Modelling of deuterium retention and outgassing in self-damaged tungsten under low-energy atomic D flux irradiation: The effects of surface processes

摘要

Deuterium (D) outgassing and retention in self-damaged tungsten (W) during low-energy D atom irradiation are systematically studied using an upgraded version of the Hydrogen Isotope Inventory Processes Code (HIIPC) with the implementation of a surface module. The surface module due to the existence of chemisorption site is mainly characterized by the surface-energy barriers of D adsorption and absorption. The simulated total D amount is in good agreement with the experimental measurement. The impact of surface dynamics on the surface retention and total bulk retention is investigated. The simulation shows that total bulk retention first increases and then decreases with the increment of material temperature (T) due to surface effects. With the increment of surface energy barriers, the saturation of surface retention is observed. With low energy barrier, surface process shows a dominant role in bulk D retention. The effect of surface barriers on D outgassing is also studied. The results suggest that variations of surface energy barriers have a significant influence on D outgassing, which is linked to fuel recycling. Simulation reveals that fuel recycling greatly depends on T and irradiation flux before surface saturation, and total bulk retention shows a remarkable dependence on the permeation barrier. Saturation of total bulk retention is observed with low permeation barrier, whereas high permeation barrier could decrease the uptake of D due to the buildup of strong inhibition on surface, thus remarkably reduce total bulk retention. (C) 2020 Elsevier B.V. All rights reserved.