白金被覆的304L不銹鋼於沸水式反應器起爐過程中的應力腐蝕龜裂起始研究

Evaluation of SCC Initiation for Platinum Treated Type 304L Stainless Steels during Simulated BWR Startup Conditions

陳岳泰(Yue-Tai Chen)

指導教授 ： 葉宗洸 ； 王美雅

國立清華大學/原子科學院/核子工程與科學研究所/碩士(2018年)

摘要

低濃度注氫配合貴重金屬化學添加(NobleChemTM)或線上貴重金屬化學添加(On-line NobleChemTM)被廣泛應用於沸水式核反應器的結構組件上。貴重金屬藉由飼水端注入後沉積於不銹鋼的結構組件表面，可以有效催化金屬表面氫氣與氧氣的結合反應，因而降低材料表面的電化學腐蝕電位(Electrochemical Corrosion Potential, ECP)，並可有效抑制不銹鋼組件應力腐蝕龜裂(Stress Corrosion Cracking, SCC)的裂縫起始與成長。
然而過去的研究顯示，在反應器啟動(Startup)過程中，爐水因缺乏氫氣的添加以及上一個運轉週期殘留下的氧化性物質，將使反應器金屬組件處於較高氧化性的水環境，對於實施貴重金屬添加的電廠，因貴重金屬的催化效果，反而會使得金屬表面的電化學腐蝕電位上升，因此將對應力腐蝕龜裂的抑制造成反效果。本研究將探討反應器中常使用的結構材料304L不銹鋼在有貴重金屬-白金被覆下，反應器啟動過程中的溶氧或含有過氧化氫的氧化性水環境對SCC裂縫起始的影響，以及啟動過程實施加氫水化學的效益。實驗結果顯示，具白金被覆之304L不銹鋼在288oC溶氧條件下具有較高的應力腐蝕龜裂裂縫成長速度，但操作溫度較低溫度的200oC及250oC度下白金催化效果較不明顯。注入氫氣的水環境下可有效抑制304L不銹鋼IGSCC的發生，在過氧化氫的水環境下比溶氧水環境下更容易發生SCC，但在過氧化氫水環境下Pt的被覆對於304L不銹鋼的SCC並無顯著的影響。

關鍵字

應力腐蝕龜裂 ； 貴重金屬化學添加 ； 反應器啟動 ； 304L不銹鋼 ； 慢應變速率拉伸測試

並列摘要

Low hydrogen concentration injection of HWC combined with noble metal chemical addition (NMCA) or Online NobleChemTM (OLNC) has been adopted for boiling water reactors (BWRs) to mitigate stress corrosion cracking (SCC) by lowering the electrochemical corrosion potential (ECP) of structural materials in BWRs. Noble metal was injected into feedwater and then deposited on inner surface of the stainless steel (SS) piping to catalyze the recombination of hydrogen with oxygen and hydrogen peroxide. When the ECP was decreased to a critical potential (-230mVSHE), the susceptibility of SCC and the crack growth rate were obviously reduced.
However, some research indicated that the ECP of SS with NMCA application was increased, even higher than that without NMCA when the materials were exposed to oxidizing environments without hydrogen injection during startup of BWRs. Additionally, a higher ECP might increase the exchange current density and be detrimental to the resistance of SCC. In this study, the SCC initiation behavior of 304L SS with Pt-treatment was investigated in dissolving oxygen, dissolving hydrogen and hydrogen peroxide water environments at different temperatures to simulate BWR water chemistry conditions during startup. The results revealed that the Pt-treated sample slightly induced higher crack growth rate in dissolving oxygen environment for the test at 288oC, but the catalytic effect of platinum on the 304L SS surface was unremarkable at lower temperature condition. The hydrogen water chemistry can effectively avoid the occurrence of IGSCC on 304L SS. Hydrogen peroxide might increase the SCC susceptibility of 304L SS in the simulated BWR water environment during reactor startup.

並列關鍵字

Stress Corrosion Cracking ； Noble Metal Chemical Addition ； Reactor startup ； 304L Stainless Steel ； Slow Strain Rate Test

參考文獻

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