Deep Dive: Neutronics & Activation

How a low-neutron design transforms the shielding, material lifetime, and waste picture — with a high-fidelity OpenMC calculation planned to fix the numbers.

Neutron fraction

~5.25–7.05% along the fuel schedule

Wall damage

30 dpa over 30 FPY (≤ 36 dpa qualification)

Shield

Compact center-stack shield; explicit fluence budget

High-fidelity

OpenMC (S63, planned)

Neutronics — how a reactor's neutrons deposit energy, damage materials, and activate structures — sets the shield thickness, the component lifetimes, and the waste profile. For Kronos it is unusually gentle, because being low-neutron changes every one of those quantities.

The neutron fraction runs 5.25–7.05% along the fuel schedule — roughly 25× below D–T. That means wall loading around 0.10–0.12 MW/m², a first wall that accumulates only ~30 dpa over 30 full-power-years (within its 36-dpa qualification, so it lasts the plant life), and far less activation and waste. It also lets the compact center-stack shield fit in the tight inboard space.

The design carries an explicit neutron-fluence budget for the shielded center stack, and a high-fidelity OpenMC neutronics calculation (S63) is planned to fix the true shield performance and lifetimes — currently based on the reduced-order fluence ledger.