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Title: Corrosion and hydrogen pickup mechanisms of zirconium alloys
Author: Setiadinata, Sylvester Brian
ISNI:       0000 0004 6496 3631
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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Zirconium alloy cladding isolates the nuclear fuel rods from water coolant in a nuclear fission reactor, but in this harsh environment experience high temperature aqueous corrosion and hydrogen pickup (HPU). The segregation of minor elements such as iron, niobium and antimony greatly affects the corrosion and HPU of Zr alloys, but often this segregation occurs at a scale too small for most characterisation techniques to observe. Atom probe tomography (APT) enables the 3D analysis of elemental distributions on the atomic scale using time-of-flight spectroscopy. The corrosion and HPU of Zr-Nb alloys with 0.5-2.5 wt% Nb were examined using APT. The oxygen-saturated metal region at the oxide/metal (O/M) interface increases with instantaneous oxidation rate and deuterium segregation to oxide grain boundaries and pores that probably contain hydrogen have been observed. The ratio of hydrogen isotopes showed that where the D-containing signal was higher, deuterium segregation to grain boundaries was more likely. Fe around β-Nb particles and on metal grain boundaries is redistributed during oxidation. This redistribution results in Fe enrichment in the oxide which would correlate with the space charge compensation predicted to decrease HPU. During oxidation, Nb leaches out from the β-Nb precipitates to the oxide matrix. Preliminary analysis on Sb-containing samples has been carried out and weak Sb segregation to metal grain boundaries has been observed. Irradiation also causes redistribution of Fe and Nb, particularly Fe in the vicinity of oxide grain boundaries and Nb leaving the β-Nb particles under irradiation, resulting in the formation of small Nb clusters. The results of this study show that APT can observe changes of elemental distributions on the atomic scale which is vital to understanding how Zr alloys behaves during corrosion.
Supervisor: Grovenor, Chris ; Moody, Christopher ; Bagot, Paul Sponsor: Westinghouse Electric LLC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Atom-probe field ion microscopy ; Microscopy ; Corrosion