The Russian Meteorological Service finally confirmed on Tuesday that it had recorded the release of "extremely high contamination" of the radioactive isotope Ruthenium-106 in the southern Urals region in late September.
That was after radiation monitoring programs in Europe had earlier detected low levels of the isotope in air as far away as Germany and France.
Here's what you need to know about ruthenium-106 and the radioactive release.
What is ruthenium-106?
Ruthenium-106 is a radioactive form of the rare heavy metal ruthenium, which is a "platinum group" metal similar to platinum. Radioactive isotopes or forms of elements naturally decay into other elements, giving off radiation in the process.
Where does ruthenium-106 come from?
Ruthenium-106 is produced from the fission or splitting of uranium-235, the type of uranium used in nuclear fission reactors, so it's found in spent nuclear fuel. It's also used in medicine for cancer radiation therapy, especially for eye and skin tumours, so it may be produced for that purpose. And it's used in radioisotope thermoelectric generators that power satellites, says BfS, the German federal office for radiation protection.
What kind of radiation does ruthenium-106 give off?
Radioactive elements give off radiation as they decay into other elements. Ruthenium-106 gives off radiation in the form of high energy electrons called beta particles as it decays into rhodium-106 and then into palladium-106, which isn't radioactive.
Ruthenium-106 has a half life of 373.6 days, or around a year. That means after a year, half of it would have decayed and only half would remain.
How are radioactive isotopes in the air detected?
In Germany, monitoring is done by collecting several hundred cubic metres of air per day at specific locations and running it through a filter system. After a week, the filter is analyzed for trace amounts of nuclear isotopes, says Jan Lauer, a spokesperson for the German nuclear safety agency, BfS. Similar techniques are used in other countries.
How much ruthenium-106 was detected?
Russian's state weather service Roshydromet reported recently that levels of ruthenium-106 from the Agrayash weather station in the southern Ural mountains was 986 times those of the previous month.
Germany's nuclear safety agency reported that between Sept. 29 and Oct. 9, "very low" levels of ruthenium-106 were detected at six stations in Germany, along with others in Austria, Switzerland and Italy.
France's nuclear safety agency reported on Nov. 9, that it had found trace amounts of ruthenium-106 at three monitoring stations between Sept. 27 and Oct. 13.
How hazardous is the release?
Not at all in Europe, the European nuclear safety agencies report. According to the German nuclear safety agency, you're normally getting a certain dose every hour of naturally occurring "background radiation." And that dose is bigger than what you'd get breathing in the detected levels of ruthenium-106 for a week.
However, in Russia, near the Agrayash weather station, things may be different.
France's nuclear safety agency has done simulations that estimate the amount of radiation released at the source was between 100 and 300 billion becquerels. It said if such a release occurred in France, measures would need to be implemented to protect populations within a few kilometres, and radiation levels would exceed guidelines in food produced within a few tens of kilometres.
What is the likely source?
The Russian branch of the environmental group Greenpeace, which has been investigating this release, suggests that it could be related to the vitrification of nuclear waste — a process where nuclear waste is mixed with molten glass and poured into a steel canister, where it solidifies. The canister is then sealed for storage and disposal.
Another possibility, Greenpeace Russia says, is that materials containing ruthenium-106 were placed in a metal remelting furnace.
Both those activities take place at the Mayak complex run by the Russia-owned nuclear firm Rosatom, which is about 30 kilometres from the Agrayash weather station where the highest levels of ruthenium-106 were detected. It's also the site of some previous nuclear disasters.
However, the Mayak complex has denied being the source, saying it hasn't extracted ruthenium-106 from spent nuclear fuel for several years, Reuters reports.
European nuclear safety agencies say the source wasn't a nuclear power plant accident because such accidents release different kinds of isotopes, and only ruthenium-106 has been detected.
Is it possible that other radioactive isotopes were released and not detected?
Jan Lauer of the German nuclear safety agency, told CBC News that was "very, very unlikely."