Displacements Per Atom (dpa)

A measure of neutron damage — how many times each atom is knocked from its lattice site.

dpa counts, on average, how many times each atom in a material has been displaced by neutron impacts. It is the standard metric for radiation damage and helps set component lifetimes, especially at the breeder's first wall.

Displacements-per-atom counts how many times, on average, each atom has been knocked from its lattice site by neutrons — the standard yardstick for radiation damage. It accumulates with fluence and, together with helium and hydrogen production, sets how long a component survives before it must be replaced, especially at the breeder's first wall.