Principle : A nuclear reator works on the principle of achieving controlled chain reaction in natural Uranium `.^(238)U` enriched with `.^(235)U`, consequently generating large amounts of heat. A nuclear reactor consits of (1) Fuel (2) Moderator (3) Control rods (4) Radiation shielding (5) Coolant.
1. Fuel and clad : In reactor the nuclear fuel is fabricated in the form of thin and long cylibndrical rods. These group of rod treated as a fuel assembly. These rods are surrounded by coolant, which is used to transfer of heat produced in them. A part of the nuclear reactor which is used store the nuclear fuel is called the core of the reactor. Natural uranium, enriched uranium, plutonium and uranium - 233 are used as nuclear fuels.
2. Moderator : The average energy of neutrons released in fission process is 2 MeV. They are used to slow down the velocity of neutrons. Heavy water or graphite are used as moderating materials in reactor.
3. Control Rods : These are used to control the fission rate in teactor by absorbing the neutrons. Cadmium and boron are used as controlling the neutrons, in the form of rods.
4. Shielding : During fission reaction beta and gamms rays are emitted in addition to neutrons. Suitable shielding such as steel, lead, concrete etc., are provided around the reactor to absorb and reduce the intensity of radiations to such low levels that do not harm the operating personnel.
5. Coolant : The heat generated in fuel elements is removed by using a suitable coolant to flow around them. The coolants used are water at high pressures, molten sodium etc.
Working : Uranium fuel rods are placed in the aluminium cylinders. The graphite moderator is placed in between the fuel cylinders. To control the number of neutrons, a number of control rods of cadmium or beryllium or boron are placed in the holes og graphite block. When a few `.^(235)U` nuclei undergo fission fast neutrons are liberated. These neutrons pass through the surrounding graphite moderator and loose their energy to become thermal neutrons. These thermal neutrons are captured by `.^(235)U` . The heat generated here is used for heating suitable coolants which in turn heat water and produce steam. This steam is made to rotate steam turbine and there by drive a generator of production for electric power.
