Nuclear energy is forecast by the European Commission to make a significant contribution to achieving a low-carbon, affordable energy, enhancing energy security during the development of renewables. However, stress corrosion cracking (SCC) is one of the biggest obstacles, as it induces unexpected failure to nuclear power plant components, threatening operational safety. Mitigating SCC requires a thorough understanding of its mechanisms, of which the current understanding is limited. In recent years, the applicant researcher and his colleagues have found that diffusible hydrogen plays a critical role in the evolution of SCC, which is beyond the existing understanding. Therefore, this project aims to uncover new SCC mechanisms in Ni-based alloys (materials used in nuclear power plants) from the perspective of the role of diffusible hydrogen, based on the good foundation of research by the applicant. The multi-scale experimental approach will focus on in-situ materials characterisation of Ni-based alloys during mechanical testing with in-situ hydrogen charging. This project employs experiments at different length-scales: a) crack initiation at the macroscale; b) strain distribution in different microstructures; and c) mechanical testing of single microstructures at the microscale. This research will make use of state-of-the-art equipment from interdisciplinary domains including materials engineering, electrochemistry, electron microscopy, mechanical engineering, and corrosion fields. The proposal emphasises the transfer of knowledge of advanced techniques between the host and researcher, while employing various training processes (including transferable skills) for both academia and non-academia sectors. Through effective and open dissemination and exploitation procedures, the results have the potential to provide practical suggestions and guidance to our end-users for producing alloys with higher SCC-resistance for a safer utilisation of nuclear energy.