Nuclear Fusion
The 2nd type of nuclear energy is fusion. Two light nuclei, usually hydrogen, deuterium (heavy hydrogen), or tritium (heavy, radioactive hydrogen), are forced to combine at very high temperature to form helium. A small amount of mass is lost in this process – becoming energy. This is the reaction fuelling the sun. The sun has the advantage of very high pressure as well as high temperature. This reaction is duplicated in the hydrogen bomb!
The theoretical energy from fusion is even greater than that from uranium fission. The fusion of one gram of hydrogen into helium yields 57 million kilocalories or nearly 240 million kilojoules – about 10 times the energy obtained by the fission of a gram of uranium! Since hydrogen is abundant, fusion sounds like a great idea.
Developing a practical energy-producing fusion reactor has proved very costly. The extreme temperature required cannot be contained by any known material. The extreme pressure found in the sun is well beyond our capability. So, the most practical fuel for a fusion reactor is deuterium, a rare and heavy isotope of hydrogen. Deuterium atoms fuse at a far lower temperature.
The ultra hot deuterium (100,000,000oC – 7 times hotter than the sun’s core!) must be kept well away from the reactor walls. To achieve this, ionised deuterium is held by a powerful magnetic field inside a toroidal (doughnut shaped) vessel. This is surrounded by electromagnets whose power depends on keeping them extremely cold (close to absolute zero), making their windings superconducting. To date, nuclear fusion has been achieved only briefly. A fusion reactor once produced more heat energy than was required to run it – for a few seconds. This is a very long way from commercial energy!