Nuclear marine propulsion is propulsion of a ship or submarine with heat provided by a nuclear reactor. The power plant heats water to produce steam for a turbine used to turn the ship's propeller through a gearbox or through an electric generator and motor. Nuclear propulsion is used primarily within naval warships such as nuclear submarines and supercarriers. A small number of experimental civil nuclear ships have been built. [1]
Compared to oil- or coal-fuelled ships, nuclear propulsion offers the advantage of very long intervals of operation before refueling. All the fuel is contained within the nuclear reactor, so no cargo or supplies space is taken up by fuel, nor is space taken up by exhaust stacks or combustion air intakes. [2] The low fuel cost is offset by high operating costs and investment in infrastructure, however, so nearly all nuclear-powered vessels are military. [2]
Most naval nuclear reactors are of the pressurized water type, with the exception of a few[ quantify ] attempts[ by whom? ] at using liquid sodium-cooled reactors. [2] A primary water circuit transfers heat generated from nuclear fission in the fuel to a steam generator; this water is kept under pressure so it does not boil. This circuit operates at a temperature of around 250 to 300 °C (482 to 572 °F). Any radioactive contamination in the primary water is confined. Water is circulated by pumps; at lower power levels, reactors designed for submarines may rely on natural circulation of the water to reduce noise generated by the pumps.[ citation needed ]
The hot water from the reactor heats a separate water circuit in the steam generator. That water is converted to steam and passes through steam driers on its way to the steam turbine. Spent steam at low pressure runs through a condenser cooled by seawater and returns to liquid form. The water is pumped back to the steam generator and continues the cycle. Any water lost in the process can be made up by desalinated sea water added to the steam generator feed water. [3]
In the turbine, the steam expands and reduces its pressure as it imparts energy to the rotating blades of the turbine. There may be many stages of rotating blades and fixed guide vanes. The output shaft of the turbine may be connected to a gearbox to reduce rotation speed, then a shaft connects to the vessel's propellers. In another form of drive system, the turbine turns an electrical generator, and the electric power produced is fed to one or more drive motors for the vessel's propellers. The Russian, U.S. and British navies rely on direct steam turbine propulsion, while French and Chinese ships use the turbine to generate electricity for propulsion (turbo-electric transmission).[ citation needed ]
Some nuclear submarines have a single reactor, but Russian submarines have two, and so had USS Triton. Most American aircraft carriers are powered by two reactors, but USS Enterprise had eight. The majority of marine reactors are of the pressurized water type, although the U.S. and Soviet navies have designed warships powered with liquid metal cooled reactors.[ citation needed ]
Marine-type reactors differ from land-based commercial electric power reactors in several respects.[ citation needed ]
While land-based reactors in nuclear power plants produce up to around 1600 megawatts of net electrical power (the nameplate capacity of the EPR), a typical marine propulsion reactor produces no more than a few hundred megawatts. Some small modular reactors (SMR) are similar to marine propulsion reactors in capacity and some design considerations and thus nuclear marine propulsion (whether civilian or military) is sometimes proposed as an additional market niche for SMRs. Unlike for land-based applications where hundreds of hectares can be occupied by installations like Bruce Nuclear Generating Station, at sea tight space limits dictate that a marine reactor must be physically small, so it must generate higher power per unit of space. This means its components are subject to greater stresses than those of a land-based reactor. Its mechanical systems must operate flawlessly under the adverse conditions encountered at sea, including vibration and the pitching and rolling of a ship operating in rough seas. Reactor shutdown mechanisms cannot rely on gravity to drop control rods into place as in a land-based reactor that always remains upright. Salt water corrosion is an additional problem that complicates maintenance.[ citation needed ]
As the core of a seagoing reactor is much smaller than a power reactor, the probability of a neutron intersecting with a fissionable nucleus before it escapes into the shielding is much lower. As such, the fuel is typically more highly enriched (i.e., contains a higher concentration of 235U vs. 238U) than that used in a land-based nuclear power plant, which increases the probability of fission to the level where a sustained reaction can occur. Some marine reactors run on relatively low-enriched uranium, which requires more frequent refueling. Others run on highly enriched uranium, varying from 20% 235U, to the over 96% 235U found in U.S. submarines, [4] in which the resulting smaller core is quieter in operation (a big advantage to a submarine). [5] Using more-highly enriched fuel also increases the reactor's power density and extends the usable life of the nuclear fuel load, but is more expensive and a greater risk to nuclear proliferation than less-highly enriched fuel. [6]
A marine nuclear propulsion plant must be designed to be highly reliable and self-sufficient, requiring minimal maintenance and repairs, which might have to be undertaken many thousands of miles from its home port. One of the technical difficulties in designing fuel elements for a seagoing nuclear reactor is the creation of fuel elements that will withstand a large amount of radiation damage. Fuel elements may crack over time and gas bubbles may form. The fuel used in marine reactors is a metal-zirconium alloy rather than the ceramic UO2 (uranium dioxide) often used in land-based reactors. Marine reactors are designed for long core life, enabled by the relatively high enrichment of the uranium and by incorporating a "burnable poison" in the fuel elements, which is slowly depleted as the fuel elements age and become less reactive. The gradual dissipation of the "nuclear poison" increases the reactivity of the core to compensate for the lessening reactivity of the aging fuel elements, thereby extending the usable life of the fuel. The compact reactor pressure vessel is provided with an internal neutron shield, which reduces the damage to the steel from constant neutron bombardment.[ citation needed ]
Decommissioning nuclear-powered submarines has become a major task for U.S. and Russian navies. [7] After defuelling, U.S. practice is to cut the reactor section from the vessel for disposal in shallow land burial as low-level waste (see the ship-submarine recycling program ). [8] In Russia, whole vessels, or sealed reactor sections, typically remain stored afloat, although a new facility near Sayda Bay is to provide storage in a concrete-floored facility on land for some submarines in the far north.[ citation needed ]
Russia built a floating nuclear power plant for its far eastern territories. The design has two 35 MWe units based on the KLT-40 reactor used in icebreakers (with refueling every four years). Some Russian naval vessels have been used to supply electricity for domestic and industrial use in remote far eastern and Siberian towns.[ citation needed ]
In 2010, Lloyd's Register was investigating the possibility of civilian nuclear marine propulsion and rewriting draft rules (see text under Merchant Ships). [9] [10] [11]
Insurance of nuclear vessels is not like the insurance of conventional ships. The consequences of an accident could span national boundaries, and the magnitude of possible damage is beyond the capacity of private insurers. [12] A special international agreement, the Brussels Convention on the Liability of Operators of Nuclear Ships, developed in 1962, would have made signatory national governments liable for accidents caused by nuclear vessels under their flag [13] but was never ratified owing to disagreement on the inclusion of warships under the convention. [14] Nuclear reactors under United States jurisdiction are insured by the provisions of the Price–Anderson Act.[ citation needed ]
By 1990, there were more nuclear reactors powering ships (mostly military) than there were generating electric power in commercial power plants worldwide. [15]
Under the direction of U.S. Navy Captain (later Admiral) Hyman G. Rickover, [16] the design, development and production of nuclear marine propulsion plants started in the United States in the 1940s. The first prototype naval reactor was constructed and tested at the Naval Reactor Facility at the National Reactor Testing Station in Idaho (now called the Idaho National Laboratory) in 1953.
The first nuclear submarine, USS Nautilus (SSN-571), put to sea in 1955 (SS was a traditional hull classification symbol for U.S. submarines, while SSN denoted the first "nuclear" submarine). [17]
The Soviet Union also developed nuclear submarines. The first types developed were the Project 627, NATO-designated November class with two water-cooled reactors, the first of which, K-3 Leninsky Komsomol, was underway under nuclear power in 1958. [18]
Nuclear power revolutionized the submarine, finally making it a true "underwater" vessel, rather than a "submersible" craft, which could only stay underwater for limited periods. It gave the submarine the ability to operate submerged at high speeds, comparable to those of surface vessels, for unlimited periods, dependent only on the endurance of its crew. To demonstrate this USS Triton was the first vessel to execute a submerged circumnavigation of the Earth (Operation Sandblast), doing so in 1960. [19]
Nautilus, with a pressurized water reactor (PWR), led to the parallel development of other submarines like a unique liquid metal cooled (sodium) reactor in USS Seawolf, or two reactors in Triton, and then the Skate-class submarines, powered by single reactors, and a cruiser, USS Long Beach, in 1961, powered by two reactors.[ citation needed ]
By 1962, the United States Navy had 26 operational nuclear submarines and another 30 under construction. Nuclear power had revolutionized the Navy. The United States shared its technology with the United Kingdom, while French, Soviet, Indian and Chinese development proceeded separately.[ citation needed ]
After the Skate-class vessels, U.S. submarines were powered by a series of standardized, single-reactor designs built by Westinghouse and General Electric. Rolls-Royce plc built similar units for Royal Navy submarines, eventually developing a modified version of their own, the PWR2.[ citation needed ]
The largest nuclear submarines ever built are the 26,500 tonne Russian Typhoon class. The smallest nuclear warships to date are the 2,700 tonne French Rubis-class attack submarines. The U.S. Navy operated an unarmed nuclear submarine, the NR-1 Deep Submergence Craft, between 1969 and 2008, which was not a combat vessel but was the smallest nuclear-powered submarine at 400 tons.[ citation needed ]
The United States and France have built nuclear aircraft carriers.
The sole French nuclear aircraft carrier example is Charles de Gaulle, commissioned in 2001 (a successor is planned). [20]
The French carrier is equipped with catapults and arresters. The Charles de Gaulle has 42,000 tonnes, is the flagship of the French Navy (Marine Nationale). The ship carries a complement of Dassault Rafale M and E‑2C Hawkeye aircraft, EC725 Caracal and AS532 Cougar helicopters for combat search and rescue, as well as modern electronics and Aster missiles. [21]
The United States Navy operates 11 carriers, all nuclear-powered: [22]
The Kirov class, Soviet designation 'Project 1144 Orlan' (sea eagle), is a class of nuclear-powered guided-missile cruisers of the Soviet Navy and Russian Navy, the largest and heaviest surface combatant warships (i.e. not an aircraft carrier or amphibious assault ship) in operation in the world. Among modern warships, they are second in size only to large aircraft carriers, and of similar size to World War II era battleships. The Soviet classification of the ship-type is "heavy nuclear-powered guided missile cruiser" (Russian : тяжёлый атомный ракетный крейсер). The ships are often referred to as battlecruisers by Western defence commentators due to their size and general appearance. [24]
The United States Navy at one time had nuclear-powered cruisers as part of its fleet. The first such ship was USS Long Beach (CGN-9). Commissioned in 1961, she was the world's first nuclear-powered surface combatant. [25] She was followed a year later by USS Bainbridge (DLGN-25). While Long Beach was designed and built as a cruiser, [26] Bainbridge began life as a frigate, though at that time the Navy was using the hull code "DLGN" for "destroyer leader, guided missile, nuclear". [27]
The last nuclear-powered cruisers the Americans would produce would be the four-ship Virginia class. USS Virginia (CGN-38) was commissioned in 1976, followed by USS Texas (CGN-39) in 1977, USS Mississippi (CGN-40) in 1978 and finally USS Arkansas (CGN-41) in 1980. Ultimately, all these ships proved to be too costly to maintain [28] and they were all retired between 1993 and 1999.[ citation needed ]
SSV-33 Ural (ССВ-33 Урал; NATO reporting name: Kapusta[ Russian for "cabbage"]) was a command and control naval ship operated by the Soviet Navy. SSV-33's hull was derived from that of the nuclear-powered Kirov-class battlecruisers with nuclear marine propulsion. [29] SSV-33 served in electronic intelligence, missile tracking, space tracking, and communications relay roles. Due to high operating costs, SSV-33 was laid up. [29]
SSV-33 carried only light defensive weapons. These were two AK-176 76 mm guns, four AK-630 30 mm guns, and four quadruple Igla missile mounts.[ citation needed ]
The Poseidon (Russian : Посейдон, "Poseidon", NATO reporting name Kanyon), previously known by Russian codename Status-6 (Russian : Статус-6), is a nuclear-powered and nuclear-armed unmanned underwater vehicle under development by Rubin Design Bureau, capable of delivering both conventional and nuclear payloads. According to Russian state TV, it is able to deliver a thermonuclear cobalt bomb of up to 200 megatonnes (four times as powerful as the most powerful device ever detonated, the Tsar Bomba, and twice its maximum theoretical yield) against an enemy's naval ports and coastal cities. [30]
The following are ships that are or were in commercial or civilian use and have nuclear marine propulsion.
Nuclear-powered civil merchant ships have not developed beyond a few experimental ships. The U.S.-built NS Savannah, completed in 1962, was primarily a demonstration of civil nuclear power and was too small and expensive to operate economically as a merchant ship. The design was too much of a compromise, being neither an efficient freighter nor a viable passenger liner. The German-built Otto Hahn, completed in 1968, a cargo ship and research facility, sailed some 650,000 nautical miles (1,200,000 km) on 126 voyages over 10 years without any technical problems.[ citation needed ] It proved too expensive to operate and was converted to diesel. The Japanese Mutsu, completed in 1972, was dogged by technical and political problems. Its reactor had significant radiation leakage and fishermen protested against the vessel's operation. All of these three ships used low-enriched uranium. Sevmorput , a Soviet and later Russian LASH carrier with icebreaking capability, has operated successfully on the Northern Sea Route since it was commissioned in 1988. As of 2021 [update] , it is the only nuclear-powered merchant ship in service.[ citation needed ]
Civilian nuclear ships suffer from the costs of specialized infrastructure. The Savannah was expensive to operate since it was the only vessel using its specialized nuclear shore staff and servicing facility. A larger fleet could share fixed costs among more operating vessels, reducing operating costs.
Despite this, there is still interest in nuclear propulsion. In November 2010 British Maritime Technology and Lloyd's Register embarked upon a two-year study with U.S.-based Hyperion Power Generation (now Gen4 Energy), and the Greek ship operator Enterprises Shipping and Trading SA to investigate the practical maritime applications for small modular reactors. The research intended to produce a concept tanker-ship design, based on a 70 MWt reactor such as Hyperion's. In response to its members' interest in nuclear propulsion, Lloyd's Register has also re-written its 'rules' for nuclear ships, which concern the integration of a reactor certified by a land-based regulator with the rest of the ship. The overall rationale of the rule-making process assumes that in contrast to the current marine industry practice where the designer/builder typically demonstrates compliance with regulatory requirements, in the future the nuclear regulators will wish to ensure that it is the operator of the nuclear plant that demonstrates safety in operation, in addition to the safety through design and construction. Nuclear ships are currently the responsibility of their own countries, but none are involved in international trade. As a result of this work in 2014 two papers on commercial nuclear marine propulsion were published by Lloyd's Register and the other members of this consortium. [10] [11] These publications review past and recent work in the area of marine nuclear propulsion and describe a preliminary concept design study for a 155,000 DWT Suezmax tanker that is based on a conventional hull form with alternative arrangements for accommodating a 70 MWt nuclear propulsion plant delivering up to 23.5 MW shaft power at maximum continuous rating (average: 9.75 MW). The Gen4Energy power module is considered. This is a small fast-neutron reactor using lead–bismuth eutectic cooling and able to operate for ten full-power years before refueling, and in service last for a 25-year operational life of the vessel. They conclude that the concept is feasible, but further maturity of nuclear technology and the development and harmonisation of the regulatory framework would be necessary before the concept would be viable.[ citation needed ]
Nuclear propulsion has been proposed again on the wave of decarbonization of marine shipping, which accounts for 3–4% of global greenhouse gas emissions. [31]
In December 5, 2023, the Jiangnan Shipyard under the China State Shipbuilding Corporation officially released a design of a 24000 TEU-class container ship — known as the KUN-24AP — at Marintec China 2023, a premier maritime industry exhibition held in Shanghai. The container ship is reported to be powered by a thorium-based molten salt reactor, making it a first thorium-powered container ship and, if completed, the largest nuclear-powered container ship in the world. [32]
Nuclear propulsion has proven both technically and economically feasible for nuclear-powered icebreakers in the Soviet, and later Russian, Arctic. Nuclear-fuelled ships operate for years without refueling, and the vessels have powerful engines, well-suited to the task of icebreaking.[ citation needed ]
The Soviet icebreaker Lenin was the world's first nuclear-powered surface vessel in 1959 and remained in service for 30 years (new reactors were fitted in 1970). It led to a series of larger icebreakers, the 23,500 ton Arktika class of six vessels, launched beginning in 1975. These vessels have two reactors and are used in deep Arctic waters. NS Arktika was the first surface vessel to reach the North Pole.[ citation needed ]
For use in shallow waters such as estuaries and rivers, shallow-draft, Taymyr-class icebreakers were built in Finland and then fitted with their single-reactor nuclear propulsion system in Russia. They were built to conform to international safety standards for nuclear vessels. [33]
All nuclear-powered icebreakers have been commissioned by the Soviet Union or Russia.[ citation needed ]
The Ship-Submarine Recycling Program (SRP) is the process that the United States Navy uses to dispose of decommissioned nuclear vessels. SRP takes place only at the Puget Sound Naval Shipyard (PSNS) in Bremerton, Washington, but the preparations can begin elsewhere.
United States naval reactors are nuclear reactors used by the United States Navy aboard certain ships to generate the steam used to produce power for propulsion, electric power, catapulting airplanes in aircraft carriers, and a few minor uses. Such naval nuclear reactors have a complete power plant associated with them. All commissioned U.S. Navy submarines and supercarriers built since 1975 are nuclear powered, with the last conventional carrier, USS Kitty Hawk, being decommissioned in May 2009. The U.S. Navy also had nine nuclear-powered cruisers with such reactors, but they have since been decommissioned also.
A pressurized water reactor (PWR) is a type of light-water nuclear reactor. PWRs constitute the large majority of the world's nuclear power plants. In a PWR, the primary coolant (water) is pumped under high pressure to the reactor core where it is heated by the energy released by the fission of atoms. The heated, high pressure water then flows to a steam generator, where it transfers its thermal energy to lower pressure water of a secondary system where steam is generated. The steam then drives turbines, which spin an electric generator. In contrast to a boiling water reactor (BWR), pressure in the primary coolant loop prevents the water from boiling within the reactor. All light-water reactors use ordinary water as both coolant and neutron moderator. Most use anywhere from two to four vertically mounted steam generators; VVER reactors use horizontal steam generators.
The A2W reactor is a naval nuclear reactor used by the United States Navy to provide electricity generation and propulsion on warships. The A2W designation stands for:
The Alfa class, Soviet designation Project 705 Lira, was a class of nuclear-powered attack submarines in service with the Soviet Navy from 1971 into the early 1990s, with one serving in the Russian Navy until 1996. They were among the fastest military submarines ever built, with only the prototype submarine K-222 exceeding them in submerged speed.
USS Narwhal (SSN-671), a unique submarine, was the third vessel of the United States Navy to be named for the narwhal, a gray and white arctic whale with a unicorn-like, ivory tusk.
An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters, and provide safe waterways for other boats and ships. Although the term usually refers to ice-breaking ships, it may also refer to smaller vessels, such as the icebreaking boats that were once used on the canals of the United Kingdom.
A nuclear-powered icebreaker is an icebreaker with an onboard nuclear power plant that produces power for the vessel's propulsion system. Although more expensive to operate, nuclear-powered icebreakers provide a number of advantages over their diesel-powered counterparts, especially along the Northern Sea Route where heavy power demand associated with icebreaking, limited refueling infrastructure along the Siberian coast, and endurance required make diesel-powered icebreaker operations challenging. As of 2023, Russia is the only country that builds and operates nuclear-powered icebreakers, having built a number of such vessels to aid shipping along the Northern Sea Route and Russian arctic outposts since the Soviet era.
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 being factors such as the need to restock food or other consumables.
A nuclear navy, or nuclear-powered navy, refers to the portion of a navy consisting of naval ships powered by nuclear marine propulsion. The concept was revolutionary for naval warfare when first proposed. Prior to nuclear power, submarines were powered by diesel engines and could only submerge through the use of batteries. In order for these submarines to run their diesel engines and charge their batteries they would have to surface or snorkel. The use of nuclear power allowed these submarines to become true submersibles and unlike their conventional counterparts, they became limited only by crew endurance and supplies.
The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator; furthermore a solid form of fissile elements is used as fuel. Thermal-neutron reactors are the most common type of nuclear reactor, and light-water reactors are the most common type of thermal-neutron reactor.
USS California (CGN-36), the lead ship of the California-class of nuclear-powered guided missile cruisers, was the sixth warship of the United States Navy to be named for the state of California. She was the last active nuclear-powered cruiser for the United States.
Air-independent propulsion (AIP), or air-independent power, is any marine propulsion technology that allows a non-nuclear submarine to operate without access to atmospheric oxygen. AIP can augment or replace the diesel-electric propulsion system of non-nuclear vessels.
The Arktika class is a Russian class of nuclear-powered icebreakers. Also known by their Russian designations Project 10520 and Project 10521, they were the world's largest and most powerful icebreakers until the 2016 launch of the first Project 22220 icebreaker, also named Arktika.
Marine propulsion is the mechanism or system used to generate thrust to move a watercraft through water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electric motor or internal combustion engine driving a propeller, or less frequently, in pump-jets, an impeller. Marine engineering is the discipline concerned with the engineering design process of marine propulsion systems.
Soviet naval reactors have been used to power both military and civilian vessels, including:
Taymyr is a shallow-draft nuclear-powered icebreaker, and the first of two similar vessels. She was built in 1989 for the Soviet Union in Finland, at the Helsinki Shipyard by Wärtsilä Marine, by order of the Murmansk Shipping Company. Her sister ship is Vaygach.
The United States Navy Nuclear Propulsion community consists of Naval Officers and Enlisted members who are specially trained to run and maintain the nuclear reactors that power the submarines and aircraft carriers of the United States Navy. Operating more than 80 nuclear-powered ships, the United States Navy is currently the largest naval force in the world.
Steam-powered vessels include steamboats and steamships. Smaller steamboats were developed first. They were replaced by larger steamships which were often ocean-going. Steamships required a change in propulsion technology from sail to paddlewheel to screw to steam turbines. The latter innovation changed the design of vessels to one that could move faster through the water. Engine propulsion changed to steam turbine in the early 20th century. In the latter part of the 20th century, these, in turn, were replaced by gas turbines.
In the early 1960s, the United States Navy was the world's first to have nuclear-powered cruisers as part of its fleet. The first such ship was USS Long Beach (CGN-9). Commissioned in late summer 1961, she was the world's first nuclear-powered surface combatant. She was followed a year later by USS Bainbridge (DLGN-25). While Long Beach was a 'true cruiser', meaning she was designed and built as a cruiser, Bainbridge began life as a frigate, though at that time the Navy was using the hull code "DLGN" for "destroyer leader, guided missile, nuclear". This was prior to the enactment of the 1975 ship reclassification plan, in which frigates (DLG/DLGN), which were essentially large destroyers, were reclassified as cruisers, so that the US Navy's numbers would compete with those of the Soviet Navy. Long Beach, the largest of all the nuclear cruisers, was equipped with a C1W cruiser reactor, while all the others were equipped with D2G destroyer reactors.