View source for United States naval reactors

{{Short description|Classes of nuclear reactors used by the United States Navy}}
{{for|the U.S. government office|Naval Reactors}}
{{Use dmy dates|date=August 2021}}
{{Coord|46|33|54.8|N|119|31|09.7|W|display=title}}
[[File:Naval Reactor Compartment Packages in Trench 94 at Hanford, WA.png|thumb|right|upright|The Naval Reactor Disposal Site, Trench 94 200 Area East [[Hanford Site]] in [[Benton County, Washington|Benton County]] in the U.S. state of [[Washington (state)|Washington]], in November 2009. Stored Reactor Compartment Packages of pre-''Los Angeles'' class, ''Los Angeles'' class, and cruisers.]]
'''United States naval reactors''' are [[nuclear reactor]]s used by the [[United States Navy]] aboard certain ships to generate the [[steam]] used to produce [[Power (physics)|power]] for [[Marine nuclear propulsion|propulsion]], [[electric power]], catapulting airplanes in [[aircraft carrier]]s, and a few minor uses. Such naval nuclear reactors have a complete [[power plant]] associated with them. All commissioned U.S. Navy [[submarine]]s and [[supercarrier]]s built since 1975 are [[nuclear power]]ed, with the last conventional carrier, {{USS|Kitty Hawk|CV-63|6}}, being decommissioned in May 2009. The U.S. Navy also had nine nuclear-powered [[cruiser]]s with such reactors, but they have since been decommissioned also. 

Reactors are designed by a number of contractors,{{who|date=December 2015}} then developed and tested at one of several [[United States Department of Energy|Department of Energy]]-owned and prime contractor-operated facilities: [[Bettis Atomic Power Laboratory]] in [[West Mifflin, Pennsylvania]] and its associated [[Naval Reactors Facility]] in [[Idaho]], and [[Knolls Atomic Power Laboratory]] in [[Niskayuna, New York]] and its associated Kesselring site in [[West Milton, New York]], all under the management of the office of [[Naval Reactors]]. Sometimes there were full-scale nuclear-powered [[prototype]] plants built at the Naval Reactors Facility, Kesselring, and Windsor (in [[Connecticut]]) to test the nuclear plants, which were operated for years to train nuclear-qualified sailors.

== Reactor designations ==
Each reactor design is given a three-character designation consisting of:
* A letter for the type of ship the reactor is intended for ("A" for [[aircraft carrier]], "C" for [[cruiser]], "D" for [[destroyer]], and "S" for [[submarine]])
* A consecutive generation number
* A letter for the reactor's designer ("W" for [[Westinghouse Electric Company|Westinghouse]], "G" for [[General Electric]], "C" for [[Combustion Engineering]], and "B" for [[Bechtel]])

For example, a [[S9G reactor]] represents a submarine ('''S'''), ninth-generation ('''9'''), General Electric designed reactor ('''G''').

== History ==
Conceptual analysis of [[nuclear marine propulsion]] started in the 1940s. Research on developing nuclear reactors for the Navy was done at [[Bettis Atomic Power Laboratory]] in [[West Mifflin, Pennsylvania]] starting in 1948. Under the long-term leadership of Admiral [[Hyman G. Rickover]], the first test reactor plant, a [[prototype]] referred to as [[S1W reactor|S1W]], started up in U.S. in 1953 at the [[Naval Reactors Facility]] in [[Idaho]]. Bettis Laboratory and Naval Reactors Facility were operated initially and for many decades afterwards by [[Westinghouse Electric Corporation|Westinghouse]]. The first nuclear-powered vessel, the [[submarine]] {{USS|Nautilus|SSN-571|6}}, put to sea in 1955. USS ''Nautilus'' marked the beginning of the transition of submarines from relatively slow and short-ranged conventional submarines to ones capable of sustaining {{convert|20|–|25|kn|lk=in}} submerged for weeks on end.

Much of the early development work on naval reactors was done at the Naval Reactors Facility on the campus of the [[Idaho National Laboratory]] (INL, previously INEL). USS ''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|6}}, which was initially powered by a [[liquid metal fast reactor|sodium-cooled]] [[S2G reactor]], and supported by the land-based [[S1G reactor]] at the Kesselring site under [[Knolls Atomic Power Laboratory]] operated by [[General Electric]]. A spare S2G was also built but never used.

USS ''Seawolf'' was plagued by superheater problems, with the result that USS ''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 [[pressurized water reactor]] (PWR) as the standard U.S. naval reactor type. The S2G was removed from USS ''Seawolf'' and replaced by the [[S2Wa reactor]], using components from the spare S2W that was part of the USS ''Nautilus'' program. All subsequent U.S. naval reactors have been PWRs, while the [[Soviet Navy]] used mainly PWRs, but also used lead-bismuth cooled [[liquid metal cooled reactor]]s (LMFR) of three types in eight submarines: {{ship|Soviet submarine|K-27||2}} and the seven-member {{sclass2|Alfa|submarine|4}}.

Experience with USS ''Nautilus'' led to the parallel development of further ({{sclass|Skate|submarine|0}}) submarines, powered by single reactors, and an [[aircraft carrier]], {{USS|Enterprise|CVN-65|6}}, powered by eight [[A2W]] reactor units in 1960. A cruiser, {{USS|Long Beach|CGN-9|6}}, followed in 1961 and was powered by two [[C1W]] reactor units. USS ''Enterprise'' remained in service for over 50 years, and was inactivated in 2012.

Full-scale land-based prototype plants in Idaho, New York, and Connecticut preceded development of several types (generations) of U.S. naval nuclear reactors, although not all of them. After initial construction, some engineering testing was done and the prototypes were used to train nuclear-qualified sailors for many years afterwards. For example, the [[A1W]] prototype at Naval Reactors Facility led to development of [[A2W]] reactors used in USS ''Enterprise''. By 1962, the US Navy had 26 nuclear submarines operational and 30 under construction. Nuclear power had revolutionized the U.S. 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 U.S. a single series of standardized designs was built by both [[Westinghouse Electric Corporation|Westinghouse]] and General Electric, with one reactor powering each vessel. [[Rolls-Royce plc|Rolls-Royce]] built similar units as the [[Rolls-Royce PWR|PWR1]] for [[Royal Navy]] submarines and then developed the design further to the PWR2. Numerous submarines with an [[S5W]] reactor plant were built.

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-powered icebreaker|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 disclosed a reactor accident,<ref>{{Cite web |url=http://www.nasa.gov/pdf/45608main_NNBE_Progress_Report2_7-15-03.pdf |title=NASA/Navy Benchmarking Exchange – Naval Reactors Safety Assurance Progress Report – July 15, 2003 |access-date=30 May 2008 |archive-date=9 October 2022 |archive-url=https://ghostarchive.org/archive/20221009/http://www.nasa.gov/pdf/45608main_NNBE_Progress_Report2_7-15-03.pdf |url-status=dead }}</ref><ref>{{cite web
 |url          = http://www.nvr.navy.mil/NVRSHIPS/FLEET.HTM
 |title        = Fleet Size
 |work         = [[Naval Vessel Register]]
 |publisher    = [[United States Navy]]
 |access-date   = 2008-05-23
 |archive-url  = https://web.archive.org/web/20160114212227/http://www.nvr.navy.mil/nvrships/FLEET.HTM
 |archive-date = 14 January 2016
 |url-status     = dead
}}</ref> but has suffered at least one coolant loss accident, on the [[USS Guardfish (SSN-612)|USS Guardfish]].<ref>[https://www.upi.com/Archives/1989/05/29/Report-Nuclear-sub-suffers-accident-off-Oregon-in-1973/5351612417600/ Report: Nuclear sub suffers accident off Oregon in 1973]</ref>

All nine of the U.S. Navy nuclear-powered cruisers (CGN) have now been stricken from the [[Naval Vessel Register]], and those not already scrapped by recycling are scheduled to be recycled. While reactor accidents have not sunk any U.S. Navy ships or submarines, two nuclear-powered submarines, {{USS|Thresher|SSN-593|6}} and {{USS|Scorpion|SSN-589|6}} were lost at sea. The condition of these reactors has not been publicly released, although both wrecks have been investigated by [[Robert Ballard]] on behalf of the Navy using [[Remotely operated underwater vehicle|remotely operated vehicles]] (ROVs).{{citation needed|date=February 2022}}

Congress has mandated that the U.S. Navy consider nuclear power as an option on all large surface combatants (cruisers, [[destroyer]]s) and [[amphibious assault ship]]s. If proven cost-effective in a [[Whole-life cost|life cycle cost]] analysis during the [[Analysis of Alternatives]] (AoA) phase of preliminary ship design, new ship classes (e.g. CG(X)) could proceed with nuclear propulsion.

==Power plants==
Current U.S. naval reactors are all pressurized water reactors,<ref>{{Cite web|title=Fact Sheet on U.S. Nuclear Powered Warship (NPW) Safety|url=https://www.mofa.go.jp/region/n-america/us/security/fact0604.pdf}}</ref> which are identical to PWR commercial reactors producing electricity, except 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%)<ref>{{cite journal | author = Morten Bremer Maerli | title = Components of Naval Nuclear Fuel Transparency | publisher = Norwegian Institute of International Affairs | date = 1 January 2002 | url = http://www.nato.int/acad/fellow/99-01/maerli.pdf | access-date = 2007-02-07 }}</ref>
* They have long core lives, so that refueling is needed only after 10 or more years, and new cores are designed to last 25&nbsp;years in carriers and 10–33&nbsp;years in submarines,
* The design enables a compact pressure vessel while maintaining safety.{{clarify|date=September 2015}}
Long core life is enabled by high uranium enrichment and by incorporating a "[[Nuclear poison|burnable neutron poison]]", which is progressively depleted as [[Nuclear poison|non-burnable poison]]s like [[fission product]]s and [[actinide]]s accumulate.  The loss of burnable poison counterbalances the creation of non-burnable poisons and result in stable long term [[fuel efficiency]].

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&nbsp;[[MWt]] (about 165&nbsp;MWe) in the larger submarines and surface ships. The French {{sclass|Rubis|submarine|2}}s have a 48&nbsp;MW reactor that needs no refueling for 30&nbsp;years.

The nuclear navies of the United States, the United Kingdom, and the Russian Federation rely on steam turbine propulsion. Those of the French and Chinese use the turbine to generate electricity for propulsion. Most Russian submarines as well as all U.S. surface ships since ''Enterprise'' are powered by two or more reactors. U.S., British, French, Chinese and Indian submarines are powered by one.

Decommissioning nuclear-powered submarines has become a major task for American and Russian navies.<ref>{{Cite web|title=Nuclear Submarine Dismantlement {{!}} NTI|url=https://www.nti.org/analysis/articles/nuclear-submarine-dismantlement/|access-date=2021-04-25|website=nti.org|date=31 July 2001 }}</ref> 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]]).

== See also ==
* [[List of United States naval reactors]]
* [[Radioisotope thermoelectric generator]]
* [[Nuclear-powered cruisers of the United States Navy]]
* [[Nuclear submarine#United States Navy|Nuclear-powered submarines of the United States Navy]]
* [[Nuclear Power School]]

==References==
{{Reflist}}

== External links ==
* [https://web.archive.org/web/20020813111848/http://www.uic.com.au/ The Uranium Information Centre] provided some of the original material in this article.

{{United States naval reactors}}
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[[Category:United States naval reactors| ]]
[[Category:Nuclear reactors]]
[[Category:Nuclear-powered ships of the United States Navy|*]]