Sodium Graphite Reactor (SGR) Power Plant

Sodium graphite reactor is a typical liquid metal reactor. The arrangement of sodium graphite reactor power plant is shown in figure.
Sodium Graphite Reactor Power Plant | enggarena.net
Sodium Graphite Reactor Power Plant

It uses graphite as a moderator and liquid sodium as coolant which reach a temperature of about 850 degree Celsius at a low pressure of only 7 bar.
In the primary circuit, the heat is absorbed by liquid sodium in the reactor. The sodium becomes radioactive while it passes through the core and reacts chemically with water.
Therefore, the heat absorbed by sodium is transferred to secondary coolant sodium potassium (NaK) in the primary heat exchanger which in turn transfers the heat in the secondary heat exchanger called Steam generator.
 Water leaving the generator is converted into super-heated steam up to a temperature of 540 degree Celsius. This steam is used for power generation in the steam plant circuit in the usual manner. The reactor vessel, primary circuit and the primary heat exchanger have to be shielded from radiations.
The liquid metal is required to be handled under the cover of an inert gas like helium to prevent the contact with air while charging or draining in the primary and secondary heat exchangers.

Advantages of Sodium Graphite Reactor (SGR) : 

1.High temperature of the steam can be obtained due to the use of liquid sodium as coolant.
2. Thermal efficiency is high.
3. System need not to be pressurized.
4. Cost of pressure vessel and piping system is reduced due to the use of low pressure sodium in primary circuit.

Disadvantages of Sodium Graphite Reactor :

1. Any leakage of sodium coolant is highly dangerous.
2. Sodium is highly violent with air and water.
3. Primary and secondary heat exchangers are needed to be shielded with concrete blocks against radiations.
4. Intermediate heat exchanger is required to separate radioactive sodium with water and steam.
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Sujit Kadus

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