What is a chain reaction?

Chain reactions are modifications in the composition of the atomic nucleus. The nucleus of a uranium atom, for instance, can be split by bombarding with neutrons. A lot of energy is released in the process. The fragments that arise as a result of the initial reaction fly off at a high speed and collide with the neighboring nuclei, which get split in turn. The whole process takes place as long as the present mass of uranium is split. An enormous amount of heat is released when several nuclei are split at once. This can lead to explosions. For this reason, this chain reaction is initiated in a controlled way in nuclear power plants.

How do atomic power plants works?

In atomic power plants - APP in short the chain reaction of the uranium decay is allowed to run in a controlled way. The uranium rods in the reactor, which are bombarded with neutrons, are dipped in water, which slows down the neutrons and helps achieve a controlled nuclear fission.  In addition, the fuel rods heat up the water to about 330 dC. This heat is transferred in a heat ex-changer to a second, non-radioactive water circulation, where the hot water evaporates and drives stream turbines. the energy is converted into electricity by means of the connected generators similar to other power plants.

Why are atomic power plants considered dangerous?

Nuclear energy is a clean energy source as it does not produce any waste gases that pollute the environment. It is available in abundance on the Earth, but is still considered dangerous. People are afraid of an MCA ('maximum credible accident' or worst-case scenario), something like Fukushima nuclear accident in Japan in March 2011 and Chernobyl in Ukraine in 1986. In both cases, the chain reaction went out of control and resulted in explosion. As a result, hazardous fission products were released in the air exposing people to harmful radiations. Problems are also faced in the normal operation, but precautions are taken to avoid any mishap. the used up fuel rods must be treated or stored at a secure place.

(All image in my blogs taken from google image so credit goes go google)