"S2G" redirects here. For the aircraft, see Grumman S-2 Tracker

The S2G reactor was 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 provide electricity generation

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...

 and propulsion

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...

 on 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 the only liquid metal cooled reactor

Liquid metal cooled reactor

A liquid metal cooled nuclear reactor, liquid metal fast reactor or LMFR is an advanced type of nuclear reactor where the primary coolant is a liquid metal. Liquid metal cooled reactors were first adapted for nuclear submarine use but have also been extensively studied for power generation...

 yet deployed by the US Navy. The S2G designation stands for:

• S = Submarine
  Submarine
  A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
  
   platform
• 2 = Second 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
• G = General Electric
  General Electric
  General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
  
   was the contracted designer

An S2G was the initial power plant of USS Seawolf (SSN-575)

USS Seawolf (SSN-575)

USS Seawolf , a unique submarine, was the third ship of the United States Navy to be named for the seawolf, the second nuclear submarine, and the only U.S. submarine built with a liquid metal cooled nuclear reactor....

. This was one of three sodium cooled fast reactors ordered for the Seawolf program at the same time as three PWR units were ordered to support the USS Nautilus (SSN-571)

USS Nautilus (SSN-571)

USS Nautilus is the world's first operational nuclear-powered submarine. She was the first vessel to complete a submerged transit beneath the North Pole on August 3, 1958...

 program; In each case, one reactor was land-based for training and research, one intended for installation on a submarine, and one spare. The land-based unit corresponding to S2G was S1G reactor

S1G reactor

The S1G reactor is a naval reactor used by the United States Navy to provide electricity generation and propulsion on warships. The S1G designation stands for:* S = Submarine platform* 1 = First generation core designed by the contractor...

.

Persistent superheater problems on Seawolf caused the superheaters to be bypassed, resulting in mediocre performance. This and concern for the dangers posed by liquid sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 coolant led to the PWR type being selected instead as the standard US naval reactor type, and the S2G on Seawolf was replaced by the spare S2Wa reactor

S2Wa reactor

The S2Wa reactor is a naval reactor used by the United States Navy to provide electricity generation and propulsion on warships. The S2Wa designation stands for:* S = Submarine platform* 2 = Second generation core designed by the contractor...

from the Nautilus program.