A ceremony in Brussels has signalled the go-ahead for ITER, the experimental nuclear fusion reactor. The agreement means work will start on the €10bn project at Cadarache in France next year.

ITER will become the world's most expensive science experiment on Earth. Only the International Space Station has swallowed more cash. The EU will fund around half the cost of ITER, with contributions from the US, Japan, Russia, Korea, China and India.

Its backers hope ITER will bring the first sustained fusion reactions to produce electricity.

EU science and research commissioner Janez Potocnik said: "We represent more than half of the world's population, and recognise that by working together today we stand a much better chance of tackling the challenges of tomorrow, so energy is an issue of concern for all of us."

Critics have questioned whether the work done over ITER's mooted 35 year operation will ever lead to a commercially viable energy source. Proponents counter that the prospect of limitless clean energy outweighs the risks.

Fusion depends on heating hydrgen isotopes to several times hotter than the Sun. The EU called the technology "inherently safe, with no possibility of meltdown, or runaway reactions". ®

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