Microstructural Evolution of Zr1NbxSnyFe Alloys Irradiated in a PWR at High Fluence: Influence of Iron and Tin Available to Purchase

Based on the M5_Framatome alloy metallurgy, several Zr1NbxSnyFe alloys were developed to make structural components, with ultra-low tin addition and slightly increased iron content (Sn = 0, 0.3, and 0.5 wt.%; Fe = 1,000 and 2,000 wt. ppm). This paper details the microstructure of five different alloys, including M5_Framatome and Q12, and their microstructural evolution after neutron irradiation, in the same campaign, as fuel rods in a PWR up to high fluence. Previous studies have detailed microstructural changes of zirconium alloys under irradiation and have underlined the influence of these changes on oxidation behavior, mechanical properties, creep, and growth. The presence of tin and iron (by iron dissolution out of the precipitates) in the matrix is suspected to influence the irradiation-induced microstructural features such as <a>-loop alignments (corduroys) and size, <c>-component loop nucleation, and “needle like” β-Nb precipitate spatial distribution and size. Relevant microstructural observations are needed to decorrelate the tin's influence from that of the iron on the microstructural changes under irradiation in alloys containing niobium, tin, and iron. In this study, the comparison between M5_Framatome and the Zr1Nb0.1Fe alloy has determined the influence of iron on alloys without tin. The effect of iron at a fixed tin content was obtained by comparing Zr1Nb0.3Sn0.1Fe and Zr1Nb0.3Sn0.2Fe alloys. Finally, the comparison of Zr1Nb0.1Fe, Zr1Nb0.3Sn0.1Fe, and Q12 (Zr-1Nb0.5Sn0.1Fe) alloys addressed the effect of different tin contents with the same iron content. The microstructural features were studied on all five alloys for fast neutron fluences up to 13 × 10²⁵ n/m²(E > 1 MeV) with analytical transmission electron microscopy. Significant differences were brought out, particularly concerning the <a>-loop distribution, the Laves phase dissolution, and the <c>-component loop linear density and spatial distribution. All of these results prompt a reconsideration of the influence of iron and tin contents on microstructural evolution under irradiation of Zr1NbxSnyFe alloys.