A4W reactor

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The A4W reactor is a naval reactor used by the United States Navy to propel warships and generate onboard electricity.

The A4W designation stands for:

  • A = Aircraft carrier platform
  • 4 = Contractor's fourth core design generation
  • W = Westinghouse, the contracted designer


These nuclear fission pressurized water reactors (PWRs) were jointly designed by Bettis Atomic Power Laboratory and Knolls Atomic Power Laboratory[1] and built by Westinghouse Electric Company. Their reactor cores are expected to operate for about 20 years before refueling is required.[1] The only ships to use these nuclear reactors are the Nimitz class supercarriers, which have two reactors rated at 550 MWth each [1100 MWth total].

Marine PWRs typically have two steam generators, this is probably the case with the A4W as well. Each PWR and its two steam generators are collectively known as a Nuclear Propulsion Plant [NPP]. Each steam generator provides steam to a separate steam turbine, each of these steam turbines is associated with [drives] one the ship's four shafts. Each steam generator also contributes some of the steam used to drive a multitude of turbo-generators [electrical power generators].

Pressurized Water Reactor steam cycle thermal efficiency is approximately 31-33%, thus one would expect that approximately 340 MW of usable mechanical power would be available [between the two NPPs] for conversion into propulsion, electrical power, as well as providing steam for powering auxiliary systems. The total propulsion power for Nimitz Class Carriers is quoted at 260,000 shaft horsepower [~194 MW] [see Nimitz Class Aircraft Carrier] distributed among the 4 shafts [65,000 HP per shaft]; this leaves enough available power to generate at least 100 MW of electrical power plus additional steam for powering auxiliary systems such as the flight deck catapult.

An interesting note: if the ship is travelling at 31.5 knots, and the ship's propulsion system is producing 260,000 HP, then assuming 75% screw efficiency, the two NPPs combined are producing a little more than 2 million pounds of thrust.

Note that some sources claim that each NPP generates 140,000 shaft horsepower (104 MW) distributed between two shafts, in addition to generating 50 MW of electrical power.[2]

See also[edit]


  1. ^ a b "A4W". US Navy Propulsion Systems. Federation of American Scientists. 1999-02-27. Archived from the original on 25 September 2006. Retrieved 2006-10-16. current cores for the NIMITZ Class aircraft carrier ... last on average about 20 years 
  2. ^ "US Navy Propulsion Systems". Federation of American Scientists. Archived from the original on 9 October 2006. Retrieved 2006-10-16. power per reactor ... 140,000 shp 

External links[edit]

  • [1] (correcting for the power output from 500 megawatts to 105.)