Deep Dive: The Staged D–³He Fuel Cycle

A walk through the Kronos fuel roadmap — from D–T commissioning through D-rich and ³He-rich D–³He to the p–¹¹B endpoint — and how the plant breeds its own helium-3.

Stage 0

D–T — commissioning

Baseline

D-rich D–³He (commercial)

Optimum

³He-rich (DEC η ≈ 0.60)

Endpoint

p–¹¹B (gated, aneutronic)

The Kronos fuel strategy is not a single fuel but a staged cycle that moves toward ever-lower neutron output as the machine and program mature. Each stage trades higher physics difficulty for a cleaner reaction.

• Stage 0 — D–T. A brief commissioning fuel; easy to ignite, used to bring the plant up.
• D-rich D–³He. The commercial baseline — low-neutron, charged-particle-rich, and directly convertible.
• ³He-rich D–³He. The conversion optimum, where DEC efficiency peaks near η ≈ 0.60 (analysis S71).
• p–¹¹B endpoint. The gated, truly aneutronic destination.

Throughout, the plant breeds its own helium-3 via the catalyzed D–D branch, so it isn't hostage to scarce external ³He. The neutron fraction is quoted as a range (5.25–7.05%) precisely because it changes along this schedule. Staging lets Kronos earn revenue on an achievable baseline while advancing toward the cleanest reactions.