Nuclear Marine Propulsion - Power Plants

Power Plants

Operation of a civil or naval ship power plant is similar to land-based nuclear power reactors. A sustained nuclear reaction in the reactor produces heat that is used to boil water. The resulting steam spins a turbine. The turbine shaft may be coupled through a gearbox speed reducer to the ship's propeller, or in a turbo-electric drive system may operate a generator that supplies electric power to motors connected to the propellers.

The Russian, U.S. and British navies rely on steam turbine propulsion, while the French and Chinese ships use the turbine to generate electricity for propulsion (turbo-electric propulsion). Most nuclear submarines have a single reactor, but Russian submarines and the USS Triton had two. Most American aircraft carriers are powered by two reactors, but the USS Enterprise has eight. The majority of marine reactors are of the pressurized water type, although the US and Soviet navies have designed warships powered with liquid metal cooled reactors.

Nuclear power for propulsion has several operating and logistic characteristics that appeal to the designers of ships for both civil and military purposes. A small amount of nuclear fuel can provide energy equivalent to millions of times its weight in coal or oil. It is quite practical to build a reactor which will operate a vessel for several years without refuelling. Although the cost of manufacturing nuclear fuel elements is high, the overall cost of fuel is much lower than that of the amount of fossil fuel required to generate the same amount of energy. Like sailing ships, nuclear vessels are independent of the vagaries of procurement of fuel at every port. The laborious and costly process of loading and burning fuel is largely eliminated for most of the vessel's operating life.

Because of its high power density and the elimination of the need for large fuel bunkers, a nuclear propulsion plant allows more space for paying cargo. It also allows a vessel to operate at higher speeds for years without refuelling. This improves the speed and efficiency of ocean-going commerce. Military vessels, such as submarines and aircraft carriers, can travel at high speeds over vast distances, limited only by the endurance of their crews. Arctic vessels can operate for months, independent of fuel supplies.

Nuclear reactors require no oxygen for combustion and emit no exhaust gas. This is a minor benefit for surface vessels, eliminating the ducts, exhaust stacks and machinery needed to support the burning of fossil fuels. For submersible vessels this is the most important advantage. With nuclear power, a submarine can be propelled at speeds comparable to those of surface ships for protracted periods, limited only by crew endurance instead of fuel supply or battery capacity. Although not a motivation for the original development of maritime nuclear power, environmental concerns have sparked increased interest on the part of some who are concerned about effects of CO₂, SO₂ and other air pollutants emitted by cargo ships. (For economic reasons, ships operate on the lowest-quality fuel their engines can tolerate, resulting in very high emissions of pollutants.)