Main Components of a Nuclear Reactor and their Functions

1. The reactor vessel is designed to withstand high pressures and it is usually made from low carbon steel.
2. It is clad with stainless steel to reduce the corrosion problems.

1. Nuclear reactors use fissionable materials like ₉₂U²³⁵, ₉₄Pu²³⁹  and ₉₂U²³³. Natural uranium found in earth’s crest has 0.714% of ₉₂U²³⁵, which is stable and capable of sustainable chain reactions, is generally used as fuel.
2. The fuel rod is fabricated in various shapes like rods, plates, tins, pallets etc. and these are placed inside the reactor core in such a way that these produce uniform heat in the reactor.
3. The fuel rods are clad with stainless steel, zirconium or by aluminium to prevent oxidation of uranium.

3. Moderator :

1. The moderator are the substances which help in reducing the speed of neutrons and make them to lose their kinetic energy by collisions but at the same time do not absorb them but scatters them. Reduced velocity of neutrons upto thermal speed help in maintaining the fission chain reaction in the reactor when the ordinary uranium is used.
2. The moderators are lighter than fuel. Various materials used for moderators are light water (H₂O), deutorium or heavy water (D₂O), graphite and beryllium.
3. Reactors using enriched uranium (5 to 10% of U²³⁵) do not require moderators since the reactor can work with fast as well slow (thermal) neutrons. But the cost of enriched uranium is very high.
4. As a moderator D₂O, is the best material having moderating ratio of 12000 as compared to 72 for H₂O and 170 for carbon. It can used as coolant as well. Only disadvantage is that it has low boiling point and it necessitates pressurization and it is expensive.

4. Control rods :

1. In case the chain reaction of fission of nuclear material is not controlled properly, the heat energy generated will be enormous which will melt the fuel rods, disintegrate coolants and destroy the reactor.
2. The control rods are used to control the chain reaction by absorbing required neutrons. The material used for control rods is boron or cadmium.
3. These rods can be moved in and out of the reactor core assembly either automatically or manually. The magnitude of insertion of control rod represents the proportionate absorption of neutrons.

5. Reflector :

1. In order to conserve fuel, it is desirable that the neutrons are not allowed to escape the reactor core. This is achieved by providing a reflector surrounding the reactor core within the thermal shielding arrangement. The reflector thus provided will sent back the neutrons into the core, there by, it improves the chain reaction.
2. Since the materials having good absorptivity are also good reflectors hence, the materials used for moderators are also used for reflectors e.g. graphite and beryllium.

6. Coolants :

1. The purpose of a coolant is to absorb the large amount of heat generated in the reactor core and transfer this heat energy finally to water for generation of steam in a heat exchanger.
2. The coolant used should have high specific heat to reduce its mass flow rate, it should not absorb neutrons and it must be non-corrosive, non-toxic, non-oxidising with high chemical stability.
3. Various coolants used are CO₂, H₂, air, He, heavy water, sodium in liquid form etc.
4. In case water is used as coolant then it takes up the heat and gets converted into steam in the reactor. This steam it directly sent to steam turbine for power generation.

7. Shielding :

1. Shielding is provided for protection of human life against the deadly alpha, beta and gamma radiations of the nuclear fuel in the reactor.
2. Shielding consists of inner lining of 50 to 60 cm thick steel plate on the reactor core called thermal shield with a few meters of thick concrete wall surrounding the inner shield called biological shield.