Zr alloys are used as fuel cladding in nuclear reactors, and as such play a crucial role in the safe and economic operation of nuclear power plants.
The corrosion resistance of Zr alloys is largely governed by the distribution of small levels of Sn, Nb, Fe, Cr and Ni alloying additions. With the exception of Sn, these alloying additions exhibit negligible solubility in α-Zr, and precipitate out as second phase particles (SPPs).
During reactor operation, the distribution of the alloying additions changes dramatically: Fe, Cr and Ni are known to leach out of SPPs, while Nb remains behind; Sn-Zr intermetallics, and metastable Fe-Zr phases have been reported to form at high radiation doses. Recent HRTEM and APT results reveal that Fe and Cr segregate at grain boundaries and dislocation loops following their re-solution from SPPs. The picture is further complicated by the inwards growth of the Zr surface oxide, which also affects the distribution of alloying.
My work focuses on understanding the mechanisms behind the microstructural evolution of Zr alloys under irradiation, and its consequences to Zr corrosion kinetics. Through a synergistic combination of computational (DFT) and experimental methods, I will show that the dissolution of SPPs is not solely due to the amorphisation caused by radiation damage, but also to the increased apparent solubility of Fe and Cr in the defective α-Zr lattice. I will further clarify the effect of irradiation on the solubility, migration and clustering of Fe, Cr and Sn in irradiated α-Zr. The effects on Zr oxidation and hydriding will also be discussed.