Gas Cooled Reactors


The Gas Cooled Reactor was one of the original designs. In the Gas Cooled Reactor (GCR), the moderator is graphite. Inert gas, e.g. helium or carbon dioxide, is used as the coolant. The advantage of the design is that the coolant can be heated to higher temperatures than water. As a result, higher plant efficiency (40% or more) could be obtained compared to the water cooled design (33-34%).

In the United States, Gulf General Atomics was the proponent of this design. Public Service of Colorado (now Xcel Energy) built the Fort Saint Vrain facility north of Denver. A short history describes the trials and tribulations experienced during the 1968 - 1995 period of construction, startup, operation, shutdown, and decommissioining of the nuclear section of the facility. The NRC has also written NUREG/CR-6839, Fort Saint Vrain Gas Cooled Reactor Operational Experience. Currently, there is little movement toward the gas cooled design in the US or elsewhere.

In the United Kingdom, the government was the proponent that developed, constructed, and operated a number of gas cooled reactors. The older design used carbon dioxide gas circulating through the core at a pressure of ~1.6 MP_aor 230 pounds per square inch to remove the heat from the fuel elements. The fuel consists of natural uranium metal clad with an alloy of magnesium known as Magnox (thus the name for the reactor type).

The newer Advanced Gas Cooled (AGR) Reactors use a slightly enriched uranium dioxide clad with stainless steel. Carbon dioxide is the coolant gas used.

Two key advantages of this design are:

higher operating temperature with a higher thermal efficiency
not susceptible to accidents of the type possible with water cooled/moderated reactors.

The Gas Cooled Reactor or Advanced Gas Reactor cycle is illustrated in the simple sketch below:

Courtesy Scottish Nuclear

In the UK, British Energy and British Nuclear Fuels operate the nuclear facilities. A number of the older Magnox units are being shutdown. UK Gas Cooled Reactors remaining in operation include the Magnox units - Bradwell 1& 2, Calder Hall 1-4, Chapelcross 1-4, Dungeness A1 & A2, Hinkley Point A1 & A2, Oldbury 1& 2, Sizewell A1 & A2, and Wylfa 1 & 2 - and the Advanced Gas Cooled reactors - Dungeness B1 & B2, Hartlepool 1 & 2, Heysham A1 & A2, B1 & B2, Hinkley Point B1 & B2, Hunterston B2 (AGR), and Torness 1 & 2 (AGR).


Capenhurst - Courtesy BNFL	Hunterston B - Courtesy Scottish Nuclear

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Gas Cooled Reactor