Experience With Extended Power Uprate at Leibstadt Nuclear Power Plant

Since the 1970s power uprates have been employed to enhance the electricity output of nuclear power plants. Extended power uprate is defined as an increase of reactor thermal power in excess of 7% up to about 20% of the original plant licensed thermal power. Such power uprates generally require significant modification of major plant equipment and were initially implemented at boiling water reactor plants approximately 15 years ago. The early experience with extended power uprates was very positive. However, in recent years an increased number of failures of nuclear power plant components totally or partly caused by those power uprates have been reported. This paper presents the issues and operating experience with extended power uprate at the Leibstadt Boiling Water Reactor Nuclear Power Plant in Switzerland concerning the mechanical and electrical equipment. Failures such as fretting-wear and fatigue damage due to an increased vibration level, structural damage due to thermal overheating as well as shortened maintenance intervals due to elevated temperature and increased pump speed are reported. As a summary, the failures of mechanical and electrical components caused by extended power uprate experienced at the plant during the last years are related to plant reliability and have not adversely impacted plant safety.