Polaris

A Legacy of Freedom

THE NUCLEAR PROPULSION PLANT

The propulsion plant of a nuclear-powered ship is based upon the use of a nuclear reactor to provide heat. The heat comes from the fissioning of nuclear fuel contained within the reactor. Since the fissioning process also produces radiation, shields are placed around the reactor so that the crew is protected.

The nuclear-propulsion plant uses a pressurized water reactor design that has two basic systems: the primary system and the secondary system. The primary system circulates ordinary water and consists of the reactor, piping loops, pumps, and steam generators. The heat produced in the reactor is transferred to the water under high pressure so it does not boil. This water is pumped through the steam generators and back into the reactor for reheating.

In the steam generators, the heat from the water in the primary system is transferred to the water in the secondary system to create steam. The secondary system is isolated from the primary system so that the water in the two systems does not intermix.

In the secondary system, steam flows from the steam generators to drive the turbine generators, which supply electricity to the ship and to the main propulsion turbines, which in turn drive the propeller through a reduction gear. After passing through the turbines, the steam is condensed into water, which is fed back to the steam generators by the feed pumps. Thus, both the primary and secondary systems are closed systems where water is recirculated and reused.

There is no step in the generation of this power that requires the presence of air or oxygen. This allows the ship to operate completely independent of the earth’s atmosphere for extended periods of time.