|Fig. 1: Decommissioned in 2013, the USS Enterprise (top) was the first nuclear aircraft carrier created in 1962. (Source: Wikimedia Commons)|
Nuclear powered vessels, whether a ship or submarine, receive its propulsion energy from nuclear power plants that sit onboard. Through the process of heating water to produce steam and ultimately power steam turbines and turbo generators, the ship generates energy.  The naval reactor model has gone on to be implemented in submarines, aircraft carriers, merchant ships and ice breakers. Collectively, these make up the "Nuclear Navy", a phrase coined after the revolutionization of naval warfare.
Under the direction of U.S. Navy Capitan Hyman G. Rickover, the technology was first explored from 1942 to 1946 to see if nuclear fission could be used for propulsion. When World War 2 came to an end, Rickover sought to leverage the technology behind the nuclear energy and reactors used in the atomic bombs for marine use. With time, the Captain was the driving force behind the manufacturing of the first nuclear powered submarine, Nautilus, in 1952 and aircraft carrier, USS Enterprise, in 1954 (See figure 1). [2,3] The success of Hyman G. Rickover's effort earned him the title of "The Father of the Nuclear Navy" as well as the recognition of Admiral in the military ranks.
Nuclear reactors on ships are fueled by bringing in sea water known as feed water.  The feed water is then heated by the primary circuit. The ship then turns it into steam where it passes through driers until ultimately ending as "super heated dry steam". While most ships and submarines run off of a single nuclear power plant, aircraft vessels are powered by two. Since ships are divided into two sides, port and starboard, there is a natural safely structure in store should one side fail.
While land based reactors are able to generate up to 1,600 megawatts of power, marine propulsion max out a couple hundred megawatts. Due to being confined to a small space and having to handle the adverse conditions of the sea, marine reactors must be able to generate more power and thus handle higher stress. This means the design of these devices must be reliable and self-sufficient especially as ships undertake thousands of mile journeys without the chance to undergo maintenance repairs.
One of the biggest problems with nuclear marine propulsion is their end of life cycle. Decommissioning is a major task consisting of de-fueling and land burial of the reactor. This waste is considered "low-level" meaning it has been contaminated with other radioactive material.  The Puget Sound Naval Shipyard provides storage to these components, yet there is no means of reuse as the protocol states they must remain secure for a duration of 600 years.
As nuclear marine ships become more common, Russia leads the way in striving to create floating nuclear power plants. With the most advancements occurring in the remoteness and increase in infrequency of refueling, time will only tell how the great advancements can be with nuclear marine propulsion. Russia plans to build two 35MWe units for icebreaking that will only require refueling every 4 years. It is predicted that with time more and more nuclear reactors will be maximized for the benefit of civilian propulsion.
© Valarie Allman. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 H. F. Crouch, Nuclear Ship Propulsion (Cornell Maritime Press, 1960).
 E. Seeger, Underway on Nuclear Power: 50th Anniversry of the U.S.S. Nautilus (Faircourt Publications, 2004).
 T. Cullen, Encyclopedia of World Sea Power (Crescent, 1988).
 R. F. Pocock, Nuclear Ship Propulsion (Littlehamption Book Services, 1970).
 "National Low-Level Waste Management Program," U.S. Department of Energy, DOE/IG-0462, February 2000.