Study on Ions Radiation Effect of New Zr Alloy by Positron Annihilation Technique

Domestic Zr-Sn-Nb type new zirconium alloy SZA-4 and SZA-6 are the main candidate materials for cladding of CAP1400 advanced pressurized water reactor. The study of the radiation effects could provide the scientific evidence for the improvement of preparation technics. Utilizing HI-13 tandem accelerator irradiation terminal at CIAE, the two new zirconium alloy cladding pipe samples were irradiated for 5 dpa by 100 MeV Fe ions at 300 ℃. Before and after irradiation, positron annihilation lifetime spectra were measured. The results show that both of the annihilation lifetime of two samples before irradiation are the lifetime of positron trapped in mono-vacancy of Zr metal, which implies that defects have not been eliminated by the final annealing with insufficient temperature and time. The positron annihilation lifetime of two post-irradiation samples decreases. Because of the redistribution of Fe induced by irradiation and the segregation of Fe atoms at the interfacial region between hcp α-Zr matrix and bcc β-Nb second phase particle, the positron is more easily trapped into the phase boundary with open space and annihilated with electrons of Fe atoms.