Project title: Multiscale Modelling of Delayed Hydride Cracking
Delayed hydride cracking (DHC) is a hydrogen embrittlement mechanism that affects zirconium alloy cladding of nuclear fuel pins. In the reactor environment, an aqueous corrosion process allows hydrogen to enter the bulk zirconium matrix. Through diffusion under the influence of gradients of stress, chemical potential and temperature, the hydrogen atoms form elevated concentration profiles ahead of stress-raisers such as loaded cracks and notches. Once the solvus is exceeded, zirconium hydride platelets precipitate in the vicinity of the flaw tip. The hydride phases are significantly more brittle than the parent metal and hence have a detrimental effect on the mechanical properties of the component. As such, these hydrides are more prone to fracture, which enables the flaw to propagate. The interplay and repetition of diffusion, precipitation and fracture can ultimately lead to structural failure of the component. The overarching aim of DHC research is to quantify this complexity and develop a rigorous failure criterion. This investigation is centred around the development of a theoretical and computational framework to study various DHC subprocesses to elucidate the history of experimental findings. Using the mathematics of continuum mechanics and linear irreversible thermodynamics, it is possible to gain some insight into the effects of notch geometry, anisotropy, heterogeneity and microstructure on hydrogen profiles and hydride morphologies.