United States Naval reactor

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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.

1 Reactor designations
2 History
3 Power plants
4 Nuclear reactors in the United States Navy
5 See also
6 External links

[edit] 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).

[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 relatively slow and short-ranged to capable of sustaining 20-25 knots submerged for weeks on end.

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 (pressurized water reactor).

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 both it and Russia have had nuclear-powered cruisers. Russia has eight nuclear icebreakers in service or building. The US Navy has accumulated over 5400 reactor years of accident-free experience^{[citation needed]}, and operates more than 80 nuclear-powered ships. [1]

[edit] Power plants

U.S. Naval reactors are pressurized water types, 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 (some French and Chinese submarines) or on highly enriched uranium (>20% U-235, current U.S. submarines use fuel enriched to 96%, compared to between 21-45% in current Russian models, although Russian nuclear-powered icebreaker reactors are enriched up to 90%), ^{[citation needed]}
the fuel is not UO₂ but a metal-zirconium alloy (c15%U with 93% enrichment, or more U with lower enrichment), ^{[citation needed]}
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).