The Products Are Helium and Neutrons

Fusion's direct products are inert helium and neutrons — not a spectrum of radioactive fission fragments locked in fuel.

What comes out of a fusion reaction determines what has to be managed. In both Kronos fuel cycles the direct products are helium and, depending on the reaction, a neutron. Helium is inert, non-toxic, and non-radioactive. The neutron is energetic and must be absorbed, but it is not itself a persistent waste — it is captured in the blanket, where it breeds fuel or deposits its energy.

The two fuel cycles' products

• Breeder D–T: ⁴He (inert) + a 14.1 MeV neutron, which breeds tritium in the lithium blanket.
• Burner D–³He: ⁴He (inert) + a proton, both charged and captured by direct energy conversion; only the 5.44% side-reaction neutrons need absorbing.
• In neither case is the product a radioactive fission fragment sealed inside a fuel pellet.

This is why fusion has no fission-product inventory: nuclides like cesium-137 and strontium-90, which dominate spent-fuel radioactivity, are simply not created, because nothing is fissioning. The radioactivity fusion does generate is in the structure the neutrons pass through, not in the reaction products themselves.

That the useful outputs are inert helium and captured neutrons is also why fusion's routine effluent is so limited: there is no stream of gaseous fission products to scrub and monitor. The environmental account is dominated by solid activated structure, which is far easier to contain than a mixed gaseous inventory.

The honest qualifier is the neutron: it does not become waste directly, but its absorption activates the structure, which is the origin of fusion's real waste stream. And the breeder's tritium, though a product to be used, is radioactive and handled as a controlled inventory. These are design-and-simulation facts for machines not yet built, grounded in the fuel-cycle physics.