Li-6, Enrichment, and Neutron Multiplication

Enriching lithium in ⁶Li and adding a neutron multiplier are the two main levers for raising breeding — both with their own limits.

Getting more tritium per neutron

Two engineering levers raise the tritium breeding ratio. The first is enriching the lithium in ⁶Li, whose capture reaction ⁶Li + n → T + ⁴He is the workhorse breeding channel; natural lithium is only about 7.5% ⁶Li, so enrichment substantially increases breeding per unit blanket. The second is adding a neutron multiplier — a material like beryllium or lead that responds to a fast neutron by emitting two — to increase the neutron population before it is captured in lithium.

Multiplication matters because self-sufficiency needs more than one bred tritium per burned tritium, yet each fusion reaction supplies only one neutron and some are always lost to structure and leakage. Without multiplication, net TBR above 1 is difficult; with it, there is enough headroom to reach the higher lever settings.

The limits

Neither lever is free. Enrichment has practical and supply constraints; multipliers add material that itself absorbs and activates neutrons, generates heat, and has its own damage and lifetime issues. The multiplier and enrichment choices interact with coverage and structure, which is why the achievable net TBR — and the fate of the 1.8 target — remains a design-and-simulation balance rather than a settled figure.

• ⁶Li enrichment raises breeding per unit blanket
• A multiplier (e.g. beryllium, lead) increases the neutron population
• Both add material, absorption, and lifetime constraints

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