Factors related to degradation of nuclear power plant concrete structures

All commercial nuclear power plants (NPPs) contain concrete structures whose performance and function are necessary for protection of the safety of plant operating personnel and the general public. Aging of these structures occurs with the passage of time and has the potential, if its effects are not controlled, to affect the engineering properties, structural resistance/capacity, failure mode, and location of failure initiation, which in turn may impact the ability of the structures to withstand various challenges in service from operating conditions, the natural environment, and accidents. Background information and data have been developed for improving and developing methods to assess the effects of degradation on the performance of NPP reinforced concrete structures, including fragility evaluations. Factors that can lead to degradation of reinforced concrete structures are identified and their manifestations described. Methods used to assess and quantify degradation are summarized. An approach for condition assessments of reinforced concrete structures in NPPs is presented. Criteria, based primarily on visual indications, are provided to assist in classification and assessment of concrete degradation. Finally, degradation effects on concrete beams are quantified through fragility curves developed for both undegraded and degraded conditions.