Sunday, September 17, 2006

When can we expect nuclear fusion?

By Joachim Grawe 

In partnership with Energie-Fakten

Nuclear fusion offers a great hope for mankind's future energy supply. It imitates in a technical process the physical phenomena occurring in the sun and all other stars, where hydrogen nuclei are combined ('fused') into helium nuclei, releasing giant quantities of energy according to Einstein's formula E=mc2.

On earth, it is impossible to achieve the enormous pressure of 100 billion bar inside the sun. Therefore, fusion of the lighter nuclei of 2 isotopes (i.e. atoms with a different number of neutrons in the nucleus) of hydrogen is being pursued: i.e. deuterium (with a nucleus of 1 proton, as in 'normal' hydrogen and 1 neutron) and tritium (1 proton + 2 neutrons). Deuterium is abundantly available in oceans at a concentration of 140 g/tonne. Tritium can be produced from the common metal lithium.

To initiate ('ignite') the fusion process, the D-T mixture needs to be converted into a plasma - i.e. a state whereby nuclei are separated from the electrons that normally surround them. The plasma needs to be heated to at least 100 million degrees, under extreme compression, and kept for a prolonged period while containing its heat inside. At all times, contact of the plasma with its container - a round tube called 'torus' - needs to be avoided. This is achieved through very strong magnets.

Containment of the plasma has been achieved already in 1951. The European test facility JET in Culham (UK) could achieve in 1997 to generate 16 MW of heat for a short while, consuming twice as much power to conduct the experiment. A larger reactor will be constructed from 2007 in Cadarache (France), through world-wide cooperation. This reactor will for the first time produce an energy surplus. It will be used for 10 years to build experience. If the results are positive, construction of the first demonstration reactor 'DEMO' will start. The energy return of this reactor should be a factor 4.

From 2060, nuclear fusion could provide a sizeable contribution to energy supply. It represents the next stage of development for nuclear technology, after the 'backup solution' nuclear fission. Fission is expected to contribute from 2020 with so-called Generation-IV reactors, which offer better reactor safety.

This contribution was originally published in the German languageon september 7, 2006 by Energie-Fakten.

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