Seismic Analysis of Large-Scale Piping Systems for the JNES ... - NRC

FOREWORD
This report documents the collaborative efforts between the U.S. Nuclear Regulatory Commission (NRC),
the Japan Nuclear Energy Safety Organization (JNES), and the Nuclear Power Engineering Corporation
of Japan (NUPEC) under the NRC-JNES agreement in the area of seismic engineering research. Under
contract to the NRC, Brookhaven National Laboratory (BNL) participated in this program and performed
this study. This piping test program is one of a series of large-scale seismic testing programs of nuclear
power plant (NPP) structures, systems and components conducted by JNES/NUPEC. The research
conducted and information exchanged under this collaborative agreement have allowed the NRC to obtain
valuable seismic data from large-scale test programs that are not available anywhere else in the world. In
addition, this program has enhanced interactions with various Japanese organizations to promote the
exchange of information and awareness of ongoing seismic research in Japan.
The NUPEC Ultimate Strength Piping Test Program was a multi-year program to investigate the behavior
of NPP piping systems under large seismic loads. The objectives were to develop a better understanding
of the elasto-plastic response and ultimate strength of nuclear piping systems, ascertain the seismic safety
margins in current piping design codes, and assess new code-allowable stress rules. The program
included static and dynamic loading tests of piping material specimens and piping components, and
seismic shaking table tests of piping systems. The seismic shaking tests included small “simplified” piping
system test specimen configurations and large-scale representative piping system configurations. In both
series of seismic tests, the specimens were shaken to levels well above typical design earthquake excitation
levels. A summary description of these tests is included in this report.
The NRC’s primary contribution to this collaborative effort was the analysis of selected piping system tests.
In an earlier phase of this collaborative program, BNL performed analyses of selected piping component
and simplified piping system seismic tests and the results were documented in NUREG/CR-6889. This
report presents the results of the final phase of this program in which BNL analyzed the large-scale piping
systems. The analyses included (1) linear analyses and stress evaluations in accordance with the piping
design rules of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, and
(2) nonlinear analyses to predict the response of representative large-scale piping systems under beyonddesign-basis
levels of earthquake motion. The results of the linear analyses provided comparative
information on the minimum safety margins in various types of piping components provided by different
versions of the ASME Code including the latest NRC-endorsed version (1993) and the most recent
version (2006) which is undergoing NRC review. The nonlinear analyses focused on evaluating the capability
of current theoretical methods and computer programs to predict the response of piping systems under large
earthquake loads. These analyses further developed and improved analysis methods and modeling
techniques that were used in the earlier simplified piping system nonlinear seismic analyses. The results
of these analyses demonstrated the difficulty of accurately predicting the piping response when it is
subjected to large earthquake loads, and the importance of validating the analytical model against test data.
The JNES/NUPEC tests have provided valuable test data on the seismic response of piping systems
subjected to strong earthquake motions. The linear code evaluation analyses have provided valuable
information on seismic safety margins that can be helpful in resolving the staff’s technical concerns in
their assessment of new seismic piping design rules in the latest version of the ASME Code including
acceptable damping values. From a regulatory standpoint, it is important for reviewers to understand the
limitations, sensitivities, and uncertainties of nonlinear analysis methods and the importance of validating
these methods against test data. The analyses conducted under this program have provided valuable
insights that will assist the staff in their review of licensee submittals involving nonlinear analysis
methods.
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