What is a Nuclear Breeder Reactor?

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Nuclear Breeder Reactor is a nuclear reactor that generates more fuel than it consumes. These reactors were initially (1940s and 1960s) considered appealing due to their contribution to fuel economy: a normal reactor consumes less than 1% of the natural uranium that begins the fuel cycle, while a breeder can burn almost all of it, also generating less waste for equal amounts of energy. Breeders can be designed to use thorium (naturally occurring slightly radio active metal), which is more abundant than uranium. Currently, there is renewed interest in both designs of breeders because of the high price of uranium.


What is Breeding ratio?

The Breeding ratio represents the number of new fissile atoms created for each fission event. Fissile material is produced by neutron irradiation (kind of radiation which consists of free neutrons) of fertile material, particularly uranium-238 and thorium-232.


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. All commercial reactors breed fuel, but they have low (still significant) breeding ratios compared to the machines traditionally considered “breeders”.


What are the types of Breeder reactors?

There are three types of breeder reactors - two traditional breeder type reactors and one based on conventional type reactor. They are:

  • Fast breeder Reactor or FBR: The superior neutron economy of a fast neutron reactor makes it possible to build a reactor that, after its initial fuel charge of Plutonium (radioactive chemical element), requires only natural uranium feedstock as input to its fuel cycle. This fuel cycle is termed as the Plutonium economy. A few prototypes have been built of fast breeders, and Japan, China, Korea and Russia have all commit funds toward continued development.
  • Thermal breeder Reactor: The excellent neutron capture characteristic of fissile uranium-238 make it possible to build a moderated reactor that, after its initial fuel charge of enriched uranium, plutonium, needs only thorium as input to its fuel cycle. Thorium-232 produces Uranium-233 after neutron capture and beta decay (type of radioactive decay in which beta particle, an electron or a positron is emitted). Thermal Breeder reactors have only been built on a small scale so far, with India taking initial steps towards industrial-scale development, have begun in 2006.
  • Reduced Moderation Reactors: In addition to this, there is an interesting “Reduced moderation reactors”, which are derived from conventional reactors and use conventional fuels and coolants, but are designed to be reasonably efficient as breeders. Such designs typically achieve breeding ratios of 0.7 to 1.01 or even higher.


How does a Nuclear power plant work?

Nuclear reactors generate energy through fission, the process by which an atomic nucleus splits into 2 or more smaller nuclei. During fission, a small amount of mass is converted into energy which ends up generating an enormous amount of heat, which can be used to generate electricity. The heat is used to generate steam from water, which is then used to rotate the turbines that drive the genertors, which eventually produce electricity.


The trick with Nuclear reactors is that, the nuclear reaction can pretty quickly pick up speed and become a nuclear bomb, unless the reaction is controlled by reducing the number of neutrons available to propagate fission. Neutrons produced by fission have high energies and move very quickly sparking a chain reaction. These fast neutrons do not lead to fission that can be effectively controlled, as slower moving neutrons since they are slowed down in most reactors by the process of moderation (using cadmium rods). These slower neutrons are called thermal neutrons. By controlling the speed and number of neutrons, the nuclear reaction is managed in such a way as to generate enough heat to power the generators, and not enough to lead to an explosion or a melt-down (as was predicted in the sci-fi theory of China Syndrome, which was a very real threat with the Chernobyl reactor incident in 1980s).


How can we compare the Breeder reactor with the Nuclear power plant?

Nuclear reactor as discussed above generates energy through nuclear fission. It uses uranium as the fuel. Breeder reactors are also another kind of a fission reactor. It operates the same way as the nuclear reactors through nuclear fission, but uses plutonium instead of uranium as its fuel. Breeder reactors use plutonium as fuel because of its lower cost and the small amount of fuel needed.  


What is the difference between Fast Breeder reactor and the Nuclear power plants?

In contrast to most normal nuclear reactors, a fast breeding reactor uses a coolant that is not an efficient moderator, such as liquid sodium, so its neutrons remain high energy. Although these fast neutrons are not as good at causing fission, they are readily captured by an isotope of Uranium -238, which then becomes plutonium-239. This plutonium isotope can be reprocessed and used as more reactor fuel or in the production of nuclear weapons. Reactors can be designed to maximize plutonium production, and in some cases they actually produce more fuel than they consume. These reactors are called breeder reactors.  

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