It has been pointed out that dissolved hydrogen is one of the key factors of PWSCC (primary water stress corrosion cracking) in the primary systems of pressurized water reactors. The authors consider that application of alternative reductant for hydrogen may mitigate PWSCC. The corrosion tests of 304 stainless steels in 2 mmol dm−3 methanol solution and 2 mmol dm−3 hydrazine solution at 320 °C were carried out under γ-ray irradiation, and the corrosion environment was evaluated. Electrochemical corrosion potential (ECP) of the stainless steels was measured during the immersion tests. The ECP values were −605 mV and −643 mV vs. SHE in 2 mmol dm−3 hydrazine solution and 2 mmol dm−3 methanol solution at 320 °C, respectively. After the immersion tests, oxide films formed on the stainless steel specimens were analyzed with scanning probe microscope and X-ray diffraction. It is concluded that from the ECP measurement and comparison with previous results corrosion environment under following conditions is similar: (1) DH 1.5 ppm without irradiation, (2) methanol 2.9 ppm without irradiation, (3) hydrazine 2 mmol dm−3 under γ-ray irradiation and (4) methanol 2 mmol dm−3 under γ-ray irradiation. During the immersion tests, the test waters were sampled several times, and analyzed, in order to understand radiolysis of the methanol solution and the hydrazine solution at 320 °C. Hydrazine is decomposed predominantly through thermal decomposition, and an ammonia molecule is formed from a hydrazine molecule. Formaldehyde and ethylene glycol were detected in the methanol solution. But, carboxylates were not detected. The present results do not demonstrate oxidation of methanol to CO or CO2. It is pointed out that irradiation experiments of higher absorbed dose are necessary.

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