The process by which fusion neutrons transmute stable atoms in structural materials into radioactive isotopes — the primary source of radioactive waste in a fusion power plant.
ReviewedLast reviewed: 9 Aug 2026·Category: Glossary
Process
When 14.1 MeV neutrons from D–T fusion reactions strike structural materials, they can be captured by atomic nuclei, transmuting them into different (often radioactive) isotopes. This neutron activation is the main mechanism by which fusion reactors generate radioactive waste.[1]
Key distinction from fission: Fusion fuel itself is not long-lived radioactive waste. The radioactivity comes from activated structural materials (steel, tungsten, etc.), not from spent fuel. By choosing “reduced-activation” structural materials (EUROFER, vanadium alloys, SiC/SiC composites), the induced radioactivity can decay to hands-on levels within 50–100 years, compared to thousands of years for fission waste.
Reduced-Activation Materials
Reduced-activation ferritic/martensitic (RAFM) steels such as EUROFER-97 are designed to avoid alloying elements (Mo, Nb, Ni, Co) that produce long-lived radioactive isotopes under neutron irradiation. Instead, they use W, V, and Ta, whose activation products have shorter half-lives.[2]
Waste Classification
Fusion activated waste is expected to qualify as low-level or intermediate-level waste, requiring near-surface disposal rather than deep geological repositories. This is a significant advantage over fission, which produces high-level waste requiring geological isolation for millennia.[3]
Sources
Zinkle, S.J. and Snead, L.L. "Designing radiation resistance in materials for fusion energy." Annual Review of Materials Research, 44, 241–267, 2014.
Tavassoli, A.A.F. "Present limits and improvements of structural materials for fusion reactors." Journal of Nuclear Materials, 302, 73–88, 2002.
IAEA. "Fusion Safety." Safety Reports Series No. 117, 2022.