On Seisimc Design Spectra For Nuclear Power Plants

As the strongly advocated new energy, nuclear power plants (NPPs) moved into a rapid development phase in 2005. In this critical time, the Fukushima Nuclear Accident after the 9.0 magnitude earthquake off the coast of Japan on March 11th 2011 cautioned the whole world that the safety of NPPs should not be neglected whatsoever. Uncongenial to the NPPs'rapid development is that the seismic design code of NPPs (GB50267-97) is compiled in 1990s. In the past decades, new theory of seismic design developed rapidly, and recordings of strong ground motion increased substantially. Thus, the revision of design spectra for NPPs is necessary and urgent.Seismic design spectra are indispensible parameters in defining earthquake action on items of NPPs. Therefore how to develop design spectra properly is of great importance to seismic safety of NPPs. The purpose of this study is to give comments on the design spectra specified in the codes, and to provide reference for the revision of the code.Works of this study was arranged as following. Firstly, different methods used to develop design spectra were introduced, then comparisons and comments followed. Secondly, statistical and comparative studies on the impacts of magnitude of earthquake, epicentral distance and PGA level on AD/V~2 and V/A (A, V and D are abbreviation for PGA, PGV and PGD respectively) were carried out. The ratio of vertical to horizontal PGA is studied as well. Thirdly, different methods with certain modification were employed to developed design spectra, and the impact of PGA level was considered simultaneously. Lastly, comparisons among results from different methods, and comparisons among the results in this study, the GB50267-97 spectra, the R G 1.60 spectra and the AP1000 spectra were made. Explanation and implication about the difference observed in the comparisons were stated. The database used in this study was consisted of 1814 strong ground motion recordings from the Wenchuan Earthquake, the Chi-chi Earthquake, the Tangshan Earthquake, the Haicheng earthquake and earthquakes in Yunnan Province, Gansu Province and Xinjiang Province etc.The major findings and observations,which derived from calculation, comparision and analysis, are as follow:(1)AD/V~2 and V/Awith large dispersion are affected by the site type, the distance, the direction of ground motion, the PGA level, and the magnitude. So the value of these ratios should not only be related to the site type, but also to other factors, such as the direction of ground motion and the PGA level.(2)Any method to develop design spectra should take the asymptotic behavior of spectra of ground motion into account, and the Newmark method and the Guo-Wang method are modified accordingly.(3)Comparisons among the results from different methods validate that the effect of PGA level on design spectra.(4)Comparatively, results from the Guo-Wang method tend lager in velocity sensitive region and displacement sensitive region. Thus, the Newmark method and the Malhotra method are recommended to develop design spectra specified in code.(5)Compared with the design spectra specified in this study, the GB50267-97 design spectra are insufficient when period is lager than 0.4 s, and the R G1.60 design spectra and the AP1000 design spectra underestimate the vertical earthquake action.