Nations to the northwest of Russia reported slightly increased levels of radiation on several days in June. The levels were harmless to human health and the environment.
The isotopes observed include Cs-134, Cs-137, Ru-103, I-131, and isotopes of cobalt. The possible source region for the June 22 and 23 observations was calculated by the monitoring organization for the Comprehensive Nuclear Test-Ban Treaty (CTBTO), which has isotope monitoring stations around the world. The tweet doesn’t say this, but that region was probably calculated by considering the winds during that period. (Lassina Zerbo is the director of the CTBTO.)
Iodine-131 was observed at more northerly stations and on different days than the other isotopes. It has a half-life of 8 days and is a fission product, as are the other isotopes except for cobalt. Cobalt is an activation product of the steel containment vessel for a reactor. It seems likely that these observations come from a leaking nuclear reactor, but where?
Russia has reactors in the suspect area, but officials there have said that none of them have leaked.
Last week, a test of the Burevestnik nuclear-powered cruise missile was thought to be planned for the Kapustin Yar test site, north of the Caspian Sea.
Nothing more than a Notice to Airmen (NOTAM) was announced by the Russian government, so it’s not clear why this exclusion would have been for Burevestnik in particular. Up until now, Burevestnik tests have been further north. The deadly test of last year was within the area calculated by the CTBTO.
There’s not enough information to conclude anything more than that these emissions were from a reactor. Russia is party to conventions requiring it to provide information on accidents involving the release of radiation. The other nations within the possible source area have been conscientious about their adherence to those conventions. Russia hasn’t.
Cross-posted to Nuclear Diner