AbatractResponse spectrum analysis method is widely used for the seismic design of equipment and piping systems of nuclear power plant, or other industrial facilities. Some of the equipment and piping systems are multiply supported with plural floors, or several different points. In these cases, conservative design methods, such as uniform response spectrum (URS) method that envelopes all of the individual response spectra, or independent support motion (ISM) method are commonly accepted. These design methods are not practical, but often mislead to design with unnecessary conservatism. This paper presents the practical seismic analysis methodologies considering the correlation coefficients of seismic responses with multi-directional excitations, which is extended to apply the correlations between modal responses and between support motions, called cross-oscillator, cross-floor response spectrum by Asfura, A. and Kiureghian, A,D., and numerical examples are also presented to examine the validity for the seismic analysis method of multiply supported secondary systems, with simultaneous three directional excitations of each X, Y, Z axis.

In FY 2000, a 3-year testing program of eroded piping was initiated with the following objectives: 1) to ascertain the seismic safety margins for eroded piping designed under the current seismic design code, 2) to clarify the elasto-plastic response and ultimate strength of eroded nuclear piping. A series of tests on eroded piping components and eroded piping systems was planned. In this paper, the results of those tests are presented and analyzed, focusing on the influence of the form and the number of thinned-wall portions on the fatigue life of the piping.

This paper describes the seismic design analysis methods, considering the correlation coefficients of seismic responses with multi-directional excitations. Through the numerical study, we focused on the seismic responses of simple secondary structures fixed on some floor level of the building structure which has the base excitation of El-Centro earthquake. Seismic response of secondary structure is introduced by the response spectrum analysis applying CCFS(Cross-oscillator, Cross-Floor response Spectrum) method to the multi-directional excitation problem. As the results, it is found the effective extension for the seismic design of multi-directional excitations to apply the CCFS analysis approach.

In 1998FY, the 6 year program of piping tests was initiated with the following objectives: i) to clarify the elasto-plastic response and ultimate strength of nuclear piping, ii) to ascertain the seismic safety margin of the current seismic design code for piping, and iii) to assess new allowable stress rules. In order to resolve extensive technical issues before proceeding on to the seismic proving test of a large-scale piping system, a series of preliminary tests of materials, piping components and simplified piping systems is intended. In this paper, the current status of the piping component tests and the simplified piping system tests is reported with focus on fatigue damage evaluation under large seismic loading.

The new seismic design guideline for nuclear power plants, which was established in September 2006 in Japan, requires the consideration of residual risk for earthquakes beyond the design base. Seismic Probabilistic Safety Assessment (PSA) is the current available method to evaluate the residual risk of the nuclear power plant. Since 2002, Japan Nuclear Energy Safety Organization (JNES) has been carrying out seismic capacity tests for several types of equipment whose malfunction would significantly affect core damage frequency. The primary purpose of those tests is to obtain seismic capacity data and use them to increase the reliability of the seismic PSA. In this study, some elastic-plastic analyses considering the dynamic buckling behavior were performed to evaluate previous seismic capacity test results. The study confirmed that response displacement, residual deformation of the elephant-foot bulge (EFB) and local strain of tank after the EFB occurred could be evaluated analytically. Besides, a 3D FEM elastic-plastic buckling analysis using kinematic hardening law could simulate the behavior in the early stage of the dynamic buckling. In addition to those analyses, dynamic response reduction factor (Ds) of the actual material tanks, and influence of different materials on the energy absorption and seismic capacity were evaluated by using previous seismic capacity tests results.