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Precision Analyses Shed Light on Mysterious Release of Radioactive Material

Precision Analyses Shed Light on Mysterious Release of Radioactive Material

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International team of experts from IRSN and Leibniz University Hannover publishes study on radioactive cloud detected in autumn 2017

Not a nuclear accident, but an accident at a reprocessing plant: An incident in September 2017, which was barely noticed by the public in Europe and described as a "small amount of radioactivity", was in fact a major nuclear accident, the most serious release of radioactive material since Fukushima. This is supported by more than 1,300 measurements compiled by 70 experts from across Europe. The conclusive data set was analysed by Dr Olivier Masson from the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) and Professor Georg Steinhauser from the Institute of Radioecology and Radiation Protection at Leibniz University Hannover. Within the scope of the study, radioactive Ruthenium-106 was measured. The measurements indicate the largest singular release of radioactivity from a civilian reprocessing plant. Led by the two researchers, the team has now published their findings in the renowned journal Proceedings of the National Academy of Sciences of the USA (PNAS).

In autumn 2017, a cloud of Ruthenium-106 reaching maximum levels of 176 millibecquerels per cubic meter of air was detected in several European countries. The radioactive isotope has a half-life of 374 days. The values were up to 100 times higher than those noted in Europe after Fukushima.

The fact that - apart from Ruthenium - no other radioactive substances were released proved that the source must have been a nuclear reprocessing plant. Therefore, the incident in 2017 was highly unusual. The Ruthenium-106 cloud also covered a remarkable distance - it was detected in most parts of Central and Eastern Europe and reached as far as the Arabian Peninsula, Asia, and the Caribbean. An informal international network consisting of measuring stations in Europe provided the evidence. 176 stations in 29 countries were involved, 23 of which are based in Germany.

Even though the release was highly unusual, the levels of radioactive material released did not pose a health risk (at least not in Europe). After analysing the data, researchers concluded that between 250 and 400 terabecquerels of Ruthenium-106 were released. To date, no state has claimed responsibility for the considerable release of radioactive material in autumn 2017.

Analyses of the concentration distribution pattern and atmospheric models suggest that the source of the release is in the Southern Ural Mountains, which is where the Russian nuclear facility Majak is located. The Russian nuclear reprocessing plant was the scene of the second worst release of nuclear material in history - bigger than Fukushima and second only to Chernobyl. In September 1957, a tank containing liquid nuclear waste from plutonium production exploded causing massive contamination of the area.

Olivier Masson and Georg Steinhauser narrowed down the time frame for the current release to sometime between 25 September 2017, 18.00 and 26 September 2017, 12.00 - almost 60 years to the day since the 1957 accident. Unlike the releases in Chernobyl or Fukushima, which lasted for several days, a short-term pulsed release occurred, explains Professor Steinhauser. "We demonstrated that the accident happened while spent fuel elements were reprocessed - to be specific at a fairly advanced stage of reprocessing, just before the end of the process chain", adds Georg Steinhauser. "Even though an official statement has not been released yet, we have a very good idea of what might have happened."

Note to editors:

For further information, please contact Prof. Dr. Georg Steinhauser, Institute of Radioecology and Radiation Protection at Leibniz University Hannover (Tel. +49 511 762 3311, Email steinhauser@irs.uni-hannover.de).