How Lithium Walls Shape the Future of Fusion Reactors: A Deep Dive into Tritium Retention

Plasma-lithium interaction inside a tokamak fusion reactor

Published: July 29, 2025 | By Quantum Server Networks

As humanity moves closer to achieving practical fusion power, understanding the behavior of plasma-facing materials becomes increasingly critical. One of the most promising materials in this domain is lithium, often used in the inner walls of tokamak fusion reactors to stabilize the plasma and protect reactor components. But what happens to fuel—especially tritium—when it encounters these lithium walls?

In a groundbreaking international study published in Nuclear Materials and Energy, researchers from nine institutions—including the Princeton Plasma Physics Laboratory (PPPL), DIFFER, General Atomics, and Lawrence Livermore National Laboratory—have revealed how lithium surfaces influence tritium retention in tokamaks. Their findings carry immense implications for both the safety and efficiency of future fusion energy systems.

Original article: https://phys.org/news/2025-07-lithium-walls-tritium-fusion-reactors.html

Why Tritium Matters in Fusion

Tritium, a radioactive isotope of hydrogen, is one half of the fusion fuel duo (alongside deuterium) that powers most proposed tokamak reactors. However, tritium is both rare and tightly regulated. If it gets trapped within reactor walls, it cannot participate in fusion reactions, reducing overall energy output and complicating reactor operations and fuel management.

Co-Deposition: A Double-Edged Sword

The study’s lead author, Maria Morbey of DIFFER and Eindhoven University of Technology, found that the dominant mechanism for fuel trapping is co-deposition—the simultaneous accumulation of lithium and fusion fuel on the reactor walls. This occurs whether lithium is pre-applied to walls or injected during operation, though the latter was shown to be more effective at maintaining uniform plasma temperature and enhancing stability.

Surprisingly, the amount of lithium applied before operation had minimal impact on fuel retention. In contrast, mid-operation lithium powder injection—already used as a surface conditioning technique—was far more influential in trapping fuel, especially deuterium, a stand-in for tritium in the experiments.

Liquid Lithium: The Next Frontier

The research supports ongoing efforts to develop liquid lithium plasma-facing components. Unlike solid coatings, liquid lithium forms a self-repairing, flowing barrier that could prevent unwanted fuel buildup and actively recover tritium through local purification processes. This approach could also shield components from extreme heat by forming a gas or vapor layer, stabilizing the plasma and enabling higher power densities in compact tokamak designs.

Challenges: Avoiding Cold Traps and Hot Spots

While lithium’s interaction with tritium has advantages, it also presents risks. In colder, less accessible areas of the reactor, trapped tritium can accumulate and remain unrecoverable. The study stresses the need for strategic thermal management and wall design to guide tritium toward regions where it can be effectively retrieved and reused.

As Florian Effenberg of PPPL explains, moving away from graphite walls toward advanced materials like tungsten and lithium is essential for achieving commercially viable fusion. But success depends on a delicate balance between fuel recycling and wall conditioning—a balance lithium could help strike.

What’s Next?

Morbey’s team plans to extend their work by conducting similar tests using heated tiles coated with liquid lithium, aiming to replicate the intended operation of future fusion power plants. The data will also guide the design of the upcoming National Spherical Torus Experiment-Upgrade (NSTX-U) and related systems like the Spherical Tokamak Advanced Reactor (STAR).

In the pursuit of harnessing the stars on Earth, every atom counts—and how it sticks to a wall may determine the future of global energy.

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