Inspection of nuclear power plant containment structures

Safety-related nuclear power plant (NPP) structures are designed to withstand loadings from a number of low-probability external and interval events, such as earthquakes, tornadoes, and loss-of-coolant accidents. Loadings incurred during normal plant operation, therefore, generally are not significant enough to cause appreciable degradation. However, these structures are susceptible to aging by various processes depending on the operating environment and service conditions. The effects of these processes may accumulate within these structures over time to cause failure under design conditions, or lead to repair. Steel and concrete containment structures in nuclear power plants are described and their potential degradation factors identified. Reported incidences of containment degradation are summarized. Current regulatory in-service inspection requirements are reviewed. Nondestructive examination techniques commonly used to inspect NPP steel and concrete structures to identify and quantify the amount of damage present are described, and their capabilities and limitations identified. Finally, areas where nondestructive evaluation techniques require development (i.e. inaccessible portions of the containment pressure boundary, and thick heavily reinforced concrete sections) are identified and prior research addressing these needed developments summarized. (orig.)