Significance
A massive atmospheric release of radioactive
106Ru occurred in Eurasia in 2017, which must have been caused by a sizeable, yet undeclared nuclear accident. This work presents the most compelling monitoring dataset of this release, comprising 1,100 atmospheric and 200 deposition data points from the Eurasian region. The data suggest a release from a nuclear reprocessing facility located in the Southern Urals, possibly from the Mayak nuclear complex. A release from a crashed satellite as well as a release on Romanian territory (despite high activity concentrations) can be excluded. The model age of the radioruthenium supports the hypothesis that fuel was reprocessed ≤2 years after discharge, possibly for the production of a high-specific activity
144Ce source for a neutrino experiment in Italy.
Abstract
In October 2017, most European countries reported unique atmospheric detections of aerosol-bound radioruthenium (
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 (yet 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 radiopurity (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 radioruthenium release may indicate a context with the production of a large
144Ce source for a neutrino experiment.
Summary
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 d 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. This study confirms high radiopurity of the radioruthenium, 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 should be considered as a likely candidate for the release.