Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017

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.