The A4W reactor is a naval reactor

United States Naval reactor

United States Naval reactor refers to nuclear reactors used by the United States Navy aboard certain ships to produce power for propulsion, electric power, catapulting airplanes in aircraft carriers, and a few more minor uses. Such Naval nuclear reactors have a complete power plant associated with...

 used by the United States Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

 to propel

Nuclear marine propulsion

Nuclear marine propulsion is propulsion of a ship by a nuclear reactor. Naval nuclear propulsion is propulsion that specifically refers to naval warships...

 warship

Warship

A warship is a ship that is built and primarily intended for combat. Warships are usually built in a completely different way from merchant ships. As well as being armed, warships are designed to withstand damage and are usually faster and more maneuvrable than merchant ships...

s and generate onboard electricity

Electricity generation

Electricity generation is the process of generating electric energy from other forms of energy.The fundamental principles of electricity generation were discovered during the 1820s and early 1830s by the British scientist Michael Faraday...

.

The A4W designation stands for:

• A = Aircraft carrier
  Aircraft carrier
  An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...
  
   platform
• 4 = Fourth-generation core
  Nuclear reactor core
  A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...
  
   designed by the contractor
• W = Westinghouse, the contracted designer

These nuclear fission

Nuclear fission

In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

 pressurized water reactor

Pressurized water reactor

Pressurized water reactors constitute a large majority of all western nuclear power plants and are one of three types of light water reactor , the other types being boiling water reactors and supercritical water reactors...

s (PWRs) were jointly designed by Bettis Atomic Power Laboratory

Bettis Atomic Power Laboratory

Bettis Atomic Power Laboratory is a U.S. Government-owned, contractor-operated research and development facility located in the Pittsburgh suburb of West Mifflin, Pennsylvania. It solely focuses on the design and development of nuclear power for the U.S. Navy....

 and Knolls Atomic Power Laboratory

Knolls Atomic Power Laboratory

Knolls Atomic Power Laboratory is a research and development facility dedicated to the support of the US Naval Nuclear Propulsion Program. KAPL is a government-owned, contractor operated laboratory run by Bechtel Marine Propulsion Corporation for the United States Department of Energy. KAPL is...

 and built by Westinghouse Electric Corporation. Their reactor cores

Nuclear reactor core

A nuclear reactor core is the portion of a nuclear reactor containing the nuclear fuel components where the nuclear reactions take place.- Description :...

 are expected to operate for about 20 years. The only ships to use these nuclear reactor

Nuclear reactor

A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

s are the Nimitz

Nimitz class aircraft carrier

The Nimitz-class supercarriers are a class of ten nuclear-powered aircraft carriers in service with the United States Navy. With an overall length of and full-load displacements of over 100,000 long tons, they are the largest capital ships in the world...

 class supercarrier

Supercarrier

Supercarrier is an unofficial descriptive term for the largest type of aircraft carrier, usually displacing over 70,000 long tons.Supercarrier is an unofficial descriptive term for the largest type of aircraft carrier, usually displacing over 70,000 long tons.Supercarrier is an unofficial...

s, which have two apiece, each of which generates enough steam

Steam generator (nuclear power)

Steam generators are heat exchangers used to convert water into steam from heat produced in a nuclear reactor core. They are used in pressurized water reactors between the primary and secondary coolant loops....

 to produce 140,000 shaft horsepower (104 MW).