Nuclear marine propulsion

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Nuclear marine propulsion is propulsion of a merchant ship powered by a nuclear reactor. Naval nuclear propulsion is propulsion that specifically refers to naval warships (see Nuclear navy).

A nuclear fuel element for the cargo ship NS Savannah. The element contains four bundles of 41 fuel rods. The uranium oxide is enriched to 4,2 and 4,6 percent of U-235

[edit] Power plants

Naval reactors are pressurized water, liquid-metal-cooled, or boiling water types, which differ from commercial reactors producing electricity in that:

• they have a high power density in a small volume; some run on low-enriched uranium (requiring frequent refuelings), others run on highly enriched uranium (>20% U-235, varying from over 96% in U.S. submarines {no refuelings are necessary during the submarine's service life^[1]} to between 30-40% in Russian submarines to lower levels in some others),
• the fuel is not UO₂ (Uranium Oxide) but a metal-zirconium alloy (c15%U with 93% enrichment, or more U with lower enrichment),
• the design enables a compact pressure vessel while maintaining safety.

The long core life is enabled by the relatively high enrichment of the uranium and by incorporating a "burnable poison" in the cores which is progressively depleted as fission products and Minor actinides accumulate, leading to reduced fuel efficiency. The two effects cancel one another out. One of the technical difficulties is the creation of a fuel which will tolerate the very large amount of radiation damage. It is known that during use the properties of nuclear fuel change; it is quite possible for fuel to crack and for fission gas bubbles to form.

Long-term integrity of the compact reactor pressure vessel is maintained by providing an internal neutron shield. (This is in contrast to early Soviet civil PWR designs where embrittlement occurs due to neutron bombardment of a very narrow pressure vessel.)

Reactor sizes range up to 190 MW in the larger submarines and surface ships. The French Rubis class submarines have a 48 MW reactor which needs no refueling for 30 years.

The Russian, US and British navies rely on steam turbine propulsion, the French and Chinese use the turbine to generate electricity for propulsion (turbo-electric propulsion). Most Russian submarines as well as all surface ships since USS Enterprise (CVN-65) are powered by two reactors. US, British, French and Chinese submarines are powered by one.

Decommissioning nuclear-powered submarines has become a major task for US and Russian navies. After defuelling, US 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). In Russia, the whole vessels, or the sealed reactor sections, typically remain stored afloat, although a new facility near Sayda Bay is beginning to provide storage in a concrete-floored facility on land for some submarines in the Far North.

Russia is well advanced with plans to build a floating nuclear power plant for their far eastern territories. The design has two 35 MWe units based on the KLT-40 reactor used in icebreakers (with refueling every 4 years). Some Russian naval vessels have been used to supply electricity for domestic and industrial use in remote far eastern and Siberian towns.

Harold Wilson the then British Prime Minister considered, but did not deploy, nuclear submarines to power Belfast during the Ulster Workers' Council Strike.

[edit] History

Work on nuclear marine propulsion started in the 1940s, and the first test reactor started up in USA in 1953. The first nuclear-powered submarine, USS Nautilus (SSN-571), put to sea in 1955. Much of the early development work on naval reactors was done at the Naval Reactor Facility on the campus of the Idaho National Laboratory.

This marked the transition of submarines from slow underwater vessels to warships capable of sustaining 20-25 knots (37-46 km/h) submerged for many weeks.

Nautilus led to the parallel development of further (Skate-class) submarines, powered by single reactors, and a cruiser, Long Beach, followed in 1961 and was powered by two reactors. The aircraft carrier, USS Enterprise (CVN-65), commissioned in 1962, was powered by eight reactor units in 1960. Enterprise remains in service.

By 1962 the United States Navy had 26 nuclear submarines operational and 30 under construction. Nuclear power had revolutionized the Navy. The technology was shared with the United Kingdom, while French, Soviet, Indian and Chinese developments proceeded separately.

After the Skate-class vessels, reactor development proceeded and in the USA a single series of standardized designs was built by both Westinghouse and General Electric, one reactor powering each vessel. Rolls Royce built similar units for Royal Navy submarines and then developed the design further to the PWR-2 (pressurized water reactor).

The largest nuclear submarines ever built are the 26,500 tonne Russian Typhoon class.

[edit] Civil vessels

Development of nuclear merchant ships began in the 1950s, but has not been commercially successful. The US-built NS Savannah, was commissioned in 1962 and decommissioned eight years later. It was a technical success, but not economically viable. The German-built Otto Hahn cargo ship and research facility sailed some 650,000 nautical miles on 126 voyages in 10 years without any technical problems.^{[citation needed]} However, it proved too expensive to operate and was converted to diesel. The Japanese Mutsu was the third civil vessel. It was dogged by technical and political problems and was an embarrassing failure. All three vessels used reactors with low-enriched uranium fuel.

In contrast, nuclear propulsion has proven both technically and economically feasible for nuclear powered icebreakers in the Soviet Arctic. The power levels and energy required for icebreaking, coupled with refueling difficulties for other types of vessels, are significant factors. The Soviet icebreaker Lenin was the world's first nuclear-powered surface vessel and remained in service for 30 years, though new reactors were fitted in 1970. It led to a series of larger icebreakers, the 23,500 ton Arktika class, launched from 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.

For use in shallow waters such as estuaries and rivers, shallow-draft Taymyr class icebreakers with one reactor are being built in Finland and then fitted with their nuclear steam supply system in Russia. They are built to conform with international safety standards for nuclear vessels.

[edit] Naval nuclear accidents

Two US nuclear submarines, the USS Thresher (SSN-593) (sank) and USS Scorpion (SSN-589) (sank) had issues unrelated to their reactor plants and still lie on the Atlantic sea floor. The Russian or Soviet Komsomolets K-278 (sank), Kursk K-141 (sank), K-8 (sank), K-11 (refueling criticality), K-19 (loss of coolant), K-27 (scuttled), K-116 (reactor accident), K-122 (reactor accident), K-123 (loss of coolant), K-140 (power excursion), K-159 (sank recently), K-192 (loss of coolant), K-219 (sank after collision), K-222 (uncontrolled startup), K-314 (refueling criticality), K-320 (uncontrolled startup), K-429 (sank twice), and K-431 (reactor accident) submarines have all had problems of some kind. The Soviet icebreaker Lenin is also rumored to have had a nuclear accident.

While not all of those were nuclear-related accidents, since they happened to nuclear vessels, they have a major impact on nuclear marine propulsion and the global politics.

See also: List of military nuclear accidents

[edit] See also

• List of civilian nuclear ships
• List of United States Naval reactors
• Naval Reactors
• Nuclear navy
• United States Naval reactor
• Army Nuclear Power Program
• Naval Nuclear Power School
• Echo class submarine

[edit] References

1. ^ NTI: Issue Brief: Global Submarine Proliferation: Emerging Trends and Problems. Retrieved on Mar 7, 2007.

• AFP, 11 November 1998; in "Nuclear Submarines Provide Electricity for Siberian Town," FBIS-SOV-98-315, 11 November 1998.
• ITAR-TASS, 11 November 1998; in "Russian Nuclear Subs Supply Electricity to Town in Far East," FBIS-SOV-98-316, 12 November 1998.
• Harold Wilson's plan BBC News story

[edit] External links

• The Uranium Information Centre provided some of the original material in this article.
• Naval Nuclear Power Training Command