Technical Considerations for Seismic Isolation of Nuclear Facility Structures Bozidar Stojadinovic, Professor UC Berkeley Disclaimer This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Berkeley National Laboratory under Contract DE-AC02-05CH11231. The U.S. Nuclear Regulatory Commission under a Federal Interagency Agreement with DOE supported this project. This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California. Ernest Orlando Lawrence Berkeley National Laboratory is an equal opportunity employer. Abstract Seismic isolation reduces the response of a structure to horizontal ground motion through the installation of a horizontally flexible and vertically stiff layer of seismic isolation hardware between the superstructure and its substructure. The dynamics of the structure are thus changed such that the fundamental vibration period of the isolated structural system is significantly longer than that of the original, non-isolated, structure. This leads to significant reductions in the accelerations and forces transmitted to the isolated superstructure during an earthquake. At the same time, the seismic isolation devices undergo large horizontal deformations: they are engineered to safely sustain such motions and thus protect the isolated superstructure. Modern seismic isolation devices and components, and engineering methodology for their use to modify the seismic response of structures have been developed in 1970’s and 1980’s. Since then, a significant number of conventional buildings, industrial structures and bridges have been seismically isolated in the US and abroad. Seismic isolation has been used to design and construct nuclear facility structures in France and South Africa in late 1970’ and early 1980’s. In the US, two seismically isolated reactor designs, PRISM and SAFR, were developed through DoE support and examined by NRC mid 1980’s and early 1990’s. The renaissance of nuclear energy is the catalyst behind the surge in exploring new civil/structural technologies to increase the seismic safety and reduce the cost and time to build new nuclear power plants. In nuclear facility structures seismic isolation can be used to, with high confidence, limit the inertial forces and vibrations transmitted from the ground to the isolated nuclear facility superstructure for a wide variety of potential nuclear power plant sites. This enables standardized design, fleet licensing, and modular construction of nuclear power plants. This report presents the technical considerations for analysis and design of nuclear power plants and safety-related nuclear facility structures using seismic isolation. It is intended to serve as a reference to those engineers planning to use seismic isolation in their designs, as well as regulators reviewing applications that employ seismic isolation hardware and systems. Seismic isolation is treated as a civil/structural sub-system of a nuclear power plant whose risk-informed design is governed by the performance objectives defined in ASCE 43-05 “Seismic Design Criteria for Structures, Systems and Components in Nuclear Facilities”. Behavior, mechanical properties, modeling, structural response analysis, design, qualification and in-service monitoring issues for seismic isolation design using the seismic isolation device most commonly used in the U.S. are presented. Table of Contents Disclaimer .................................................................................................................................................... 3 Abstract ....................................................................................................................................................... 4 Table of Contents ........................................................................................................................................ 5 Acknowledgement....................................................................................................................................... 9 1 Introduction ........................................................................................................................................ 11 1.1 Objective ...................................................................................................................................... 11 1.2 Scope............................................................................................................................................ 11 1.3 Fundamentals of Seismic Isolation............................................................................................... 12 1.3.1 Traditional Approach to Seismic Design................................................................................ 12 1.3.2 Basic Mechanics of Seismically Isolated Structures............................................................... 14 1.3.3 Types of Seismic Isolation Units ............................................................................................ 14 1.3.4 Role of Damping in Seismic Isolation .................................................................................... 16 1.4 Benefits and Challenges of Seismic Isolation for Nuclear Facility Structures............................... 17 1.4.1 Challenges Associated with Seismic Isolation ....................................................................... 18 1.5 History of Seismic Isolation .......................................................................................................... 20 1.5.1 Recorded Performance of Seismically Isolated Structures.................................................... 21 1.5.2 Seismically Isolated Nuclear Facility Structures .................................................................... 22 1.6 Report Content............................................................................................................................. 22 2. PERFORMANCE OBJECTIVES AND ACCEPTANCE CRITERIA USED IN SEISMIC ISOLATION DESIGN FOR NUCLEAR FACILITY STRUCTURES ............................................................................................................... 23 2.1. Design Basis................................................................................................................................. 23 2.2. Acceptable Performance for Seismically Isolated Structures...................................................... 24 2.2.1. Isolation System ................................................................................................................... 24 2.2.2. Superstructure and Foundation ........................................................................................... 25 2.3. Acceptance criteria...................................................................................................................... 25 3. MECHANICS OF SEISMIC ISOLATORS.................................................................................................. 27 3.1. Basic Mechanics of Seismic Isolators........................................................................................... 27 3.1.1. Elastomeric Bearings ............................................................................................................ 27 3.1.2. Sliding Bearings .................................................................................................................... 29 3.2. Types of Seismic Isolators ........................................................................................................... 29 3.2.1. Low Damping Bearings ......................................................................................................... 29 3.2.2. Lead Rubber Bearings........................................................................................................... 33 3.2.3. High Damping Bearings ........................................................................................................ 38 3.2.4. Friction Pendulum™ Bearings............................................................................................... 40 3.3. Recommendations for Nuclear Facility Applications................................................................... 45 4. REVIEW OF MODELING AND ANALYSIS TECHNIQUES FOR SEISMICALLY ISOLATED STRUCTURES..... 46 4.1. Isolation System .......................................................................................................................... 46 4.1.1. Mechanical Properties.........................................................................................................