Gas-cooled Reactor (AGR)
This type of reactor is used mainly in the UK. It was developed from another gas-cooled reactor, the Magnox reactor, a
number of which are still operating there.
Figure 4 (Courtesy of the World Nuclear Association)
The Advanced Gas-cooled Reactors, like the Magnox reactors before them, use graphite as a moderator and carbon dioxide as a coolant. This differs from the
previous reactors where water was used as both moderator and coolant.
The AGR uses enriched uranium oxide pellets (2.5-3.5%) in stainless steel tubes
for fuel rods, and control rods penetrate the graphite moderator. The carbon dioxide coolant circulates through the reactor core at temperatures up to 650°C.
The steam generator tubes run inside the reactor core, keeping the water separate from the carbon dioxide coolant, but keeping the steam in the tubes heated to turn the turbine.
A secondary shutdown system involves injecting nitrogen to the coolant.