Liquid Metal Reactor or Sodium Graphite Reactor (SGR) Power Plant and its Advantages and Disadvantages
- Sodium graphite reactor is a typical liquid metal reactor. The arrangement of a sodium graphite reactor power plant is shown in Figure.
- It uses graphite as the moderator and liquid sodium as coolant which can reach temperature of about 850°C at 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 sodiun potassium (Nak) in the primary heat exchanger which in turn transfers the heat in the secondary heat exchanger called steam generator.
- Water leaving the steam generator is converted into superheated steam upto temperature of 540°C. 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 contact with air while charging or draining in the primary and secondary heat exchangers.
Advantages of Sodium Graphite Reactor :
- High temperatures of steam can be obtained due to use of liquid sodium as coolant.
- System need not be pressurized.
- Thermal efficiency is high.
- Cost of pressure vessel and piping system is reduced due to use of low pressures sodium in primary circuit.
Disadvantages of Sodium Graphite Reactor :
- Sodium reacts violently with air and water.
- Intermediate heat exchanger is required to separate radioactive sodium with water and steam.
- Primary and secondary heat exchanger are needed to be shielded with concrete blocks against radiations.
- Any leakage of sodium coolant is highly dangerous.