The International Thermonuclear Experimental Reactor (Iter) is to be built in the European Union’s choice location, Cadarache in France. The rejected site, Rokkasho in Japan, wins the consolation prize of a materials testing facility and a large share of the research work as part of a ‘privileged partnership’.

The siting announcement came after 18 months of tedious negotiations during which both the EU and Japan were insisting that their candidate locations would be chosen. The project’s six member countries were evenly divided: China and Russia backed the EU, while South Korea and the USA backed Japan. The enduring deadlock was broken by a deal which will see France host the Iter fusion reactor itself and Japan host a vital materials testing facility.

Favourable terms for Japan include that the EU will pay half the construction cost of the materials facility, to be built at Rokkasho. Japan will also get about 20% of the project’s 200 research posts and the position of director general although it will pay only 10% of the overall project cost. The EU will pay 50% of the construction costs of Iter itself and 10% of that budget will be spent with Japanese firms. Other member countries will pay 10%.

The €10 billion scientific project, second only to the International Space Station in budget terms, has achieved mythic status. It has taken 19 years and 344 days to reach this point since the start of Iter discussions.

Iter will be a tokomak fusion reactor that should be capable of producing a sustained 500MW of thermal power. It’s plasma volume of 837m3 will be five times that of the UK’s Joint European Torus (JET) – currently the largest tokomak in the world – which can sustain plasmas of a few megawatts for a few seconds.

Construction should begin this year and be completed by 2015. After that the reactor should operate for another 20 years, during which fusion scientists hope to learn enough to design a plant which could produce several gigawatts. The EU has agreed to support any Japanese bid to host a demonstration plant.

Sir Christopher Llewellyn Smith, director of JET, said: “It’s great news because it will enable us to get on with fusion. Iter is the absolutely vital step on the way to building a real fusion power station.”