不同前處理條件之氧化鋯被覆304不銹鋼在模擬沸水式反應器環境中的電化學行為研究

Electrochemical Studies of Different Pre-treatment Conditions of ZrO2 Coating on Type 304 Stainless Steels in Simulated Boiling Water Reactor Environments

簡源進(Y. C Chien) ； 葉宗洸(T. K. Yeh) ； 蔡春鴻(C. H Tsai)

《防蝕工程》 20卷2期 (2006/06) Pp. 181-197

https://doi.org/10.6376/JCCE.200606.0181

摘要

為解決核電廠沸水式反應器(Boiling Water Reactor, BWRs)長時間運轉下，組件材料沿晶應力腐蝕龜裂(Intergranular Stress Corrosion Cracking, IGSCC)的問題，核能工業多採用加氫水化學(Hydrogen Water Chemistry, HWC)技術，降低材料的電化學腐蝕電位，減緩沿晶應力腐蝕龜裂的發生。但HWC技術在較高的飼水注氫量下（高於0.6 ppm），會伴隨管路輻射劑量增加的副作用。
本研究利用抑制性被覆防蝕技術，針對304不銹鋼以氧化鋯(ZrO2)進行被覆處理，在不同溫度條件下採用動態循環的熱水沈積法(hydrothermal deposition)。研究中以SEM、EDX對覆膜試片進行表面成分分析，並模擬BWR 爐心中因輻射水解產生溶氧與過氧化氫的高溫高壓純水環境，在兩種氧化劑濃度變化下進行動態電位極化掃瞄，及常溫下交流阻抗分析(Electrochemical Impendence Spectroscopy, EIS)，以了解不同覆膜溫度條件的腐蝕特性差異。結果顯示在90℃與150℃兩組不同的溫度被覆條件，SEM影像觀察到氧化鋯在不銹鋼表面皆呈現局部分佈，而EIS 結果證明了兩組被覆試片阻抗值皆為升高，並由極化曲線結果驗證了氧化鋯被覆對於溶氧有抑制的效果，但是對低濃度的過氧化氫才有抑制效果，而且以90℃溫度條件的氧化鋯被覆，對於降低腐蝕電位、腐蝕電流及交換電流密度效果較顯著。

關鍵字

沿晶應力腐蝕龜裂 ； 氧化鋯 ； 熱水沈積法 ； 動態極化掃瞄 ； EIS

並列摘要

As the boiling water reactors (BWRs) age, incidents of intergranular stress corrosion cracking (IGSCC) take place. In the early 1980s, technique of hydrogen water chemistry (HWC), which reduces the oxidizing power of the BWR coolant environment by hydrogen injection and subsequently lowers the susceptibility of stainless steel components to SCC, was developed to mitigate the IGSCC problems. This technique is not without problem. In addition to the risk of exposing operators to elevated level of irradiation, it is not at all clear that HWC is effective in protecting components in high level of irradiation. To enhance HWC, technique of inhibitive protective coatings (IPC) were brought into consideration.
In this study, an experiment was conducted to investigate the effects of inhibitive coating with 1μm ZrO2 on Type 304 SS by chemical immersion at 150℃ and 90℃ for one week. The primary task in this study is to determine necessary electrochemical parameters such as electrochemical corrosion potential, corrosion current density, exchange current density and Tafel constant of the reduction reactions of oxygen and hydrogen peroxide before and after inhibitive protective coatings. Specimens before and after the ZrO2 treating process were examined by the scanning electron microscopy and the energy dispersive X-ray spectroscopy. Effects of inhibitive coating with ZrO2 on Type 304 are measured by electrochemical potentiodynamic polarization tests in simulated BWR environment. Test results showed that treated SS specimens in dissolved oxygen exhibits lower ECP than pre-oxidized specimen, and that specimen exhibits lower ECP only in lower hydrogen peroxide concentration. In high hydrogen peroxide concentration, IPC can't reduce ECP.

並列關鍵字

Intergranular Stress Corrosion Cracking IGSCC ； Hydrothermal deposition ； ZrO2 ； Potentiodynamic polarization ； EIS