Tritium Breeding as a Design Lever

The breeder makes its own tritium in a lithium blanket; the breeding ratio is a design lever, and self-sufficiency at the low end is an open question.

Tritium is radioactive and scarce in nature, so a D-T machine that had to buy tritium would face a supply wall. The breeder (Hyperion) avoids this by breeding its own tritium in a lithium blanket. How much it breeds relative to how much it burns is the tritium breeding ratio, treated across design values of 1.1, 1.5, and 1.8.

What the ratio means

A breeding ratio above 1.0 means the plant makes more tritium than it consumes, allowing self-sufficiency plus a surplus (the ~4 kg/yr-class product) to start other machines or supply other uses. The ratio is a lever because it depends on blanket design, neutron multiplication, and coverage — engineering choices, not a fixed constant.

The honest open question

• At TBR 1.1, self-sufficiency is tight and depends on minimizing losses; this is an open reconciliation, not a settled result.
• Higher ratios need effective neutron multiplication (e.g., beryllium), raising the multiplier-material question.
• Local blanket breeding versus net plant self-sufficiency is a distinction we do not blur.
• All values are design-and-simulation; blanket breeding is not yet demonstrated at plant scale.

The defensible framing is that tritium supply for the breeder is solved in principle by breeding — the fuel is made, not mined — while the margin at the low end of the breeding-ratio lever is a genuine open design question. We present the lever honestly rather than asserting a settled self-sufficiency.