Klaus Hesch: Materials and Fuels – The Technological Pillars of Viable Fusion

This article has been translated using artificial intelligence

The Fusion Forward series continues. After exploring the industrial roadmap and technological challenges of fusion, we now turn to one of the most complex issues: materials and fuel.

Klaus Hesch, Strategic Advisor at the Karlsruhe Institute of Technology (KIT), took part in the Future Trends Forum to dive deeper into the technological pillars that will make fusion energy viable.

In his presentation, Hesch highlights three essential functions of breeding blankets: tritium production, neutron energy extraction, and the shielding of magnets in magnetic confinement systems. He also addresses the challenges posed by structural material damage, coolant management, and the urgent need for infrastructures IFMIF-DONES to enable progress toward fully integrated systems.

His message is clear: as long as research remains focused solely on plasma physics, fusion power plants will stay “30 years away.”

If you want to watch Klaus Hesch’s presentation, you can do so in this video:

Klaus Hesch: “Materials and Fuel: Technological Pillars for Viable Fusion” #FusionForward

The Breeding Blanket: Producing Fuel, Harnessing Energy, and Protecting the Reactor

One of the biggest challenges in fusion energy is that it requires tritium, a fuel that barely exists in nature. So, how do we obtain it? The answer lies in the breeding blanket –a system that surrounds the core of the reactor and performs three essential functions.

The first is tritium production. Every fusion reaction consumes tritium and releases a neutron—a particle that, when it collides with lithium inside the blanket, can generate new tritium. In theory, it’s a self-sustaining cycle; in practice, however, many neutrons are lost. To compensate, engineers add neutron-multiplying materials such as beryllium or lead, which help create more neutrons and, consequently, more tritium.
Lithium is also used in more manageable forms—ceramics, alloys, or molten salts—instead of pure lithium, which is highly corrosive.

The second function is energy extraction. About 80% of the energy produced in a fusion reaction travels as high-energy neutrons. As they pass through the blanket, these neutrons collide with atoms, releasing their energy as heat. That heat is what will later be converted into electricity. But there’s an important detail: to slow down the neutrons and fully capture their energy, the blanket must be between one and one and a half meters thick. This means that even compact reactors require a sizeable blanket to operate effectively.

The third function is shielding the reactor’s magnets, which are responsible for keeping the plasma confined. In magnetic fusion reactors, these magnets sit very close to the reaction zone and would be quickly damaged by neutron radiation without protection. The blanket acts as a protective shield, extending their operational lifetime.

In short, the breeding blanket is indispensable: it produces the fuel, captures the reaction’s energy, and protects the reactor’s most delicate components. Without it, fusion simply wouldn’t be viable.

Challenges in Structural Materials

Fusion energy doesn’t just generate heat—it also produces a constant bombardment of high-energy particles known as neutrons. When these neutrons collide with the reactor’s materials, they cause significant damage.

Imagine a brick wall being hit repeatedly by fast-moving balls. Over time, the bricks start to shift and the wall weakens. Something similar happens inside a fusion reactor: the atoms that make up materials are displaced, and over time, components lose their strength. This means they need to be replaced periodically. Engineers are working to extend that replacement cycle from one year to five, since the difference in cost and operational uptime is enormous.

But that’s not the only problem. Neutrons can also generate gases like helium or hydrogen inside the material, which accumulate and make it more brittle. They also activate certain atoms, turning them radioactive—forcing maintenance operations to rely on robots and remote systems. To address this, researchers are developing low-activation steels, which degrade more slowly and make reactor maintenance easier and safer.

Another major challenge is the coolant, the fluid that transfers heat to the turbines that generate electricity. In fission reactors, water is the standard, but in fusion it becomes unstable before reaching the high temperatures required to maintain material integrity. Alternatives such as helium or even CO₂ are being explored, but each comes with trade-offs in cost, availability, and safety.

In short, developing materials that can withstand years of extreme conditions is one of the greatest technological challenges facing fusion energy.

The Engineering Gap: From Isolated Parts to an Integrated System

Klaus Hesch sums it up with a vivid metaphor: “We have the pieces of the puzzle, but not the complete system.”
Around the world, researchers have tested individual solutions—how to produce tritium, extract heat, or understand material behavior under radiation. The problem is that these elements have never been tested together, under conditions that truly replicate what will happen inside a working reactor.

To make that leap, we need large-scale infrastructures. One of the most important is IFMIF-DONES, now under construction in Granada, Spain. There, materials will be tested under neutron bombardment conditions similar to those in fusion reactors—a decisive step that will reveal which materials can actually perform in realistic environments.

Still, Hesch warns that one facility won’t be enough. A coordinated international effort will be required to cover the full range of validation needs. Otherwise, fusion risks remaining trapped in what he calls the “30-year horizon”—always three decades away, never quite arriving.

His conclusion is clear: we need to give greater weight to engineering and technology, not just plasma physics. Without tackling the technical challenges now, the transition from experimental setups to industrial-scale power plants will keep slipping further into the future.

Watch the full talk by Klaus Hesch:

Klaus Hesch: “Materials and Fuel: Technological Pillars for Viable Fusion” #FusionForward

Klaus Hesch: “Materials and Fuel: Technological Pillars for Viable Fusion” #FusionForward

This article is part of the ongoing analysis by the Fundación Innovación Bankinter. The full report, “Fusion Energy: A Revolution in Progress,” brings together insights from more than 20 international experts and identifies the five critical levers to scale fusion as a climate, economic, and technological driver.

Download it here to explore how we can start building tomorrow’s energy system today.

And if you want to keep following this transformation, don’t miss the next articles in the Fusion Forward series – where we continue to bring the future of energy closer to society, with rigor, foresight, and purpose.