The micromechanics of fracture of hydrides in Zr-2.5Nb CANDU pressure tubes

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CANDU reactors have been contributing significantly in providing clean energy to Ontario and Canada. More than 50% of electricity in Ontario is generated by CANDU reactors. Most of CANDU reactors are built in 1970s and 1980s and are aging. In order to continue to operate these reactors, engineers are required to demonstrate to regulatory authorities that they are safe. One of the main components that determine the lifetime of CANDU reactors is the zirconium-alloy pressure tubes that contain fuel bundles and separate the hot water coolant from the cold moderator. During operation, hydrogen from hot water diffuses towards the flaws induced in the tube and with time, forms a brittle phase called zirconium hydrides. To ensure the integrity of the tubes and safety of the reactors, it is important to show that a crack will not nucleate in these hydrides. This project focuses on using advanced numerical techniques and diffraction-based experiments to understand how the hydrides that form in the vicinity of flaws will crack and how such cracks lead to failure. Finite element models will be developed and used at Western University, and with the help of graduate students, experiments will be done at Canadian Nuclear Laboratories to study formation of cracks at nano and meso-scales. This will help understand the underlying mechanisms that control fracture of hydrides. The results from this research are expected to help improve the accuracy of the models used in nuclear industry and improve the lifetime of the pressure tubes used in the core of CANDU reactors.