Question

The reaction that takes place in a nuclear reactor is:
(A) Nuclear fusion
(B) Nuclear fission
(C) Controlled nuclear fission
(D) Double decomposition

Answer 1

The process, in which the heavy nucleus of a radioactive atom breaks down into smaller nuclei when bombarded with low energy neutrons, is called nuclear fission.Nuclear power plants use the nuclear fission reaction to generate electricity but in a controlled way.

Complete step by step answer:
In nuclear power plants, a large amount of heat is required to make steam and turn the turbines. In Nuclear fission reaction when the parent nuclei such Uranium is bombarded with slow-moving neutrons, the heavy uranium breaks up to produce two medium weight atoms Barium and Krypton with emission of 3 neutrons. A tremendous amount of energy is produced during fission of Uranium. So in Nuclear fission neutrons are used up as well as produced.Since lots of neutrons are produced during fission, control rods are used inside the nuclear reactor to absorb excess of neutrons and prevent the fission reaction from going out of control.
Hence the correct option is $C.$ The reaction that takes place in a nuclear reactor is controlled nuclear fission.

Note: Nuclear fusion is a process where two nuclei of light elements combine to form a heavy nucleus. Energy produced by nuclear fusion is much more than that produced in nuclear fission. But the energy produced in nuclear fusion has not been controlled so far.
The highly destructive nuclear bomb is based on the nuclear fission reaction of Uranium-$235$ or plutonium$- 239.$