[Note that this article is a transcript of the video embedded above.]

This is my friend Jade, creator of the Up and Atom channel. She makes these incredible math and physics explainers that I absolutely love, and she recently got the opportunity to visit ITER (eater) in France. You may have seen this place in the news: 35 nations working together to build an enormous, industrial-scale nuclear fusion reactor. The size of the project is mind-boggling. It’s been under construction since 2013, and… I like construction. So, when Jade and I were chatting about her tour, she said, “Why don’t you just make a video about it too?!”

If everything goes to plan, ITER’s tokamak reactor will house plasma at temperatures in the hundreds of millions of degrees, ten to twenty times hotter than the center of the sun, hopefully paving the way for an entirely new form of electricity generation. I don’t know much about superconducting coils or cyclotron resonance heating or breeder blankets, but I do know it takes a lot of earthwork and steel and concrete to build the biggest nuclear fusion reactor on earth. So let me give you the civil engineer’s tour of what might be the most complicated science experiment in human history. I’m Grady,

Jade: And I’m Jade, and this is Practical Engineering. Today we’re exploring the ITER megaproject.

Jade: I was fairly new to fusion when I went to visit, and although I'm still no expert, I still felt I should explain it rather than let a civil engineer. Before we dive into the mechanics. Here's a question. Why is the world so interested in nuclear fusion? Basically, it comes down to the huge potential payoff. If we could harness the power of nuclear fusion here on Earth.

It would be a way more powerful energy source than fossil fuels, without the environmental baggage. This water bottle full of seawater plus one gram of lithium could provide electricity to a family of four for a whole year. Unlike nuclear fission, there's no long lived waste and no chance of nuclear meltdowns. It's a clean, sustainable and powerful energy source.

Some scientists go so far as to say that commercial nuclear fusion is the next step for humanity. That's exactly what ITER, which translates to the way in Latin aims to do. To nail down the technologies needed for a fully functioning commercial fusion reactor. For you to get an idea of how ambitious their goal is, they plan to import 50 megawatts of thermal power and get out 500 megawatts of fusion power, a gain of ten in fusion talk.

Nothing close to this has ever been achieved or even attempted in fusion history. So how are they going to do it? Right in here. "So this is where the Tokamak is going to be built?" This is the Tokamak pit where ITER is assembling the largest nuclear fusion device in the world, a giant tokamak. Here's a man for comparison. It's going to be huge.

A tokamak is a nuclear fusion machine that works by magnetic confinement. It will hold about 840 cubic meters of piping hot plasma. Why plasma? Plasma is what the sun is primarily made of. And it has the perfect conditions for fusion. To get fusion started in the ITER tokamak, two isotopes of hydrogen, deuterium and tritium are pumped into a large donut shaped chamber.

This is just one of the six vessels that will make up the chamber. The fuel is heated to temperatures of up to 150 million degrees celsius. When they fuse, the energy they unleash is of epic proportions. But here's a question for you engineers. How is it possible to contain so much plasma? No regular material can withstand those kinds of insane temperatures.

Imagine trying to hold onto a piece of the sun. These giant magnets produce magnetic fields of almost 12 tesla, over 200,000 times stronger than Earth's magnetic fields. Plasma is electrically charged. And just like iron filings align with magnetic fields, so does plasma. How cool is that? But how does this fusion stuff actually lead to electricity? ITER itself will not actually produce any electricity.

It's our learning ground, an experimental arena to fine tune how a real reactor might operate. But in a real reactor, the walls of the tokamak will be filled with cooling fluid. When the deuterium and tritium atoms fuse, they release a neutron and a helium atom. About 80% of the energy released is carried by the neutrons and being electrically neutral, they pass straight through the magnetic field.

When these high energy neutrons strike the tokamak walls, they heat up the fluid, turning it into steam. Then, just like a regular power plant, the steam will spin turbines, which will generate electricity. But how will ITER heat the plasma to such insane temperatures? And when can we expect commercial nuclear fusion to get off the ground? Check out my video after you've finished watching Grady's and find out.

Grady: Jade’s video goes into a lot more of the groundbreaking science at ITER, but all that science requires a lot of actual breaking ground. This is a bird’s eye view of the whole facility, and this is where the Tokamak lives. So if all the nuclear fusion is going to happen in there, what are all these other buildings and structures for? Fortunately, there’s a civil engineer there in France amongst all the technicians and scientists who knows the answer, and I was lucky enough to chat with him. This is Laurent Patisson, the civil engineering and interface section leader at ITER, and he’s been there almost since the very beginning, including taking delivery of some truly massive pieces of equipment.

Laurent: “So the largest one is the vacuum vessel sector which is more or less 600 tons. And which is 600 tons, okay, 600-tons yes, on a multi-wheel truck. Very impressive. And with the protection around, it's like transporting an house, two-story house. It's very large. So all the roads are closed. They are dismantling some traffic light just for the passage, some specific display, you know...”

Laurent walked me through the whole campus, and gave me an overview of how construction is progressing across the facility. Many of those big deliveries get stored in one of the many tents scattered around the site until they’re ready to be installed, and then onto one of the various buildings. For example, the poloidal field coils that form superconducting magnets to help shape and contain the plasma in the reactor are just too big to be completed offsite and shipped to ITER, so instead, they built a manufacturing facility right on campus in this long building on the south side. Similarly, the cryostat workshop was built to assemble the massive, vacuum-tight structure that will surround the reactor and magnets. The cryostat parts, the poloidal field coils, and lots of other truly large pieces of equipment destined for the Tokamak itself are then moved to the adjacent assembly hall as needed. Pretty much every part of the Tokamak reactor is not only huge but sensitive to environmental conditions too, so this building makes it possible to protect, stage, assemble and install each one without having to worry about temperature or weather.

Laurent: “It’s one of the highest building and longest buildings, 120 meter long, 70 meter high, very large, 80 meter wide, and actually very large place dedicated really for assembly purpose.”

That’s about 21 stories tall and longer (and wider) than an American football field, end zones included! And maybe the most critical part of the whole building is what runs along the top of it.

Laurent: “We have two 700-tonne overhead cranes. I didn’t mention that. But those are coupled to transfer the modules, the central solenoid. So those are very impressive cranes.”

These two bridge cranes combine to become one of the largest cranes in the world with a combined capacity of 1500 tonnes needed to assemble all the parts of the tokamak. And everything has been tested and tested before each critical lift operation happens with dummy loads before they do the real thing. But material and equipment aren’t the only things flowing through this project site. There’s also a lot of electricity. Imagine what your utility bill would be if your toaster got as hot as the sun!

ITER connects to the European power grid from a 400 kilovolt transmission line. During peak periods of plasma production, the facility may need upwards of 600 megawatts! That’s the capacity of a small nuclear power plant. Obviously you can’t just turn the reactor on with a flip of a switch. ITER has to coordinate with the power grid manager to carefully time the huge power draws with surrounding power plants to make sure it doesn’t cause brownouts or surges on the grid. The 400 kV line feeds a large switchyard and substation on the ITER campus. Electricity is stepped down to a lower voltage using transformers. Then it flows through busbars, cables, and breakers to feed all the various buildings and equipment.

Like many electronic devices, the superconducting magnets that surround the tokamak run on direct current, DC. So the AC power from the grid has to be rectified. For a phone or a flashlight, an AC to DC converter looks like this. But at ITER, it takes up two full buildings. The magnet power converter buildings have enormous rectifiers dedicated to each one of the magnet systems. Once energized, those magnets can collectively store upwards of 50 gigajoues of energy in their fields, though, so you also need a way to quickly get rid of that energy if the magnets lose superconductivity (called a quench). Fast discharge units, located in this building, allow ITER to dissipate that stored energy as heat in a matter of seconds. There are also a lot of critical safety systems and parts to maintaining the expensive and delicate equipment at ITER that require power 24/7/365. So, there are two huge diesel generators that can provide backup power in case the grid goes down.

The flow of electricity is closely tied to the flow of heat through all the parts of ITER. Really the whole thing is an experiment in heat, and there are so many ways things are being warmed or cooled throughout the campus. Of course, you have heating, ventilation, and air conditioning in all the buildings, and it’s not just for the comfort of the people working in them. Even tiny temperature swings can affect the size of these huge components, complicating the assembly.

Laurent: “What we are facing for civil is to merge, at the end, tolerances of equipment which are at the level of millimeter with tolerance of construction building which is at centimeter. And the main challenge that we face in the past and we are continuing to face is that, not to merge but to make compliant, to make compliant the tolerance scales.”

And it’s not just temperature, but humidity and cleanliness as well. So, ITER has a robust ventilation and chilling system located in the site services building along with a lot of the other industrial support systems like air compressors, water treatment, pipes, pumps, and more.

Heat is also important for the electromagnets, which have to be cooled to cryogenic temperatures so they act as superconductors. That’s made possible by the Cryoplant, a soccer-field-sized installation of helium refrigerators, liquid nitrogen compressors, cold boxes, and tanks that keep the various parts of the tokomak supercool during operation. But, although some parts of the machine have to be cryogenically cooled, to create nuclear fusion, you need to heat the plasma to incredible temperatures, and there’s three external heating systems at ITER. One, called neutral beam injection, fires particles into the plasma where they collide and transfer energy. The other two, ion and electron cyclotron heating (say that three times fast), use radio waves, like huge microwave ovens. Those systems are located in the RF Heating building near the Tokamak complex.

And then there’s the matter of the heat output. The whole point of exploring nuclear fusion is to use it as an energy source, to convert tiny amounts of tritium and deuterim into copious amounts of heat. ITER’s goal is to produce a Q of ten, to get ten times as much thermal energy out as it puts into the reactor. But there’s no electrical generator on site. In a commercial fusion facility, you would need to convert that output heat to electricity, probably using steam generators like typical nuclear fission plants. That part of the process is pretty well understood, so it’s not part of this research facility. Instead, ITER needs a way to dissipate all that heat energy they hope the fusion will create. That’s the job of the water cooling system and the enormous cooling tower nearby. Water is circulated around the tokomak and then to the tower where it can reject all that heat into the atmosphere.

That brings us back to where we started, the Tokamak complex itself. That machine, once its finished, will weigh an astounding 23,000 tonnes, more than most freight trains. And with all the heating and cooling going on, there are some serious challenges in just holding the thing up. As the tokomak is cooled cryogenically, it shrinks, but the building stays the same size.

Laurent: “And actually, we had to find out some solution to decouple, physically, the movement of the machine and the building. And for that purpose, we designed some specific bearings allowing displacement, but keeping always the capacity to support and to restrain the machine. So it's one important thing, I could speak about that hours, because it was maybe one of the most challenging parts we had in the design of the building. The support of the machine, which is quite simple when now it is built, but to reach this robust supporting system, it took years.”

And, because, you know, this is an actual nuclear reactor, it has to follow all the safety regulations of any nuclear power plant. No one will be inside the Tokamak complex when it’s running. They’ll be nearby in a separate control building, physically distant from the reactor. And the complex itself has been engineered to withstand a host of disastrous conditions, from floods to plane crashes to explosions on the nearby highway. Like all nuclear power plants, it has a containment structure to confine any fusion products that might be released into the atmosphere in the event of an accident. And that’s made using a special concrete formula developed over two years just for this application that contains extra heavy aggregate and boron to provide radioactive shielding.

Laurent: “So you can see the dark, those are the, the aggregate with content of iron inside, okay. And the white inclusions are colemanite, okay?”

And, it’s not just thermal movement that the designers planned for, but seismic movement too. An earthquake could ruin the entire structure in an instant if the Tokamak was violently shaken, so engineers had to get creative.

Laurent: “One thing I need to mention as well, that the Tokamak complex building is built on elastomeric bearings. For seismic reason, allowing to decouple as much as possible horizontal movement of the soil with the building. And we have 493 anti-seismic bearings. The same type of bearing that you can see underneath bridges. So not large, 90 by 90 centimeters, 18 cm high, but we have a forest of plinths supporting those anti-seismic bearings, and then all the buildings are located on the anti-seismic bearings. It's incredible, incredible.”

Big thanks to the folks at ITER for taking the time to help me understand all this. I only had time to scratch the surface of all the incredible engineering involved. And, go check out Jade’s video to learn more about this awesome project; she actually got to be inside some of the buildings we showed. The civil engineering at the Tokamak building just wrapped up, but there’s a long way to go before fusion experiments start. Like all ambitious projects, this one has struggled through its share of setbacks and iterations. But with 10 times the plasma volume of any fusion reactor operating today, they’re hoping to eventually demonstrate the potential for fusion as a viable source of energy. And that might eventually change the world. Only time will tell if it happens, but it’s exciting right now to see countries across the world collaborating on such a grand scale to invest in the long-term future of energy infrastructure.