In fast breeder reactor, enriched Uranium (U235) or Plutonium is kept in the casing without using moderator. The casing is surrounded by a thick blanket of fertile Uranium (U238). This is known as breeding material. Fig shows a schematic diagram of a fast breeder reactor. Fast moving neutrons are liberated due to fission of enriched Uranium (U235). The ejected excess neutrons are absorbed by the fertile Uranium (U238) which is converted into fissionable material (PU239). The fissionable material (PU239) is capable of sustaining chain reaction.
This reactor employs two liquid metal coolant circuits as shown in fig. Liquid sodium (Na) is used as primary coolant. Sodium potassium (NaK) alloy is used as secondary coolant.
There are two heat exchangers used in this power plant. One is intermediate heat exchanger (IHE) and other is steam generator. The intermediate heat exchanger is used to transfer heat from primary coolant (Na) to secondary coolant (NaK). The feed water is heated in the steam generator by the hot secondary coolant. The steam produced in the steam generator is then utilized for power generation.
- No moderator is required.
- High breeding is possible.
- It gives high power density than any other reactor.
- High efficiency in the order of 40% can be obtained.
- Better fuel utilization.
- Absorption of neutrons is low.
- It requires highly enriched fuel.
- Special coolants are required to carry out the large quantity of heat from the reactor core.
- Handling of sodium is a major problem because it becomes hot and radioactive.
- Specific power of reactor is less.
- Safety must be provided against melt down.
- Neutron flux is high at the center of the core.