S7G reactor
Encyclopedia
The S7G reactor was a prototype
naval reactor
designed for the United States Navy
to provide electricity generation
and propulsion
on warship
s. The S7G designation stands for:
This prototype design was a land-based nuclear reactor
that did not use control rods. It was tested in the late 1970s and early 1980s at the Modifications and Additions to a Reactor Facility (MARF) plant located at the Knolls Atomic Power Laboratory
's Kesselring Site in Ballston Spa, New York
. It consisted of an experimental reactor core installed in a modified S5W reactor
plant.
-based control rod
s used in all of the other United States Naval reactors, reactivity in the S7G core was controlled by stationary gadolinium
-clad tubes partially filled with water. Water could be pump
ed from the portion of the tube inside the core up to a reservoir above the core, or allowed to flow back down into the tube. A higher water level in the tube slowed more neutron
s in the core, causing more neutron capture by the gadolinium tube cladding rather than by the uranium
fuel, thus lowering the power level.
The system was configured with the pump running continually to keep the water level low; on loss of electrical power, all of the water would flow back into the tube, shutting down the reactor. As with all pressurized water reactor
s, the design also had the advantage of negative feedback
: an increase in reactor power caused the water to expand, leading to reduced thermalization
of neutrons and lowering absorption by the fuel, therefore lowering the power. Thus, changes in the average coolant temperature, notably from the steam demand of engine throttles, naturally maintains reactor power without intervention from a reactor operator.
The S7G reactor was never used on a ship, and the prototype was fitted with rods in the late 1980s when the reactor was refueled.
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
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...
designed for 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. The S7G designation stands for:
- S = SubmarineSubmarineA 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 - 7 = Seventh reactorNuclear reactor coreA 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 ElectricGeneral ElectricGeneral 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
This prototype design was a land-based 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...
that did not use control rods. It was tested in the late 1970s and early 1980s at the Modifications and Additions to a Reactor Facility (MARF) plant located at the 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...
's Kesselring Site in Ballston Spa, New York
Ballston Spa, New York
Ballston Spa is a village in Saratoga County, New York, United States. The population was 5,556 at the 2000 census. It is the county seat of Saratoga County. The village is named after Rev. Eliphalet Ball, a Congregationalist clergyman and an early settler. The village lies on the border of two...
. It consisted of an experimental reactor core installed in a modified S5W reactor
S5W reactor
The S5W reactor is a nuclear reactor used by the United States Navy to provide electricity generation and propulsion on warships. The S5W designation stands for:* S = Submarine platform* 5 = Fifth generation core designed by the contractor...
plant.
Design and operation
Instead of the movable hafniumHafnium
Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869. Hafnium was the penultimate stable...
-based control rod
Control rod
A control rod is a rod made of chemical elements capable of absorbing many neutrons without fissioning themselves. They are used in nuclear reactors to control the rate of fission of uranium and plutonium...
s used in all of the other United States Naval reactors, reactivity in the S7G core was controlled by stationary gadolinium
Gadolinium
Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. It is found in nature only in combined form. Gadolinium was first detected spectroscopically in 1880 by de Marignac who separated its oxide and is credited with...
-clad tubes partially filled with water. Water could be pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...
ed from the portion of the tube inside the core up to a reservoir above the core, or allowed to flow back down into the tube. A higher water level in the tube slowed more neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s in the core, causing more neutron capture by the gadolinium tube cladding rather than by the uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
fuel, thus lowering the power level.
The system was configured with the pump running continually to keep the water level low; on loss of electrical power, all of the water would flow back into the tube, shutting down the reactor. As with all 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, the design also had the advantage of negative feedback
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...
: an increase in reactor power caused the water to expand, leading to reduced thermalization
Thermalisation
In physics, thermalisation is the process of particles reaching thermal equilibrium through mutual interaction....
of neutrons and lowering absorption by the fuel, therefore lowering the power. Thus, changes in the average coolant temperature, notably from the steam demand of engine throttles, naturally maintains reactor power without intervention from a reactor operator.
The S7G reactor was never used on a ship, and the prototype was fitted with rods in the late 1980s when the reactor was refueled.