Corrosion behavior of Zircaloy-4 in aqueous solution of methanol at 320degC under gamma-irradiation

It has been pointed out that high concentration dissolved hydrogen is one of the important factors of PWSCC (primary water stress corrosion cracking) in the primary systems of pressurized water reactors. Application of a substitution for hydrogen may be a fundamental countermeasure of PWSCC. The authors are developing a new water chemistry technology of a hydrogen alternative to suppress PWSCC. In the present paper, corrosion tests of Zircaloy-4 were performed in deaerated 5x10^-3 mol dm^-3 methanol solution at 320degC in the absence and presence of gamma-irradiation. The nominal absorbed dose of the test water was 100 kGy. After the immersion tests, the specimens were analyzed. Weight gain per unit surface area, thickness of oxide film and hydrogen storage were measured. In addition, Raman spectroscopy was carried out, to investigate possible deposition of organic compounds on surface of the specimens. The corrosion behavior of Zircaloy-4 without irradiation agreed with literature data. It was concluded that the presence of methanol did not affect the corrosion behavior of Zircaloy-4. The corrosion behavior of Zircaloy-4 hardly depended on 100 kGy gamma-irradiation. On the Raman spectra of the specimens after the immersion tests, the Raman peaks ascribed to polyethylene or graphite were not found. The deposit of decomposition products of methanol would be negligible if any. It seems that polymerization is not the major process in thermal decomposition and radiolysis of methanol, but methanol decomposes into CO₂ or carboxylic acids. (author)