The Big Boy Fusion Reactor Takes a Big Boy Step

Caroline Delbert
Photo credit: ITER

From Popular Mechanics

  • Construction has finally begun on site at the International Thermonuclear Experimental Reactor (ITER) facility, beginning with a 1,250-ton base.
  • The planning and assembly of ITER parts has lasted 30 years, with plans to "fuse" by 2025.
  • The cryostat parts alone have taken 10 years to build, first in ITER partner India and then on site.

Engineers have installed the first and largest piece of the International Thermonuclear Experimental Reactor (ITER) fusion project in France. The gigantic assembly begins with this piece, the steel base, which weighs more than 1,200 tons.

ITER has been in the works for 30 years. The experimental tokamak fusion reactor—a nuclear fusion plasma reactor where extremely hot, charged plasma spins and generates virtually limitless energy—is one of a handful of extremely costly “miniature suns” around the world. The tokamak is on track to switch on in 2025, and then the reactor will begin to heat up to temperatures hot enough to induce nuclear fusion. That will take years.

So ... baby steps. Making this single part, which is 30 meters high and 30 meters wide, has taken 10 full years by itself. It’s the base of the cryostat, which is the supercooling chamber that enables the rest of the reactor to function. The life of the cryostat began in India, where massive tech conglomerate Larsen & Toubro Ltd began fabricating and welding portions of it under ITER’s Indian Domestic Agency’s supervision.

In 2015, the partial assemblage was brought to France, where more assembly and work began in 2016 and lasted until late 2019. At that point, the ITER home team took over. Now, the chamber is ready to begin assembly, starting with the base. The whole thing will be 3,850 tons, with mostly hollow—but absolutely gigantic—steel cylinder sections that form the outside of the cryostat.

Photo credit: ITER

It’s all put together and sealed with welds. From ITER's website:

“In total, the Indian Domestic Agency estimates that one kilometre of full penetration weld joints will have to be carried out to exacting standards for the sub-assemblies in the site workshop, followed by several hundred metres of weld joints to assemble the cryostat sections in the Tokamak Pit.”

On May 26, a crane slowly lifted the base of the cryostat from its support frame to a height of 24 meters, according to World Nuclear News. “It was then transported 110 [meters] from the entrance of the Assembly Hall, passing above and over the two 20-[meter]-high sector sub-assembly tools, eventually reaching the circular opening of the machine assembly pit,” per the report.

Putting the base in place is a landmark for ITER, but it’s also a huge engineering feat unto itself.

“We trust the materials science,” ITER’s director general Bernard Bigot said on site. “We trust the metrology. But my confidence today is because I trust you to work as one committed and highly professional team, convinced as we all are that failure is not an option.”

The remaining pieces are already assembled and elsewhere on site, and they will be installed later. They’re stored outside under several layers of plastic to help insulate the pieces further and keep dust and detritus out.

One reason the ITER team chose its location in southern France is the short trip to the nearest shipping waterway. Even so, ITER had to build a custom heavy-duty road to carry parts over the roughly 40-mile distance. If the steel base were traveling on a U.S. interstate highway, the truck carrying it would need 120 axles. (Just to be clear, that’s not physically possible, plus the federal limit is “just” 40 tons.)

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