Redistribution of alloying elements in Zircaloy-2 after in-reactor exposure

Highlights: • We have conducted an atom probe tomography study on a Zircaloy-2 fuel cladding material that has been subjected to 9 annual cycles of in-reactor exposure. • The results show that large numbers of nanosized Fe and Cr rich particles have precipitated along parallel planes in the matrix. • Fe and Sn are seen to segregate to ring-shaped features that are interpreted to be c-loops. • A sub-oxide of approximate composition ZrO is found at the metal–oxide interface. - Abstract: An atom probe tomography study of the microstructure of a Zircaloy-2 material subjected to 9 annual cycles of BWR exposure has been conducted. Upon dissolution of secondary phase particles, Fe and Cr are seen to reprecipitate in large numbers of clusters and particles of 1–5 nm sizes throughout the Zr metal matrix. Fe and Sn were observed to segregate to ring-shaped features in the metal that are interpreted to be -component vacancy loops. This implies that these two elements play a major role in the irradiation growth phenomenon in Zr alloys, which is believed to be caused by the formation of -loops. Similarly to autoclave-corroded Zr alloys, the formation of a sub-oxide layer of approximate composition ZrO was observed. On the other hand, no oxygen saturated metal phase was detected underneath the oxide scale