SEISMIC ANALYSIS STUDY OF THE HP TURBINE STEAM SUPPLY PIPING FOR APR1400

The high pressure (HP) turbine steam supply piping for APR1400 (Korea's advanced power reactor 1400 MW-class) is routed from the Containment Building to the Turbine building via the Main Steam Isolation Valve Room in the Auxiliary building and supported by multiple structures. As such, the seismic analysis utilizing the Independent Support Motion (ISM) is preferable to the Enveloped Response Spectrum (ERS) method which is overly conservative but more widely used in seismic evaluation of piping systems. The ISM method is a mathematically rigorous technique that utilizes the principle of modal analysis to calculate the piping responses from each structure or support group and combines them to obtain the final results. In spite of the more realistic and less conservative approach of the ISM method for the piping systems subjected to multiple support excitations, the application of ISM method on a regular basis has been limited in nuclear power plant piping design because guidelines from the nuclear industry and the regulator are conservative and unclear. In this study, several related studies are performed to evaluate the adequacy of utilizing the ISM method for seismic analysis of the HP turbine steam supply piping for APR1400. Topics studied include support grouping effects, combination effects of responses between support groups, damping effects between PVRC and 4% damping per Regulatory Guide 1.61, and closely spaced modes effects. The results show that the support grouping by each floor of buildings, SRSS combination of support groups, 4% damping with +/- 15% spectrum peak broadening and absolute double sum (ADS) of modal combination are technically sound and preferable.