The promise of clean (no fossil fuels used) and virtually unlimited electrical power may be realized someday if the fusion reactor is perfected. Presently the only nuclear reactors that are available are fission nuclear reactors. This type of nuclear reactor produces energy by splitting atoms and are dangerous because they create radioactive waste products during their use that have to be safely stored for thousands of years until their radioactive levels decay to the point where they are harmless.
Fusion reactors produce energy by combining (fusing) the nuclei of two light atoms into one large nucleus. The fuel required for fusion reactors are two isotopes of hydrogen, deuterium and tritium. Deuterium (heavy hydrogen) occurs naturally in water while tritium (heavy-heavy hydrogen) can be made from lithium. Isotopes are different forms of the same element that have a different atomic mass. The nucleus of an atom is made up of protons (positive charge) and neutrons (no charge) with electrons (negative charge) orbiting around it. You calculate the atomic mass (weight) by adding the total number of protons and neutrons. The nucleus of a hydrogen atom has one proton but doesn't have a neutron. The nucleus of a deuterium atom has one proton and one neutron. The nucleus of a tritium atom has one proton and two neutrons. The joining together (fusion) of deuterium's nucleus and tritium's nucleus can only be achieved when the temperature is very hot. When fusion occurs a larger nucleus is formed and becomes helium, a free neutron is released and a large amount of energy is produced. This released energy produces heat which is used to generate electricity. Fusion reactors still produce radioactive materials but these materials become harmless after a small number of years. The fusion reactor has not yet been perfected. Presently many different nations (Including the United States) are working on the Iter project. Iter stands for "International Thermonuclear Experimental Reactor". The people working on this project hope to test this experimental fusion reactor by 2016. For more information on Iter and fusion reactors click on the links below.
Princeton Plasma Physics Laboratory - Here you will find a very good explanation about how fusion reactors will work.
Iter - This web site has information about the Iter fusion reactor which is an international project being worked on by the United States and other countries.
Department Of Energy - Clicking on this link will open a documennt that is found on the United States Department of Energy's web site. This document is a PDF file which means you must have the Adobe Reader installed on your computer before you can read it. You can download it here.