Characterization of surface roughness and wettability of oxidized Zircaloy-4

초록

In nuclear power systems, fuel cladding serves as the primary barrier against fission product release, and its surface condition after high temperature oxidation can influence subsequent thermal-hydraulic behavior. In this study, flat Zircaloy-4 specimens were oxidized in 80% relative humidity air at 600 °C, 700 °C, and 800 °C to systematically examine the coupled evolution of oxide layer thickness, surface roughness (Sa), and wettability in a relatively thick oxide regime. Over the investigated conditions, oxide layer thickness increased steadily over the measured time periods, but the current dataset was not sufficient to establish a definitive oxidation regime classification. On the other hand, Sa exhibited oxide layer thickness dependent behavior. In the thinner oxide regime (<60 μm), Sa increased gradually, whereas in the thicker-oxide regime more pronounced roughness amplification occurred within specific thickness intervals, likely associated with growth-induced stresses and volumetric expansion. Concurrently, the contact angle decreased monotonically with increasing Sa and approached complete wetting or absorptive wetting behavior once Sa exceeded ∼3 μm, largely independent of oxidation temperature. These results indicate that substantial surface modifications can develop in relatively thick oxide layers formed under accelerated humidified air oxidation. Such changes may provide a useful basis for future comparative studies on boiling heat transfer and rewetting behavior on oxidized Zircaloy surfaces. © 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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