How does a nuclear submarine work?

The "submarine" part of a nuclear submarine works in basically the same way as a conventional submarine. The differences lie primarily in the propulsion area and some support functions. Nuclear reactors generate a lot of heat energy because of the nuclear fisson reactions occurring in the fuel, and that is the key to nuclear propulsion.

The reactor is used to heat water to make steam. Air is unnecessary in this process. The reactor coolant system circulates water (very hot water) into a steam generator in a closed loop. The steam that is generated is then used by conventional steam turbines (the main engines) which drive the propellor (called a screw) through a reduction gear. Small steam turbines are used to drive electric generators. There is a back up battery bank and also a conventional diesel engine (the emergency diesel engine) that drives an electric generator.

Provisions have to be made to treat the atmosphere as the craft is intended to remain submerged for extended periods.

The diving and control systems are largely the same as on a conventional submarine.

Weapons systems include the conventional torpedo (with or without nuclear capability) and (sub)surface to surface missiles like the cruise missile. As the new submarines are superior weapons platforms, large missile systems are included on some designs.

Electronics systems for communications as well as detection and countermeasures are all modern. The new nuclear submarines owe a huge debt in technological development to the old units, but they far outclass them in capability.