Cathodic Polarization Properties of Hydrogen Peroxide and the Effect on Electrochemical Corrosion Potential Calculation under Simulated BWR Environment

Hydrogen peroxide (H₂O₂) is the most important oxidant to determine the corrosive environment of boiling water reactors (BWRs). Since H₂O₂ is unstable at high temperature and electrochemical measurement in high purity water is difficult, H₂O₂ polarization characteristics in the BWR environment are not known well especially at less than 10 ppb. Cathodic polarization curves of the H₂O₂ were measured in simulated BWR conditions at 553 K over range of 1 to 1000 ppb. A polytetrafluoroethylene chamber was set in a circulating autoclave to reduce decomposition of H₂O₂, and the potential step method developed for measurements under BWR conditions was employed. The exchange current density of the 2 ppb H₂O₂ condition was the same as the 100 ppb O₂ condition though the O₂ concentration was about fifty-fold higher than that of the H₂O₂. The results indicated that the H₂O₂ reduction reaction occurred faster than that of O₂. The electrochemical corrosion potentials (ECPs) in the H₂O₂ environment were calculated using the obtained polarization curves. The ECPs increased from -0.55 Vvs.SHE to about 0 Vvs.SHE even at 10 ppb, and were in good agreement with the ECPs measured by electrometers. The obtained polarization curves of H₂O₂ are applicable to calculation of ECPs.