United States Naval reactor

United States Naval reactor refers to nuclear reactors used by the United States Navy. Reactors are designed by a variety of contractors, then developed and tested at one of three government owned or operated facilities (Naval Reactors Facility, Bettis Atomic Power Laboratory, and Knolls Atomic Power Laboratory), all under the management of the office of Naval Reactors.

Reactor designations

Each reactor design is given a three-character designation consisting of:
*a letter representing the type of ship for which the reactor is intended (the ship types are "A" for aircraft carrier, "C" for cruiser, "D" for destroyer, and "S" for submarine),
*a consecutive generation number, and
*a letter indicating the reactor's designer (the designers are "W" for Westinghouse, "G" for General Electric, "C" for Combustion Engineering, and "B" for Bechtel).

As an example, a S9G reactor would represent a submarine (S), ninth-generation (9), General Electric designed reactor (G).

History

Conceptual analysis of nuclear marine propulsion started in the 1940s. Under the long-term leadership of Admiral Hyman G. Rickover, the first test reactor started up in USA in 1953. The first nuclear-powered vessel, the submarine USS|Nautilus|SSN-571, put to sea in 1955. "Nautilus" marked the beginning of the transition of submarines from relatively slow and short-ranged conventional submarines to ones capable of sustaining 20–25 knots (35–45 km/h) submerged for weeks on end.

Much of the early development work on naval reactors was done at the Naval Reactor Facility on the campus of the Idaho National Laboratory. "Nautilus" was powered by the S2W reactor, and crew were trained on the land-based S1W reactor at INL.

The second nuclear submarine was USS|Seawolf|SSN-575, which was initially powered by a sodium-cooled S2G reactor, and supported by the land-based S1G reactor at Knolls Atomic Power Laboratory. A spare S2G was also built but never used.

"Seawolf" was plagued by superheater problems, with the result that "Nautilus" delivered far superior performance. This and the risks posed by liquid sodium in the event of an accident at sea led Admiral Rickover to select the PWR (pressurized water reactor) as the standard US naval reactor type. The S2G was removed from "Seawolf" and replaced by the S2Wa reactor, using components from the spare S2W that was part of the "Nautilus" program. All subsequent US naval reactors have been PWRs, while the Soviet Navy used mainly PWRs, but also used lead-bismuth cooled LMFRs of three types in eight submarines: "K-27" and the seven-member "Alfa" class.

"Nautilus" led to the parallel development of further ("Skate"-class) submarines, powered by single reactors, and an aircraft carrier, USS|Enterprise|CVN-65, powered by eight reactor units in 1960. A cruiser, USS|Long Beach|CGN-9, followed in 1961 and was powered by two of these early units. Remarkably, "Enterprise" remains in service.

By 1962 the US 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 technological development in France, China, and the Soviet Union 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.

At the end of the Cold War in 1989, there were over 400 nuclear-powered submarines operational or being built. Some 250 of these submarines have now been scrapped and some on order canceled, due to weapons reduction programs. The Russian Navy and United States Navy had over one hundred each, with the United Kingdom and France less than twenty each and China six. The total today is about 160.

The United States is the main navy with nuclear-powered aircraft carriers (10), while Russia has nuclear-powered cruisers. Russia has eight nuclear icebreakers in service or building. Since its inception in 1948, the U. S. Navy nuclear program has developed 27 different plant designs, installed them in 210 nuclear powered ships, taken 500 reactor cores into operation, and accumulated over 5,400 reactor years of operation and 128,000,000 miles safely steamed. Additionally, 98 nuclear submarines and six nuclear cruisers have been recycled. The U. S. Navy has never experienced a reactor accident. [ [http://www.nasa.gov/pdf/45608main_NNBE_Progress_Report2_7-15-03.pdf NASA/Navy Benchmarking Exchange - Naval Reactors Safety Assurance Progress Report - July 15, 2003] ] [ cite web
url= http://www.nvr.navy.mil/nvrships/FLEET.HTM
title= Fleet Size
date= |year= |month= | work= Naval Vessel Register | publisher= United States Navy
accessdate= 2008-05-23 ]

Power plants

U.S. Naval reactors are pressurized water reactors, which differ from commercial reactors producing electricity in that:

*they have a high power density in a small volume and run either on low-enriched uranium (as do some French and Chinese submarines) or on highly enriched uranium (>20% U-235, current U.S. submarines use fuel enriched to at least 93%, [cite paper | author = Morten Bremer Maerli | title = Components of Naval Nuclear Fuel Transparency | publisher = Norwegian Institute of International Affairs | date = 2002-01-01 | url = http://www.nato.int/acad/fellow/99-01/maerli.pdf | format = pdf | accessdate = 2007-02-07 ] compared to between 21–45% in current Russian models, although Russian nuclear-powered icebreaker reactors are enriched up to 90%),Fact|date=February 2007
*the fuel is not UO₂ but a metal-zirconium alloy ("c."15% U with 93% enrichment, or more U with lower enrichment),Fact|date=February 2007
*they have long core lives, so that refueling is needed only after 10 or more years, and new cores are designed to last 50 years in carriers and 30–40 years in submarines,
*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 actinides accumulate, leading to reduced fuel efficiency. The two effects cancel one another out.

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 ~500 MWt (about 165 MWe) 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. Most Russian submarines as well as all surface ships since "Enterprise" are powered by two or more 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, remain stored afloat indefinitely.

Other small, easily field-deployed reactor designs have been developed but have no connection to the U.S. Naval Reactor program. A small reactor was used to supply power (1.5 MWe) and heating to McMurdo Station, a US Antarctic base, for ten years to 1972, testing the feasibility of such air-portable units for remote locations. Two others were installed in Arctic locations, all constructed as part of the US Army Nuclear Power Program. A fourth mounted on a barge provided power and fresh water in the Panama Canal Zone. Russia is well advanced with plans to build a floating 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).

Nuclear reactors in the United States Navy

References

See also

* List of United States Naval reactors
* Naval Reactors
* Nuclear marine propulsion

External links

* [http://www.uic.com.au/ The Uranium Information Centre] provided some of the original material in this article.