A gas reactor or GCR (English gas cooled reactor) is a type of nuclear nuclear reactor of nuclear fission. The neutron moderator of this type of nuclear reactor is graphite. The coolant of the nuclear gas reactor is carbon dioxide in the gaseous state. According to the classification made by the International Atomic Energy Agency of the United Nations, IAEA, this type of reactors includes those of the AGR type (of the English Advanced Gas-cooled Reactor) and Magnox (of the English Magnesium Non-OXidising), both of British technology.
Within the history of nuclear energy there was also a type of French GCR, called UNGG (from the French Uranium Naturel Graphite Gaz), but it is a totally obsolete type and of which there is currently no operational nuclear power plant in the world. They were the first generation of nuclear reactors in France, developed in the wake of World War II.
The essential differences between the AGR, Magnox and UNGG models are the fuel they use and the coating around the pellets. The Magnox and the UNGG developed at the same time, they are the oldest and quite similar, they use natural uranium as a nuclear fuel and they differ in that the Magnox surrounds the tablets with an alloy of magnesium and aluminum while the UNGG did it with a of magnesium and zirconium. The new generation of GCR, the ACR (or advanced gas reactors), use enriched uranium as fuel.
Disadvantages of the gas cooled nuclear reactor
The heat capacity and thermal conductivity of the coolant gas is low, the necessary thermal output is ensured by increasing the gas pressure. However, there is also the problem that the reactor inevitably becomes large due to the small thermal power density compared to the light water reactor.
With the Magnox reactor as a prototype, many gas-cooled power generation reactors were started up. Since the excess reactivity is originally small, in the Magnox nuclear reactor it is difficult to burn the fuel efficiently and, for it to work stably, it is necessary to replace the nuclear fuel frequently.