Development of Aluminum Alloy Coating for Advanced Nuclear Systems Using Lead Alloys

Small and medium reactors using lead alloys as coolant are one of the promising reactor concepts with improved safety because of their thermal-physical and chemical properties. This paper focuses on development of Al-alloy coating for nuclear systems using liquid lead-bismuth eutectic (LBE). Since corrosion attack becomes severe against structural steels at high temperatures in liquid LBE, it is necessary to improve corrosion resistance of steels. An Al-alloy coating method using Al, Ti and Fe powders, and laser beam heating has been developed. Main defects formed in an Al-powder-alloy coating process are surface defects and cracks. Conditions required to avoid these defects are employment of the laser beam scanning rate of 20 mm/min and adjustment of the Al concentration in the coating layer. According to results of the corrosion tests at 550°C in liquid LBE, the Al-alloy coating layers on 316SS protect severe corrosion attack such as grain boundary corrosion and LBE penetration observed in 316SS without coating. The good corrosion resistance of the Al-alloy coating is based on the thin Al-oxide film which can be regenerated in liquid LBE. From the viewpoints of the soundness of produced Al-powder-alloy coating layers and preservation of their corrosion resistance, it is estimated that the range of the adequate Al concentration in the coating layer is from 4 to 12 wt%.