Center-Post Neutron Damage
Fast-neutron fluence displaces atoms and embrittles the center-post; damage accumulation, not wear, sets its short life.
Damage measured in displacements
Neutron damage in metals is often measured in displacements per atom (dpa): how many times, on average, each atom has been knocked from its lattice site. High dpa drives swelling, hardening, embrittlement, and property changes that degrade the center-post's ability to carry current and load. In the poorly-shielded center stack, dpa accumulates fast.
Why the center-post is worst
The center-post sits closest to the plasma's neutron source with the least shielding between them. It therefore sees the machine's highest neutron flux and accumulates damage faster than any other structural component. This is the direct physical reason behind the ~0.01 fpy lifetime note: it is damage-limited, not wear-limited.
- Damage tracked as displacements per atom (dpa).
- High dpa causes swelling, hardening, and embrittlement.
- Center-post sees the highest flux, least shielded.
- Damage rate, not mechanical wear, sets the replacement interval.
Qualification gap
Predicting property change at high dpa under a 14 MeV spectrum is an open materials question for the whole field, because no facility yet reproduces that spectrum at full fluence. The breeder treats center-post damage as a monitored, replaced-on-schedule reality rather than claiming a settled high-dpa material, and it feeds the machine's materials-qualification program.
Damage monitoring
Because the center-post is damage-limited, the breeder plans to track its accumulated fluence and property indicators through operation, so replacement is triggered by measured damage against the ~0.01 fpy basis rather than by a fixed calendar alone. This monitoring turns an uncertain high-dpa lifetime into a managed, evidence-based maintenance decision.
This page documents a design and simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. Figures are computed, reproducible targets, not measurements.