The Breeding-Ratio Lever

Tritium breeding ratio is treated as a design lever studied across 1.1, 1.5, and 1.8, not as a single fixed number.

TBR as a lever

Tritium breeding ratio (TBR) is the ratio of tritium bred in the blanket to tritium consumed by the plasma. The breeder treats TBR as a design lever, studied across 1.1, 1.5, and 1.8, rather than committing to a single value, because the achievable ratio depends on blanket design choices that trade against each other.

What each value means

• TBR 1.1: modest surplus, tighter blanket, less margin for penetrations
• TBR 1.5: substantial surplus supporting product output and fuel self-sufficiency
• TBR 1.8: high design-level surplus, most demanding blanket configuration

Why not fix one number

Real blankets have penetrations for heating, diagnostics, and maintenance, plus structure that absorbs neutrons. These reduce net breeding below the idealized figure. Studying a range makes the design honest about the gap between a one-dimensional design value and net three-dimensional performance, and lets the blanket be tuned to the product requirement.

The open reconciliation

There is a flagged reconciliation between a design-level TBR of 1.8 and the net breeding a real three-dimensional blanket delivers. The program does not paper over this. It is one of the specific items the fuel-loop gate G3 is designed to settle by measurement at first tritium.

TBR values here are design levers for a machine not yet built. The product figure near 4 kg/yr tritium class follows from the chosen point on this lever and remains a projection until G3.