Out-of-pile corrosion properties of HANA alloys

Corrosion properties of HANA-3 (Zr-1.5Nb-0.4Sn-0.1Fe-0.1Cu), HANA-6 (Zr-1.1Nb-0.05Cu) were investigated in out-of-pile conditions. Microstructure and oxide characteristics were also examined to develop a further mechanistic understanding on the corrosion behavior. The corrosion resistance of HANA claddings was superior to Zircaloy-4. HANA-6 showed a better corrosion resistance than HANA-3 and their corrosion resistance decreased with increase of the final annealing temperature. β-Nb with bcc structure and Zr(Nb,Fe)2 with hcp structure were observed in HANA-3 while β-Nb with bcc structure and (Zr,Nb)2Fe with fcc structure in HANA-6, β-Nb was a major precipitate in both alloys and its stability was higher in HANA-6. The particle size increased with increase of the final annealing temperature. Synchrotron radiation microdiffraction experiment was performed on the oxide. The tetragonal phase fraction of HANA-6 maintained its higher value to a further distance from the interface than those of HANA-3 and Zircaloy-4. As one of the reasons why HANA-6 showed the best corrosion resistance, it was though that the fine distribution of precipitates promoted the stability of tetragonal phase in the oxide and the protectiveness against oxidation, thereby increasing the corrosion resistance. (author)