Abstract
The regulation for nuclear power plants (NPPs) has been enhanced after the Great East Japan earthquake and the accident at TEPCO’s Fukushima Daiichi Nuclear Power Stations in March 2011 to take countermeasures against beyond-design-basis events. The importance of seismic probabilistic risk assessment (PRA) has drawn much attention to improve the seismic safety of nuclear facilities against earthquakes that exceed the design input ground motion. The realistic seismic response of the equipment and piping in NPPs for fragility assessment in seismic PRA needs to be evaluated. In particular, as piping systems have plant-specific complex configurations, the arrangement and stiffness of piping support structures have a significant impact on the seismic response characteristics of the entire piping system. By contrast, the current seismic design procedure adopts an evaluation method assuming an elastic response. Hence, this study aims to develop an elastic-plastic response analysis method that can estimate the realistic response of piping systems, including piping support structures.
The authors have conducted loading tests on piping support structures and optimization studies of elasto-plastic property models to develop an elasto-plastic response analysis method for piping systems, including piping support structures. In this study, the applicability of the method is confirmed through a simulation analysis of the elasto-plastic response for the piping support structure loading test previously reported. As the results, a good correlation is found for the ductility factor and the damage status between the test and simulation analysis results. Therefore, the ductility factor is concluded to be effective as a damage evaluation index for piping support structures.
