Energy evolved during nuclear fission can be used for the welfare of mankind' - discuss briefly .

Explanation

A thermal neutron is used to disintegrate U-235 resulting in the emission of either 2 or 3 neutrons which in turn disintegrate U-235 again in the next step . So, in a very small time the number of disintegrated nuclei increases in multiples and the reaction becomes uncontrolled . The energy evolved due to this uncontrolled chain reaction leads to explosion.
However, if the chain reaction is maintained in a controlled manner by using only one neutron to bombard the U-235 in each step , the energy produced can be utilised for the welfare of mankind. The reaction will be under control. This will help of evolve energy at the same rate as the rate of the reaction. Usually nuclear reactors are used for this purpose. Boron is used in these reactions to absorb the excess neutrons.