Determining factors for anodic polarization curves of typical structural materials of boiling water reactors in high temperature – high purity water

Abstract

In order to examine the anodic polarization characteristics of typical structural materials of boiling water reactors (BWRs), the anodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in deaerated high purity water at 553 K using the previously reported measurement method which was confirmed suitable for high temperature -high purity water. In order to specify which constituent element determines the dissolution characteristics of these materials, the anodic polarization curves of pure iron, pure nickel, and pure chromium were also surveyed. The anodic polarization curve of 316L SS was determined to have active, passive, and transpassive states which were the same as type 304 SS (304 SS) showed. But, Alloy 182 had different polarization characteristics especially near the corrosion potential as it had no active state. From comparison results of the polarization characteristics of these materials and their constituent elements, the corrosion characteristics of these materials were concluded to be mainly determined by the corrosion characteristics of chromium.

In situmeasurement of corrosion of type 316L stainless steel in 553 K pure water via the electrical resistance of a thin wire

“…Passive current density was also reported to be 5 mA m 72 [11]. Corrosion rate calculated from passive current density was 6.7 6 10 74 mm h 71 , with which the result of the present work is in good agreement (3.7 6 10 74 mm h 71 at 100 h for the NWC condition).…”

“…Corrosion rates were calculated using the fitting equation for the HWC condition (Run 1) and the NWC condition (Run 2), and are shown in Figure 15. Corrosion rate of the HWC condition is larger than that of the NWC condition excluding the initial period of less than 0.1 h. The active state at low ECP (70.34 V vs. SHE) was observed by anodic polarization curve measurement and the critical current of passivation was reported to be 28 mA m 72 [11]. Corrosion rate was calculated from the critical current of passivation as about 3.7 6 10 73 mm h 71 supposing corrosion by divalent metal ions and density of 79.8 t m…”

“…The corrosion rate of 316L SS in high-temperature pure water depends upon the water chemistry, which can include some amounts of dissolved oxygen, hydrogen and hydrogen peroxide, as well as the resulting electrochemical corrosion potential (ECP) [10,11]. Corrosion rate was seen to increase, depending on the dissolved oxygen concentration between 55 mg kg 71 and 1000 mg kg 71 , in corrosion tests of specimens immersed in 556 K pure water for up to 1000 h [10].…”

“…Corrosion rate was seen to increase, depending on the dissolved oxygen concentration between 55 mg kg 71 and 1000 mg kg 71 , in corrosion tests of specimens immersed in 556 K pure water for up to 1000 h [10]. However, the polarization curve in 553 K de-oxygenated pure water was reported to have an active state peak at about 70.36 V vs. standard hydrogen electrode (V vs. SHE) and passive state at about 70.27 V vs. SHE [11].…”

“…The corrosion depth of 316L SS in 553 K pure water has been reported to be of the order of a micrometre or less [8][9][10][11][12]. The corrosion depths of 316L SS wire specimens (diameter 50 mm) were evaluated using electrical resistance measurements applying a constant current (I) and measuring the potential drop (V) intermittently to obtain the resistance (R) via Ohm's law (Equation (1)).…”