Chemical and microstructural characterization of a 9 cycle Zircaloy-2 cladding using EPMA and FIB tomography

Research output: Contribution to journalArticle

Authors

  • Adrienn Baris
  • R. Restani
  • R. Grabherr
  • K. Ammon
  • M Limback
  • Sousan Abolhassani

Colleges, School and Institutes

External organisations

  • Paul Scherrer Inst
  • Kernkraftwerk Leibstadt (KKL), CH-5325 Leibstadt, Switzerland
  • Westinghouse Electric Sweden AB, SE-721 63 Västerås, Sweden

Abstract

A high burn-up Zircaloy-2 cladding is characterised in order to correlate its microstructure and composition to the change of oxidation and hydrogen uptake behaviour during long term service in the reactor. After 9 cycle of service, the chemical analysis of the cladding segment shows that most secondary phase particles (SPPs) have dissolved into the matrix. Fe and Ni are distributed homogenously in the metal matrix. Cr-containing clusters, remnants of the original Zr(Fe, Cr)2 type precipitates, are still present. Hydrides are observed abundantly in the metal side close to the metal-oxide interface. These hydrides have lower Fe and Ni concentration than that in the metal matrix.

The three-dimensional (3D) reconstruction of the oxide and the metal-oxide interface obtained by Focused Ion Beam (FIB) tomography shows how the oxide microstructure has evolved with the number of cycles. The composition and microstructural changes in the oxide and the metal can be correlated to the oxidation kinetics and the H-uptake. It is observed that there is an increase in the oxidation kinetics and in the H-uptake between the third and the fifth cycles, as well as during the last two cycles. At the same time the volume fraction of cracks in the oxide significantly increased. Many fine cracks and pores exist in the oxide formed in the last cycle. Furthermore, the EPMA results confirm that this oxide formed at the last cycle reflects the composition of the metal at the metal-oxide interface after the long residence time in the reactor.

Details

Original languageEnglish
Pages (from-to)144-160
Number of pages15
JournalJournal of Nuclear Materials
Volume504
Early online date12 Feb 2018
Publication statusPublished - Jun 2018

Keywords

  • Zircaloy-2, Hydrogen uptake, Corrosion, Hydride oxidation, Crack formation, Chemical changes, FIB tomography, Electron probe microanalysis, High burnup