RUSSIA is finally going to demolish its “floating Chernobyl”, a ship full of highly radioactive waste from the Soviet Arctic fleet, 21 years after its existence was first revealed by New Scientist.

Even if it is dismantled safely, more dangerous radioactive junk lurks in the Kara Sea off north-west Russia, much of it unmapped and in the path of oil and gas exploration.

The ex-Soviet ship Lepse contains 2.7 × 1016 becquerels of radioactivity – comparable to the caesium released by the 1986 Chernobyl accident. It comes from 638 fuel assemblies, submarine reactor parts containing spent fuel rods. Half are from the submarine Lenin, which lost reactor coolant in a 1966 accident, overheating and deforming the fuel so it could not be removed

The European Union is worried that radioactivity will leak out and contaminate Arctic fishing grounds, and it offered to cut up the ship and remove its contents in 1994. But Russia resisted, possibly because it didn’t want foreign operators to learn that the uranium was more enriched than usual, says Nils Bøhmer of Norwegian environmental group Bellona, who took part in the negotiations. That would reveal how long the military subs could stay at sea without refuelling – more enriched fuel lasts longer.

The Lepse was finally towed into dry dock in late October, and will be cut up using Russian technology starting this December, says Bøhmer. The midsection containing the fuel assemblies will be taken onto dry land for dismantling in 2016. “That is the most dangerous part,” says Bøhmer. “No one knows the condition of the fuel assemblies.” If one breaks and falls, the change in geometry could start a chain reaction. This would heat, melt and ignite the highly radioactive material. “It would be a real mess,” says Bøhmer.

Meanwhile, 16 whole submarine reactors dumped as waste by Russia still lie offshore, some complete with fuel. Two reactors are still in their subs. One sank in 2003 as it was towed to be scrapped, and another was scuttled in 1981 after an accident. The two sunken subs alone account for “about half the radioactivity in spent nuclear fuel on the seabed in the Arctic”, says Per Strand of the Norwegian Radiation Protection Authority.

In 2015 Norway and Russia will release a scientific assessment on whether the two subs should be raised, but so far Russia has no plans to clear the rest of the sea’s sunken radioactive hazards. Its own scientists, however, fear that severe contamination is imminent.

Strand took part in joint Russian-Norwegian surveys of the wrecks in 2012 and 2014, which found no radioactive leakage. But, he says, because saltwater will corrode the metal around the radioactive material, the “radioactivity from the spent nuclear fuel will eventually leak into the environment”. This could even happen by 2020, according to a September report by Valery Osminov of the Nuclear Safety Institute of the Russian Academy of Sciences. And given that the nearby facility for demolishing submarine reactors is due to close in 2020, the wrecks should be raised by then, he says.

Meanwhile, there are also 17,000 containers of solid radioactive waste sunk in the area. Recent surveys by Russia and the EU found only a little contamination in nearby sediments. But, says Osminov, 4000 were judged to be in poor shape and could corrode even faster. And unlike the sunken vessels and reactors, we know only roughly where the containers are – and some lie within an area where oil and gas companies plan to explore. “If oil drilling takes place and you hit one of the containers, you could release the radioactivity,” warns Bøhmer. “Unfortunately,” Strand says, “there are no concrete plans for raising the objects.” That is a Russian responsibility – but so far, says Bøhmer, no Russian ministry wants to take charge.