Investigating the effect of zirconium oxide microstructure on corrosion performance: a comparison between neutron, proton, and nonirradiated oxides

Alistair Garner, Felicity Baxter, Philipp Frankel, Matthew Topping, Allan Harte, Thomas Slater, Pia Tejland, Javier E. Romero, Edward C. Darby, Aidan Cole-Baker, Mhairi Gass, Michael Preuss

Research output: Chapter in Book/Report/Conference proceedingConference PaperOther

7 Citations (Scopus)

Abstract

Scanning precession electron diffraction in the transmission electron microscope has been used to simultaneously map the phase, orientation, and grain morphology of oxides formed on Zircaloy-2 after three and six cycles in a boiling water reactor in unprecedented detail. For comparison, a region of a preoxidized autoclave-formed oxide was also proton-irradiated at the Dalton Cumbrian Facility. The proton irradiation was observed to cause additional stabilization of the tetragonal phase that was attributed to the stabilizing effect of irradiation-induced defects in the oxide. In the reactor-formed oxides, no extra stabilization of the tetragonal grains was observed under neutron irradiation, as indicated by the similar tetragonal phase fraction and transformation twin-boundary distributions between the nonirradiated and reactor-formed oxides. It is suggested that the damage rate is too low in the newly formed oxide to cause significant stabilization of the tetragonal phase. This technique also reveals that the oxide formed under reactor conditions has a more heterogeneous microstructure, and the growth of well-oriented columnar monoclinic grains is significantly reduced compared with a nonirradiated oxide. High-angle annular dark-field scanning transmission electron microscopy also revealed the development of extensive networks of intergranular porosity and eventually grain decohesion in the reactor-formed oxides. These results suggest that the tetragonal-monoclinic transformation is not responsible for the accelerated corrosion exhibited under reactor conditions. It is proposed that the usual out-of-reactor oxide growth and nucleation processes are significantly modified under reactor conditions, resulting in a more heterogeneous and randomly oriented oxide microstructure with reduced columnar grain growth. It is suggested that this disordered oxide microstructure allows for the formation of extensive intergranular porosity that could lead to accelerated in-reactor corrosion.

Original languageEnglish
Title of host publicationZirconium in the Nuclear Industry
Subtitle of host publication18th International Symposium
EditorsRobert J. Comstock, Arthur T. Motta
PublisherASTM International
Pages491-523
Number of pages33
ISBN (Electronic)9780803176416
DOIs
Publication statusPublished - 2018
Externally publishedYes
EventInternational Symposium on Zirconium in the Nuclear Industry 2016 - Hilton Head, United States of America
Duration: 15 May 201619 May 2016
Conference number: 18th
https://www.astm.org/DIGITAL_LIBRARY/STP/SOURCE_PAGES/STP1597.htm

Publication series

NameASTM Special Technical Publication
VolumeSTP 1597
ISSN (Print)0066-0558

Conference

ConferenceInternational Symposium on Zirconium in the Nuclear Industry 2016
CountryUnited States of America
CityHilton Head
Period15/05/1619/05/16
Internet address

Keywords

  • BWR
  • HAADF STEM
  • Oxide microstructure
  • Porosity
  • Proton irradiation
  • TEM
  • Tetragonal phase
  • Texture
  • Zircaloy-2

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