A fire broke out at the Yekaterinburg nuclear submarine on Thursday during repairs at a shipyard in northern Russia, the local emergencies ministry department said.
Fire safety violations during routine maintenance works are seen as the most likely cause of the blaze at a floating repair dock.
"No deaths or injuries have been reported. There is no threat of nuclear pollution," the department said in a statement.
Wooden scaffolding around the submarine caught fire, which spread to the submarine's light outer hull, Northern Fleet spokesman Capt. 1st Rank Vadim Serga said.
"There is no possibility of fire burning through the hull and no threat to on-board equipment," Serga said.
The K-84 Yekaterinburg nuclear submarine is one of seven Delta-IV class submarines in service, all deployed in the Northern Fleet. It carries 16 Sineva (NATO classification "Skiff") submarine-launched ballistic missiles.
The Delta-IV class submarines are the core of the naval component of the Russian nuclear triad at present and may remain in service for another 10 years.