TBR 1.8: the Reference Target
TBR 1.8 is Hyperion's reference target — the breeding performance behind the ~4 kg/yr class — and the point where the local-vs-net reconciliation is open.
The target that sets the product figures
TBR 1.8 breeds eighteen tritium atoms per ten fusion neutrons, an 80% surplus. It is the reference target because it is the breeding level consistent with the ~4 kg/yr tritium class, the ~1.97 kg/yr helium-3 coproduct, and enough surplus to seed additional units on a useful timescale.
Reaching 1.8 requires favorable choices across the board: high lithium-6 enrichment, an effective neutron multiplier, and high blanket coverage. Those same choices compete with the practical need for ports and penetrations, which is exactly why 1.8 is a target rather than a settled result.
The open reconciliation
This is the crux flagged plainly in Hyperion's open-questions record. A local TBR of 1.8 computed for an idealized, fully covered blanket cell is not the same as the net TBR of the real machine with its access ports, structural gaps, coolant channels, and tritium holdup. Whether realistic blanket coverage and losses leave net TBR high enough to hit the product targets is not yet resolved.
- Local (cell-level, ideal) TBR: 1.8 target
- Net (as-built) TBR: lower by an amount still being quantified
- Gate: net must stay ≥ 1.0 with margin AND support ~4 kg/yr surplus
Kronos states this as an unresolved design-and-simulation question. The product figures are contingent on closing it; no self-sufficiency claim is made in hardware before FOAK.
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.