Method for elasto-plastic seismic time history analysis of piping system that imitate internal fluids as acoustic elements

After the Great East Japan Earthquake in 2011, the necessity of reassess seismic safety of nuclear power plants components and system has emerged reconsidered worldwide. For reassessment, leading countries in nuclear power plant-related technologies, such as Japan and the United States, are developing new evaluation criteria based on current safety assessment techniques. Until now, operating nuclear power plants are designed through stress-based safety criteria which is differently applied by system and components according to specific safety design level. However, stress-based evaluation does not account for problems such as low cycle fatigue because it does not consider plastic deformation due to cyclic loading of earthquakes. To complement this, many studies including strain-based evaluation criteria have been published in Japan's JSME and United States' ASME. In order to confirm the evaluation criteria, an analytical model capable of simulating elastoplastic behavior by finite element model is required. Particularly, when building finite element analysis model for piping, it is essential to discuss the effects of internal fluids. In this study, we have studied how to properly simulate the effects of internal fluids in simulating the elasto-plastic behavior of the nuclear power plant piping system.