Ruthenium-106 event in Europe, Autum 2017

Between ca. 25 September and 10 October 2017, radioactive ruthenium-106 was observed over wide stretches of Europe in mBq/m3 quantities (highest reported value is from Bucarest with 145 mBq/m3), accompanied by uBq/m3 concentrations of ruthenium-103. Nuclide ratios indicate a decay time of 1 to 2 years after irradiation in a reactor for various burnups. Meteorological analyses point to a source in the southern Ural region. Here is a collection of important links related to this event.

The Nuclear Safety Institute of the Russian Academy of Sciences (IBRAE) has set up an international commission to investigate the event. Its first meeting was held on 31 January 2018. IBRAE has published a short summary of this first meeting (Note: This link has disappeared. The report is now available at a higher news number as http://en.ibrae.ac.ru/newstext/915/. They stated that the total released activity is estimated at about 100 TBq. No conclusions on the source location are presented, but it is said that Rostechnadzor inspections were conducted at the PO "Mayak" and NIIAR (Dimitrovgrad) facilities covering the operations during the period August - November 2017, and no deviations from normal technological processes were found. The next meeting of the Commission is scheduled for April 11, 2018 in Moscow.

IRSN (French agency for radiological protection) has probably done the most comprehensive studies. They can be downloaded from the IRSN News page. The second, longer report (PDF) is very comprehensive and also contains a list of all available measurements as collected by IAEA.

The main content of this paper, including the latest hypothesis that the release may be related to the failed production of a Ce-144 source intended for neutrino measurements in the Gran Sasso lab, is summarised nicely on one page in a Science Magazine news article from 16 Feb 2018 (as PDF).

The German Federal Radiation Protection Agency BfS has also a useful BfS page on the Ru events.

The Russian news site geoenergetics.ru has published an article in Russian which has two lists of measurement results collected by the IAEA but originally not published so far (now they are in the IRSN report mentioned above) attached:

In the April 2018 EGU General Assembly, in the new Emergency response with atmospheric dispersion models session, there were three PICOs on the event:

PICO5a.5, EGU2018-13577, Tracing back the elevated Ru-106 measurements in Europe end of September/beginning of October 2017, Christian Maurer, Kathrin Baumann-Stanzer, Marielle Mulder, Paul Skomorowski, Gerhard Wotawa, and Delia Arnold
PICO5a.5, EGU2018-15285, A method to locate an accidental release: application to RU106 case in September 2017, Rostislav Kouznetsov and Mikhail Sofiev
PICO5a.10, Inverse modelling method to analyze detections of radionuclides within Europe: illustration on an actual case, Olivier Saunier, Anne Mathieu, Damien Didier, and Olivier Masson

The the session link above has also links to PDF versions of the abstracts of these presentations.

In April 2018, the second meeting of the Commision has taken place. A short report on the 2nd Meeting (11 April) has been released by IBRAE. It states, inter alia,

... the Commission made considerable efforts collecting and analysing the available data ... as well as organized sampling in the Chelyabinsk Region and their spectrometric analysis in three independent laboratories, and carried out additional calculations. An extensive database was created. ...
Having considered the information provided, the Commission was unable to indicate any reliable hypothesis of the Ru-106 origin within the investigated activities in the field of the atomic energy use ....
The Commission Members decided to present the collected information for open access and prepare it for open scientific publications.
After a thorough analysis of the information collected as a result of the Commission's activities, the Members of the Commission will decide on the need for additional work and follow-up meetings to discuss the results.

According to a Reuters news information, the commission ... decided that its member groups ... could return to their countries and carry on their research independently, said Sweden.

In 2019, a study with authors from the Commission appeared in PNAS supporting the hypothesis of an accident in Mayak related to the manufactering of a Ce-144 source. A second study in PNAS by the IRSN team presents their source reconstruction, which concludes that Mayak is the likely source, and ca. 250 TBq (2.5E14) Bq were released on 26 September 2017. The references are:

O. Masson et al.: Airborne concentrations and chemical considerations of radioactive ruthenium from an undeclared major nuclear release in 2017, PNAS, 20 August 2019, 116(34), pp. 16750-16759, http://www.pnas.org/cgi/doi/10.1073/pnas.1907571116

O. Saunier, D. Didier, A. Mathieu, O. Masson, and J. Dumont Le Brazidec (2019): Atmospheric modeling and source reconstruction of radioactive ruthenium from an undeclared major release in 2017. PNAS,10 December 2019, https://doi.org/10.1073/pnas.1907823116

A further paper in Nature Communications (2020) presents evidence from ruthenium isotopic ratios on filters indicating that the ruthenium was part of fuel used in VVER reactors (which run in Russia and countries having been former Soviet allies):

T. Hopp, D, Zok. T. Kleine, G. Steinhauser (2020): Non-natural ruthenium isotope ratios of the undeclared 2017 atmospheric release consistent with civilian nuclear activities. Nature Communications, 11:2744, https://doi.org/10.1038/s41467-020-16316-3