The role of hydrogen in zirconium alloy corrosion

JOURNAL OF NUCLEAR MATERIALS

卷:496

Article

Ensor, B.^1,2  Lucente, A. M.²  Frederick, M. J.²  Sutliff, J.²  Motta, A. T.¹ 

[1] Penn State Univ, Dept Mech & Nucl Engn, University Pk, PA 16802 USA

[2] Naval Nucl Lab, Knolls Atom Power Lab, Schenectady, NY 12309 USA

关键词: Zirconium alloy;    Zircaloy-4;    Corrosion;    Hydrogen Terminal solid solubility;    Autoclave;   

DOI  :  10.1016/j.jnucmat.2017.08.046

来源: Elsevier

【 摘 要 】

Hydrogen enters zirconium metal as a result of the corrosion process and forms hydrides when present in quantities above the solubility limit at a given temperature. Zircaloy-4 coupons of different thicknesses (0.4 mm-2.3 mm) but identical chemistry and processing were corroded in autoclave at 360 degrees C for various times up to 2800 days. Coupons were periodically removed and weighed to determine weight gain, which allows follow of the corrosion kinetics. Coupon thickness differences resulted in different volumetric concentrations of hydrogen, as quantified using hot vacuum extraction. The thinnest coupons, having the highest concentration of hydrogen, demonstrated acceleration in their corrosion kinetics and shorter transition times when compared to thicker coupons. Furthermore, it was seen that the post-transition corrosion rate was increased with increasing hydrogen concentration. Corrosion rates increased only after the terminal solid solubility (TSS) was exceeded for hydrogen in Zircaloy-4 at 360 degrees C. Therefore, it is hypothesized that the corrosion acceleration is caused by the formation of hydrides. Scanning electron microscope (SEM) examinations of fractured oxide layers demonstrate the oxide morphology changed with hydrogen content, with more equiaxed oxide grains in the high hydrogen samples than in those with lower hydrogen content. Additionally, locations of advanced oxide growth were correlated with locations of hydrides in the metal. A hypothesis is proposed to explain the accelerated corrosion due to the presence of the hydrides, namely that the metal, locally, is less able to accommodate oxide growth stresses and this leads to earlier loss of oxide protectiveness in the form of more frequent oxide kinetic transitions. (C) 2017 Elsevier B.V. All rights reserved.

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