Gas Cooled Reactor
Encyclopedia
A gas-cooled reactor is a nuclear reactor
that uses graphite
as a neutron moderator
and carbon dioxide
(helium
can also be used) as coolant
. Although there are many other types of reactor cooled by gas, the terms GCR and to a lesser extent gas cooled reactor are particularly used to refer to this type of reactor.
The GCR was able to use natural uranium
as fuel, enabling the countries that developed them to fabricate their own fuel without relying on other countries for supplies of enriched uranium
, which was at the time of their development only available from the United States
or Soviet Union
.
There were two main types of generation I GCR:
The main difference between these two types is in the fuel cladding material. Both types were mainly constructed in their countries of origin, with a few export sales: Magnox plants to Italy
and Japan
, and a UNGG to Spain
. Both types used fuel cladding materials that were unsuitable for medium term storage under water, making reprocessing
an essential part of the nuclear fuel cycle
.
Both types were, in their countries of origin, also designed and used to produce weapons-grade plutonium, but at the cost of major interruption to their use for power generation despite the provision of online refuelling
.
In the UK, the Magnox was replaced by the advanced gas-cooled reactor
(AGR), an improved Generation II
gas cooled reactors. In France, the UNGG was replaced by the pressurized water reactor
(PWR). More recently, GCRs based on the declassified drawings of the early Magnox reactors have been constructed by North Korea
at the Yongbyon Nuclear Scientific Research Center
.
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 uses graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
as a neutron moderator
Neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
can also be used) as coolant
Nuclear reactor coolant
A nuclear reactor coolant is a coolant in a nuclear reactor used to remove heat from the nuclear reactor core and transfer it to electrical generators and the environment....
. Although there are many other types of reactor cooled by gas, the terms GCR and to a lesser extent gas cooled reactor are particularly used to refer to this type of reactor.
The GCR was able to use natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...
as fuel, enabling the countries that developed them to fabricate their own fuel without relying on other countries for supplies of enriched uranium
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...
, which was at the time of their development only available from the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
or Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
.
There were two main types of generation I GCR:
- The MagnoxMagnoxMagnox is a now obsolete type of nuclear power reactor which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of plutonium for nuclear weapons...
reactors developed by the United KingdomUnited KingdomThe United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. - The UNGG reactorUNGG reactorThe UNGG is an obsolete design of nuclear power reactor developed by France. It was graphite moderated, cooled by carbon dioxide, and fueled with natural uranium metal....
s developed by FranceFranceThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
.
The main difference between these two types is in the fuel cladding material. Both types were mainly constructed in their countries of origin, with a few export sales: Magnox plants to Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
and Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, and a UNGG to Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
. Both types used fuel cladding materials that were unsuitable for medium term storage under water, making reprocessing
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...
an essential part of the nuclear fuel cycle
Nuclear fuel cycle
The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...
.
Both types were, in their countries of origin, also designed and used to produce weapons-grade plutonium, but at the cost of major interruption to their use for power generation despite the provision of online refuelling
Online refuelling
In nuclear power technology, online refuelling is a technique for changing the fuel of a nuclear reactor while the pile is critical.Online refuelling has been provided for three main reasons:...
.
In the UK, the Magnox was replaced by the advanced gas-cooled reactor
Advanced gas-cooled reactor
An advanced gas-cooled reactor is a type of nuclear reactor. These are the second generation of British gas-cooled reactors, using graphite as the neutron moderator and carbon dioxide as coolant...
(AGR), an improved Generation II
Generation II reactor
A generation II reactor is a design classification for a nuclear reactor, and refers to the class of commercial reactors built up to the end of the 1990s...
gas cooled reactors. In France, the UNGG was replaced by the 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...
(PWR). More recently, GCRs based on the declassified drawings of the early Magnox reactors have been constructed by North Korea
North Korea
The Democratic People’s Republic of Korea , , is a country in East Asia, occupying the northern half of the Korean Peninsula. Its capital and largest city is Pyongyang. The Korean Demilitarized Zone serves as the buffer zone between North Korea and South Korea...
at the Yongbyon Nuclear Scientific Research Center
Yongbyon Nuclear Scientific Research Center
The Yongbyon Nuclear Scientific Research Center is North Korea's major nuclear facility, operating its first nuclear reactors. It is located in the county of Nyŏngbyŏn in North Pyongan province, about 90 km north of Pyongyang...
.
Types
Gas-cooled reactor types include:- Gas-cooled reactor (graphite moderated)
- MagnoxMagnoxMagnox is a now obsolete type of nuclear power reactor which was designed and is still in use in the United Kingdom, and was exported to other countries, both as a power plant, and, when operated accordingly, as a producer of plutonium for nuclear weapons...
- UNGG reactorUNGG reactorThe UNGG is an obsolete design of nuclear power reactor developed by France. It was graphite moderated, cooled by carbon dioxide, and fueled with natural uranium metal....
(French design, 10 built, last retired in 1994)
- Magnox
- Advanced gas-cooled reactorAdvanced gas-cooled reactorAn advanced gas-cooled reactor is a type of nuclear reactor. These are the second generation of British gas-cooled reactors, using graphite as the neutron moderator and carbon dioxide as coolant...
- Gas-cooled fast reactorGas-cooled fast reactorThe Gas-Cooled Fast Reactor system is a nuclear reactor design which is currently in development. Classed as a Generation IV reactor, it features a fast-neutron spectrum and closed fuel cycle for efficient conversion of fertile uranium and management of actinides...
- Gas turbine modular helium reactorGas turbine modular helium reactorThe Gas Turbine Modular Helium Reactor is a nuclear fission power reactor design under development by General Atomics. It is a helium cooled, graphite moderated reactor and uses TRISO fuel compacts in a prismatic core design.-Construction:...
, General Atomics design : He-cooled, Graphite moderated - High temperature gas cooled reactor
- Pebble bed reactorPebble bed reactorThe pebble bed reactor is a graphite-moderated, gas-cooled, nuclear reactor. It is a type of very high temperature reactor , one of the six classes of nuclear reactors in the Generation IV initiative...
- AVR reactorAVR reactorThe AVR reactor was a prototype pebble bed reactor at Jülich Research Centre in West Germany. Construction began in 1960, first grid connection was in 1967 and operation ceased in 1988....
- THTR-300THTR-300The THTR-300 was a thorium high-temperature nuclear reactor rated at 300 MW electric . The German state of North Rhine Westphalia, in the Federal Republic of Germany, and Hochtemperatur-Kernkraftwerk GmbH financed the THTR-300’s construction. Operations started on the plant in Hamm-Uentrop,...
- Pebble bed modular reactorPebble bed modular reactorThe Pebble Bed Modular Reactor is a particular design of pebble bed reactor under development by South African company PBMR Ltd since 1994...
- AVR reactor
- Very high temperature reactorVery high temperature reactorThe Very High Temperature Reactor , or High Temperature Gas-cooled Reactor , is a Generation IV reactor concept that uses a graphite-moderated nuclear reactor with a once-through uranium fuel cycle. The VHTR is a type of High Temperature Reactor that can conceptually have an outlet temperature of...