Increase in the volumetric activity of iodine-131 (131I) radionuclide within the range from 2.1 to 3.3 µBq/m3 at an acceptable concentration of 4 Bq/m3 was detected in air samples taken from 18 to 25 February 2018 by the automated radiation monitoring systems in Chornobyl, Dytiatky, Naftobaza, VRP-750.
These data are confirmed by measurements carried out at Ukrainian NPPs. For example, the results of radioactivity measurements at four points around the Rivne NPP recorded similar indicators from 2.02 to 2.48 µBq/m3.
The Finnish Radiation and Nuclear Safety Authority (STUK) informed that minor concentration of iodine-131 isotope in the atmosphere was recorded at the end of January in Kotka to the east of Helsinki (Finland). Last week this isotope was detected again, but in Kajaani that is to the north of Finnish capital. The levels recorded by STUK were insignificant from 0.7 to 1.6 µBq/m3.
Nuclear reactor, enterprises involved into isotope production for medical purposes, nuclear fuel processing plant or testing related to nuclear weapons can be the possible source of iodine-131 release. In view of the fact that in addition to iodine-131 other radioactive isotopes of chemical elements were detected, it is possible to assume that the enterprise involved into its production, in particular for medical purposes, is the source of iodine-131.
Since iodine-131 has a short half-life (8 days), it can be assumed that the release occurred in February this year. The source of radioactive isotope is not known as of the moment.
It should also be noted that Russia is one of the largest producers of iodine-131 radionuclide, and the release of pharmaceuticals with this isotope started at Leningrad NPP in the summer of 2017.