Nuclear reactors

Nuclear reactors (atomic boilers, reactors) devices, which are controlled chain reaction of nuclei of the atoms of heavy elements (uranium, plutonium , and thorium.
In a result chain reaction releases massive amounts of heat energy, the formation of new radioactive elements (fission fragments) and powerful streams of neutron radiation (see) and gamma radiation (see).

the scheme of a nuclear reactor
The scheme of a nuclear reactor: 1 - heat exchanger; 2 - control rods; 3 - uranium; 4 - pump.

Nuclear reactors are classified by purpose (energy, research and others), by mutual location of nuclear fuel and moderator (homogeneous and heterogeneous), the neutron energy that supports a fission chain reaction, and other characteristics. The main constructive element of the nuclear reactor of any type is active zone, in which the fission of nuclear fuel (Fig.).
Managing the chain reaction is carried out by the regulating devices. In the simplest case is the rods from materials strongly absorbing neutrons (boron, cadmium and others). Introducing or removing absorbing rods from the core, respectively, decrease or increase of neutron fluxes in the active zone, and hence the power of a nuclear reactor.
The heat released when the chain reaction is a fluid (liquid or gaseous)circulating through the core of a nuclear reactor.
Nuclear reactors are used: for production of radioactive isotopes and nuclear fuel; for the production of electricity in nuclear power plants, as the transport power installations; for research in nuclear physics and technology, radiation chemistry, radiobiology and medicine.
In addition, nuclear reactors can be used as sources of thermal neutrons for holding neitronografiya therapy (see, Neutron therapy).