Gas Cooled Reactors (GCR) Power Plant

A gas cooled reactor was first developed in U.K. which uses C02 as coolant instead of water and graphite as moderator. It is also called as Gas Cooled Graphite Moderated (GCGM) reactor. The basic diagram of gas cooled reactor power plant is shown in figure,
Gas Cooled Reactor Power plant | enggarena.net
Gas Cooled Reactor Power Plant
It uses natural Uranium as fuel. The coolant pressure is about 7 bar and temperature about 336 degree Celsius.
There was another gas cooled reactor developed in U.S.A which uses helium as coolant and graphite as moderator. It is called high temperature gas cooled (HTGC) reactor. The pressure and temperature of the coolant are 15 bar to 30 bar and 800 degree Celsius respectively.
HTGCR may work up to a thermal efficiency of 40%.
The advantage of using gas as coolant as compared to water is that it is safe, easy to handle and most important it can be heated up to any temperature without change of phase at any pressure though the gas has low heat transfer properties as compared to water.
However, while working with gas ass coolant in the reactors, large rate of gas circulation is required which is supplied with the help of blowers for affecting the required rate of energy transfers.
Therefore, for driving the large number of blower, large amount of energy is required as compared to the power needed for running the feed water pumps in case water is used as coolant. Thus, it reduces the thermal efficiency of the plant as compared to water cooled or liquid cooled power plants.

Advantages of Gas Cooled Reactors :

1. It has no corrosion problems.
2. As mentioned earlier, gases are easy to  handle.
3. These can be operated at high temperatures.
4. Gases can be pressurized easily.
5. Graphite remains stable at high temperatures and radiation problems are minimum.

Disadvantages of Gas Cooled Reactors :

1. Fuels have to be operated at high temperatures.
2. If helium is used as in case of HTGC reactor, leakage is a major problem.
3. Gases have lower heat transfer coefficient thus it requires large heat exchangers.
4. Large amount of fuel loading is required.
5. More power is needed for coolant circulation compared to water cooled reactors.
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Sujit Kadus

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