Fusion reactor work gets go-ahead

Seven international parties involved in an experimental nuclear fusion reactor project have initialled a 10bn-euro (£6.8bn) agreement. The International Thermonuclear Experimental Reactor (ITER) will be the most expensive joint scientific project after the International Space Station. Wednesday's agreement in Brussels gives the go-ahead for practical work on the project to start.

Generatingnonap energy from reactions like those that power the Sun, fusion will lead to a cheaper, safer, cleaner and endless energy resource in the years ahead, says the the seven-party consortium, including the European Union, the US, Japan, China, Russia and others. They agreed last year to build ITER in Cadarache, in the southern French region of Provence.

The experimental reactor will produce the first sustained fusion reactions, the last stage to be proved before a full prototype commercial reactor is built. Construction will start in 2007 and building will take about eight years to build. If all goes well, officials hope to set up a demonstration power plant at Cadarache by 2040.

In a fusion reaction, energy is produced when light atoms - the hydrogen isotopes deuterium and tritium - are fused together to form heavier atoms. To use controlled fusion reactions on Earth as an energy source, it is necessary to heat a gas to temperatures exceeding 100 million Celsius - many times hotter than the centre of the Sun. The technical obstacles to this, which scientists have spent decades overcoming, are immense; but the rewards, if ITER can be made to work successfully, are extremely attractive. One kilogram of fusion fuel would produce the same amount of energy as 10,000,000kg of fossil fuel.

Fusion does produce radioactive waste but not the volumes of long-term high-level radiotoxic materials that have so burdened nuclear fission. Officials project that 10-20% of the world's energy could come from fusion by the end of the century, but environmental groups have criticised the project, saying there was no guarantee that the billions of euros would result in a commercially viable energy source.

The Cadarache site lies about 60km (37 miles) inland from Marseille, and has been a nuclear research centre ever since President Charles de Gaulle launched France's atomic energy programme in 1959.

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