Nuclear Reactors

What is a nuclear reactor? What are its uses? What is role of moderator, reflector, control rods and other components in a nuclear reactor?

The nuclear reactors are used for the following purposes :

1. To produce heat for thermo-electric power.
2. To produce fissionable materials. 
3. To propel ships, submarines and aircrafts.
4. For research testing and irradiation work.

The nuclear reactor has the following components :

(a) Moderator. A moderator is a material introduced into the fuel mass in order to slow down the speed of fast moving electrons. The slowing down of fast neutrons is desirable because slow moving electrons are more effective than fast neutrons in triggering fission. A moderator, apart from its high neutron slowing power and low non-productive neutron, should be

(i) stable under nuclear radiation,
(ii) corrosion resistant,
(iii) good thermal conductor, and
(iv) available in adequate.

The graphite and concrete are generally used as moderator.

(b) Reflector. A reflector is used to reflect neutrons back into the active core. Due to reflector, less fuel is needed to generate sufficient neutrons to sustain a chain reaction. The reflectivity of a reflector is defined as the fraction of neutrons entering the reflector which are returned to the core. It depends upon the geometry of the reflector, energy of neutrons and the properties of the reflector.

(c) Control rods. The control rods in the nuclear reactors are used to absorb excess neutrons.