Nuclear submarine

A nuclear submarine is a submarine powered by a nuclear reactor, but not necessarily nuclear-armed.
Nuclear submarines have considerable performance advantages over "conventional" submarines. 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 periods, and the long interval between refuelings grants a virtually unlimited range, making the only limits on voyage times factors such as the need to restock food or other consumables. Thus nuclear propulsion solves the problem of limited mission duration that all electric submarines face. Furthermore nuclear submarines can regenerate consumables to a certain extent, producing oxygen and fresh water from seawater via electrolysis and desalination.
The high cost of nuclear technology means that relatively few of the world's military powers have fielded nuclear submarines. Radiation incidents have occurred within the Soviet submarines, including serious nuclear and radiation accidents, but American naval reactors starting with the S1W and subsequent designs have operated without incident since the launch of USS Nautilus in 1954.

Nomenclature

In the US classification, nuclear-powered submarines are designated as SSxN, where the SS denotes submarine, x=G means that the submarine is equipped with guided missiles, x=B means that the submarine is equipped with ballistic missiles and the N means that the submarine is nuclear-powered. SSN refers to nuclear-powered attack submarines, which do not carry missiles.

History

The idea for a nuclear-powered submarine was first proposed in the United States Navy by the Naval Research Laboratory's physicist Ross Gunn in 1939. The Royal Navy began researching designs for nuclear propulsion plants in 1946.
Construction of the world's first nuclear-powered submarine was made possible by the successful development of a nuclear propulsion plant by a group of scientists and engineers in the United States at the Naval Reactors Branch of the Bureau of Ships and the Atomic Energy Commission. In July 1951, the U.S. Congress authorized construction of the first nuclear-powered submarine, Nautilus, under the leadership of Captain Hyman G. Rickover, USN.
The Westinghouse Corporation was assigned to build its reactor. After the submarine was completed at the Electric Boat Company, First Lady Mamie Eisenhower broke the traditional bottle of champagne on Nautilus bow, and the submarine was commissioned, on 30 September 1954. On 17 January 1955, she departed Groton, Connecticut, to begin sea trials. The submarine was long and cost about $55 million. Recognizing the utility of such vessels, the British Admiralty formed plans to build nuclear-powered submarines.
The Soviet Union soon followed the United States in developing nuclear-powered submarines in the 1950s. Stimulated by the U.S. development of Nautilus, Soviets began work on nuclear propulsion reactors 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, K-3 Leninskiy Komsomol of the Project 627 Kit class, called a by NATO, entered service in the Soviet Navy in 1958.
The United Kingdom's first nuclear-powered submarine was fitted with an American S5W reactor, provided to Britain under the 1958 US-UK Mutual Defence Agreement. The hull and combat systems of Dreadnought were of British design and construction, although the hull form and construction practices were influenced by access to American designs. During Dreadnoughts construction, Rolls-Royce, in collaboration with the United Kingdom Atomic Energy Authority at the Admiralty Research Station, HMS Vulcan, at Dounreay, developed a completely new British nuclear propulsion system. In 1960, the UK's second nuclear-powered submarine was ordered from Vickers Armstrong and, fitted with Rolls-Royce's PWR1 nuclear plant, was the first all-British nuclear submarine. Further technology transfers from the United States made Rolls-Royce entirely self-sufficient in reactor design in exchange for a "considerable amount" of information regarding submarine design and quietening techniques transferred from the United Kingdom to the United States. The rafting system for the Valiant class provided the Royal Navy with an advantage in submarine silencing that the United States Navy did not introduce until considerably later.
Nuclear power proved ideal for the propulsion of strategic ballistic missile submarines, greatly improving their ability to remain submerged and undetected. The world's first operational nuclear-powered ballistic missile submarine was with 16 Polaris A-1 missiles, which conducted the first SSBN deterrent patrol November 1960 – January 1961. The Soviets already had several SSBs of the Project 629 and were only a year behind the US with their first SSBN, ill-fated K-19 of Project 658, commissioned in November 1960. However, this class carried the same three-missile armament as the Golfs. The first Soviet SSBN with 16 missiles was the Project 667A, the first of which entered service in 1967, by which time the US had commissioned 41 SSBNs, nicknamed the "41 for Freedom".
At the height of the Cold War, approximately five to ten nuclear submarines were being commissioned yearly from the four Soviet submarine yards. 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.
In the United Kingdom, all former and current nuclear submarines of the British Royal Navy have been constructed in Barrow-in-Furness where construction of nuclear submarines continues. Conqueror the only nuclear-powered submarine in the world ever to have engaged an enemy ship with torpedoes, sinking the cruiser with two Mark 8 torpedoes during the 1982 Falklands War.
Today, six countries deploy some form of nuclear-powered strategic submarines: the United States, Russia, the United Kingdom, France, China, and India. Several other countries including Brazil and Australia have ongoing projects in various phases to build nuclear-powered submarines. In the meantime, the United States is developing Columbia-class submarines. It is expected to have 16 missile tubes and to have its first patrol mission in 2031. Twelve submarines of this class, with a service life of ca. 42 years, are expected to be commissioned.

Technology

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's heat to produce steam that drives steam turbines. Reactors used in submarines typically use highly enriched fuel 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. Also, virtually all nuclear reactors employed in submarines so far have been of the pressurized light-water reactor type. Due to concerns about nuclear proliferation some nuclear submarines have been fueled by low-enriched uranium comparable to the fuel used in civilian light water reactors used for electricity production on land. For example the French Rubis-class submarines use low-enriched uranium with 7% ²³⁵U in the fuel. The downside to using lower enriched fuel is that refueling cycles are shorter which reduces availability of the submarine. Furthermore, the ²³⁸U contained in the fuel will absorb neutrons and be transmutated into plutonium and minor actinides which can be a problem in disposal of the used fuel. Reactors other than PWRs have been deployed on the Soviet Alfa class submarines as well as USS Seawolf. However, those were seen as technological dead-ends and not pursued further.
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. In practice psychological considerations also apply as it is not desirable for the crew to spend too long in the enclosed space that is a submerged submarine.
The stealth technology 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, also creates noise, as opposed to a conventional submarine, which can move about on almost silent electric motors.