The Akademik Lomonosov sailed away from Murmansk with three tugs
Russia has launched a pioneering floating nuclear power station, which will sail 5,000km (3,000 miles) from the Arctic port of Murmansk to Chukotka in the far east.
The nuclear agency Rosenergoatom says the Akademik Lomonosov's mobility will boost the power supply to remote areas.
One of its targets is to power the Chaun-Bilibin mining complex in Chukotka, which includes gold mines.
Greenpeace sees the project as high-risk, in a harsh weather environment.
Critics including Greenpeace point to previous Russian and Soviet nuclear accidents and warn that the Akademik Lomonosov's mission increases the risk of polluting the Arctic - a remote, sparsely-populated region with no big clean-up facilities.
The launch comes just two weeks after a nuclear-powered engine blew up on a Russian naval test range in the Arctic, killing five nuclear engineers and releasing radiation, though the 1986 Chernobyl disaster was far worse.
The floating power station's highly radioactive spent fuel will be stored on board. Others of similar design will follow to serve remote areas.
The Akademik Lomonosov is also destined to supply electricity to offshore oil rigs in Russia's Arctic. Another idea is to hook it up to a desalination plant, to produce fresh water, and in future island states could benefit from such power stations.
The Northern Sea Route connecting European Russia with far eastern ports is becoming navigable for longer periods because global warming is reducing pack ice.
Three tugs will tow the facility to Pevek, where it is expected to dock in late September. In good weather conditions it will sail at 4-5 knots (7-9km/h).
The Lomonosov was built in St Petersburg and has two nuclear reactors of the type used in Russian icebreakers. They are KLT-40S reactors with a combined capacity of 80 megawatts, and are reported to be tsunami-proof.
Russia's Vesti news programme says the facility will have enough power to illuminate and heat a town of about 100,000 inhabitants.
The crew on board is expected to be about 70-strong.
It is 140m (459ft) long, 30m (98ft) wide and is expected to operate for 40 years.
In the period 1968-1976 the US Army used a floating nuclear power plant at the Panama Canal, for canal operations, called the MH-1A Sturgis. It was a converted World War Two cargo ship, and was later decommissioned.