Local vs Net Breeding Ratio

The gap between an idealized local breeding ratio and the real net value across the whole machine is Hyperion's most important open reconciliation.

Two different numbers

Neutronics calculations can report breeding at two levels. The local tritium breeding ratio is what a well-covered patch of blanket achieves in isolation. The net breeding ratio is what the whole machine delivers after accounting for every port, penetration, structural gap, and loss. The net value is always lower, and it is the one that determines whether the machine is tritium self-sufficient.

Why the gap opens

Every neutron that escapes through a diagnostic port, a neutral-beam duct, or an uncovered region of the vessel is a neutron unavailable for breeding. Structure and coolant absorb their share. In a compact spherical tokamak the inboard side has little room for blanket at all, since the center stack occupies it, so coverage there is inherently limited. These effects accumulate into a real shortfall between local and net TBR.

An open question, stated plainly

At the target TBR of 1.8, closing the gap between the idealized local value and a realistic net value is not yet done. Tritium self-sufficiency, breeding at least as much tritium as the plasma consumes across the whole machine, remains unproven for Hyperion. It is one of the reconciliations the design-and-simulation program is explicitly working, and the first-of-a-kind machine is the test that will settle it.

• Local TBR (ideal patch) exceeds net TBR (whole machine)
• Ports, penetrations, structure, and inboard gaps drive the loss
• Self-sufficiency at target 1.8 is unproven and openly flagged

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.