The Breeder's 14 MeV Neutron Flux

Hyperion is a D-T machine: about 80% of its 88.7 MW fusion power leaves as 14.1 MeV neutrons that breed tritium and drive activation.

The breeder (Hyperion) is the opposite case from the burner. Its reaction, D + T → ⁴He + n, sends roughly four-fifths of the fusion energy into a single 14.1 MeV neutron. At the design point of 88.7 MW fusion power, that is a large, energetic neutron source by design — the neutrons are the product, not a nuisance.

Why the breeder wants neutrons

• Each 14 MeV neutron entering the lithium blanket can breed tritium via ⁶Li(n,α)T, sustaining the fuel cycle across breeding ratios of 1.1, 1.5, and 1.8.
• Neutron multiplication in beryllium or lead lets one fusion neutron yield more than one tritium, which is how a breeding ratio above unity is reached.
• The same flux produces 14 MeV neutrons as a saleable product for materials testing and isotope work.

The consequence is that the breeder's activation and shielding engineering is more demanding than the burner's. High-energy neutrons cause displacement damage and transmutation in the first wall and blanket, which is exactly why Hyperion is built from low-activation materials and why its waste story is managed rather than trivial.

The breeder's neutron output is thus a resource to be captured, not a loss to be minimized: shielding, breeding, and materials testing all depend on it. Managing that flux well — directing it into the blanket and away from the magnets — is as much about using the neutrons as about protecting against them.

These are design-and-simulation figures for a machine whose construction begins Q2 2027, with first-of-a-kind tritium targeted around 2030. No hardware net-gain is claimed before that first-of-a-kind milestone; the flux values are modeling inputs to the blanket and activation design.