Effect of local microstructure on cracking of materials for next generation reactors

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The global drive for low-carbon energy sources, combined with a growing worldwide energy consumption, is a challenge to which nuclear energy, in combination with renewables such as wind and solar, provides a realistic, sustainable solution. Canada aims to position itself at the forefront of advanced nuclear reactor designs, with substantial investment in the development of small nuclear modular reactors (SMRs). However, SMRs are still a decade from implementation, and a range of urgent questions must first be answered. Many of the limitations to SMR delivery arise from materials issues: how they will respond, age and fail under the conditions they will experience. This proposal will address key basic research questions into material performance, which will be required to enable safe SMR operation. Specifically, it will investigate the damage processes associated with irradiation in SMR-proposed materials, and the subsequent effect on fracture and especially fatigue of SMR-relevant metals. Real materials are made up of grains or crystallites - each individual crystallite is typically highly anisotropic in its response to stress. In many practical applications we cannot ignore this local heterogeneity and must understand how irreversible microstructural changes occur and propagate at this local scale. Diffraction techniques are able to reveal many of the microstructural changes which will have an influence, including inter-granular strains induced by elastic and plastic crystallographic anisotropy, intra-granular strains generated by crystallographic defects (dislocations), as well as deformation-induced phase transformations or crystallographic reorientation. The aim of this proposal is to investigate the extent to which monitoring these effects can provide insights into understanding the mechanisms of fatigue and the processes of initial crack propagation. In addition, we will investigate the way that irradiation influences microstructural damage accumulation. While temperature and stress provide two key variables that influence material properties, they are not the only ones. Materials behave differently in an energetic radiation environment (e.g., in a nuclear reactor or in space) than in conventional applications due to the flux of high energy particles which introduce point defects and dislocations, and alter the microchemistry of the material. This proposal will train HQP directly in advanced techniques (both experimental and modeling) and in a research area which is of current and ongoing interest to a wide range of industry, not just nuclear power. Building on existing successes, it will strive to deliver a diverse group of HQP with skills and knowledge that will be valuable to Canadian industry.