Russian state atomic agency ROSATOM has refuted claims that a nuclear accident from a Russian plant was the source of a radiation cloud detected over Europe in 2017.

Responding to a study published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), a ROSATOM statement said, "We maintain that there have been no reportable events at any of Rosatom-operated plants or facilities. Both the national regulator and experts from an independent international inquiry inspected the Mayak facility back in 2017 and found nothing to suggest that the ruthenium-106 isotope originated from this site, nor any traces of an alleged accident, nor any evidence of personnel exposure to elevated levels of radioactivity."

The statement added that the PNAS study did not contain any new data or facts that were not already covered by both the national and international regulatory authorities that reviewed the site.

In addition, ROSATOM refuted the PNAS study's claims that 250 TBq (Terabecquerel — units of radiation) were emitted, stating that measurements of radiation at the facility and of its workers did not find levels commensurable with the PNAS claims. It says that if 250 TBqs had been emitted, "the facility's automated control and monitoring systems would have recorded radioactivity thousands of times."

The statement also addresses the PNAS report's hypothesis that a Russian experiment to produce Cerium-144 could have triggered the leak. "The cerium-144 project activities conducted on Mayak from August to November 2017 were related only to rare-earth concentrate which could only contain barely detectable traces of ruthenium-106 isotope."