Multiscale Modelling: the role of helium in iron

The mechanisms and processes of bubble nucleation and growth are still not completely solved and research in this field is ongoing. This is an important issue for materials used in fission and fusion reactors. In such environments, one of the main gaseous by-products is helium, whose presence and further production is known to decrease ductility, fatigue life and weldability, induce creep and stress rupture properties of materials, as well as promote swelling. These effects lead to the drastic modification of the material's mechanical properties. In the past, experiments have been used to offer clues into the structure of the materials; now, modelling offers the possibility to understand the structure of the material and from this information, to elucidate a fundamental understanding of material properties. This review discusses the modelling paradigms used to investigate and obtain an understanding of the mechanisms at play in helium bubble nucleation and growth in ferritic steels.