Although the basis of the operation of any nuclear reactor fission is a radioactive substance, accompanied by the release temperature, depending on the design features distinguish two varieties - fast reactor and slow, sometimes called heat.
The neutrons released in the reaction process, have a very high muzzle velocity, theoretically overcoming of thousands of kilometers per second.This - the fast neutrons.In the process of moving from the collision with the atoms of matter surrounding their speed slows down.One simple and affordable ways to artificially reduce the occupancy rate is in the way of water or graphite.Thus, learning to adjust the kinetic energy of these particles, the man was able to create two types of reactors.The name of the "thermal" neutrons obtained because the speed of their movement after slowing substantially corresponds to the natural intra-speed thermal motion.In numerical terms, it is up to 10 kilometers per second.For microcosm this value is relatively low, so the capture of particles by nuclei occurs very frequently, causing new coils division (chain reaction).The consequence of this is the need for a much smaller amount of fissionable material than can not boast of fast reactors.In addition, some other reduced overhead.Currently just explains why most operating nuclear power plants use exactly slow neutrons.
It would seem - if all is counted, then why do we need fast breeder reactor?It turns out, not so simple.The major advantage of such systems - the ability to provide nuclear fuel other reactors, as well as to create an increased division cycle.Let us examine this in more detail.
Fast Reactor uses a fully loaded into the core fuel.Let's start from the beginning.Theoretically, the use as a fuel can only two elements: plutonium and uranium-239 (isotopes 233 and 235).In nature, it found only isotope U-235, but very little to talk about the prospects of such a choice.These uranium and plutonium - is derived from Thorium-232 and uranium-238, which are formed as a result of exposure to neutron flux.And now these two radioactive material is much more likely to occur in a natural form.Thus, if it was possible to run a self-sustaining fission chain reaction of U-238 (or plutonium-232), its result would be the emergence of new portions of fissile material - uranium-233 or plutonium-239.When slowing down neutrons to thermal velocities (classical reactors) such a process is impossible: they are the fuel is of U-233 and Pu-239, but the fast breeder reactor allows you to perform such additional conversion.
process is as follows: load uranium-235 or thorium-232 (raw materials), as well as a portion of the uranium-233 or plutonium-239 (fuel).The last (any of them) enable the flow of neutrons, needed for the "ignition" of the reaction in the first element.In the process of disintegration released thermal energy converted to electricity generators of the station.Fast neutrons affect the feedstock by converting these elements ... new fuel charge.Typically, the amount of burnt fuel and the resulting equal, but if the raw material is loaded more, the generation of new portions of the fissile material is even faster than consumption.Hence, the second name of such reactors - breeders.Excess fuel can be used in the classical slow species reactors.
Lack of models of fast neutron that before loading the uranium-235 must be enriched, which requires additional investments.Besides, the structure of the core is more complex.
