Engineers building the world’s first commercial nuclear fusion plant are using expertise from building rockets like Europe’s Ariane 5, to create the super-strong structures needed to cope with conditions similar to those inside the Sun.
The techniques used for building launcher and satellite components have turned out to be the best way for constructing rings to support the powerful magnetic coils inside the machine.
Meaning “the way” in Latin, the International Thermonuclear Experimental Reactor, Iter, is the world’s largest nuclear fusion experiment. It aims to generate constant amounts of electricity, and vitally to use less energy to initialise and maintain the fusion reaction than it generates.
The 500 MW Iter reactor is being built in Cadarache, in the south of France at an estimated cost of more than $15 billion. The fusion plasma will be held in place within the Iter tokomak reactor by a powerful and complex magnetic field, generated by a series of superconducting magnets.
Part of the tokomak’s magnetic field will be generated by large toroidal field (TF) coils. The 18 coils have to be held in place by “compression rings” on the top and bottom of the reactor. These rings have to be able to withstand a radial load of up to 7,000 tons per coil.
Spanish company Casa Espacio is making the rings using a method they have used for the last 20 years to build parts for the Ariane 5, Vega and Soyuz rockets, as well as for satellites and the International Space Station.
Jose Guillamon, head of commercial and strategy at Casa Espacio said: “Forces inside ITER present similar challenges to space.
“We can’t use traditional materials like metal, which expand and contract with temperature and conduct electricity. We have to make a special composite material which is durable and lightweight, non-conductive and never changes shape.”
At Casa Espacio’s centre of excellence in Spain, with its track record in composites for space applications, Casa Espacio has been developing a technique for embedding carbon fibres in resin to create a strong, lightweight material.
The composite is ideal for rocket parts because it retains its shape and offers the robust longevity needed to survive extreme launches and the harsh environment of space for over 15 years.
Now, the team is using a similar technique to build the largest composite structures ever attempted for a cryogenic environment. Iter’s compression rings will have a diameter of 5m and a solid cross-section of 30x30 cm.
Cut the cloth to fit the spacecraft
The Carbon fibres are woven like fabric and embedded in a resin matrix to create a lightweight, durable and stable composite. “In the same way that you’d weave a different fabric for a raincoat than you would for a summer shirt, we can lay the fibres in different directions and alter the ingredients to adapt the resulting material to its role, making it extra strong, for example, or resistant to extreme temperatures in space,” says Guillamon.
For Iter, glass fibres are laid to maximise their mechanical strength and can be built up in slices and stacked like doughnuts to create the cylindrical structure.
The ESA´s Technology Transfer Network helps companies employ technologies from space to improve their businesses. Richard Seddon from Tecnalia worked with the Network
“Space expertise can provide a tremendous resource to so many companies in non-space sectors, helping them to improve their product and increase their revenues,” says “In this case, CASA Espacio had just the right proven expertise to provide the best solution for ITER.”
Harnessing star energy
Nuclear fusion powers the Sun and stars, with hydrogen atoms colliding to form helium while releasing energy. It has long been a dream to harness this extreme process to generate an endless supply of sustainable electricity from seawater and Earth’s crust.
The Iter project is a worldwide research collaboration between China, the EU, India, Japan, South Korea, Russia and the US.
Construction of the prototype reactor is expected to be completed by 2019 and initial trials are scheduled for 2020. A commercial successor for generating electricity is not predicted before 2050.
Designed to generate 500 MW while using only a tenth of that to run, Iter aims to demonstrate continuous controlled fusion and, for the first time in fusion research, produce more energy than it takes to operate.
According to the the Iter project, the reactor will be inherently safe with no atmospheric pollution or long-lived radioactive waste and one kilogram of fuel could produce the same amount of energy as 10 000 tonnes of fossil fuel.
At Iter’s core is a doughnut-shaped magnetic chamber, 23 m in diameter. It will work by heating the electrically charged gases to more than 150 000 000ºC.
Hotter than the Sun, the plasma would instantly evaporate any normal container. Instead, giant electromagnets will hold the plasma away from the walls by suspending it within a magnetic ‘cage’. Building something that can withstand this powerful magnetic field is an extreme engineering challenge.
Now under construction, ITER’s rings will each withstand 7000 tonnes – the equivalent of the Eiffel Tower pressing against each one of the six rings.
Source: ESA Technology Transfer Programme