A gas-cooled reactor (GCR) 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.
Gas-cooled reactor types include:
- Heavy Water Gas Cooled Reactor (HWGCR)
- Gas-cooled reactor (graphite moderated)
- Advanced gas-cooled reactor
- Gas-cooled fast reactor
- Gas turbine modular helium reactor, General Atomics design : He-cooled, Graphite moderated
- High temperature gas cooled reactor
- Pebble bed reactor
- Very high temperature reactor
See also 
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