The Tritium Breeding Ratio Open Question

The breeder treats the tritium breeding ratio as a design lever across 1.1, 1.5, and 1.8; whether the 1.8 target survives realistic blanket geometry is an open reconciliation.

A lever, studied at three values

The tritium breeding ratio (TBR) is the number of tritium atoms bred per tritium atom burned. A D-T machine that consumes its own fuel must breed at least as much as it burns plus losses, so TBR above one is necessary for self-sufficiency. The breeder (Hyperion) record does not assert a single TBR; it studies the machine as a lever across 1.1, 1.5, and 1.8.

Why 1.8 is a target, not a claim

A local TBR computed for an idealized, fully surrounding blanket is optimistic. A real machine has ports, heating penetrations, diagnostic lines, and structural gaps that no breeding blanket covers, plus process losses in the fuel cycle. The gap between the idealized local figure and the net figure a real machine achieves is the open reconciliation. At the 1.8 target it is stated as unresolved.

What closing it requires

Closing the question means a neutronics model with realistic geometry, validated against the neutronics benchmarks, that reproduces a net TBR meeting the target. Until that model exists and FOAK measurements confirm it, tritium self-sufficiency remains a design target rather than a demonstrated property.

This page describes a design-and-simulation study, not a built machine. Construction of the breeder (Hyperion) begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. No hardware net-gain claim is made before FOAK.