Breeder reactor is the one which converts non-fissionable material (U²³⁸) into fissionable material (U²³⁵).

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A nuclear reactor that produces (breeds) some kind of fissile material as it burns is called breeder reactor. These reactors produce more fuel than what they consume.

• The fissionable nucleides such as U235 and Pu239 are called fissile nucleides.
• The non-fissionable nucleides such as U²³⁸ and Th²³² are called fertile nucleides.

Conventional nuclear reactors use U²³⁵ as their fuel. But U²³⁵ is available in very less quantity. However, non-fissionable U²³⁸ is about 100 times more plentiful in nature. However, if U²³⁸ could be used as a nuclear fuel, there would be sufficient uranium to run nuclear reactors for hundreds of years.

The breeder reactor was developed to use U²³⁸.

A reactor is built with a core of fissionable plutonium, Pu²³⁹. The Pu²³⁹ core is surrounded by a layer of uranium -238. As the plutonium 239 undergoes spontaneous fission, it releases neutrons. The neutrons released by the core are absorbed by the blanket of U-238. These neutrons convert U²³⁸ to Pu²³⁹.

₉₂ U²³⁸ + ₀n¹ → ₉₄Pu²³⁹ + 2 _-1e⁰

₉₄ Pu²³⁹ + ₀n¹ → ₃₈Sr⁹⁰ +₅₆Ba¹⁴⁷ + 3₀n¹

In a breeder reactor, the Pu²³⁹ isotope produces about three neutrons per fission. One neutron released by Pu²³⁹ produces another fission. A second neutron is absorbed by a U²³⁸ nucleus and produces a new Pu²³⁹ nucleus. In this way the concentration of the Pu²³⁹ fuel remains constant.

If the third neutron is also absorbed by U²³⁸, two Plutonium nuclei are produced for each Pu²³⁹ fission. Since more fuel is produced than is consumed, the reactor is said to breed nuclear fuel.

Advantages and disadvantages of breeder reactor