Russian Northern coast is a vast territory lays for a few thousand of miles and all this coastline is inside the Polar Circle. Long polar winters mean no daylight at all, just one day changes another without any sign of the Sun rising above the horizon. There is only polar night for 100 day a year.

But across this Northern coast there was always a short way for the cargo boats to travel from Eastern part of Russia to the Western. Now this trip can be made fairly easy with the appearance of all the satellite navigation equipment like GPS and others, but during the Soviet Era they had none of this.

So, special lightweight small atomic reactors were produced in limited series to be delivered to the Polar Circle lands and to be installed on the lighthouses.
http://englishrussia.com/?p=2198