Effect of irradiation defects on the corrosion behaviors of steels exposed to lead bismuth eutectic in ADS: a first-principles study.

In accelerator driven systems (ADSs), steels will suffer not only from the irradiation damage produced by protons or neutrons, but also from the dissolution corrosion induced by the liquid lead-bismuth eutectic (LBE). In this work we investigate the interactions between LBE atoms (Pb, Bi) and the irradiation induced defects X (X is helium, vacancy or divacancy) in α-Fe based on first-principles calculations. It is found that LBE atoms repulse each other without irradiation defects, while they aggregate easily with the defects to form X-Pbn and X-Bin complexes. This indicates that the irradiation defects could promote the aggregation of LBE atoms in iron, especially Bi atoms. The total binding energies of the X-Pbn and X-Bin complexes increase with the number of Pb and Bi atoms, respectively. The origin of the total binding energies of the complexes is further discussed via the electronic structures and the distortion of the crystalline lattice. Finally, the concentration evolutions of the Vac-(Bi)n complexes and unbound vacancies with temperature are predicted by the mass action analysis. This work provides important information for the synergistic effect of irradiation and LBE corrosion on the steels in the ADSs, which can be used as basic parameters for further study.

Nanostructured fuzz growth on tungsten under low-energy and high-flux He irradiation.

We report the formation of wave-like structures and nanostructured fuzzes in the polycrystalline tungsten (W) irradiated with high-flux and low-energy helium (He) ions. From conductive atomic force microscope measurements, we have simultaneously obtained the surface topography and current emission images of the irradiated W materials. Our measurements show that He-enriched and nanostructured strips are formed in W crystal grains when they are exposed to low-energy and high-flux He ions at a temperature of 1400 K. The experimental measurements are confirmed by theoretical calculations, where He atoms in W crystal grains are found to cluster in a close-packed arrangement between {101} planes and form He-enriched strips. The formations of wave-like structures and nanostructured fuzzes on the W surface can be attributed to the surface sputtering and swelling of He-enriched strips, respectively.