An Overview of Recent Standard and Accelerated Molecular Dynamics Simulations of Helium Behavior in Tungsten

Anomalous shape effect of nanosized helium bubble on the elastic field in irradiated tungsten

Bubble pressure and elastic response in helium-irradiated tungsten are systematically investigated in this study. An anomalous shape effect is found that the radial normal stress and mean stress distributions around a nanosized void or bubble are far from the spherical symmetry, which is ascribed to polyhedral geometry characteristic of the nanosized bubble and physical mechanism transition from crystal surfaces dominated to the surface ledges and triple junctions dominated. Molecular simulation shows that Young–Laplace equation is not suitable for directly predicting equilibrium pressure for nanosized bubble in crystals. Consequently, a new criterion of average radial normal stress of spherical shell is proposed to polish the concept of equilibrium pressure of helium bubbles. Moreover, the dependences of bubble size, temperature and helium/vacancy ratio (He/Vac ratio) on the bubble pressure are all documented, which may provide an insight into the understanding of mechanical properties of helium-irradiated tungsten.

Special Issue: Radiation Damage in Materials-Helium Effects

Despite its scarcity in terrestrial life, helium effects on microstructure evolution and thermo-mechanical properties can have a significant impact on the operation and lifetime of applications, including: advanced structural steels in fast fission reactors, plasma facing and structural materials in fusion devices, spallation neutron target designs, energetic alpha emissions in actinides, helium precipitation in tritium-containing materials, and nuclear waste materials. The small size of a helium atom combined with its near insolubility in almost every solid makes the helium–solid interaction extremely complex over multiple length and time scales. This Special Issue, “Radiation Damage in Materials—Helium Effects”, contains review articles and full-length papers on new irradiation material research activities and novel material ideas using experimental and/or modeling approaches. These studies elucidate the interactions of helium with various extreme environments and tailored nanostructures, as well as their impact on microstructural evolution and material properties.