Determination of degradation acceptance criteria for structures and passive components in nuclear power plants

The rate of age related degradation of structures and passive components (SPCs) in nuclear power plants (NPPs) is not significantly large, but increases as the plants get older. Since the degradation of the SPCs always increases the risk of NPPs, in light of long term operation, it is necessary to determine acceptable levels of degradation for effective inspection and maintenance. In contrast to degraded active components, degraded SPCs may not impose an immediate threat to plant safety during normal operation. However, it can be a dramatic safety threat during the low probability of high consequence events, such as large earthquakes. This paper presents a procedure for a determination of degradation acceptance criteria (DAC) for SPCs in NPPs, based on the potentially increased seismic risk to the plant owing to a degradation of SPCs