Understanding the influence of final annealing on the behaviour of Zr-Nb-Sn Fe alloys during irradiation

Zirconium based alloys are typically employed as structural materials within the nuclear reactor core of light water reactors (LWRs) where they are subjected to high temperatures, pressures and neutron fluences. Throughout their service and storage lifetime, structural integrity retainment is essential if coolant/fuel interactions and fission gas release are to be avoided. A significant threat to the cladding's structural integrity is the introduction of irradiation induced defects which could lead to irradiation hardening as well as irradiation-induced dimensional changes. The metallurgical state of the cladding (i.e., deformed or recrystallised) has been shown to influence the irradiation-induced growth behaviour, whereby annealing appears to slow and reduce its severity. The key microstructural changes underpinning this phenomenon are not well understood and are required if a holistic understanding of this process is to be attained.