Helium pre-irradiation effect on deuterium permeation in stainless steel

Ab initio study of helium and hydrogen interactions in $α$-Fe

“…In this sense, substantial research efforts have been devoted to the experimental and theoretical study of the interaction of He-defects, [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] or H-defects 23,24 in iron-based alloys and different ferritic steels which are important structural materials for fusion reactors. A few experimental investigations evidenced that helium could act as trap for hydrogen, hence reducing diffusivity and increasing embrittlement in iron alloys, [25][26][27] although experiments could not clarify whether the origin of these synergetic effects was due to the interaction between H and He itself or due to the trapping at damage produced during irradiation. A detailed study of interactions between hydrogen, helium and displacement damage is thus necessary to understand and predict their simultaneous evolution.…”

“…These ab initio calculations show that, although the direct interaction between H and He is weak, they both bind strongly to vacancies, which could be at the origin of the experimentally observed synergic effects. [25][26][27] To investigate this point, we simulated the evolution of H and He in α-Fe under irradiation, in conditions similar to those expected in fusion environment. Nuclear transmutation continously generates H and He that evolve in the presence of a large amount of defects created by atomic displacements due to collisions between energetic neutrons and lattice atoms.…”

“…the apparent strong positive interaction reported in the litera- ture is due to the much larger V-H and V-He attraction that conceals the repulsive interaction between He and H. They both tend to be trapped by voids, and this, rather than the He-H interaction, could explain the reduction of hydrogen permeation, and the larger cavity sizes in ferritic alloys simultaneously irradiated with H and He. [25][26][27] This has important implications for modeling damage evolution in materials for fusion, that until now have mainly considered the role of isolated He or H aggregates, and not their coexistence. To understand in which conditions synergetic effects could be expected, further work will be needed on the energetics of larger clusters or bubbles containing both He and H in steels, and on the effect of solutes and grain boundaries where bubbles tend to nucleate.…”

Binary effect of He and H on the intra- and inter-granular embrittlement in Fe

“…Some early studies [7] suggested that irradiation-induced He acted as traps for hydrogen to reduce the diffusivity and permeability. Such a synergistic effect of H and He embrittlement in stainless steels was confirmed by Louthan et al [8].…”