The hard part — a solved, reproduced power balance — is closed. What remains is engineering and procurement with known solutions: environment, siting, waste, and balance-of-plant. Every figure here is from the frozen record and carries its condition. No cost figures. Low-neutron, never aneutronic.
Public dose CLOSES. Required detritiation factor 1–34 across realistic HTO release — versus ITER-class 1,000–10,000 demonstrated. A design task with an off-the-shelf solution, not a physics gap.
Waste ≤ Class C. At a certified low-activation RAFM steel heat (Nb < 10 ppm). A steel procurement spec, routinely certified; ordinary steel would be higher class. Open: the Ag-108m residual needs a certified-heat assay + regulatory determination.
Designed in. Remote federal siting; tritium containment and detritiation scoped from the outset; emergency plan built in. Durability → capacity factor is a single design lever.
Low-neutron, not aneutronic. f_n 5.44% at the design point; the fleet's wall-loading is 41× (Aegis) / 168× (MetroVolt) below the breeder, and falls further as the ³He fraction rises.
Scheduled waste ≈ zero. 0.035–0.144 first-wall changes in 30 years (first-wall life 104–428 fpy) — a direct consequence of the low neutron fraction.
No breeding blanket, no divertor. An open magnetic system with direct energy conversion — fewer activated components to begin with.
| Subsystem | Conventional D–T tokamak | HYPERION breeder | Kronos burner (mirror) |
|---|---|---|---|
| Breeding blanket | required | the breeding blanket is the product | none |
| Divertor | required | divertor exhaust (open design item) | none — open field lines |
| Edge instabilities | ELMs to mitigate | negative-triangularity, ELM-free | none — open system |
| Energy conversion | thermal — steam cycle + turbine | gain only (no electricity) | direct — no steam cycle, no turbine |
| Neutron shielding | heavy (14 MeV, ~80% of power) | heavy (D–T, its product) | light (low-neutron D–³He) |
| Fuel supply | external tritium | breeds its own T + He-3 | helium-3 (lunar at commercial scale) |
The burner removes the blanket, the divertor, and the entire thermal island — a large balance-of-plant simplification that follows directly from low-neutron D–³He fuel plus direct conversion.
| Fuel | Ignition / reactivity | Neutron output | Needs | Kronos use |
|---|---|---|---|---|
| D–T | lights first (~4–13 keV; peaks ~64 keV) | ~80% of energy as 14 MeV neutrons | tritium breeding | BREEDER (gain only) |
| Catalysed D–D | moderate | neutron-heavy | no external tritium | studied; not the burner |
| D–³He | turns on hot (~60–90 keV) | low — ~5.4% (D–D side reactions only) | helium-3 (lunar at scale) | BURNER — direct conversion |
| p–¹¹B | very hot | ~aneutronic in principle | bremsstrahlung-limited | not chosen — see note |
Kronos's own "four-way test" shows aneutronic fuel, native direct-conversion, and low cost are mutually exclusive — you cannot have all three. D–³He is the deliberate choice: low-neutron and directly convertible. See the reactivity curves.
Mainstream fusion is D–T magnetic confinement (ITER, and the high-field tokamak class such as SPARC): powerful, but ~80% of the energy is 14 MeV neutrons, converted thermally through a steam cycle behind heavy blankets, divertors, and shielding. Kronos takes a different path — breed the scarce fuel first, then burn it low-neutron with direct conversion. Against published reference points:
| Reference point | Kronos | Comparator (sourced) |
|---|---|---|
| Buildability (plasma current) | HYPERION 9.66 MA | ~⅔ (66%) of ITER's 15 MA — inside built practice |
| Heating power density | 2.37 MW/m³ | ≈ 2.2× SPARC |
| Plug magnet field | 26.49 T | 0.82× an existing 32.35 T magnet record |
| Strategic supply | TBR lever 1.03–1.20 (marginal) | frozen OpenMC lever (BR-L2-A7): TBR 1.03–1.06 → 1.18–1.20 solid-Be (marginal) (TBR 1.8) ≈ 2× today's world commercial tritium flow |
| Public dose (detritiation) | factor 1–34 required | vs ITER-class 1,000–10,000 demonstrated |
| Plant | no blanket · no divertor · no steam cycle (burner) | conventional D–T reactor needs all three |