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What is a Fast Breeder Reactor?
When uranium U-235 is fissioned by slow neutrons it produces heat and an additional neutron.
In case a fertile material like U-238 is kept in the same reactor surrounding the core of U-235, the fast-moving additional neutron is absorbed by U-238 and converts it into plutonium (Pu-239), a fissile material. This man-made fuel Pu-239 can be used for further fission.
Therefore, these types of reactors are important since they not only produce heat but also produce more secondary fissile fuels like plutonium more than fuel consumed in the reactor.
This is known as Breeding.
Similarly, Thorium (Th-232) can be converted into U-233 which is also a secondary fissile material.
Since India has massive reserves of thorium and limited resources of uranium, the development of these fast breed reactors is important.
A fast breeder reactor is shown in the figure below.
|Fast Breeder Reactor Power Plant|
The enriched uranium U-235 or plutonium Pu-239 is kept without a moderator in the reactor core surrounded by a thick blanket of depleted U-238.
One additional neutron available from the fission of U-235 is used to convert U-238 or Th-232 into U-233 as secondary fuels.
As in the case of the sodium graphite reactor, this reactor also uses two liquid metal coolants in which sodium is used as primary coolant and sodium-potassium as secondary coolant.
In fast breeder reactors, neutron shielding is provided by the use of boron or graphite. In order to protect against gamma radiations, a shield is provided made of lead or concrete or of other materials.
See Also: Types of Nuclear Reactors