106 hovered for weeks before radiation levels dropped to normal, per Newsweek. The ruthenium-106 in the cloud was the key; its presence meant the radioactivity had to be caused by a nuclear reprocessing accident. "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," one of the lead authors of the paper said. The cloud wasn't radioactive enough to hurt anyone on the ground, but it still held 30 to 100 times the level of radiation released in 2011 after the Fukushima accident in Japan, one of the researchers said. One scientist said they're not interested in placing blame for the release, "but we would like to learn our lessons from it, just like after Fukushima when safety standards were revised." (Read more radioactive leaks stories.)