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Physics & Fusion Science

Deuterium–Helium-3 (D–³He) Fuel

D–³He is the reason the burner can convert energy directly to electricity. It trades a far cleaner neutron budget for a much hotter, harder-to-confine plasma.

Physics & Fusion ScienceUpdated 2026-08-11
Reaction
D + ³He → &sup4;He + p
Energy
18.3 MeV
Neutron fraction
5.44%
Temperature
~90 keV

Deuterium and helium-3 fuse to helium-4 and a proton, releasing 18.3 MeV as charged particles — which can be converted to electricity directly. The Kronos burner runs this reaction at about 90 keV with a neutron fraction of only 5.44%.

Because most of the energy is in charged particles, the burner uses direct energy conversion rather than a steam cycle. That is the architectural payoff of choosing this fuel.

Low-neutron, not aneutronicSide D–D reactions still produce neutrons, so the burner's neutron fraction is 5.44% — low, but not zero. Kronos never describes it as aneutronic.

D–³He is the reason the burner can convert energy directly: with 18.3 MeV released almost entirely as charged particles and a neutron fraction of only 5.44%, its energy can be recovered electrostatically instead of through a steam cycle. The price is a far hotter, harder-to-confine plasma at 90 keV.

Common questions

Why does D–³He run so much hotter?

Its reaction peaks at a higher energy than D–T, so the burner operates at about 90 keV — far hotter and harder to confine. The payoff is charged-particle energy that direct conversion can capture.

Where does the helium-3 come from?

The breeder co-produces about 1.97 kg/yr/yr, giving Kronos an internal terrestrial supply of a genuinely scarce isotope rather than depending on lunar mining or reactor by-product.

← PreviousCurrent DiffusionNext →Deuterium–Tritium (D–T) Fuel
Content reviewed August 2026 · design-and-simulation stage