Corrosion of New Zirconium Claddings in 500 °C/10.3 MPa Steam: Effects of Alloying and Metallography

Abstract

With the aim of improving corrosion resistance of rod cladding for in-service and accident conditions, six new zirconium alloys (named N1–N6) have been designed. The contents of Sn and Nb were optimized for better behavior at high-temperature pressurized water, and Fe, Cr, V, Cu or Mo elements were added to the alloys to adjust the corrosion behavior. The current work focused on the rapid corrosion behavior in 500 °C/10.3 MPa steam for up to 1960 h, aiming to test the corrosion resistance at high temperature. The structure of matrix and properties of second-phase particles (SPPs) were characterized to find the main differences among these alloys. All the six alloys exhibited better corrosion resistance than N36, and N1 was shown to have the best performance. A careful analysis of the corrosion kinetics curves revealed that Cr was beneficial for severe condition. Elements Fe, Cr, V, Cu or Mo aggregated into SPPs with different concentrations and structures. This was demonstrated to be the main reason for different corrosion resistance. Due to good processing control, all alloys had a uniform structure and a uniform distribution of SPPs. As for N4, N6 and N36, the existing of large-size SPPs (450 nm) might be a contributing factor of the relatively poor corrosion resistance.