Breeder Reactors

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Natural uranium contains very little (0.72%) of its fissionable isotope ²³⁵U needs to be enriched in the latter to be useful as a fuel in nuclear reactor.

A breeder reactor is one that produces more fissionable nuclei than it consumes.

Another serious problem about U-235 is that its frequent use in nuclear reactors for the production of power may cause the present stock getting exhausted very soon.

Thus scientists are involved in finding other suitable fissionable materials. Lately it is discovered that Plutonium-239 and Uranium-233 are alternative fissionable materials, which can be used as fuel in nuclear reactors.

These fissionable materials can be produced by the bombardment of more abundantly available U-238 or Th-232 (which are non-fissionable) with neutrons. The reactors in which this conversion is carried out are referred to as breeder reactors.

When is bombarded with fast neutrons, the following nuclear transmutation occurs:

Here the breeder reactor produces fissile from non-fissile uranium.

In breeder reactors the conditions are so controlled that out of the 3 neutrons emitted by each U-235 nuclide during its disintegration, one is used in propagating the fission chain with U-235 while the other 2 neutrons are used in producing plutonium-239 from U-238. Thus for each U-235 atom the two Pu-239 atoms are produced.

Thus in breeder reactors, the formation of fissionable nuclei is more in comparison to their respective consumption.

Fissionable nuclides like U-235 or Pu-239 are also called fissile nuclides.

On the other hand, non-fissionable nuclides like U-238, which can be converted to fissile nuclide is called a fertile nuclide.

In short, in breeder reactors, a small amount of fissile nuclide provides the neutrons that convert a large quantity of fertile nuclides into fissile nuclides. The fissile nuclide further participates in self-sustaining chain reaction.

In all reactors, heat from the core is extracted by heat exchangers and is used to convert water into steam, this is then used to drive turbo alternators for producing electricity. In breeder reactors, an alloy of sodium and potassium is used as coolant. The liquid metal gives its heat to water in a heat-exchanger.