The Tritium-Breeding Gate

Why tritium breeding ratio is carried as a lever, and why net breeding in real geometry is an open gate.

A breeder must close its own fuel loop

The breeder (Hyperion) burns deuterium and tritium; tritium does not occur naturally in useful quantity, so the machine must breed it in a lithium-bearing blanket where 14 MeV neutrons produce fresh tritium. The tritium breeding ratio (TBR) is tritium bred per tritium burned. Below 1.0 the fuel loop bleeds out; sustained operation and a surplus for products require a TBR comfortably above 1.0.

Why a lever, not a number

• An idealized blanket cell can compute a high local TBR, but ports, structure, and diagnostics in a real three-dimensional machine reduce it.
• Tritium is lost to radioactive decay, permeation, and processing inefficiency, so breeding must beat these before any surplus exists.
• The product case (roughly 4 kg/yr tritium class) depends on net surplus after the machine feeds itself.

The open reconciliation

Kronos explicitly flags a local-versus-net TBR reconciliation as unresolved: breeding looks favorable in an idealized geometry but must be re-demonstrated once realistic ports and structure are included. Until a whole-machine net-breeding case closes — first in high-fidelity neutronics, then in FOAK hardware — the program treats robust net breeding as an open gate, not an achieved result.