A breeder reactor is a specialized type of nuclear reactor that generates more fissile material than it consumes while simultaneously producing energy.

The primary function of a breeder reactor is to create additional fissile material (fuel) through a process known as breeding. This process involves converting fertile materials—such as uranium-238 or thorium-232—into fissile materials like plutonium-239 or uranium-233. During the reactor’s normal operation, fertile materials are exposed to high-energy neutrons that are released during fission, facilitating this conversion.

Inside the core of a breeder reactor, there exists a mixture of both fissile and fertile materials. The fissile materials, which can include uranium-235 or plutonium-239, undergo fission when they are struck by a neutron. This reaction releases energy as well as additional neutrons. Some of these newly released neutrons are then absorbed by the fertile materials, converting them into additional fissile material. The newly created fissile material can subsequently be utilized as fuel, allowing the reactor to produce more fuel than it consumes.

Breeder reactors are specifically designed to maximize the absorption of neutrons by the fertile materials. This is accomplished by operating with a fast neutron spectrum, which means that the neutrons are not significantly slowed down (or moderated) as they are in conventional thermal reactors. Fast neutrons have a higher likelihood of being absorbed by fertile materials, thus enhancing the breeding rate.

The implementation of breeder reactors has the potential to significantly extend the global supply of nuclear fuel. By effectively converting fertile materials into fissile materials, breeder reactors can tap into a much larger proportion of natural uranium or thorium resources. However, several substantial challenges accompany the use of breeder reactors. They are typically more complex and costly to construct and operate compared to standard thermal reactors. Additionally, the use of plutonium as a fuel raises concerns regarding nuclear proliferation. Moreover, the high-energy neutrons generated in breeder reactors can cause considerable damage to reactor materials, leading to technical challenges in their design and operation.