Specific Issues for Seismic Performance of Power Plant Equipment0 pages

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Peter Nawrotzki

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Specific Issues for Seismic Performance

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of Power Plant Equipment

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Power plant machinery can be dynamically decoupled

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from the substructure by the effective use of helical steel

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springs and viscous dampers. Turbine foundations, coal

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mills, boiler feed pumps and other machine foundations

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benefit from this type of elastic support systems to miti-

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gate the transmission of operational vibration. The appli-

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cation of these devices may also be used to protect

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against earthquakes and other catastrophic events, i. e.

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airplane crash, of particular importance in nuclear facili-

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ties.

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This article illustrates basic principles of elastic sup-

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port systems and applications on power plant equipment

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and buildings in medium and high seismic areas. Spring-

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damper combinations with special stiffness properties are

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used to reduce seismic acceleration levels of turbine com-

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ponents and other safety or non-safety related structures.

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For turbine buildings, the integration of the turbine sub-

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structure into the machine building can further reduce

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stress levels in all structural members. The application of

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this seismic protection strategy for a spent fuel storage

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tank in a high seismic area is also discussed.

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Safety in nuclear facilities is of particular importance

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and recent seismic events and the resulting damage in

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these facilities again brings up the discussion. One of the

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latest events is the 2007 Chuetsu earthquake in Japan. The

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resulting damage in the Kashiwazaki Kariwa Nuclear

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Power Plant can be found in several reports, e. g. in Ya-

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mashita [1], [2].

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1 Introduction

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Seismic control strategies as described by the introduction

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of PrEN 15129 - Anti-Seismic Devices: "... design of de-

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vices that are provided in structures with the aim of mod-

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ifying their response to seismic action [3]. The modifica-

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tion ... may be obtained by ...

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- modifying the shape of the fundamental mode

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- increasing the fundamental period

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- increasing the damping.

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Usually, in combination with the modification of the mode

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shape the predominant frequency of the system is re-

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duced. When the response spectrum of recorded or artifi-

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cial earthquakes is plotted this strategy can easily be justi-

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fied (Fig. 1 left). Here, the spectrum according to the

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Turkish Standard (Specification for Structures to be Built

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in Disaster Areas) is plotted for the seismic zone 1 and the

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soil class Zl.

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Flexible structures are usually not in danger of col-

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lapse during an earthquake. Low natural frequencies are

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indicators for a low level of induced seismic energy. Struc-

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tures with higher natural frequencies take more energy

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from the given base excitation. For the particular example

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according to the Turkish regulation the frequency range

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with the highest acceleration starts at approximately

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3,3 Hz. Up to about 10 Hz an average amplification factor

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of 2,5 must be considered. Here, the peak ground acceler-

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© 2010 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin - Special Kraftwerksbau 67

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