Hydrogen pickup mechanism in zirconium alloys

Adrien Couet, Arthur T. Motta, Antoine Ambard, Robert J. Comstock

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

7 Scopus citations


Because hydrogen ingress into zirconium cladding can cause embrittlement and limit cladding lifetime, hydrogen pickup during corrosion is a critical life-limiting degradation mechanism for nuclear fuel. However, mechanistic knowledge of the oxidation and hydrogen pickup mechanisms is still lacking. In an effort to develop such knowledge, we conducted a comprehensive study that included detailed experiments combined with oxidation modeling. We review this set of results conducted on zirconium alloys herein and articulate them into a unified corrosion theoretical framework. First, the hydrogen pickup fraction (Fh) was accurately measured for a specific set of alloys specially designed to determine the effects of alloying elements, microstructure, and corrosion kinetics on fH. We observed that fH was not constant and increased until the kinetic transition and decreased at the transition. fH depended on the alloy and was lower for niobium-containing alloys. These results led us to hypothesize that hydrogen pickup during corrosion results from the need to balance the charge during the corrosion reaction such that fH decreases when the rate of electron transport through the protective oxide increases. To assess this hypothesis, two experiments were performed: (1) micro-X-ray absorption near-edge spectroscopy (u, -XANES) to investigate the evolution of the oxidation state of alloying elements when incorporated in the growing oxide and (2) in situ electrochemical impedance spectroscopy (EIS) to measure oxide resistivity as a function of exposure time on different alloys. With the use of these results, we developed an analytical zirconium alloy corrosion model based on the coupling of oxygen vacancies and electron currents. Both modeling and EIS results show that as the oxide electric conductivity decreases the fH increases. These new results support the general hypothesis of charge balance. The model quantitatively and qualitatively predicts the differences observed in oxidation kinetics and hydrogen pickup fraction between different alloys.

Original languageEnglish (US)
Title of host publicationZirconium in the Nuclear Industry
Subtitle of host publication18th International Symposium
EditorsRobert J. Comstock, Arthur T. Motta
PublisherASTM International
Number of pages38
ISBN (Electronic)9780803176416
StatePublished - 2018
Event18th International Symposium on Zirconium in the Nuclear Industry - Hilton Head, United States
Duration: May 15 2016May 19 2016

Publication series

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


Other18th International Symposium on Zirconium in the Nuclear Industry
Country/TerritoryUnited States
CityHilton Head

All Science Journal Classification (ASJC) codes

  • General Materials Science


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