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How does radioactive waste from fusion reactors differ from waste from fission reactors?

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3D illustration of the interior reaction chamber of a tokamak fusion reactor, showing a large, cylindrical, metallic structure with curved walls and bright light panels. — fusion reactor A tokamak is a device used in nuclear-fusion research for magnetic confinement of plasma.

The radioactive waste produced by fusion reactors differs significantly from that of fission reactors in terms of composition, toxicity, and longevity.1

In fission reactors, the process involves splitting heavy nuclei, which generates highly unstable fission products that remain dangerous for extremely long periods. Conversely, the primary by-product of a fusion reaction is helium, which is not radioactive.21

While fusion reactors do generate some radioactive waste, it is produced indirectly when neutrons—released during the fusion process—are absorbed by the reactor's surrounding structural materials. This waste profile is more manageable because:1

Lower Toxicity: The radioactive by-products of fusion are generally less toxic than the waste generated by fission.1
Shorter Half-lives: By utilizing specific low-activation materials, such as specialized steels or ceramic composites like silicon carbide, the resulting radioactive waste has significantly shorter half-lives compared to the long-lived waste associated with fission.1

Consequently, while fission waste requires complex, long-term geological containment, fusion technology offers the potential for a much cleaner energy cycle with significantly reduced environmental impact.13