ITER - NUCLEAR FUSION PROJECT Project estimated to cost 10bn euros and will run for 35 years It will produce the first sustained fusion reactions Final stage before full prototype of commercial reactor is built

The project is the latest stage in the quest to develop fusion power - the energy source of the Sun and other stars.

Advocates say it could be cheap and environmentally friendly, though very expensive and time-consuming to develop.

Iter, the International Thermonuclear Energy Reactor, will run for 20 years and cost about $10bn.

It will bridge the gap between current fusion reactors and the first ever prototype commercial plant that could follow.

Delegations from China and the US joined those from Canada, the European Union, Japan and the Russian Federation at the Eighth Iter Negotiations Meeting held in Russia a few days ago.

The US had previously withdrawn from Iter negotiations undertaking a review of its fusion policy. Now, however, the US and China have declared their commitment to develop fusion energy as a potential source of energy.

Alternate energy sources

At the meeting, the Chinese delegation said that, as the largest developing country in the world, it had a great need to pursue alternative energy sources.

Dr Jerome Pamela, of Jet (Joint European Torus, a European flagship fusion project based at Culham in Oxfordshire, UK), said: "China is probably the country in the world that has the largest needs for development of electrical power production."

POSSIBLE ITER SITES Clarington, Canada Cadarache, France Vandellos, Spain Rokkasho-mura, Japan

The US delegation reiterated President Bush's recent announcement that "the results of Iter will advance the effort to produce clean, safe, renewable, and commercially available fusion energy by the middle of this century."

US Secretary of Energy Spencer Abraham said: "This international fusion project is a major step towards a fusion demonstration power plant that could usher in commercial fusion energy."

He added: "Iter also provides a cost-effective way to proceed with fusion research worldwide with the collaborating parties sharing in the project's cost of construction and operation."

Virtually inexhaustible

In a fusion reaction, energy is produced when light atoms are fused together to form heavier atoms.

To use fusion reactions 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. At these temperatures, the gas becomes a plasma.

Under these conditions, the plasma particles, from deuterium and tritium, fuse to form helium and high speed neutrons, releasing significant amounts of energy.

A commercial power station will use the heat generated by the neutrons, slowed down by a blanket of denser material (lithium), to generate electricity.

The fuels used are virtually inexhaustible. Deuterium and tritium are both isotopes of hydrogen. Deuterium is extracted from water and tritium is manufactured from a light metal, lithium, which is found all over the world.

One kilogram would produce the same amount of energy as 10,000,000 kg of fossil fuel.

Essential technologies

Iter would be the world's largest international cooperative research and development project next to the International Space Station.

The goal of Iter is to produce 500 megawatts of fusion power for 500 seconds or longer during each individual fusion experiment and in doing so demonstrate essential technologies for a commercial reactor.

Iter could begin construction in 2006 and be operational in 2014. Fusion research would last for up to 20 years.

Iter officials are hoping to decide where the fusion reactor will be based within the next few years or so and have agreed to meet in Vienna in May.