The Russian government has confirmed it plans to locate the plant on a vessel in Pevek, a remote and sparsely populated port town in Russia's Far East, 215 miles north of the Arctic Circle.
The $254m (pounds 150m) station will be powered by two pressurised-water reactors adapted from Russian nuclear-powered icebreakers, a fleet which has long been cited by Western safety experts as a source of severe environmental threat.
Every 13 years the plant will be towed by barge to Murmansk, near the Finnish border - a journey of 2,500 miles, which will take it from one end of Russia to the other - for a refit and to reload with fuel.
The project drew immediate condemnation from Greenpeace in Moscow. "This is very threatening to the environment," said Andrei Simyonov, a spokesman. "Any nuclear waste that ends up in the sea will be distributed more quickly than on the earth itself."
The plan is certain to arouse fears about what would happen if the power- plant sank. It would not be the first vessel laden with radioactive material to do so; in 1989 the Soviet nuclear submarine Komsomolets went down in the sea 300 miles off Norway after a fire on board.
It had nuclear fuel in its reactor and nuclear warheads on board, but both Russian and international surveys found no evidence of substantial contamination.
The Pevet project comes amid international anxiety about Russia's nuclear- power programme, which has been reactivated after coming to a stand-still following the 1986 Chernobyl disaster. Western and Russian scientists are alarmed about the lack of safety standards in Russia's nuclear fleet (it has more than 200 nuclear-powered submarines) and within its 99 nuclear facilities, including 29 nuclear power-stations.
Ageing and inadequate equipment, dangerous storage, a lack of safety consciousness and an absence of effective independent regulatory bodies top the list of concerns. So does the lack of funds; in July, nuclear workers from four power stations grew so desperate about pay arrears that they marched to Moscow from the Smolensk nuclear power-plant, a 400-mile journey that took two weeks.
Russia's Ministry of Atomic Energy (Minatom) says the floating station has been approved by the International Atomic Energy Agency. It argues the plant is needed to replace a far more costly, 40-year-old coal-powered station, for which 100,000 tons of coal have to be shipped in every year. The fact that the region it will mostly supply, Chukotka, is rapidly depopulating has not derailed the plan; in the past four years half the 12,300 population of Pevek have left.
The Russians - who have been fiercely criticised for dumping nuclear reactors and other radioactive waste in the Kara and Barents seas and the Sea of Japan - say spent nuclear fuel will be kept on board the floating station, and not dumped. Such assurances may not convince environmentalists worried by the level of pollution in the Arctic, which has been contaminated by nuclear weapons tests, releases from nuclear fuel reprocessing plants and Chernobyl fall-out.
This year, a report commissioned by eight Arctic nations, including Russia, warned that the region's ecological system was far more vulnerable to radioactive contamination than elsewhere. It identified a "large number" of radioactive sources in the region, including storage of spent nuclear fuel, decommissioned nuclear submarines and nuclear reactors.
The Russians say the Pevet station - which is to stand in the east Siberian sea - is the first of its kind. It may not be the last; if they can raise the money they want to build two more.
5 Claims by Russia's former security chief, Alexander Lebed, that Russia has lost track of scores of tactical nuclear weapons were partly supported yesterday by his former deputy. Vladimir Denisov, an ex-deputy head of the Security Council, said an investigation last year had been unable to rule out that small nuclear bombs were left behind in former Soviet republics.