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How to build a star

23rd of February 2015

Deep in the French countryside, some of the world’s cleverest scientists are building a vast thermonuclear reactor. If all goes well, says Alok Jha, this “star in a box” could be the key to providing clean, safe energy for the next centuryThe countryside of Saint-Paul-lez-Durance in Provence is a picture-perfect terrain of wooded hills and vineyards, beneath a bright blue winter sky. It seems incongruous that this is where the most sophisticated, expensive machine ever built is slowly taking shape, at the local Cadarache nuclear facility. It is a scientific collaboration on a worldwide scale, meant to tackle one of the biggest challenges of the 21st century – how do we continue to make ever more electricity past 2050 (the date that the EU has set for full decarbonisation of power generation) without destroying the environment? The scientists and engineers in Saint-Paul-lez-Durance think the solution is nuclear fusion: they want to recreate a star in a box on Earth.Everything about the project, known as Iter (formerly the International Thermonuclear Experimental Reactor), is huge. The main fusion reactor will be built on a flattened area of concrete that has been blasted into the hills at Cadarache and stretches to 60 football pitches. That concrete baseplate sits on dozens of pillars containing layers of rubber sandwiched between the mortar and cement – not only do these pillars raise the building above the height of the surrounding countryside (the height was calculated to be above the maximum height that water would flow past if the nearby dam broke), they also create a “seismic isolation pit” that will protect the building from earthquakes.At the centre of the concrete box where the main building will go, you can already see a circle of steel bars that trace the shape of what will become the ring-shaped vacuum vessel, where the fusion reactions will take place. Ready to haul in the huge components over the coming years, four giant cranes are rooted into the site. When the main building containing the reactor is complete, it will rise 60 metres into the air and reach ten metres below the ground. When the million or so pieces that make up the Iter machine have been delivered to site and are finally bolted and welded together, the whole thing will weigh around 23,000 tonnes, three times the weight of the Eiffel Tower. The entire reactor complex – including the foundations and buildings that will sit in the seismic isolation pit – will weigh 400,000 tonnes, more than the weight of the Empire State Building.

The Week