The nuclear reactors are classified on the following basis:
1. On the basis of neutron energy
a) Fast reactors
In these reactors, the fission is effected by fast neutrons without any use of moderators.
b) Thermal reactors
In these reactors, the fast neutrons are slowed with the use of moderators. The slow neutrons are absorbed by the fissionable fuel and chain reaction is maintained. The moderator is the most essential component in these reactors.
2. On the basis of fuel used
a) Natural fuel
In this reactor, the natural uranium is used as fuel and generally heavey water or graphite is used as moderator.
b) Enriched uranium
In this reactor, the Uranium used contains 5 to 10% U235 and ordinary water can be used as moderator.
3. On the basis of moderator used
a) Water moderated
b) Heavy water moderated
c) Graphite moderated
d) Beryllium moderated
4. On the basis of coolant used
a) Water cooled reactors (ordinary or heavy),
b) Gas cooled reactors
c) Liquid metal cooled reactors
d) Organic liquid cooled reactors
A nuclear power plant is similar to a conventional steam power plant except how that energy is evolved. The heat is produced in the nuclear power plant by fission, whereas in steam and gas turbine plants, the heat is produced by combustion in the furnace. The nuclear reactor acts as a furnace where nuclear energy is evolved by splitting or fissioning of the nucleus of fissionable material like Uranium U-235. It is claimed that 1 kg U-235 can produce as much heat energy that can be produced by burning 4500 tones of high grade coal or 1700 tons of oil.
