Neutron Wall Loading

The flux of 14 MeV neutrons crossing the first wall drives breeding, heating, and material damage, and it concentrates in a compact machine.

The neutron flux that does the work

Every D-T fusion reaction releases a 14 MeV neutron, and the rate of these neutrons crossing the first wall, the neutron wall loading, is the quantity that drives the whole breeder. It sets how fast tritium and helium-3 are bred, how much heat is deposited in the blanket, and how quickly materials accumulate damage. In a compact machine the same fusion power crosses a smaller wall, so the loading is high.

A double-edged concentration

High wall loading is favorable for productivity: more neutrons per unit of wall means more breeding and irradiation service per unit of machine. But it is unfavorable for endurance: the same intensity that breeds efficiently also damages the first wall, blanket structure, and especially the lightly shielded center post more quickly. The compact spherical-tokamak geometry sharpens both effects at once.

Designing for the flux

The design balances productive flux against component life by choosing materials that tolerate damage, by making close-in components replaceable, and by accepting a limited center-post lifetime as a planned constraint. Accurately predicting the wall loading and its spatial pattern, which feeds both the breeding calculation and the damage estimate, is central to the neutronics work supporting the first-of-a-kind design.

• 14 MeV neutron flux drives breeding, heating, and damage
• Compact geometry concentrates the loading
• Productivity and component life trade against each other

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.