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Report No.
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In-situ measurement of corrosion environment in high temperature water without electrolyte utilizing electrochemical impedance spectroscopy

Sato, Tomonori ; Yamamoto, Masahiro ; Tsukada, Takashi ; Kato, Chiaki  

In the boiling water reactors (BWRs), reactor cooling water is maintained in high purity condition by controlling of a deionizing and deaerating apparatus, however H$$_{2}$$O$$_{2}$$ contains by water radiolysis. In order to determine the corrosive condition in high-temperature pure water containing H$$_{2}$$O$$_{2}$$, 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 H$$_{2}$$O$$_{2}$$ 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$$times$$10$$^{-6}$$ S/cm, was obtained as the conductivity of the pure water at 288$$^{circ}$$C. The reciprocal of the obtained polarization resistance increased in proportion with H$$_{2}$$O$$_{2}$$ concentration. This indicates that the corrosion current density was determined by the diffusion limiting current density of H$$_{2}$$O$$_{2}$$. The diffusion coefficient of H$$_{2}$$O$$_{2}$$ at 288$$^{circ}$$C was determined using the relationship between the reciprocal of the polarization resistance and H$$_{2}$$O$$_{2}$$ concentration. The obtained diffusion coefficient was 1.5$$times$$10$$^{-4}$$ cm$$^{2}$$/s. This is about twice larger than that of the reported value of O$$_{2}$$.

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