In 1991, in Culham, England, nuclear fusion was first harnessed to produce a significant amount of power. Though lasting for only two seconds, about 1.7 megawatts of electric power was produced. The experiment by an international team of scientists at JET, the Joint European Torus was the first to produce controlled fusion power. Fusion differs from the fission reactions used in current nuclear power plants for it occurs when light nuclei travelling at high speed combine, without radioactive waste as a byproduct. The JET programme was set up to make it possible to carry out fusion tests under conditions that closely resemble those of a commercial fusion power plant. Construction of JET began in 1978 and the device has been in operation since 1983.[Image: Inside JET's toroidal vacuum vessel. The height of the inside of the vessel is 4.2 metres]