Seismic responses and resistance of age degraded structures and components Original Research Article

Nuclear power plants, as with many other structures, can experience aging degradation on a continuing basis. In some cases, the environmental or operating conditions, which they are subjected to, may be more severe than those affecting non-nuclear structures. This degradation needs to be understood and adequately managed for the continued safe operation of nuclear power plants. To date a limited number of nuclear power plants in the US have specific monitoring and inspection programs for structures. The evaluation for seismic loading is particularly important because the degraded structures or components could be more vulnerable to the seismic loads. From a seismic analysis point of view, the aging or degradation may affect dynamic properties, structural response, resistance or capacity, failure modes, and locations of failure initiation. Further, the NRC license renewal rule requires in part that the current licensing basis (CLB) be maintained throughout the period of extended operation. To meet this requirement, an assessment and timely maintenance of the degraded structures and components becomes necessary. An international cooperative program is being considered to pull together resources to tackle the issue of seismic effects on aged/degraded structures and components, and to augment existing databases by using experience of nuclear power plants worldwide. Based on the insights and lessons learned from this program, technical bases could be established for each participating country, as needed, to develop guidelines to address the seismic capability of aged/degraded structures and components for continued and extended service. The extent of the program will depend on the results of a scoping or bounding study to be performed in the initial phase.