Classification of Nuclear Reactors
The nuclear reactors can be classified based on the following systems :
1. Based on neutron energy :
There are further classified as :
(i) Fast reactors : A reactors in which the fission is due to non-moderated neutrons is called fast reactor. Such reactors use enriched uranium.
(ii) Slow or thermal reactors : In these reactors the fission is brought about by slow neutrons by passing the fast neutrons over moderators. These neutrons called thermal neutrons possess the thermal velocity of 2200 m/s which is attained in a state of thermal equilibrium with the medium. These reactors use natural uranium.
(iii) Intermediate reactors : These reactors use neutrons in the region between fission and thermal energies i.e. fission events are caused by neutrons in the course of slowing down.
2. Based on type of fuel used :
(i) Natural uranium fuel reactors : In this reactors the natural fuel is used as fuel.
(ii) Enriched uranium fuel reactor : In this reactor the enriched uranium of 5 to 10% of US is used as fuel.
3. Based on coolant used :
These are further classified as :
(i) Water cooled reactors
(ii) Heavy water cooled reactors
(iii) Liquid metal (Sodium or Bismith) cooled reactors : These reactors are useful when the reactor has to work at high temperatures and pressures. However, working with sodium raises the problem of corrosion since it reacts with water and burns in air.
(iv) Gas cooled reactors : These reactors present difficulty when gases are used under pressure.
4. Based on moderators used :
These reactors are further classified as :
(i) Water and heavy water reactors
(ii) Graphite reactors
(iii) Beryllium reactors
5. Base on type of core used :
These are further classified as,
(i) Homogeneous reactors : In this type of reactor, both the fuel and moderator represent a uniform mixture in the fluid form. Such reactors have better heat transfer characteristics and its control is better. However, the repair or these reactors poses a problem since the mixture is highly radioactive.
(ii) Heterogeneous reactors : The fuel used in these reactors is in solid form and the coolant is in the liquid form. In this, the fuel rods are inserted in moderators and these are arranged in some regular order so as to generate heat energy uniformly.