Validating the Neutronics Model

The neutron transport and activation model underpins every product number; its accuracy is bounded by nuclear-data uncertainty, which the record propagates rather than ignores.

From neutrons to products

Once the 14.1 MeV source rate is fixed, a neutronics model determines how those neutrons breed tritium, produce helium-3, activate materials, and deposit heat. The breeder (Hyperion) product figures — near 4 kg/yr tritium class and 1.97 kg/yr helium-3 — are outputs of this model, so its validation is central.

How it is validated

• Benchmark cases against published integral neutronics experiments for shared materials.
• Cross-section libraries cited to their evaluated nuclear-data source.
• Propagation of nuclear-data uncertainty into product-yield intervals.
• Consistency checks between deposited energy and the fusion power balance.

The nuclear-data floor

Neutronics accuracy is bounded below by the uncertainty in evaluated cross-sections, which is real and not reducible by better geometry alone. The record reports product yields with intervals that include this floor. The step where model geometry matters most — realistic blanket coverage — feeds directly into the local-vs-net TBR gate, which is why that gate is open.

The neutronics model therefore sits at the junction of two different uncertainty types: an irreducible nuclear-data floor that better geometry cannot remove, and a geometry-and-coverage uncertainty that a more faithful model can reduce. The record keeps them distinct so a reader knows which part of a product-yield interval could tighten with more work and which part is set by the state of evaluated nuclear data.

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