The propulsion plant of a nuclear powered ship is based upon the use of a nuclear reactor to provide heat. The heat, which comes from the fission process, also produces radiation; shields are placed around the reactor so that the crew is protected from the harmful effects of this radiation.
The nuclear propulsion plants in SSNs use a pressurized water reactor design which has two basic systems: the primary system and the secondary system. The primary system consists of the reactor, piping loops, pumps, and steam generators. The reactor superheats the pressurized water and circulates it through the steam generators, where the heat is transferred to the secondary system without any mixture of the systems. Once the water is passed through the steam generators, it is pumped back to the reactor for reheating.
In the steam generators, the heat from the water in the primary system is transferred to 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, the steam flows from the steam generators to drive the turbine generators, which supply the ship with electricity, and to main propulsion turbines, which drive the propeller. 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 in which water is recirculated and reused.
The Smithsonian Institution has just begun a groundbreaking exhibit on modern American submarines, including displays of complete compartments. A Maneuvering Room mockup is part of the exhibit, showing how the engineering spaces are controlled. Some of the systems in the exhibit are taken from our recently decommissioned sister ship USS James K. Polk (SSN-645).