Studies regarding corrosion mechanisms in zirconium alloys

M. Preuss, P. Frankel, S. Lozano-Perez, D. Hudson, E. Polatidis, N. Ni, J. Wei, C. English, S. Storer, K. B. Chong, M. Fitzpatrick, P. Wang, J. Smith, C. Grovenor, G. Smith, J. Sykes, B. Cottis, S. Lyon, L. Hallstadius, R. J. ComstockA. Ambard, M. Blat-Yrieix

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

29 Citations (Scopus)

Abstract

Understanding the key corrosion mechanisms in a light water reactor primary water environment is critical to developing and exploiting improved zirconium alloy fuel cladding. In this paper, we report recent research highlights from a new collaborative research programme involving 3 U.K. universities and 5 partners from the nuclear industry. A major part of our strategy is to use the most advanced analytical tools to characterise the oxide and metal/oxide interface microstructure, residual stresses, as well as the transport properties of the oxide. These techniques include three-dimensional atom probe (3DAP), advanced transmission electron microscopy (TEM), synchrotron X-ray diffraction, Raman spectroscopy, and in situ electro-impedance spectroscopy. Synchrotron X-ray studies have enabled the characterisation of stresses, tetragonal phase fraction, and texture in the oxide as well as the stresses in the metal substrate. It was found that in the thick oxide (here, Optimized-ZIRLO, a trademark of the Westinghouse Electric Company, tested at 415C in steam) a significant stress profile can be observed, which cannot be explained by metal substrate creep alone but that local delamination of the oxide layers due to crack formation must also play an important role. It was also found that the oxide stresses in the monoclinic and tetragonal phases grown on Zircaloy-4 (autoclave testing at 36°C) first relax during the pre-transition stage. Just before transition, the compressive stress in the monoclinic phase suddenly rises, which is interpreted as indirect evidence of significant tetragonal to monoclinic phase transformation taking place at this stage. TEM studies of pre- and post-transition oxides grown on ZIRLO, a trademark of the Westinghouse Electric Company, have used Fresnel contrast imaging to identify nano-sized pores along the columnar grain boundaries that form a network interconnected once the material goes through transition. The development of porosity during transition was further confirmed by in situ electrochemical impedance spectroscopy (EIS) studies. 3DAP analysis was used to identify a ZrO sub-oxide layer at the metal/oxide interface and to establish its three-dimensional morphology. It was possible to demonstrate that this sub-oxide structure develops with time and changes dramatically around transition. This observation was further confirmed by in situ EIS studies, which also suggest thinning of the sub-oxide/barrier layer around transition. Finally, 3DAP analysis was used to characterise segregation of alloying elements near the metal/oxide interface and to establish that the corroding metal near the interface (in this case ZIRLO) after 100 days at 360C displays a substantially different chemistry and microstructure compared to the base alloy with Fe segregating to the Zr/ZrO interface.

Original languageEnglish
Title of host publicationZirconium in the Nuclear Industry
Subtitle of host publication16th International Symposium
EditorsPierre Barbéris, Magnus Limbäck
PublisherASTM International
Pages649-681
Number of pages33
ISBN (Print)9780803175150
DOIs
Publication statusPublished - 1 Jan 2011
Externally publishedYes
Event16th International Symposium on Zirconium in the Nuclear Industry - Chengdu, Sinchuan Province, China
Duration: 9 May 201013 May 2010

Publication series

NameASTM Special Technical Publication
Volume1529 STP
ISSN (Print)0066-0558

Conference

Conference16th International Symposium on Zirconium in the Nuclear Industry
CountryChina
CityChengdu, Sinchuan Province
Period9/05/1013/05/10

Keywords

  • Corrosion kinetics transition
  • Corrosion mechanisms
  • Oxide porosity
  • Residual stress
  • Sub-oxide

ASJC Scopus subject areas

  • Materials Science(all)

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  • Cite this

    Preuss, M., Frankel, P., Lozano-Perez, S., Hudson, D., Polatidis, E., Ni, N., ... Blat-Yrieix, M. (2011). Studies regarding corrosion mechanisms in zirconium alloys. In P. Barbéris, & M. Limbäck (Eds.), Zirconium in the Nuclear Industry: 16th International Symposium (pp. 649-681). (ASTM Special Technical Publication; Vol. 1529 STP). ASTM International. https://doi.org/10.1520/JAI103246