Our best hope for an abundant energy source here on earth is nuclear fusion . Fission starts with a heavy element that has large atoms, such as uranium. Uranium nuclei, orbited by clouds of electrons, are so large that they are unable to remain in one piece and tend to lose fragments. These emitted fragments dissipate their energy as heat, but they are still radioactive and continue to break down into smaller atoms in time. This is the fission process, and these radioactive fragments create a serious waste disposal problem.
Nuclear fusion begins instead with atoms of the lightest element, hydrogen, abundant in water.
Fuel cost is negligible. Fusion is not easy to achieve, though it happens naturally in stars because gravity causes large amounts of gaseous matter in space to collapse in upon itself. The hydrogen bomb works on fusion, but the energy release is uncontrolled. The central problem for physicists and engineers working on controlled nuclear fusion is due to the electrical nature of matter. Nuclei consist of positively charged protons and neutral neutrons, and are surrounded by negatively charged electrons.