Abstract
In the boiling water reactors (BWRs), reactor cooling water is maintained in high purity condition by controlling of a deionizing and deaerating apparatus, however H2O2 contains by water radiolysis. In order to determine the corrosive condition in high-temperature pure water containing H2O2, the electrochemical impedance spectroscopy was performed in this study. To simulate BWR condition precisely, the measurements were performed without any electrolyte.
The obtained impedance responses were changed with the H2O2 concentration. The solution resistance and polarization resistance were determined by the equivalent circuit analyses.
The conductivity was determined by the obtained solution resistance and the calculation of the current flow between the working electrode and the counter electrode by the 3-demensional finite element method. The value, 4.4×10−6 S/cm, was obtained as the conductivity of the pure water at 288°C.
The reciprocal of the obtained polarization resistance increased in proportion with H2O2 concentration. This indicates that the corrosion current density was determined by the diffusion limiting current density of H2O2. The diffusion coefficient of H2O2 at 288°C was determined using the relationship between the reciprocal of the polarization resistance and H2O2 concentration. The obtained diffusion coefficient was 1.5×10−4cm2/s. This is about twice larger than that of the reported value of O2.
