Defects in the Metal of Welded Joints of Collectors to Steam Generators in Nuclear Power Plants

This article presents a study of the metal of coolant collectors' welded joints to steam generators in nuclear power plants. During the operation of nuclear power plants of the VVER-1000 type, metal defects were found in the collectors' welds to the steam generator body. The general cause for the defects' occurrence and development is the combination of: 1) the influencing stresses, and 2) the corrosively aggressive working environment. The specific manifestation and development of defects differs across different NPPs. This study focuses on examining the on-site working conditions. It describes observations on the occurrence and development of defects in the metal of the welded joints and possible facility degradation scenarios. The resulting data come from actual observations spanning a 30-year-period. This information is important for the safe operation of steam generators in NPPs. The data can be used for probabilistic safety analyses at NPPs as well as for NPP lifetime extension.