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

• Main Authors: Chen, Yue-Tai, 陳岳泰
• Other Authors: Yeh, Tsung-Kuang
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/s5m638

碩士 === 國立清華大學 === 核子工程與科學研究所 === 107 === 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.