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HELIUM AND HYDROGEN EFFECTS IN STRUCTURAL MATERIALS FOR NUCLEAR APPLICATIONS

Displacement cascades produce a variety of defects under reactor conditions, but of particular concern is the simultaneous production of helium (He) and hydrogen (H), which enhances the degradation of structural materials. The overall majority of performed studies on helium and hydrogen interactions with materials were based on ion beam irradiation, which served as a convenient tool for the simulation of neutrons exposure over a variety of temperature and dose regimes due to the ability to widely vary and control the irradiation parameters. Experimental investigations of the hydrogen-defect interaction performed by thermal desorption spectroscopy, and the parameters of this interaction obtained by numerical simulations based on diffusion-trapping codes are debated. In this review, we also summarize previous studies on grain boundaries and nanoprecipitate effects on hydrogen transport in metals, as well as the role of hydrogen in the corrosion and cracking of steels. We discuss here issues of helium bubbles formation and some of the evidence for the synergistic effects of hydrogen and helium in the presence of displacement damage, and their influence on irradiation hardening and swelling. Particular attention was devoted to the features of hydrogen interaction with noble-gas bubbles, which were considered on the basis of most recent published data.