Abstract
The analysis of one-mass and two-mass models indicates that the earthquake-generated horizontal forces and deformations of the main structures of a nuclear power plant can be reduced by a factor of about ten times by mounting the overall power plant building on a recently developed base-isolation system. The very high forces which the ‘resonant appendage‘ effect may induce in some critical components (such as fuel elements, control rods and essential piping) may be reduced by a factor of 40 or more times by the isolation system. The parameters of the isolation system have been chosen as appropriate to the level of protection which should be provided for a nuclear plant in a seismically active area. Consideration is given to flexible mounts and dampers suitable for such an isolator.
Highlights
It is difficult to provide adequate earthquake resistance for nuclear power plants located in seismically active areas
The combination of short period and low self-damping results in large dynamic magnifications of the applied earthquake forces since they correspond to the severe range of the response spectra of appropriate design earthquakes
Base isolation should provide a greater degree of safety under earthquake attack than would be provided in a nonisolated plant
Summary
It is difficult to provide adequate earthquake resistance for nuclear power plants located in seismically active areas. A severe situation arises when a small but very important component of a nuclear plant, such as a fuel element, control rod, or essential pipe, has a natural period which is close to that of the supporting structure. Such resonant appendages may be subjected to accelerations which are 20 or more times the maximum ground acceleration. The recent development of appropriate hysteretic dampers[2,3,4] leads to practical baseisolation systems for various types of structure These dampers may be combined with mounts which provide horizontal flexibility, together with a centring force. DECEMBER 1976 of the mounts being damaged by excessive horizontal motions, or by vertical deformation of the foundations
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