This paper, which is part of the series entitled “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”, shows the linear seismic response of crossover piping installed in a seismically isolated plant. The crossover piping, supported by both isolated and non-isolated buildings, deforms with large relative displacement between the two buildings and the seismic response of the crossover piping is caused by two different seismic excitations from the buildings. A flexible and robust structure is needed for the high-pressure crossover piping. In this study, shaking tests on a 1/10 scale piping model and FEM analyses were performed to investigate the seismic response of the crossover piping which was excited and deformed by two different seismic motions under isolated and non-isolated conditions. Specifically, as linear response analysis of the crossover piping, modal time-history analysis and response spectrum analysis with multiple excitations were carried out and the applicability of the analyses was confirmed. Moreover, the seismic response of actual crossover piping was estimated and the feasibility was evaluated.

This paper provides a part of the series titled “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. This part shows the failure behavior of crossover piping installed in a seismic isolated plant. The considered crossover piping is supported on one side by an isolated building and by a non-isolated building on the other side. During an earthquake, the piping structure is deformed due to the large relative displacements between the two buildings and at the same time excited by the different building seismic responses. Therefore, the high-pressure crossover piping structure requires both flexibility and strength. In this study, 1/10 scaled shaking tests and FEM analyses have been performed to investigate the failure behavior of the crossover piping, where both seismic motions and excitations have been taken into account. It was confirmed that the failure occurs at the piping elbow through low cycle fatigue. Moreover, the results of the elastic-plastic response analysis, which simulates an extreme level of excitation corresponding to more than three times the design level, are in good agreement with the test results. The simulation also succeeded in predicting the experimental failure location.

This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities” [1]–[4]. This part describes the work schedule of this project and the summary of a seismic design for crossover piping system. Since the Southern Hyogo Prefecture Earthquake in 1995, a seismic isolated design has been widely adopted for Japanese typical buildings. The Japanese government accepted utilizing seismic isolation technology for nuclear power facilities with the 2006 revision of the “Regulatory Guide for Reviewing Seismic Design of Nuclear Power Reactor Facilities”. Under these backgrounds, the Japan national project with the participation of all electric power companies and reactor vendors has been started from 2008 to develop seismic isolation systems of nuclear power facilities under the support of the Ministry of Economy, Trade and Industry. In the design of seismic isolated plant, the crossover piping systems, such as Main Steam line and other lines related to the safety system have the important roles for overall plant safety. Therefore, the design of multiply supported piping systems between isolated and non-isolated buildings is one of the major key issues. This paper focuses on the seismic response analysis of Main Steam crossover piping between seismic isolated Reactor Building and non-isolated Turbine Building. Multiple input response spectra and time history analyses of the crossover piping have been performed and the structural integrity of piping and the validity of the multiple input analysis method have been verified based on comparisons with the results obtained by conventional response spectrum analysis using enveloped floor response spectrum.

In this study, static loading tests were conducted in order to investigate ultimate seismic performance of reinforced concrete foundation (pedestal) for seismic isolated nuclear power plant. Half-scale four test specimens, which consist of Lead Rubber Bearings (LRBs) of 800mm in diameter and reinforced concrete pedestals of 1200mm 1200mm in horizontal view, were used with the parameters of cyclic pattern of axial stress of seismic isolator, existence or non-existence of reinforcing bars at the top of pedestal, and concrete compressive strength. As a result of the study, it was confirmed that the reinforced concrete pedestal shows structural integrity within design level loads. In ultimate level loads, no damage was observed in the case of non-variable axial stress in the area near the center of buildings, and no brittle failure was observed and supporting function of axial loads was retained in the area near the outer edge of buildings, where variable axial stress in ultimate level was extremely large.

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