A nuclear chain reaction is a series of fission reactions wherein the products become the driving forces for further chain reactions. This type of reaction generates constructive forces in the form of usable energy and destructive forces in the form of an explosion.
The underlying principle of a nuclear chain reaction is fission. The fission process involves splitting the nucleus of an atom into smaller, generally more stable nuclei. Nuclear fission is an exothermic process, which releases a tremendous amount of energy that is harnessed for electrical power.
A nuclear chain reaction can either occur in a controlled environment, such as a nuclear power plant, or in an uncontrolled setting, such as the inside of an atomic bomb. The first sustained nuclear chain reaction was demonstrated by the Italian physicist Dr. Enrico Fermi on December 2, 1942 at the University of Chicago. This scientific achievement led to the development of the atomic bomb in 1945.
The most commonly occurring atom that undergoes a nuclear chain reaction is the uranium-235 isotope. When the atom absorbs a low-energy neutron, sometimes referred to as a "slow neutron" or "thermal neutron," the nucleus of uranium-235 splits into two fragments, emitting three neutrons in the process. The three neutrons are then captured by other uranium-235 atomic nuclei to produce a chain reaction. However, not all neutrons that are absorbed by an atom can trigger the fission process.