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<p>The surface roughness of nuclear-grade structural material shows a significant influence on its corrosion behavior under high-temperature and high-pressure (HTHP) water exposure condition in the pressurized water reactor (PWR) system. In this investigation, the surface roughness induced oxide film evolution on 304 stainless steel (SS) in simulated HTHP water has been investigated by in-situ cyclic electrochemical impedance spectroscopy (EIS) and ex-situ characterizations. The results indicate that cyclic-EIS data interpretation can well understand the surface roughness induced oxide film growth and its structures evolution on 304 SS electrodes under HTHP water condition. Besides, the 240#-sample with a much higher surface roughness has the thickest oxide film with the largest and increasing |<i>Z</i>|<sub>0.01&#xa0;Hz</sub> value. In contrast, the polished-sample with a much lower surface roughness has the thinnest oxide film with the lowest but stabilized |<i>Z</i>|<sub>0.01&#xa0;Hz</sub> value. A higher surface roughness facilitates the formation of a thicker oxide film but with the loose outer layer in higher thickness than the compact inner layer. Although a lower surface roughness leads to the formation of a thinner oxide film, the compact and thus corrosion resistant inner layer contributes to a relatively lower corrosion rate of 304 SS under HTHP water environment of PWR system. In addition, cyclic-EIS data interpretation indicates that the compact inner layer contributes mainly but the loose outer layer contributes less to the measured impedance on 304 SS electrodes.</p> Graphical abstract <p>The surface condition of nuclear power structural materials exerts a significant influence on their corrosion behavior in high-temperature and high-pressure water. In this work, the effect of surface roughness on the corrosion behavior of 304 stainless steel (304 SS) in the simulated secondary water was investigated. The results indicate that surface roughness has minimal impact on the composition of oxide films, but&#xa0;it exerts a significant influence on their structural characteristics and consequently affects the corrosion behavior. Electrochemical impedance spectroscopy (EIS) measurement and transmission electron microscope (TEM) observation suggested that the 304 SS with a&#xa0;higher surface roughness can lead&#xa0;to an&#xa0;oxide film with heterogeneous inner oxide layer, where a porous and discontinuous Cr-rich inner oxide layer can be observed, implying its limited protective ability. Therefore, it is recommended to regulate the surface roughness of materials in PWR for effective corrosion control. </p>

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EIS investigation on surface roughness induced oxide film evolution on 304 SS in simulated secondary circuit water of PWR system

  • 期刊论文

  • 发表日期：

    2025年2月3日

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  • Yuefei Ji,
  • Long Hao,
  • Jianqiu Wang,
  • Wei Ke

摘要

The surface roughness of nuclear-grade structural material shows a significant influence on its corrosion behavior under high-temperature and high-pressure (HTHP) water exposure condition in the pressurized water reactor (PWR) system. In this investigation, the surface roughness induced oxide film evolution on 304 stainless steel (SS) in simulated HTHP water has been investigated by in-situ cyclic electrochemical impedance spectroscopy (EIS) and ex-situ characterizations. The results indicate that cyclic-EIS data interpretation can well understand the surface roughness induced oxide film growth and its structures evolution on 304 SS electrodes under HTHP water condition. Besides, the 240#-sample with a much higher surface roughness has the thickest oxide film with the largest and increasing |Z|0.01 Hz value. In contrast, the polished-sample with a much lower surface roughness has the thinnest oxide film with the lowest but stabilized |Z|0.01 Hz value. A higher surface roughness facilitates the formation of a thicker oxide film but with the loose outer layer in higher thickness than the compact inner layer. Although a lower surface roughness leads to the formation of a thinner oxide film, the compact and thus corrosion resistant inner layer contributes to a relatively lower corrosion rate of 304 SS under HTHP water environment of PWR system. In addition, cyclic-EIS data interpretation indicates that the compact inner layer contributes mainly but the loose outer layer contributes less to the measured impedance on 304 SS electrodes.

Graphical abstract

The surface condition of nuclear power structural materials exerts a significant influence on their corrosion behavior in high-temperature and high-pressure water. In this work, the effect of surface roughness on the corrosion behavior of 304 stainless steel (304 SS) in the simulated secondary water was investigated. The results indicate that surface roughness has minimal impact on the composition of oxide films, but it exerts a significant influence on their structural characteristics and consequently affects the corrosion behavior. Electrochemical impedance spectroscopy (EIS) measurement and transmission electron microscope (TEM) observation suggested that the 304 SS with a higher surface roughness can lead to an oxide film with heterogeneous inner oxide layer, where a porous and discontinuous Cr-rich inner oxide layer can be observed, implying its limited protective ability. Therefore, it is recommended to regulate the surface roughness of materials in PWR for effective corrosion control.