Nuclear Reactor:
With the help of nuclear reactors, power is generated by changing the energy obtained from nuclear fission into electric energy. As we have already mentioned the controlled chain reactions are used in nuclear reactors. Here we will discuss nuclear reactor based on fission of 235U by thermal neutrons. Such type of reactor and equipments related to it are shown by a simple diagram in fig. The core of the reactor contains Uranium as the nuclear fuel in suitably fabricated form. The core contains a moderator (water, heavy water (D20) or graphite) to slow down the moderator.
When fission takes place in a Uranium rod, then the fast neutrons produced enter the moderator from the rods where they are collided with the atoms of moderator. After few collisions, the energy of the neutrons decreases from 2 MeV to that of the range of thermal energy. The distance between the rods are so arranged that the neutrons come into the range of thermal energy before entering into a rod after emerging from rod. This way, the neutrons in the range of 1-100 eV have lesser possibility to absorb the 238U nuclei present in a rod. The geometry of core is such that the loss of neutrons is limited so that on an average, 1 out of 2.5 neutrons per fission is available in the next fission. In this case, multiplication factor, K – 1 and the chain reaction continues at a stable rate. If the rate of loss of neutrons decreases, then K > 1, and there is a possibility of explosion in the reactor and to solve this problem, control rods which are of Cadmium are used. Cadmium are good absorbers of neutrons. Initially, it is kept at K > 1. We can get the state of K = 1 when required, Cadmium rods are inserted completely to get the state’of K < 1 and the nuclear reactor can be shut down. This is done for the safety reasons and proper treatment of reactors.
Due to the energy obtained from the nuclear high pressure fission in reactor, water or molten Sodium at high pressure is passed in the region of core to remove heat, which acts as a coolant. The heat taken from reactor by the coolant is used to convert water into steam. This steam is used to drive the turbine and to produce electricity.
Thick concrete walls are made around reactor so that the radioactive radiations from the fission products do not enter the atmosphere. This is for the safety of people working in and near the nuclear power production centres.
The other uses than the power production of nuclear reactors is to produce radioactive isotopes, research for neutrons, etc. Although nuclear reactors contribute towards electric energy production, but the disposal of its toxic radioactive wastes is a big problem for which it is very important to follow .the international rules. Also, its operation in done with strict management. Carelessness in safety management can be lethal for years. In 1986 in Russia (Ukraine in present), such incident happened in Chernobyl nuclear plant, whose result can till be seen in the local people. Indian Atomic Energy Programme is in accordance with the international systems in view of safety.
