Abstract
As the boiling water reactors (BWRs) age, incidents of intergranular stress corrosion cracking (IGSCC) are more readily seen in the vessel internals. To mitigate the problem of stress corrosion cracking (SCC) in the structural components, the technology of hydrogen water chemistry (HWC) has been widely adopted in BWRs around the world. The principle of HWC is to reduce the oxidizing power of the BWR coolant environment by injecting hydrogen into feedwater to recombine H2 with O2 or hydrogen peroxide (H2O2) under radiative environment. The recombination can decrease the concentration of the oxidants subsequently to lower the susceptibility of stainless steel components to SCC. As reactor startup begins, the Electrochemical Potential (ECP) is initially high in the oxygenated water environment established during a cold shutdown. Consequently, the components would show higher crack initiation and propagation rates of IGSCC during startup period than other periods of the cycle. Therefore, HWC during startup was applied and tested to demonstrate the suppression of SCC initiation. For a safer operation of a new BWR, predicted water chemistry in the primary coolant circuit and corrosion behavior of structural materials in the BWR will be presented. The outcome would assist the reactor engineers in the design and the optimal operation of these types of reactors, ensuring nuclear safety in a proactive manner. In this study, The corrosion potentials and corrosion current densities of 304 SS、304L SS and 316L SS will be tested in pure water at three different temperatures (200℃、250℃、288℃) with different dissolved oxygen, hydrogen peroxide or hydrogen concentrations. The results reveal that the corrosion potentials of these specimens in same water chemistry decrease while most of the current densities increase along with the increasing temperature. The outcomes also indicate the importance of adding hydrogen into feedwater while startup.