Microstructural evolution of Q12^TM alloy irradiated in PWRs and comparison with other Zr base alloys - 2016-0061

Based on the M5^R* alloy metallurgy, the Q12^TM alloy (Zr-1Nb-0.5Sn-0.1Fe) was developed by AREVA NP for structural components, with ultra-low tin addition and slightly increased iron content. The behavior of this alloy was tested under irradiation in a pressurized water reactor (PWR) and has shown improvement in irradiation creep strength and similar free growth compared with M5. This paper provides results on dimensional stability and details the microstructural evolution of the Q12 alloy under neutron irradiation in PWRs. The Q12 microstructural evolution under irradiation was studied for fast neutron fluences up to 13 X 10²⁵ n/m² (E>1 MeV) with analytical transmission electron microscopy observations. We focused on radiation-enhanced needle-like particles, Laves phases, and the linear density of -component loops. These results are compared with other quaternary zirconium-niobium-tin-iron alloys and with M5. All these results allow a general discussion about microstructural evolution and behavior under irradiation of quaternary-type alloys compared to M5 alloy. This study, in agreement with previous works on Zr-1Nb and quaternary alloys, seems to show that increasing the iron content with the presence of niobium and tin will decrease the -component loop linear density and delay the growth breakaway. (authors)