Hydrogen trapping and dynamic distribution in iron voids: A molecular dynamics study

ZQ Li and YW Li and YL Mai and W Wu and Q Qi and SX Qiao and XC Li and HS Zhou, JOURNAL OF NUCLEAR MATERIALS, 617, 156112 (2025).

DOI: 10.1016/j.jnucmat.2025.156112

The supersaturated vacancies in the structural materials of nuclear fusion reactor blankets, induced by highenergy neutron irradiation, migrate and aggregate to form voids. Hydrogen (H) isotopes are captured and absorbed by these voids, forming gas bubbles within the voids, leading to H isotope retention and undesirable structural properties. However, most existing studies have primarily focused on small-sized vacancy clusters, with limited attention given to the behavior of H atoms in large-sized nanovoids. This study investigates the dynamic distribution of H in nanovoids of alpha-iron (Fe). The capture behavior of H atoms by vacancy clusters is calculated using dynamic annealing relaxation and molecular statics methods. Studies indicate that H primarily attaches to the quasi-octahedral interstitial sites at the void boundary in atomic form. Additionally, the number of H atoms absorbed by the vacancy clusters before saturation is linearly correlated with the cluster surface area, while the number of H molecules is linearly proportional to the cluster volume. As the amount of H increases, H molecules are generated in the voids, and the void surface gradually forms saturated H adsorption. After saturation, the H molecules subsequently dissociate into H atoms and diffuse out of the voids. H atoms permeating the Fe lattice displace vacancies and Fe atoms, causing the Fe atoms to collapse inward into the voids. Consequently, voids with a high H-to-vacancy ratio cannot remain stable. This study not only quantifies the capture efficiency and pressure evolution characteristics of nanovoid-H complexes but also provides a theoretical basis for the design of H-resistant alloys.

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