Nuclear marine propulsion is propulsion of a 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 of the pressurized water type 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 (They do not need to be refueled as often^[1] and are quieter in operation from smaller core^[2]) 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 (circa 15% 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 each other 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 55 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, U.S. and British navies rely on steam turbine propulsion, while the French and Chinese use the turbine to generate electricity for propulsion (turbo-electric propulsion). Most Russian submarines as well as most American aircraft carriers since CVN-65 are powered by two reactors (although Enterprise has eight). U.S., 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, 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). 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 MW 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.

[edit] History

Under the direction of Admiral Hyman G. Rickover^[3], the design, development and production of nuclear marine propulsion plants started in the USA in the 1940s, with the first test reactor being started up 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^{[citation needed]}.

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, USS Long Beach (CGN-9), in 1961, powered by two reactors. The aircraft carrier USS Enterprise, 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 generally 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 (1,200,000 km) 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.

The fourth nuclear merchant ship, Sevmorput, operates successfully in the specialised environment of the Northern Sea Route. Recently there has been renewed interest in nuclear propulsion, and some proposals have been drafted. For example, the cargo coaster^[4] is a new design for a nuclear cargo ship. Using the new micro nuclear reactors, other existing cargo ships could potentially be converted to nuclear propulsion as well.

When the Arktika class NS 50 Let Pobedy was put into service in 2007, it became the world's largest icebreaker.

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 (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

[edit] United States

• USS Thresher (SSN-593) (sank, 129 killed)
• USS Scorpion (SSN-589) (sank, 99 killed)

Both sank for reasons unrelated to their reactor plants and still lie on the Atlantic sea floor.

[edit] Russian or Soviet

• Komsomolets K-278 (sank, 42 killed)
• Kursk K-141 (sank, 118 killed)
• K-8 (loss of coolant) (sank after fire, 52 killed)
• K-11 (two refueling criticalities)
• K-19 (two loss of coolant accidents, 27 killed due to one accident)
• K-27 (scuttled)
• K-116 (reactor accident)
• K-122 (reactor accident)
• K-123 (loss of coolant)
• K-140 (power excursion)
• K-159 (radioactive discharge) (sank recently, 9 killed)
• K-192 (loss of coolant)
• K-219 (sank after collision, 6 killed)
• K-222 (uncontrolled startup)
• K-431 (refueling criticality, 10 killed)
• K-320 (uncontrolled startup)
• K-429 (sank twice, 16 killed)
• The Soviet icebreaker Lenin is also rumored to have had a nuclear accident.

While not all of these were reactor accidents, they have a major impact on nuclear marine propulsion and the global politics because they happened to nuclear vessels. Many of these accidents resulted in the sinking of the boat containing nuclear weapons on board, which remain there to this day.^[5]

[edit] See also

• List of civilian nuclear ships
• List of United States Naval reactors
• Naval Reactors
• Nuclear navy
• United States Naval reactor
• Knolls Atomic Power Laboratory
• Soviet naval reactor
• Army Nuclear Power Program
• Naval Nuclear Power School
• Echo class submarine
• Air-independent propulsion

[edit] References

1. ^ James Clay Moltz (March 2006). "Global Submarine Proliferation: Emerging Trends and Problems". NTI. http://www.nti.org/e_research/e3_74.html. Retrieved 2007-03-07. 
2. ^ James Acton (December 13, 2007). "Silence is highly enriched uranium". http://www.armscontrolwonk.com/1738/silence-is-highly-enriched-uranium. Retrieved 2007-12-13. 
3. ^ Groves, Leslie R.; Edward Teller (1983). Now it can be told. p. 388. ISBN 9780306801891. 
4. ^ [1]
5. ^ Database of radiological incidents and related events

• 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 World Nuclear Association
• Naval Nuclear Power Training Command
• Nuclear Ships of the Merchant Navy