IS THIS THE SAFE WAY TO GO?

Nuclear fusion reactor.

A decision has finally been made to site the 10bn-euro (£6.6bn) Iter nuclear fusion reactor at Cadarache in France. The announcement brings to an end months of argument between the project partners - the EU, the US, Japan, Russia, China and South Korea.

Iter will produce relatively clean energyWhat is Iter (International Thermonuclear Experimental Reactor)? Iter is an experimental reactor that will attempt to reproduce on Earth the nuclear reactions that power the Sun and other stars. It will consolidate all that has been learnt over many decades of study. If it works, and the technologies are proven to be practical, the international community will then build a prototype commercial reactor, dubbed Demo. The final step would be to roll out fusion technology across the globe.

What exactly is fusion?

Fusion works on the principle that energy can be released by forcing together atomic nuclei rather than by splitting them, as in the case of the fission reactions that drive existing nuclear power stations. In the core of the Sun, huge gravitational pressure allows this to happen at temperatures of around 10 million degrees Celsius. At the much lower pressure that is possible on Earth, temperatures to produce fusion need to be much higher - above 100 million degrees Celsius. No materials on Earth could withstand direct contact with such heat. To achieve fusion, therefore, scientists have devised a solution in which a super-heated gas, or plasma, is held and squeezed inside an intense doughnut-shaped magnetic field.

What are the advantages of fusion?

The best fuel for fusion comprises two types, or isotopes, of hydrogen: deuterium and tritium. The former can be derived from water which is abundant and available everywhere. The latter can be produced from lithium, which is plentiful in the Earth's crust. Unlike the burning of fossil fuels, fusion reactions produce no carbon dioxide, the greenhouse gas blamed by scientists for warming the planet. Fusion scientists also say the system would be inherently safe because any malfunction would result in a rapid shutdown.