What is the nuclear material that has leaked?

Russia’s meteorological service has confirmed that “extremely high” concentrations of a radioactive isotope, ruthenium-106, were found in several parts of the country in late September. Ru-106 is a decay product from nuclear reactions: the initial fuel is typically uranium or plutonium, and this splits into smaller nucleii, which decay through a series of different radioactive elements. Most of the isotopes in the sequence have very short half-lives, meaning they exist for only a few seconds or minutes, but Ru-106 has a half-life of just over a year. That means if it leaks, it sticks around long enough to be detected.

Could it have come from a bomb?

Nuclear scientists say that if the radiation had come from a bomb, or an incident at a nuclear reactor, they would expect unusually high levels of a range of different radio-isotopes. However, since only a peak in Ru-106 was spotted, this points to a fuel reprocessing plant or medical facility as the most likely source.

Do we know which facility the leak originated from?

The Russian authorities have not confirmed the source of the leak, but the country’s meteorological service reported that the highest concentration of Ru-106 was registered in Argayash, a village in the Chelyabinsk region in the southern Urals. This is close to the Mayak nuclear facility, a reprocessing site for spent nuclear fuel.

Is it dangerous?

The highest levels reported were 986 times the background levels, which sounds alarming. However, the background levels are close to zero and nuclear safety experts believe the leak is unlikely to pose a health risk or require people in the vicinity to be evacuated. Professor Paddy Regan, a nuclear expert at the University of Surrey told me: “The levels detected may be extremely high relatively to the background, but they’re not extremely dangerous.”

How long will it stick around for?

The half-life of Ru-106 is 374 days, meaning that in just over a year, half of the material will have decayed away. So the leak will still be detectable for five or six years, but it is unlikely to require any major environmental cleanup operation.