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A Less-Conservative Approach to Simplified Seismic Analysis for Small Bore Nuclear Piping System

[+] Author Affiliations
Joon Ho Lee, In Yeung Kim

Korea Electric Power Corporation Engineering & Construction Company, Inc., Yongin, Gyeonggi, Korea

Paper No. PVP2014-28183, pp. V008T08A031; 7 pages
  • ASME 2014 Pressure Vessels and Piping Conference
  • Volume 8: Seismic Engineering
  • Anaheim, California, USA, July 20–24, 2014
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 978-0-7918-4607-0
  • Copyright © 2014 by ASME


Per guidelines for piping system reconciliation such as EPRI NP-6628 (NCIG-14), simplified seismic design methods have been used by nuclear piping designers to deal with small bore piping for many years. These methods are generally based on enveloping the results of rigorous dynamic or conservative static analysis.

Small bore piping is generally more flexible with larger margin in support design comparing to large bore piping. Consequently, Classes 2 & 3 piping less than 2-1/2 inch NPS that is analyzed by a conservative “cookbook method” is excluded from the as-built verification actions in IE Bulletin 79-14. The ASME code’s Subsection NF and B31.1 provide recommended pipe spans by pipe size considering only piping weight; therefore, the seismically qualified piping span must be developed for the peak acceleration of the applicable amplified or floor response spectra.

Simplified seismic analysis method being considered for the Korean nuclear power plants is based on the Load Coefficient Method provided in Appendix N-1225 of ASME Section III. However, since the simplified analysis method involves conservative and enveloping approach in an effort to comply with applicable requirements and results in an excessive number of supports and unrealistically high support loads, the successful implementation largely depends on how the issues related to the excessive conservatism are resolved when determining allowable pipe spans and support design loads of the piping system.

In this paper, simplified engineering equations are presented as a less-conservative approach based on a detailed computer analysis method, which is alternative to the various handbooks and design charts that are based on the conventional hand calculation method.

Copyright © 2014 by ASME



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