TBR 1.5: the Working Point

At TBR 1.5 the blanket breeds a 50% surplus over plasma burn — enough margin to absorb real losses and still deliver offtake.

Margin you can spend

TBR 1.5 breeds fifteen tritium atoms per ten fusion neutrons. The 50% surplus is large enough that even after ports, structural absorption, coolant, streaming, and holdup are subtracted, a net TBR comfortably above 1.0 can remain. That surviving margin is what becomes shippable tritium and startup inventory for new units.

This point is attractive because it is a plausible working target: reachable with moderate lithium-6 enrichment and a beryllium or lead multiplier, without pushing coverage to impractical fractions. It balances breeding performance against the need to keep penetrations for heating, diagnostics, and maintenance.

What the surplus buys

• Net self-sufficiency with a real safety margin
• Surplus tritium for external offtake
• Startup inventory to fuel the next unit (fleet doubling)
• Robustness to blanket degradation and outages

Still a design-and-simulation value

1.5 is a neutronics result under specific blanket assumptions, not a measured quantity. The as-built net value depends on the final coverage fraction and loss budget, which is why the reconciliation between local and net TBR remains the governing open question even at this favorable point. A local 1.5 that erodes to a net figure near breakeven would still fail the surplus mission, so the margin at 1.5 is best read as a buffer against the reconciliation penalty rather than a guaranteed surplus.

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