Russian officials have confirmed they measured "extremely high" concentrations, relative to normally nonexistent levels, of the radioactive isotope ruthenium-106 in late September in the southern Urals.
France's nuclear-safety agency said the release appeared to have come from an area close to the Mayak nuclear facility, which reprocesses nuclear fuel and produces radioactive material for research purposes.
RFE/RL spoke with two independent nuclear experts who said evidence suggested no health threat from the incident, but suspect it was similar to an accident that occurred in 1993 at a nuclear facility in Tomsk involving reprocessed fuel that was being stored.
RFE/RL: Ruthenium-106 concentrations are known to be man-made rather than occurring in nature and the isotope has a relatively short radioactive half-life of only about one year compared to other isotopes. How deadly is ruthenium-106 and how far could the fallout of this radioactive isotope travel?
Vitaly Fedchenko, an expert on nuclear energy, nuclear materials, and fuel at the Stockholm International Peace Research Institute: So, these are wrong questions, especially the part about whether it is deadly or not, because what we are talking about is not just the specific isotope but also its concentration in the air. From the public statement by radiation-protection authorities in the three counties -- Russia, France, and Germany -- the concentration of ruthemium-106 involved in this particular case is way too low to be any kind of health and safety concern of the public.
RFE/RL: What evidence leads you to believe that a release of Ru-106 was not something that happened while spent nuclear fuel was being reprocessed at the Mayak nuclear facility in the Chelyabinsk region?
Fedchenko: Spent fuel contains hundreds of different types of isotopes. So if something would break or there would be some kind of uncontrolled release [during reprocessing], we would see a lot more than just one type of isotope. And there would probably be more of other isotopes because they are produced in fuel in higher quantities. Mayak also issued a statement saying that they did not produce this particular isotope this year and, if I understand correctly, for a while now. If there is anything, I would rather think that one should look for facilities handling or producing this particular isotope.
RFE/RL: What about a storage facility or laboratory working with nuclear material that has already been reprocessed? Is it true that there was a similar situation in Russia during the early 1990s where a leak involved mostly only ruthenium-106?
Lars-Erik De Geer, former expert with the Swedish Defense Research Agency and member of monitoring teams verifying compliance with the Comprehensive Nuclear Test Ban Treaty: It actually was in Tomsk. There is a reprocessing plant in Tomsk, and that was an accident which happened in 1993 where they had some kind of a facility where ruthenium-106 was stored. There was an explosion there. It was disseminated in the atmosphere and we picked it up in Sweden.
It was not only ruthenium-106. There were also small, small amounts of iodine and another type of isotope. But it was totally dominated by ruthenium-106. So that's why I suspect [this latest incident] has something to do with reprocessing.
RFE/RL: Is there a possibility that this latest incident involved previously reprocessed nuclear material that was being stored or buried near the Mayak facility?
De Geer: Yeah, that's what comes into my head -- much based on what happened in 1993. But also, this time it is quite a big amount that must have been spread out -- much more than in 1993. I cannot see any other establishments that work with such amounts of single isotopes except reprocessing plants.
Why so much ruthenium? I mean, what they do in reprocessing is separate things into different types of elements. And obviously, based on the Tomsk incident, there was some separated parts that were dominated by ruthenium-106. I cannot imagine any other type of establishment which would do that.
RFE/RL: One of the few uses for ruthenium-106 is for medical applications involving eye treatment. Why would a reprocessing plant separate this material from other radioactive isotopes?
De Geer: At the reprocessing plant, you want to separate the various material into different half-lives. So something which has a very short half-life, you don't have to care too much about it to bury it down. And if it is very long-lived, you have to do it very carefully. That is why you want to have it in separate pieces, so to speak.
RFE/RL: What other evidence suggests that this release was related to the Mayak reprocessing facility?
De Geer: If you look at the maps where it has been detected, it very much focuses on Mayak. Mayak is a place where they do bury lots of things. Of course, it can be a little bit older -- reprocessed years ago. Some years ago, I mean. Not from the 1960s, '70s, '80s, or even 1990s. But maybe a few years ago. This could [also] be some type of separated things from another reprocessing plant and they were in the process of burying it, or something like that.
