Activation and Material Damage Modeling

Turning neutron flux into activation inventories and displacement damage for the breeder blanket and burner structure over their lives.

From flux to consequences

Monte Carlo gives the neutron flux; activation and damage modeling turns that flux into the quantities that govern material life. On L0, flux spectra from the neutronics runs are folded with reaction and damage cross-sections to compute nuclide inventories, decay heat, and displacements per atom (dpa) throughout both machines.

Activation inventories

Neutron capture and threshold reactions transmute structural nuclides into radioactive products. An activation solve integrates the coupled decay and transmutation equations over an assumed operating history to produce time-dependent inventories, activity, and decay heat. For the breeder, this drives maintenance planning; for the burner, it characterizes the modest activation from the 5.44 percent neutron fraction.

# Bateman-type transmutation-decay system:
# dN_i/dt = sum_j (lambda_ji + phi * sigma_ji) N_j
#         - (lambda_i + phi * sigma_i) N_i
# N_i : nuclide density  phi : neutron flux (from Monte Carlo)
# lambda : decay constants  sigma : transmutation cross-sections

Displacement damage

The 14 MeV neutrons of the breeder are especially damaging: each one can displace many atoms, accumulating dpa in the first wall, blanket, and the CrMoNbV vessel. The damage model folds the flux spectrum with a displacement cross-section to estimate dpa rate, which bounds component life and feeds the structural-health-monitoring assumptions.

• Time-dependent nuclide inventories and decay heat
• Displacements per atom in first wall and vessel
• Gas production, helium and hydrogen, in structure
• Waste classification and hands-on maintenance windows

The two machines pose different damage problems. The breeder's high 14 MeV fluence makes dpa and gas production in the blanket and center column the dominant concern. The burner's lower neutron load shifts emphasis to protecting the precise direct-conversion train and magnets from cumulative activation and localized damage.

These results close the neutronics chain that began with transport. Flux feeds heating into thermomechanics and feeds activation and damage into life and maintenance models, so a single Monte Carlo campaign propagates into structural design, waste planning, and the twin's assumptions about how the machine ages.