Irradiation Damage Modeling
Damage codes predict how energetic neutrons degrade materials over time, from atomic displacements to swelling, embrittlement, and property change.
Neutrons damage materials
A 14 MeV fusion neutron knocks atoms from their lattice sites, creating cascades of displacements and, through transmutation, helium and hydrogen gas within the material. Over time these defects accumulate, changing the material's strength, ductility, dimensions, and thermal properties. Predicting this evolution is essential to component lifetime.
The damage metric
The standard measure of exposure is displacements per atom, computed from the neutron flux and spectrum with a model of how much displacement each collision causes. Codes convert a neutronics flux map into a displacement-per-atom rate throughout a component, giving a spatial picture of accumulated damage.
Multiscale modeling
- Atomic-scale simulations of displacement cascades and defect formation
- Mesoscale models of how defects cluster, migrate, and form voids
- Continuum models linking microstructure to bulk property changes
- Coupling to the neutron spectrum, since gas production scales with high-energy flux
Why the fusion spectrum matters
The hard 14 MeV fusion spectrum produces more helium and hydrogen per displacement than fission neutrons, and helium bubbles at grain boundaries drive embrittlement and swelling. Damage models must use the correct spectrum, not a fission analogue, to predict fusion-relevant degradation, a recognized gap that dedicated irradiation sources aim to fill.
Design use
Damage predictions set component replacement intervals, guide low-activation material selection, and feed structural lifetime analysis, since irradiated properties differ from as-built ones. They connect the neutron transport calculation to the engineering assessment of how long a component lasts.
For a D-T device, irradiation-damage modeling is part of the honest accounting of component life under the neutron flux, with its uncertainties clearly stated.