In basic terms, it is a method of memory enhancement which uses visualization to organize and recall information. A lot of memory contest champions claim to use this technique to recall faces, digits, and lists of words.
Nuclear energy is energy that is stored in the nucleus or center core of an atom. The nucleus of an atom is made of tiny particles of protons (+ positive charge) and neutrons (no charge). The electrons (- negative charge) move around the nucleus. Nuclear energy is the force that holds the nucleus together in an atom.
Nuclear energy is mostly used to power steam turbines. The heat  that generates from nuclear materials is used to boil water,  powering turbines that then power cities. Nuclear energy is simply electricity produced by a nuclear reactor, which is just a different way to heat steam to turn a turbine.