A breeder reactor is a type of nuclear specifically designed to create more fissile material (nuclear fuel) than it consumes. Depending on the Breeding Ratio of a reactor, it can produce new fuel at a greater or lesser rate. The Breeding Ratio represents the number of new fissile atoms created for each fission event. The theoretical upper limit for the Breeding Ratio is 1.8, while most breeder reactors are designed to produce just about as much fissile material as they consume. It is hoped that breeder reactors will replace the current generation of conventional reactors as progress in nuclear power continues.
Most traditional nuclear reactors create some additional fuel as they operate, increasing fuel efficiency. As the nuclear industry has developed, these ratios have been pushed higher and higher, leading to better fuel economies. There are still technical hurdles to developing cost-effective breeder reactors, but breeders can claim a number of advantages that traditional reactors can’t. The greatest is that, after an initial loading of enriched uranium or plutonium, a breeder reactor can thereafter be powered just by periodic loadings of unenriched (natural) uranium or (in another type of breeder reactor) thorium. Thorium is about four times more abundant in the Earth’s crust than uranium, poses very little weaponization risk, and produces nuclear waste which decreases in intensity to background levels much quicker than the waste from a conventional plant.
One concern with breeder reactors is that by producing bomb-ready nuclear fuel, such as plutonium, they create a nuclear weapons risk. This problem is addressed by a stage in nuclear preprocessing where other elements such as curium and neptunium are added in tiny quantities to the plutonium. This form of processing has no effect on the use of plutonium as a reactor fuel, but makes it extremely difficult to use the material to create an atomic bomb, even if utilizing a very sophisticated design.
There are two types of breeder reactors that have been proposed. The first, the fast breeder reactor, uses an initial fuel charge of plutonium, thereafter only requiring natural uranium for energy. A few prototypes have been built of fast breeders, and Japan, China, Korea, and Russia are all committing funds towards continued development. The second type of breeder reactor is a thermal breeder reactor, which uses an initial fuel charge of enriched uranium, thereafter using only thorium. Thermal breeder reactors have only been built on a small scale thus far, with India taking the first steps towards industrial-scale development, having begun in 2006.