Harnessing nuclear fusion has been a dream of technologists almost from the moment that nuclear processes taking place within the sun were recognised early in the 20th century. Fusion is attractive because it promises almost limitless energy from a simple process that is largely free of atmospheric emissions or toxic by-products. The principle reactions that take place within the sun involve hydrogen atoms fusing to produce heavier atoms. There are two important fusion reactions in the sun and the stars. The first involves fusion of two hydrogen atoms to generate a deuterium or heavy-hydrogen atom. In the second, deuterium and hydrogen atoms fuse to create a helium atom. However it is a third reaction between deuterium and the even heavier hydrogen isotope tritium that interests fusion scientists because it proceeds more easily than the other two and under relatively more benign conditions. A fusion reaction between these two hydrogen isotopes produces one helium atom and one neutron and it is the latter that carries most of the energy released during the fusion process. That energy must then be captured and used to generate electricity. The potential is massive. The energy from one tonne of deuterium is equivalent to 3 x 1010 tonnes of coal. Unfortunately the prize is not easily won. The reaction will only take place in a plasma at massively high temperatures and in the case of inertial confinement, under conditions of enormous pressure. Reaching the conditions necessary for fusion to take place - and then controlling and maintaining them - have been the primary challenge of fusion research. The future So what does the future hold for fusion? Optimistically, a fusion plant based on inertial confinement might deliver a commercial plant by 2030, although based on experience with other complex projects, the timeline is likely to be a little longer than this. It is often said that a commercial fusion plant is always 30 years away. While there is clearly still a long way to go and nobody has yet demonstrated that fusion can produce electricity rather than simply consuming it, that threshold does seem palpably closer today than at any time in the past. Paul Breeze.
Posted on: Tue, 08 Oct 2013 14:06:25 +0000
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