Remedies for PWR (Pressurized Water Reactor) Recirculating Steam Generator Tube Aging

摘要

Pressurized water reactor (PWR) steam generator tubes form well over one-half of the primary system pressure boundary and have experienced significant aging degradation at some plants. Tube failures have caused contamination of the secondary coolant by the primary coolant, and radiological releases to the environment when atmospheric relief valves were actuated. Degraded steam generator tubes may fail during a severe accident and allow radioactive material to bypass containment. Simultaneous rupture of several tubes may lead to a major plant temperature and pressure transient with potential impact on the structural integrity of various components in the system. Tube leakages result in unscheduled plant outages when the leakage rate exceeds acceptable limits. Finally, repair and replacement associated with steam generators account for much of the personnel radiation exposure (manrems) at PWR plants. Therefore, industry has developed various remedies for steam generator tube aging. This paper evaluates the effectiveness of current remedies used to reduce aging damage to recirculating type steam generator tubes (Shah and MacDonald, 1988). The following topics are discussed: degradation mechanisms, mitigation techniques, repair methods, and conclusions and recommendations. 11 refs., 2 tabs.