Abstract
Intergranular stress corrosion cracking(IGSCC) of sensitized stainless steel components in boiling water reactors(BWRs) has been a major concern to worldwide BWR operators. Research has demonstrated that below a critical electrochemical corrosion potential(ECP) of -230 mVSHE, the susceptibility of stainless steel to IGSCC is dramatically reduced. In past decade, several methods have been developed to mitigate IGSCC by lowering the ECP. One is Hydrogen Water Chemistry(HWC). Hydrogen is added to the feedwater of BWRs to reduce the dissolved oxidant concentrations produced by radiolysis of water in the core of BWRs. However, several drawback of H2 addition have been discovered gradually, such as increased N16 carry-over to the turbine, higher Co60 deposition rate, high H2 cost,etc. In addition, the IGSCC protection potential(-230 mVSHE) is difficult to achieve in highly oxidizing and/ or high fluid flow regions. Another one is termed Noble Metal Chemical Addition (NMCA). But it still needs lower H2 additions to achieve a low corrosion potential (~500 mVSHE). Apart from the high cost of noble metals, the main drawback of this technology is that sufficient hydrogen level cannot be maintained in the certain locations of a BWR (e.g. in the vicinity of the core spray and top guide), Because the H2 is insufficient, NMCA may accelerate the speed of IGSCC on the contrary. Recently, a new approach was explored to lower the corrosion potentials at all locations of BWRs, even without the presence of H2. This method is formed a dielectric films on a metal surface. It is termed Inhibitive Protective Coating (IPC). In this study, an experiment will be conducted to investigate the effects of inhibitive coating with ZrO2 (different treating conditions) by hydrothermal deposition on Type 304 SS. The effect of ZrO2 coatings were investigated by electrochemical potentiodynamic polarization tests in simulated BWR environment. And surface analyses were conducted by X-ray、SEM、AES to identify the surface structure and components. Test results showed that with IPC treated 304 SS specimens exhibited lower ECP、lower corrosion current density and lower exchange current density(ECD) of oxidant or reductant than the untreated specimen. Comparison the treatments of different particle size were obtained: the effectiveness of 100nm was better than 700 nm. Comparison the treatments of different deposition temperature were obtained : 90 ℃ is better than 150 ℃. Finally, Comparison the treatments of different deposition time were obtained : 2weeks is better than 1 week.