document: Zirconium alloys are used as cladding to encapsulate fuel pellets in pressurised and boiling water nuclear reactors. Research into oxidation of these alloys has been significant since the introduction of the material. However, the microstructure and electro-chemical processes during oxidation are complex and many questions still remain unanswered. One such issue is the formation of lateral cracks near the metal-oxide interface. Small cracks have been seen to form continuously during oxidation, with large scale networks of lateral cracks forming cyclically every ∼2μm of oxide growth. These networks of cracks can be correlated with acceleration in the corrosion kinetics [1–7]. These lateral cracks might enable the link up of nano pores along grain boundaries perpendicular to the metal/oxide interface as reported in [8,9]. Experiments using Synchrotron X-Ray Diffraction (S-XRD) by both Polatidis et al. and Petigny et al., have separately shown that oxides formed on Zircaloy-4 are composed of monoclinic and stabilised tetragonal phases, with an ∼7% reduction in the tetragonal phase fraction from 1 to 3μm oxide growth [4,10]. One theory is that the lateral cracks may destabilise the tetragonal phase close to the metal-oxide interface. The phase transformation has an ∼6% expansion associated with it, which could lead to fracture perpendicular to the metal-oxide interface, thereby generating fast ingress routes for oxygen containing species [11,12].
extractive_keyphrases: alloys cladding corrosion kinetics fracture fuel pellets grain ingress link up of nano pores monoclinic and stabilised tetragonal phases oxidation oxides oxygen containing species phase transformation tetragonal phase water nuclear reactors
abstractive_keyphrases: ∼7% reduction in the tetragonal phase metal-oxide interface metal/oxide interface microstructure and electro-chemical processes oxidation of these alloys s-xrd synchrotron x-ray diffraction zircaloy-4 zirconium alloys