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A nuclear submarine is a submarine powered by a nuclear reactor. The performance advantages of nuclear submarines over "conventional" (typically diesel-electric) submarines are considerable: nuclear propulsion, being completely independent of air, frees the submarine from the need to surface frequently, as is necessary for conventional submarines; the large amount of power generated by a nuclear reactor allows nuclear submarines to operate at high speed for long durations; and the long interval between refuellings grants a range limited only by consumables such as food. Current generations of nuclear submarines never need to be refueled throughout their 25-year lifespans. Conversely, the limited power stored in electric batteries means that even the most advanced conventional submarine can only remain submerged for a few days at slow speed, and only a few hours at top speed; recent advances in air-independent propulsion have eroded this disadvantage somewhat. The high cost of nuclear technology means that relatively few states have fielded nuclear submarines. Some of the most serious nuclear and radiation accidents ever to occur have involved Soviet nuclear submarine mishaps.
Construction of the Nautilus was made possible by the successful development of a nuclear propulsion plant by a group of scientists and engineers at the Naval Reactors Branch of the Atomic Energy Commission. In July 1951 the U.S. Congress authorized construction of the world's first nuclear-powered submarine, under the leadership of Captain Hyman G. Rickover, USN.
The Westinghouse Corporation was assigned to build its reactor. After the submarine was completed, Mamie Eisenhower broke the traditional bottle of champagne on Nautilus' bow. On 17 January 1955, it began its sea trials after leaving its dock in Groton, Connecticut. The submarine was 320 feet (98 m) long, and cost about $55 million.
The Soviet Union soon followed the United States in developing nuclear-powered submarines in the 1950s. Stimulated by the U.S. development of the Nautilus, Soviet work on nuclear propulsion reactors began in the early 1950s at the Institute of Physics and Power Engineering, in Obninsk, under Anatoliy P. Alexandrov, later to become head of the Kurchatov Institute. In 1956, the first Soviet propulsion reactor designed by his team began operational testing. Meanwhile, a design team under Vladimir N. Peregudov worked on the vessel that would house the reactor.
After overcoming many obstacles, including steam generation problems, radiation leaks, and other difficulties, the first nuclear submarine based on these combined efforts entered service in the Soviet Navy in 1958.[unreliable source?]
At the height of the Cold War, approximately five to ten nuclear submarines were being commissioned from each of the four Soviet submarine yards (Sevmash in Severodvinsk, Admiralteyskiye Verfi in St. Petersburg, Krasnoye Sormovo in Nizhny Novgorod, and Amurskiy Zavod in Komsomolsk-on-Amur). From the late 1950s through the end of 1997, the Soviet Union, and later Russia, built a total of 245 nuclear submarines, more than all other nations combined.
Today, six countries deploy some form of nuclear-powered strategic submarines: the United States, Russia, France, the United Kingdom, People's Republic of China, and India. Several other countries, including Argentina and Brazil, have ongoing projects in different phases to build nuclear-powered submarines.
In the United Kingdom, all former and current nuclear submarines for their British Royal Navy (with the exception of three: HMS Conqueror, HMS Renown and HMS Revenge) have been constructed in Barrow-in-Furness (at BAE Systems Submarine Solutions or its predecessor VSEL) where construction of nuclear submarines continues. Conqueror is[update] the only nuclear-powered submarine ever to have engaged an enemy ship with torpedoes, sinking the cruiser ARA General Belgrano with two Mark 8 torpedoes during the 1982 Falklands War.[note 1]
The main difference between conventional submarines and nuclear submarines is the power generation system. Nuclear submarines employ nuclear reactors for this task. They either generate electricity that powers electric motors connected to the propeller shaft or rely on the reactor heat to produce steam that drives steam turbines (cf. nuclear marine propulsion). Reactors used in submarines typically use highly enriched fuel (often greater than 20%) to enable them to deliver a large amount of power from a smaller reactor and operate longer between refuelings – which are difficult due to the reactor's position within the submarine's pressure hull.
The nuclear reactor also supplies power to the submarine's other subsystems, such as for maintenance of air quality, fresh water production by distilling salt water from the ocean, temperature regulation, etc. All naval nuclear reactors currently in use are operated with diesel generators as a backup power system. These engines are able to provide emergency electrical power for reactor decay heat removal, as well as enough electric power to supply an emergency propulsion mechanism. Submarines may carry nuclear fuel for up to 30 years of operation. The only resource that limits the time underwater is the food supply for the crew and maintenance of the vessel.
The stealth weakness of nuclear submarines is the need to cool the reactor even when the submarine is not moving; about 70% of the reactor output heat is dissipated into the sea water. This leaves a "thermal wake", a plume of warm water of lower density which ascends to the sea surface and creates a "thermal scar" that is observable by thermal imaging systems, e.g., FLIR. Another problem is that the reactor is always running, creating steam noise, which can be heard on SONAR, and the reactor pump (used to circulate reactor coolant), also creates noise, as opposed to a conventional submarine, which can move about on incredibly silent electric motors.
Some of the most serious nuclear and radiation accidents by death toll in the world have involved nuclear submarine mishaps. To-date, all of these were units of the former Soviet Union. Reactor accidents that resulted in core damage and release of radioactivity from nuclear-powered submarines include:
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