Corrosion Behaviors and Mechanisms of ODS Steel Exposed to Static Pb-Bi Eutectic at 600 and 700°C

With good neutron properties, anti-irradiation performances, heat transfer properties and inherent safety characteristics, liquid lead or Pb-Bi eutectic (LBE) has been a primary candidate coolant for accelerator driven system and advanced nuclear reactors. However, corrosion of structural materials is a critical challenge in the use of liquid lead and LBE in high temperature nuclear reactors. Therefore, research on corrosion compatibility of structural materials with LBE at elevated temperatures is of great significance. In this work, the long-term corrosion experiments in static LBE for a oxide dispersion strengthened (ODS) steel were carried out at 600 and 700 degrees C. The temperature effects on different corrosion behaviors were studied by the analyses of XRD, SEM and EDS, and the underlying mechanisms were clarified. After exposing to LBE at 600 degrees C for up to 2000 h, a typical double-layer oxide scale with the thickness of about 10 mu m was formed on the surface of ODS steel, which was composed of outer layers of Pb-Fe-O and Fe3O4 and inner layer of Fe-Cr-Al spinal. In addition, a thin Al-rich layer was also formed under the inner layer. Due to the protective effect of the relatively dense inner layer and the Al-rich layer, ODS steel showed excellent resistance to LBE corrosion at 600 degrees C with a significantly lower corrosion rate. On the contrary, when exposed to LBE at 700 degrees C, the structure and thickness of the oxide scale formed on the surface of the ODS steel were obviously different. After exposure for 100 h, a dense protective Al2O3 oxide layer with a thickness of about 500 nm was formed, greatly reducing the corrosion rate. With the corrosion time prolonging to 500 h at 700 degrees C, most of Al2O3 layer was still remained. However, a few of nodular-like oxides were formed originated from local weak areas, which broken off the continuity of protective Al2O3 and led to deeper corrosion by LBE.