The Gas Cooled Reactors (GCR) and its Advantages and Disadvantages

The Gas Cooled Reactors (GCR) and its Advantages and Disadvantages

1. A gas cooled reactor was first developed in U.K. uses CO₂, as coolant instead of water and graphite as moderator. It is called gas cooled graphite moderated (GCGM) reactor.
2. It uses natural uranium as fuel. The coolant pressure is about 7 bar and temperature 336°C. Another gas cooled reactor developed in U.S.A uses helium as coolant and graphite as moderator.
3. It is called high temperature gas cooled (HTGC) reactor. The fuel used in U as fissile material and thorium as fertile material.
4. The pressure and temperatures of the coolant are 15 bar to 30 bar and 700°C to 800°C respectively. HTGCR may work upto a thermal efficiency of 40%.
5. The advantage of using gas as coolant compared to water is that it is safe, easy to handle and it can be heated upto any temperature without change of phase at any pressure though the gas has low heat transfer properties compared to water.
6. However, working with gas coolants in the reactors, a large rate of gas circulation with the help of blowers is needed for affecting the required energy transfers.
7. Therefore for driving the blowers a large amount of power is needed compared to power needed for running the feed water pumps in case water is used as coolant. It lowers the thermal efficiency of the gas cooled reactors compared to liquid cooled reactors.

Advantages of gas cooled reactor :

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

Disadvantages of gas cooled reactor :

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

As discussed above, coolant used is CO₂, for (GCGM) reactor and He in case of HTGC reactor in the primary circuit. The coolant transfers the heat energy to feed water in the heat exchanger. The steam so generated is used in conventional power plant to generate power working on Rankine cycle.