The toxic legacy of the Cold War lives on in Russia's Arctic, where the Soviet military dumped many tonnes of radioactive hardware at sea.
For more than a decade, Western governments have been helping Russia to remove nuclear fuel from decommissioned submarines docked in the Kola Peninsula - the region closest to Scandinavia.
But further east lies an intact nuclear submarine at the bottom of the Kara Sea, and its highly enriched uranium fuel is a potential time bomb.
This year the Russian authorities want to see if the K-27 sub can be safely raised, so that the uranium - sealed inside the reactors - can be removed.
They also plan to survey numerous other nuclear dumps in the Kara Sea, where Russia's energy giant Rosneft and its US partner Exxon Mobil are now exploring for oil and gas.
Seismic tests have been done and drilling of exploratory wells is likely to begin next year, so Russia does not want any radiation hazard to overshadow that. Rosneft estimates the offshore fossil fuel reserves to be about 21.5bn tonnes.
In a statement to the BBC, Exxon Mobil said that before drilling offshore "it is standard industry practice to conduct extensive studies at and below the seabed" to check for hazards, using tools including remote sonar and a magnetometer.
It said Rosneft had also carried out a study focused on nuclear waste disposal in the Kara Sea.
The two companies "are confident that we can safely drill in the Kara Sea and avoid hazards from radioactive materials on the seabed", Exxon Mobil said.
The Kara Sea region is remote, sparsely populated and bitterly cold, frozen over for much of the year. The hostile climate would make cleaning up a big oil spill hugely challenging, environmentalists say.
Those fears were heightened recently by the Kulluk accident - a Shell oil rig that ran aground in Alaska.
But Charles Emmerson, an Arctic specialist at the Chatham House think tank, says Arctic drilling is a "strategic imperative" for Russia, which relies heavily on oil and gas exports.
It is a bigger priority for Russia than Alaskan energy is for the US, he says, because the US now has a plentiful supply of shale gas. That and environmental concerns make the Arctic more problematic for Americans, he told BBC News.
"In the US the Arctic gets great public scrutiny and it's highly political, but in Russia there is less public pressure."
Russia is rapidly developing the energy-rich Yamal Peninsula, on the eastern shore of the Kara Sea. The retreat of Arctic summer sea ice, believed to be evidence of global warming, means liquefied natural gas tankers will be able to reach the far east via Russia's Northern Sea Route in future.
On the western flank is a closed military zone - the Novaya Zemlya archipelago. It was where the USSR tested hydrogen bombs - above ground in the early days.
Besides K-27, official figures show that the Soviet military dumped a huge quantity of nuclear waste in the Kara Sea: 17,000 containers and 19 vessels with radioactive waste, as well as 14 nuclear reactors, five of which contain hazardous spent fuel. Low-level liquid waste was simply poured into the sea.
Norwegian experts and the International Atomic Energy Agency (IAEA) are satisfied that there is no evidence of a radiation leak - the Kara Sea's radioisotope levels are normal.
But Ingar Amundsen, an official at the Norwegian Radiation Protection Authority (NRPA), says more checks are needed.
The risk of a leak through seawater corrosion hangs over the future - and that would be especially dangerous in the case of K-27, he told BBC News.
"You cannot exclude the possibility that there is more waste there which we don't know about," he said.
Igor Kudrik of the Norwegian environmental group Bellona says there is even a risk that corrosion could trigger a nuclear chain reaction, in the worst-case scenario.
With international help Russia did manage to lift the wreck of the Kursk submarine after it sank in the Barents Sea during exercises in 2000. A torpedo explosion and fire killed 118 Russian sailors, in a drama which gripped the world's media. The Russian navy was heavily criticised for its slow response.
But another ill-fated Russian nuclear-powered sub - the K-159 - remains at the bottom of the Barents Sea, in international waters.
And in the Norwegian Sea lies the K-278 Komsomolets, reckoned to be too deep to be salvaged.
Mr Amundsen says Russia is finally giving the radioactive waste problem the attention it deserves, and "we're very happy they are focusing on this now".
K-27 was an experimental submarine - the first in the Soviet navy to be powered by two reactors cooled by lead-bismuth liquid metal.
Disaster struck in 1968, when radioactive gases escaped from one reactor, poisoning crew members who tried to repair it at sea.
Nine sailors died of radiation sickness, but the Soviet military kept it secret for decades.
The navy gave up trying to repair K-27 and scuttled it illegally in 1981 off Novaya Zemlya. It lies just 30m (99ft) beneath the surface of Stepovogo fjord - though international guidelines say decommissioned vessels should be buried at least 3,000m down.
Last September a joint Norwegian-Russian expedition examined the wreck with a remotely operated vehicle (ROV) equipped with a video camera. Some other nuclear dump sites were also examined and they found no signs of any leak, but the investigations are continuing.
Beyond the Kara Sea, Russia is forging ahead with exploration of the Arctic seabed, collecting data for a claim to areas beyond its waters.
Other Arctic countries are doing the same, aware of the frozen wilderness's importance as the planet's more accessible resources are depleted. A UN body, the UN Convention on the Law of the Sea (UNCLOS), will adjudicate on the claims.
As if to underline the strategic priorities, Russia is boosting its military presence in the Arctic and the Northern Fleet is getting a new generation of submarines, armed with multiple nuclear warheads.