United States Naval reactor
United States Naval reactors are given three-character designations consisting of a letter representing the ship type the reactor is designed for, a consecutive generation number, and a letter indicating the reactor's designer.
The ship types are "A" for
aircraft carrier, "C" for
cruiser, "D" for
destroyer,or "S" for
submarine. The designers are "W" for
Westinghouse, "G" for
General Electric, "C" for
Combustion Engineering, and "B" for
Bettis Laboratory.
As an example, a
S6G reactor would represent a submarine, sixth-generation, General Electric designed reactor.
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, put to sea in
1955. Much of the development work on naval reactors was done at the
Idaho National Engineering Laboratory (
Naval Reactor Facility).
This marked the transition of submarines from slow underwater vessels to warships capable of sustaining 20-25 knots submerged for weeks on end. The submarine had come into its own.
Nautilus led to the parallel development of further (
Skate-class) submarines, powered by single reactors, and an aircraft carrier,
USS Enterprise, powered by eight reactor units in
1960. A cruiser, USS
Long Beach, 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 revolutionised the Navy.
The technology was shared with
Britain, while
French,
Soviet, and
Chinese developments proceeded separately.
After the
Skate-class vessels, reactor development proceeded and in the USA a single series of standardised 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.
The largest submarines are the 26,500 tonne Russian
Typhoon-class.
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 cancelled, due to weapons reduction programs.
Russia and the
United States 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, and operates more than 80 nuclear-powered ships.
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. 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. These three vessels used reactors with low-enriched uranium fuel.
In contrast, nuclear propulsion has proven both technically and economically feasible 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
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 dwt
Arktika-class, launched from
1975. These vessels have two reactors and are used in deep Arctic waters.
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.
* See also:
List of Civilian Nuclear ShipsU.S. Naval reactors are pressurised 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%
HEU, compared to between 21-45% in current Russian models, although Russian nuclear-powered icebreaker reactors are enriched up to 90%),
*the fuel is not UO
2 but a metal-
zirconium alloy (c15%U with 93% enrichment, or more U with lower enrichment),
*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 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.
A marine reactor was used to supply power (
1.5 MWe) and heating to 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).
:See also: Nuclear marine propulsion*
A1W reactor**
USS Enterprise (CVN-65) prototype
*
A2W reactor**
USS Enterprise (CVN-65)*
A3W reactor** designed for
USS John F. Kennedy (CV-67) but never installed
*
A4W/A1G reactor**
Nimitz-class aircraft carriers (CVN-68)*
A1B reactor** next generation aircraft carrier class
CVN-21 (or
CVX)
*
C1W reactor**
USS Long Beach (CGN-9)*
D1G reactor**
USS Bainbridge (DLGN/CGN-25) prototype
*
D2G reactor**
USS Bainbridge (DLGN/CGN-25)**
USS Truxtun (CGN-35)**
California-class cruisers (CGN-36)**
Virginia-class cruisers (CGN-38)*
S1C reactor**
USS Tullibee (SSN-597) prototype
*
S1G reactor**
USS Seawolf (SSN-575) prototype
*
S1W reactor**
USS Nautilus (SSN-571) prototype
*
S2C reactor**
USS Tullibee (SSN-597)*
S2G reactor**
USS Seawolf (SSN-575)*
S2W reactor**
USS Nautilus (SSN-571)*
S3G reactor**
USS Triton (SSN-586) prototype
*
S3W reactor**
Skate (SSN-578)**
Sargo (SSN-583)**
USS Halibut (SSGN-587)*
S4G reactor**
USS Triton (SSN-586)*
S4W reactor**
Swordfish-class submarines (SSN-579)**
Seadragon-class submarines (SSN-584)*
S5G reactor**
USS Narwhal (SSN-671)*
S5W reactor**
Skipjack-class submarines (SSN-585)**
Permit-class submarines (SSN-594)**
Sturgeon-class submarines (SSN-637)**
USS Parche (SSN-683)**
USS Glenard P. Lipscomb (SSN-685)**
George Washington-class submarines (SSBN-598)**
Ethan Allen-class submarines (SSBN-608)**
Lafayette-class submarines (SSBN-616)**
James Madison-class submarines (SSBN-627)**
Benjamin Franklin-class submarines (SSBN-640)*
S6G reactor**
Los Angeles-class submarines (SSN-688)*
S6W reactor**
Seawolf-class submarines (SSN-21)*
S7G reactor** MARF
*
S8G reactor**
Ohio-class submarines (SSBN-726)*
S9G reactor**
Virginia-class submarines (SSN-774)*
The Uranium Information Centre provided some of the original material in this article.
