The breeder-first strategy.

You cannot burn D–³He at scale until you can make helium-3. So Kronos builds the fuel-maker first: a D–T breeder whose product decays into the fuel the mirror needs.

Step one

HYPERION — D–T spherical-tokamak breeder

Tritium output

≈ 4.0 kg/yr at the 88.7 MW design point

Helium-3 output

≈ 1.97 kg/yr from tritium decay

Step two

The D–³He tandem-mirror burner

Helium-3 is scarce on Earth. The clean D–³He reaction that the Kronos burner runs is only useful if there is fuel to run it on — so the company sequences the two machines rather than betting on one.

1. Breed the fuel. HYPERION, a compact D–T spherical tokamak, produces about 4 kg of tritium per year at its frozen design point. Tritium decays (12.3-year half-life) into helium-3 — roughly 1.97 kg/yr becomes available as the inventory ages. The breeder is therefore a fuel factory, not just a power source.
2. Prove the burner small. That decay helium-3 is enough to run a ~10 MWe burner demonstrator — the mirror physics tested at honest scale before any fleet.
3. Gate the fleet honestly. A commercial D–³He fleet needs far more helium-3 than terrestrial decay can supply. Kronos states plainly that the commercial burner fleet is gated on an external helium-3 supply (lunar, ~2036), rather than pretending the fuel is already in hand.

This is what "neutrons first" means. The breeder embraces D–T's neutrons — using them to breed — so that the burner can later run a low-neutron fuel. The order is deliberate: make it, then burn it.