Corrosion and electrochemical investigations of low-alloyed and austenitic stainless steel used in the steam generators of Kozloduy nuclear power plant

摘要

The corrosion behavior of austenitic stainless steel 18Crl ONiTi used for pipe bundles in the steam generators (SG) of WWER reactor in Kozloduy nuclear power plant (NPP) as well as of construction low-alloyed steel (Cr, Ni, Mn and Si — 6% total) is investigated under model operation conditions — temperature of 220°C, pressure of 150 atm. and the water-chemical regime used in the second contour. A specially constructed autoclave and electrochemical polarization technique in combination with scanning electron microscopy (SEM), X-ray photoelectron (XPS) and Moessbayer spectroscopy are used. The corrosion and electrochemical parameters of both kinds of steels are obtained. It is demonstrated that the corrosion processes on the austenitic steel differ in the uniform distribution of corrosion damages and stable passive state. Additionally, the rate of general corrosion of the austenitic steel is much lower compared to that of the low-alloyed steel. The chemical and phase composition of the layer of corrosion products, formed on the surface of the pipe bundle during the exploitation of the Energy Block 3 (EB 3) of NPP, is determined using XPS and Moessbayer analysis. It is established that the main components of the layer are magnetite Fe_3O_4 (about 90%), γ-FeOOH and small amounts of CuO and ZnO. The results confirm that the corrosion products have formed a uniform and compact protective film on the pipe surface.