The objective of this study is to characterize thesteam generator (SG) tube flakes collected from anoperating pressurized water reactor (PWR) and elucidatethe effect of tube flakes on the galvanic corrosionbehavior of secondary system materials (steam generatortube materials: Alloy 600 and Alloy 690, steam generatortube sheet materials: SA508 Gr.3, feedwater pipingmaterials: SA106 Gr.B). Based on the results ofmicrostructural analyses, the SG tube flakes mainlyconsisted of magnetite and contained only small amountsof trevorite, jacobsite, and Cu particle. Some aggressiveimpurities such as Cu, Pb, P, S, and Cl were existed in thepores of flakes. In particular, Cu is expected to exist in ametallic state in the pores of the flakes by using thethermodynamic calculation. The SG materials act as ananode of the galvanic pair with the corrosion products(magnetite and Cu) and the corrosion rate of secondarysystem materials was greatly accelerated. When the arearatio (AR) was increased 1 to 5, 10, and 20, the corrosionrate of secondary system materials was more accelerated.The galvanic effect of Cu particles as well as themagnetite must be considered in the corrosion behavior ofsecondary system materials contacted to the flakes.
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