Seismic Spans for Cold Piping Based on Simplified Dynamic Analysis in APR1400

The process piping of nuclear power plants have been seismically qualified for many years by rigorous dynamic analyses utilizing piping analysis computer programs or simplified dynamic analyses such as the constant-pitch span method or the seismic load coefficient method specified in ASME Sec. III, Appendix N-1225. In the case of OPR1000 (Korea standard nuclear power plants, e.g., Ulchin 3&4, 5&6 including Shin-Kori 1&2 and Shin-Wolsong 1&2 which are under construction), almost all of the nuclear piping have been seismically qualified by rigorous dynamic analyses to reduce the cost for the excessive number of supports required by simplified methods. Whereas, for the up-to-dated APR1400 (Korea’s advanced power plant 1400 MW-class) project, the application of simplified design approach is to be considered in depth to catch up with the growing demands in recent years for reducing engineering man-hours and the level of efforts required by rigorous piping analyses. The key to overcoming the excessive number of supports required by simplified method is how to determine the allowable range of seismic piping spans. To develop seismic piping spans for non-safety related cold piping in APR1400, some piping span models are introduced herein based on simplified dynamic analysis, and several topic studies for those models are performed. Topics studied are dead weight and seismic spans, lateral to vertical support span ratio, and span reduction factors as well as the design conditions including the pressure-temperature, pipe sizes, materials and insulations. The study results show that determined seismic spans are conducive to achieving the economical goal and complying with the prevailing code requirements.