Masson, and 65 co-authors, reported in 2019 that in October 2017, most European countries reported unique atmospheric detections of aerosol-bound radio-ruthenium (106Ru). The range of concentrations varied from some tenths of μBq·m−3 to more than 150 mBq·m−3. The widespread detection at such considerable (although innocuous) levels suggested a considerable release. To compare activity reports of airborne 106Ru with different sampling periods, concentrations were reconstructed based on the most probable plume presence duration at each location. Based on airborne concentration spreading and chemical considerations, it is possible to assume that the release occurred in the Southern Urals region (Russian Federation). The 106Ru age was estimated to be about 2 years. It exhibited highly soluble and less soluble fractions in aqueous media, high radio-purity (aka lack of concomitant radionuclides), and volatility between 700 and 1,000 °C, thus suggesting a release at an advanced stage in the reprocessing of nuclear fuel. The amount and isotopic characteristics of the radio-ruthenium release may indicate a context with the production of a large 144Ce source for a neutrino experiment.
The authors concluded that almost exactly 60 y after the Kyshtym and Windscale nuclear accidents in 1957, both substantial sources of 106Ru in the environment (23), a significant release of 106Ru occurred in the southern Eurasian border region in September 2017. It led to detectable yet innocuous levels of this airborne fission product
in the rest of Europe. Based on times series of detections at various locations in Central Europe, the event was characterized as a short release. The plume duration lasted about 1 to 3 days on average, depending on the location, with the exception of a few areas (e.g., in Italy where the labeled air mass, once arrived, stayed longer than elsewhere).
The release was too substantial to be associated with the incineration of a medical radionuclide source. A satellite crash can also be excluded as the source of the 106Ru. It is much more likely that the 106Ru escaped during reprocessing of spent nuclear fuel, possibly in the course of the miscarried production of a highly radioactive 144Ce source for research applications in the Gran Sasso Laboratory in Italy.
The authors confirmed high radio-purity of the radio-ruthenium, an age of about 2 y or less, as well as both relatively high solubility and volatility of the Ru species on the air filters. According to detection time series, a back-trajectory analysis, and chemical considerations, the Mayak nuclear complex in southern Urals of Russia should be considered as a likely candidate for the release.
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