Technical Considerations for Seismic Isolation of Nuclear Facilities (NUREG/CR-7253)

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Publication Information

Manuscript Completed: February 2013
Date Published: February 2019

Prepared by:
A. M. Kammerer1 , A. S. Whittaker2, and M. C. Constantinou2

1Formerly, Office of Nuclear Regulatory Research
  US Nuclear Regulatory Commission

2MCEER, University at Buffalo
  State University of New York, 212 Ketter Hall
  Buffalo, NY 14260

Ramón L. Gascot, Scott P. Stovall, and
Richard Rivera-Lugo, NRC Project Managers

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Seismic isolation (SI) is a technology that has proven useful in constructing structures capable of withstanding intense earthquake ground motions. Although various techniques for isolating a structure from the effects of earthquake shaking have been known for centuries, the global use of modern seismic (or base) isolation devices has greatly expanded in recent decades. Seismically isolated structures now number in the thousands around the world and the technology has been shown to meet the performance needs of important non-nuclear structures. SI has been used in the design and construction of nuclear power plants (NPPs) in France and South Africa and was recently used to isolate new emergency response centers at NPPs in Japan. As a result, SI is currently being considered for nuclear facilities in the United States.

Base isolation, an application of SI, reduces the response of a structure to horizontal ground motion through the installation of horizontally flexible and vertically stiff seismic isolators between the superstructure and its foundation. The dynamics of the supported structure change such that the fundamental vibration period of the isolated structural system is significantly longer than that of the fixed-base (non-isolated) structure. This leads to significant reductions in the horizontal accelerations and forces transmitted to the isolated superstructure (and the systems and components therein). The reduction in horizontal acceleration is accompanied by an increase in lateral displacement between the foundation and the superstructure, which is accommodated by deformation of the isolators. SI devices are designed and tested to undergo safely and with significant margin the large horizontal deformations expected in design basis shaking.

This report was developed under the NRC’s Seismic Research Program Plan with the goal of providing technical information necessary for NRC staff to develop regulatory guidance on the use of SI technology. This report develops a performance-based and risk-informed design philosophy for SI derived based on NRC objectives and approaches. This design philosophy, in turn, leads to a set of recommended performance objectives and criteria that can serve as the foundation for future NRC guidance on the use of SI and related technology.

This report is the first comprehensive NRC technical document related to SI. As such, it provides background information on seismic isolators and isolation systems, a discussion of the history and performance of seismically isolated structures during earthquakes, and a summary of SI provisions in relevant existing codes and standards. It also provides a series of preliminary recommendations that have resulted from the NRC’s research program on SI.

The focus of this NUREG/CR is surface-mounted or near-surface-mounted large light water reactors. Although vertical isolation systems, the isolation of individual systems or components, and the isolation of deeply embedded reactors are not discussed in detail in this NUREG/CR, there is no technical reason that the principles and recommendations contained herein cannot be extended to these and other cases. However, additional considerations, constraints and recommendations may be needed. Some are discussed briefly in this report.

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