What is the science behind nuclear energy?

The science behind nuclear energy involves getting the atomic nuclei of atoms to undergo changes and release energy. We know that setting conditions involves finding materials that will, under the right circumstances, undergo fission or fusion and "rearrange" their atomic nuclei. The fission or fusion reactions release energy that we can use. Currently we can only use fission effectively to generate energy. (We left out thermonuclear fusion weapons.) Let's look a bit further.

If we gather some fissionable material like uranium, we can set up a machine in which we can cause it to undergo fission. A nuclear reactor is that machine. If we permit a critical mass to be achieved, a fission reaction will begin, and we can sustain this reaction to continuously release nuclear energy. Most of the useful energy released in the nuclear reactions appears in the form of heat, and we can pump coolant around inside the reactor, we can collect that heat. The thermal energy can be used to boil water to make steam, and the steam can be used to spin conventional steam turbines.

Nuclear energy is converted into both thermal and mechanical energy as atoms "break up" in the fission reactions. The mechanical energy is converted into thermal energy in the fuel elements, and that heat is carried off via the coolant to steam generators. The thermal energy is converted into mechanical energy in the turbines, and the turbines spin generators. The mechanical energy of the spinning generator is converted into electromagnetic energy, and we see that as electricity that we can distribute to points of use.