A new study released in PNAS on July 26, 2019, confirmed that massive atmospheric release of radioactive Ruthenium 106 (106Ru) occurred in Eurasia in September 2017.
"This must have been a sizeable, yet undeclared nuclear accident," study authors said. The study 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), suggested by local authorities, 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.
"In October 2017, most European countries reported unique atmospheric detections of aerosol-bound radioruthenium (106Ru), the authors said in an abstract of the new paper. 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.
"Nuclear accidents are serious threats due to their immediate and perceived consequence for both health and environment. The lay public thus relies on the responsibility of their leaders to provide information on radioactive releases and their impact on human and environment health. Early in the 1960s, and even more after the Chernobyl accident, European radioprotection authorities established or strengthened radionuclide monitoring networks on a national scale. Today most of these European networks are connected to each other via the informal “Ring of Five” (Ro5) platform for the purpose of rapid exchange of expert information on a laboratory level about airborne radionuclides detected at trace levels. The Ro5 was founded in the mid-1980s by 5 member countries: Sweden, Federal Republic of Germany, Finland, Norway, and Denmark. Today, the memberships have grown to laboratories in 22 countries (while the name was kept), and the Ro5 is still an informal arrangement on a laboratory level and between scientists. In January 2017, the Ro5 alerted its members regarding the widespread detection of airborne 131I in Europe. In October 2017, an unprecedented release of ruthenium-106 (106Ru; T1/2 = 371.8 d) into the atmosphere was the subject of numerous detections and exchanges within the Ro5. The goal of this report is to give an overview of the global spreading of this fission product through airborne concentrations observed in Europe and beyond, its forensic history, and chemistry."
This is an update to our reports published October 11, November 10 and 21, 2017:
1. Spike in radioactive particles detected in Europe (October 11, 2017)
2. Detection of Ruthenium 106 in Europe: IRSN investigation results (November 10, 2017)
3. Extremely high concentrations of radioactive Ru-106 in Urals confirmed and denied (November 21, 2017)
From the study
On October 2, 2017, an informal alert by an Italian laboratory was issued to the Ro5 network, reporting the detection of airborne 106Ru in the millibecquerel per cubic meter (mBq·m−3) range in Milan, Italy. Limits of detection (LOD) in laboratories connected to the Ro5 are typically in the range of 0.1 to 10 microbecquerels per cubic meter (μBq·m−3). This first report occurred on a Monday, when most European laboratories usually exchange their aerosol filters, which are operated on a weekly basis. Later that day, 106Ru detections were reported from Czech Republic, Austria, and Norway in the 1- to 10-mBq·m−3 range. This widespread detection in such range immediately suggested a considerable release.
After 2 days, and further detection reports from Poland, Austria, Switzerland, Sweden, and Greece, official information notes were published by national radioprotection authorities, for example, in Switzerland, Austria, and Norway. On October 7, 2017, the International Atomic Energy Agency (IAEA) requested data and possible known sources of radioruthenium from all 43 European member states.
(Left) Map of uncorrected average concentrations at European stations, and (Right) map of 7-d corrected average concentrations (based on average plume duration of 7 d at each location). Credit: PNAS/Authors
On October 9, 2017, Chelyabinsk and Sverdlovsk regional authorities ruled out any possible 106Ru release from their region (Russian Federation). On November 21, 2017, the Russian Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet) declared to have measured 106Ru in the southern Urals in the late September.
However, one possible source in the region, the Federal State Unitary Enterprise “Production Association Mayak” in Ozersk, immediately declared that it was not the source of increased 106Ru. On November 23, 2017, the IAEA addressed the release of 106Ru in a press conference.
All members submitted the requested data, but none declared an accident and none declared being aware of any source.
On December 8, 2017, Russian officials once again claimed that Mayak could not be the source because of the lack of any radioruthenium traces in the soil around the facility. Instead, the officials pointed at the possibility of a radionuclide battery of a satellite that had burned during its reentry into the atmosphere.
On January 22, 2018, the Nuclear Safety Institute of the Russian Academy of Sciences invited radiation protection experts from Germany, France, Finland, Sweden, the United Kingdom, and Russia to aid in the elucidation of the release.
Two commissions of inquiry were held: on January 31, 2018 and on April 11, 2018. The second meeting concluded by emphasizing that not enough data were yet available to point out any verified hypothesis of the origin of the 106Ru. The present article [the new study] aims at closing this gap, study authors said.
Find the entire study at https://doi.org/10.1073/pnas.1907571116
Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017 - Open Access - Article published in Proceedings of the National Academy of Sciences (PNAS) on July 26, 2019. - O. Masson, G. Steinhauser, D. Zok, O. Saunier, H. Angelov, D. Babić, V. Bečková, J. Bieringer, M. Bruggeman, C. I. Burbidge, S. Conil, A. Dalheimer, L.-E. De Geer, A. de Vismes Ott, K. Eleftheriadis, S. Estier, H. Fischer, M. G. Garavaglia, C. Gasco Leonarte, K. Gorzkiewicz, D. Hainz, I. Hoffman, M. Hýža, K. Isajenko, T. Karhunen, J. Kastlander, C. Katzlberger, R. Kierepko, G.-J. Knetsch, J. Kövendiné Kónyi, M. Lecomte, J. W. Mietelski, P. Min, B. Møller, S. P. Nielsen, J. Nikolic, L. Nikolovska, I. Penev, B. Petrinec, P. P. Povinec, R. Querfeld, O. Raimondi, D. Ransby, W. Ringer, O. Romanenko, R. Rusconi, P. R. J. Saey, V. Samsonov, B. Šilobritienė, E. Simion, C. Söderström, M. Šoštarić, T. Steinkopff, P. Steinmann, I. Sýkora, L. Tabachnyi, D. Todorovic, E. Tomankiewicz, J. Tschiersch, R. Tsibranski, M. Tzortzis, K. Ungar, A. Vidic, A. Weller, H. Wershofen, P. Zagyvai, T. Zalewska, D. Zapata García, and B. Zorko https://doi.org/10.1073/pnas.1907571116
Featured image credit: PNAS/Authors