Burner Neutron Fraction and Shielding
Deuterium-helium-3 fuel keeps neutrons to 5.44 percent of the fusion power, easing shielding compared with deuterium-tritium.
A low-neutron burn
The primary deuterium-helium-3 reaction produces a proton and a helium-4 nucleus, both charged, and no neutron. The burner still makes some neutrons from side reactions, chiefly deuterium burning with deuterium, but far fewer than a deuterium-tritium machine. The design carries a neutron fraction of 5.44 percent of the fusion power.
Why this matters
- Neutrons activate materials and require heavy shielding; fewer neutrons means less activation.
- Charged particles can be converted directly to electricity, neutrons cannot.
- Lower neutron flux eases the burden on structure and magnets over the machine's life.
- The remaining 5.44 percent still requires real shielding, so it is not zero.
The honest caveat
A low neutron fraction is a genuine advantage, but it is not a neutron-free machine, and the model does not pretend otherwise. The 5.44 percent still demands shielding around the central cell and structural attention to activation. Deuterium-helium-3 also burns less readily than deuterium-tritium and helium-3 is scarce, so the low-neutron benefit is paid for elsewhere.
In the model
Shielding appears around the central cell where most neutrons originate, thinner than a comparable deuterium-tritium blanket would be because there is less flux to stop. Selecting the shield reports the neutron fraction it is sized against. The contrast with Hyperion's thick breeding blanket is visible directly when the two machines are compared.
Fuel context
See the deuterium-helium-3 fuel cycle for why the neutron fraction is low, and the Hyperion blanket for the deuterium-tritium contrast.