Like fossil fuels, nuclear energy is produced by performing some reaction, which heats up water, spinning the turbines and generating electricity. In the case of oil, the reaction is combustion; a chemical reaction where the re-arrangement of bonds releases energy. Nuclear energy, like the name suggests, is generated when we alter the nucleus in nuclear reactions.
The nucleus is made up of protons and neutrons held together, against the electromagnetic repulsion of protons, by the strong nuclear force. The strong force acts as a sort of rubber band, storing the potential energy of the EM force. Cutting this rubber band would rip the nucleus apart and release the energy.
A neutron is a convenient way to deliver a punch to the nucleus and disturb it from it’s spherical shape. The nucleus can hold itself together only if it remains spherical. If it begins to wobble into an elliptical shape, then the minor axis tends to neck down and pinch off into two nuclei plus a few loose neutrons. Those two daughter nuclei then repel each other electrostatically and fly off with great speed.
Fusion energy is released when two small nuclei fuse together forming a larger nucleus and a lot of energy.
But where did that energy come from? Where was it before the fusion?
Since nucleus is essentially a bunch of protons and neutrons, the mass of a nucleus should be equal to the sum of the masses of the neutrons and protons. But the mass of a nucleus is lower than the sum of the masses of its protons and neutrons. What happened to that mass?
So there’s missing mass, and unexplained energy.
E = mc^2 explains that mass and energy are just different manifestations of each other. The difference in mass is released as energy, when the nucleus is formed.
- The energy released during fission was present as potential energy, due to the suppression of electromagnetic force.
- The energy released during fusion was present as mass of protons and neutrons.