Displacements Per Atom (dpa)

dpa measures neutron damage to materials — how many times each atom is knocked from its lattice site. Kronos's low-neutron wall stays within its qualification.

What

Average times each atom is displaced by neutrons

Measures

Cumulative material radiation damage

Kronos first wall

30 dpa over 30 full-power-years

Qualification

≤ 36 dpa (within margin)

Displacements per atom (dpa) is the standard measure of neutron radiation damage to a material: it counts, on average, how many times each atom is knocked out of its position in the crystal lattice over the component's life. Accumulated dpa embrittles and swells materials, and it is the usual limit on how long a fusion first wall or structure can last before replacement.

Because Kronos MetroVolt is low-neutron, its first wall accumulates only about 30 dpa over 30 full-power-years — within its ≤ 36 dpa qualification, so the wall lasts the plant's full design life (analysis S81). A D–T plant's much higher wall loading forces repeated component changeouts; keeping dpa under the qualification is precisely what lets Kronos run without a breeding blanket and with high availability.