On the consequences of neutron induced damage for volumetric fuel retention in plasma facing materials

Abstract

In burning deuterium–tritium (D–T) fusion experiments, such as ITER, plasma-facing components (PFCs) will for the first time be subject to intense 14 MeV neutron bombardment, which cause displacement damage uniformly distributed throughout PFCs. A literature review indicates these displacements typically lead to hydrogenic trap sites ∼1% solid concentration in refractory metals tungsten (W) and molybdenum, a level reached within ∼1000 ITER shots. Simple analytic and numerical models indicate this is a concern for reaching the T fuel retention limit in ITER of 350 g, mostly due to the efficient permeation of D/T into the W allowing access to the volumetric trap sites. The sensitivity of the retention results to the incident plasma parameters, PFC temperature, surface flux balance model and plasma duty-cycle is explored. Within the range of experimental and model uncertainties a limit for an all-W ITER divertor is found ∼100–1000s of shots. It is shown that ambient temperatures in excess of ∼1000 K could control T inventory in a W-clad reactor despite the presence of large trap concentrations, an option which is not possible for ITER with water-cooled walls.