Helium, a product of the deuterium–tritium fusion reaction, is a valuable industrial gas.

All power plants produce waste during operation and ultimately during decommissioning. In a deuterium–tritium fusion plant, the direct product of the fusion reaction is helium, but high-energy neutrons will also activate reactor materials and create radioactive waste that must be managed safely.

Helium

The deuterium–tritium reaction produces an alpha particle, which becomes a helium nucleus, and a high-energy neutron. Helium ash must be removed continuously from the plasma through the exhaust and vacuum systems. After separation from unburned fuel and impurities, the helium could in principle be recovered for industrial use. The fusion neutrons, meanwhile, carry most of the reaction energy into the surrounding blanket and structural materials.

Helium is a valuable industrial gas used in cryogenics, leak detection, welding, semiconductor manufacturing and many scientific and medical applications. A gigawatt-scale fusion plant would produce roughly one hundred kilograms of helium per gigawatt of fusion thermal power during one full-power year.

Neutrons

The high-energy neutrons produced by deuterium–tritium fusion are the main source of radioactive waste in a fusion plant. Neutron interactions can displace atoms from the crystal lattice, transmute nuclei into other isotopes and gradually change the mechanical properties of materials. This irradiation can cause embrittlement, swelling and other forms of structural damage, while neutron activation makes many reactor components radioactive.

Future fusion power plants are expected to expose the first wall to neutron loads of roughly 1–2 MW/m², depending on the reactor design. Over time, in-vessel components such as the first wall, divertor and breeding blanket will become activated and suffer radiation damage. These components will require periodic remote replacement, while larger structures such as the vacuum vessel are expected to remain in place much longer.

Materials research therefore focuses on reduced-activation alloys that minimise long-lived radioactivity while retaining acceptable mechanical properties under intense neutron irradiation. Examples include reduced-activation ferritic–martensitic steels such as EUROFER.

Interim Storage and Recycling

Removed radioactive components will require remote handling and temporary storage while their decay heat and radiation levels decrease. The exact storage method will depend on the component, its activation level and national regulations; water pools are not a universal requirement. Some components may be transferred to hot-cell facilities for inspection, detritiation or refurbishment, while others will be stored until they can be recycled, cleared from regulatory control or sent for disposal.

Decommissioning

Decommissioning a fusion power plant will require remote dismantling, decontamination and radioactive-waste management, but its waste inventory will differ significantly from that of a fission plant. Fusion will produce no spent nuclear fuel or fission products; instead, most radioactive material will consist of neutron-activated structures and components contaminated with tritium. Non-activated buildings and equipment can be dismantled conventionally, while activated materials will require classification, interim storage, recycling where practical, or disposal according to their radioactivity and national regulations.