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 periods of time; 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.
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.
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.
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 propellershaft or rely on the reactor heat to produce steam that drives steam turbines (cf. nuclear marine propulsion). Reactors used in submarines typically use highly enrichedfuel (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.
K-14, 1961, reactor compartment replaced due to unspecified "breakdown of reactor protection systems."
K-19, 1961, loss-of-coolant accident resulting in 8 deaths and more than 30 other people being over-exposed to radiation. The events on board the submarine are dramatized by the film K-19: The Widowmaker.
K-11, 1965, both reactors damaged during refueling while lifting the reactor vessel heads; reactor compartments scuttled off the east coast of Novaya Zemlya in the Kara Sea in 1966.
K-140, 1968, reactor damaged following an uncontrolled, automatic increase in power during shipyard work.
K-429, 1970, an uncontrolled start up of the ship's reactor led to a fire and the release of radioactivity
K-116, 1970, loss-of-coolant accident in the port reactor; substantial radioactivity released.
K-64, 1972, failure of the first Alfa-class liquid-metal cooled reactor; reactor compartment scrapped.
K-222, 1980, Papa-class submarine had a reactor accident during maintenance in the shipyard while the ship's naval crew had left for lunch.
K-123, 1982, Alfa-class submarine reactor core damaged by liquid-metal coolant leak; the sub was forced out of commission for eight years.
K-431, 1985, a reactor accident while refueling resulted in 10 fatalities and 49 other people suffered radiation injuries.
K-219, 1986, suffered an explosion and fire in a missile tube, eventually leading to a reactor accident; a 20-year old enlisted seaman, Sergei Preminin, sacrificed his life to secure one of the onboard reactors. The submarine sank three days later.
USS Thresher (SSN-593), 1963, was lost during deep diving tests; later investigation concluded that failure of a brazed pipe joint and ice formation in the ballast blow valves prevented surfacing. The accident motivated a number of safety changes to the U.S. fleet.
K-3, 1967, the first Soviet nuclear submarine, a fire associated with the hydraulic system killed 39 sailors.
USS Scorpion (SSN-589), 1968, lost at sea, evidently due to implosion upon sinking. What caused Scorpion to descend to its crush depth is not known.
K-141 Kursk, 2000, the generally accepted theory is that a leak of hydrogen peroxide in the forward torpedo room led to the detonation of a torpedo warhead, which in turn triggered the explosion of half a dozen other warheads about two minutes later.
Ehime Maru & USS Greeneville, 2001, the American submarine surfaced underneath the Japanese training vessel. Nine Japanese were killed when their ship sank as a result of the collision.
K-159, 2003, sank in the Barents Sea while being towed to be scrapped, killing nine crewmen.
USS Miami (SSN-755), 2012, the submarine's forward compartment was destroyed by an arsonist-set fire while in shipyard, causing damage with an estimated $700 million in repair costs. While repairs were initially planned upon, due to budget cuts the boat was subsequently scrapped.