Gas Cooled Reactor (GCR) and Advanced Gas Cooled Reactor (AGR)

Two views of the Sizewell nuclear power plant in Suffolk, Great Britain. In the foreground, there is the part with the Magnox reactor being decommissioned; in the background a newer operating part B with a single pressurized water reactor. (Source: © sw67 / stock.adobe.com)

Two views of the Sizewell nuclear power plant in Suffolk, Great Britain. In the foreground, there is the part with the Magnox reactor being decommissioned; in the background a newer operating part B with a single pressurized water reactor.

Gas cooled reactors (GCR) are used exclusively in Great Britain and Japan. The older type, known as the “Magnox” (for “magnesium oxide”), is being gradually phased out and no new blocks are being constructed. There are 14 operating reactors of the advanced type (AGR), which also uses graphite as the moderator. These reactors were developed in Great Britain.

The GCR reactor is fueled by natural uranium housed in rods covered with magnesium oxide. The reactor core is a steel spherical vessel 8 meters high and 14 meters in diameter encased in concrete. There are several thousand fuel channels each containing several fuel rods. These reactors may be refueled under power.

GCR (Magnox) schematic diagram

GCR (Magnox) schematic diagram

View of the Vandellos nuclear power plant from a beach of the Spanish resort L’Almadrava. (Source: © Marlee / stock.adobe.com)

View of the Vandellos nuclear power plant from a beach of the Spanish resort L’Almadrava.

Brick shaped graphite is used as the moderator. The fuel channels transverse the graphite bricks. Carbon dioxide CO2 is used as the coolant pressurized to 2.75 MPa at a temperature of 400 °C. The modern type AGR may reach temperatures of up to 650 °C. The gas transfers its energy in a steam generator to the secondary water circuit. The generated steam powers a turbine. This type of power station is a double-circuit power plant.

There are two reactors in the Spanish nuclear power plant Vandellos. The first gas cooled 500 MW reactor was decommissioned in 1990 after a fire in the turbine generator set. The second 1,000 MW pressurized water reactor is still in operation. (Source: © Marlee / stock.adobe.com)
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The Wylfa nuclear power plant in North Wales is the last power plant in the world that uses the original Magnox gas cooled reactor. The pressure vessel is made of pre-stressed reinforced concrete. (Source: © Gail Johnson / stock.adobe.com)
The Heysham nuclear power plant in Great Britain has two independent double-blocks with advanced gas cooled reactors, total installed power output is 2,400 MWe. (Source: © Sue Burton / stock.adobe.com)
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One of the oldest nuclear power plants was the Oldbury plant. It was a Magnox GCR type reactor and was decommissioned in 2012.