Study on Site Specific Design Earthquake Ground Motion of Nuclear Power Plants in China

The main technical backgrounds and requirements are introduced with regard to earthquake ground motion design parameters in several domestic and American standards, codes and guides involved in the seismic analysis and design activities of nuclear power plants in China. Based on the research results from site seismic safety evaluation of domestic nuclear power plant projects in the last years, characteristics and differences of site specific design spectra are analyzed in comparison with standard response spectra, and the suitability of standard response spectra for domestic nuclear power plant projects is discussed.     

AP1000抗震分析与设计特点研究

对AP1000抗震分析与设计的主要特点进行分析,并将这些特点同现有核电站的设计状况和我国潜在厂址的情况进行对比.研究侧重于抗震分类、抗震设防水准及设计地震、地基岩土条件、抗震裕度分析等几个主要方面.通过研究,把握AP1000抗震分析与设计的主要特点,对其设计特点和适应性加深理解,并提出需要继续跟踪研究和关注的问题.研究成果可以为后续研究和AP1000堆型的工程引进提供参考和基础素材.其中关于抗震裕度分析的研究内容对于在我国开展在役核电厂的地震安全评估和3级PRA分析亦有借鉴意义.     

DISCUSSION ON THE SPECTRA SHAPE OF SEISMIC MARGIN EARTHQUAKE OF NUCLEAR POWER PLANT IN CHINA

Fukushima nuclear accident caused widespread concern of earthquake initiated severe accident. Under this background, China nuclear utilities carried out research and application of seismic margin assessment(SMA)approach to evaluate the seismic margin of the existing nuclear power plants(NPP)by different spectra shape of seismic margin earthquake(SME). By reviewing the method used to determine SME of operational NPP in central and eastern United States(CEUS), this paper analyzed the seismic hazard characteristic of China NPP sites, contrasted the design basis ground motion between NPP in CEUS and China, and suggested giving priority to evaluating the seismic margin of operational NPP that adopted the improved second generation technology for the urgency and importance of assessment on the actual seismic capacity of NPP. Comparing RG1.60 spectrum to normalized site-specific SL-2 level acceleration spectra, we found that some normalized spectra overtook the RG1.60's in high frequency range, so it is not always adequate to scale RG1.60 spectrum to evaluate the seismic margin for sites of the improved second generation NPP. We selected a sample site whose site-specific SL-2 level ground motion is close to the standard design of improved second generation NPP(0.2g scaled RG1.60 spectrum)to determine the seismic margin earthquake by probabilistic seismic hazard analysis method of the sample site. Compared to the given PGA(0.3g)scaled scenario earthquake ground motions and the uniform hazard response spectrum(UHRS), whose PGA is 0.3g to PGA(0.3g)scaled standard spectra(median NUREG/CR0098 spectrum and RG1.60 spectrum), the results demonstrated that uniform hazard response spectrum and scaled scenario earthquake ground motions are both significantly higher than the PGA scaled median NUREG/CR0098 spectrum, and all the three spectra are enveloped by PGA scaled RG1.60 spectrum. Then, this paper suggests adopting the uniform hazard response spectrum or scenario earthquake ground motions to evaluate the seismic margin of improved second generation NPP beyond site SL-2 ground motion; and to evaluate the seismic margin of improved second generation NPP beyond standard design, we recommend to use PGA scaled RG1.60 spectrum.     

基岩输入时程随机数对场地峰值加速度的影响研究

研究基岩输入时程随机数对场地峰值加速度的影响,对核电厂设计地震动参数的合理确定具有重要意义。本文选取了某重要核电站场地具有代表性的3个钻孔,建立了场地计算模型。根据确定性方法、概率性方法得到的基岩反应谱及其包络谱,基于不同随机数,分别合成了400条基岩输入时程。采用LSSRLI-1程序进行了场地地震反应,根据4800个计算结果,研究了不同随机数对地表峰值加速度的影响,给出了自然对数下峰值加速度标准差的估计,揭示了峰值加速度的分布规律,提出了对核电厂设计地震动参数合理确定的建议。     

地形效应对于核电场地地震反应分析影响研究

目前,在进行核电场地安全性评价时,主要采用一维等效线性化程序LSSRLI-1,而一维等效线性化方法在考虑地形效应时有很大的局限性,特别是在研究场地地形效应的影响时偏差较大。对于抗震设计要求远高于一般建筑的核电站来说,选用合适的方法进行二维建模分析是非常必要的。选取了某核电场地典型剖面15个钻孔资料,在MIDAS二维等效线性分析环境下进行了建模,并选取了以年超越概率10^-4合成的地震动中10条最大样本时程作为基底输入进行分析。通过与LSSRLI-1的计算结果进行对比,研究了地形效应对地表和核岛基础处（8.5m）加速度反应谱的影响,并提出了设计建议。分析得出:二维分析中地形效应对地表加速度最大值反应谱的双峰形态影响较大,并且计算结果对AP1000谱的超越情况有所变化;对核岛基础处（8.5m）峰值加速度的影响程度比地表要小,没有表现双峰形态变化较大的形态。     

核电站抗震研究综述

核电站抗震性一直是核电站设计的主要问题之一。随着此问题各方面研究的深入和研究手段的进步,核电站的抗震计算理论也在不断发展,本文试图根据已有的资料,在核电站抗震问题的一些主要方面（地震输入参数的确定,抗震计算理论,结构与地基的相互作用,支加速度谱及反应谱的确定,建筑物及设备的抗震计算,地基,基础及地下建筑的抗震计算等）研究状况作一些综述,并在此基础上展望一下需要解决的问题。     

工程结构等延性地震抗力谱研究

研究结构的非弹性反应谱对改进现有的结构抗震设计、发展基于性态的抗震设计以及了解复杂地面运动特性与结构动力特性之间的关系具有重要的意义。利用大量的单自由度在强震记录作用下的弹塑性动力时程分析,对等延性地震抗力谱这一重要的非弹性反应谱进行了较为详尽的研究,给出了四类场地条件(基岩、硬土、一般土和软土)下的平均等延性地震抗力谱,总结了对工程结构的抗震设计和研究具有实际意义的规律和特征,并分析了场地条件、结构的延性系数以及周期等对等延性地震抗力谱的影响,提出了新的拟合公式,其成果可供抗震研究和设计直接应用。     

土层结构对反应谱平台值的影响

本文利用目前工程上广泛应用的场地地震反应的一维等效线性化波动方法,计算了不同场地模型在三种不同强度的地震动输入下的地表加速度反应谱。为了研究不同的土层结构对反应谱平台值的影响,本文将计算得到的地表加速度反应谱拟合成建筑抗震设计规范规定的设计反应谱的形式,分析对比了不同的覆盖层厚度、软弱土层对反应谱平台值的影响,得到了一些有价值的研究成果。     

非岩基厂址条件下核电厂标准化地基模型研究

核电厂标准化设计方法是节省核电建设成本的重要手段,开展非岩基厂址地基标准化设计地基模型的研究对拓宽核电厂地基适用范围有重要意义。首先,基于国内外典型软质岩和硬土厂址动参数的调研数据进行数理统计分析,归纳动参数随深度的变化规律,并通过归一化分析得到地基剪切波速剖面特征曲线,从而确定初步的标准化地基模型;进而,基于SuperFLUSH/2D Ver6.0软件开展初步标准地基模型的地震反应分析,以最大加速度随深度变化与加速度反应谱为考量指标探究动参数变化对于地震反应的影响程度及规律;最后,依据初步地基模型的剪切波速剖面的相似性及包络性,定义软质岩和硬土厂址条件下的核电厂标准化地基模型,并给出相应的动参数合理取值。该模型及研究成果可为我国“核电走出去”战略中主力堆型的核电厂标准化设计提供重要的参考。     

Deterministic and probabilistic floor response spectra

The paper presents a comparative study for computing floor response spectra (FRS) for complex structures. For the purpose of validation and evaluation of the methods for practical application, a systematic comparison of two concepts, classical deterministic and probabilistic, was carried out as an example of a nuclear power plants structure. The deterministic method utilizes time history analyses compatible with the prescribed design response spectrum. The probabilistic method uses an analysis of random vibrations for defining the probabilistic FRS influenced by random seismic soil movement. The seismic input is a power spectral density function (PSDF) compatible with the design response spectrum. The probabilistic approach based on PSDF provides satisfying FRS with far less effort and time consumption needed for calculation.     

一致概率谱衰减指数的取值方法探讨

在重大工程的地震安全性评价工作中,根据概率法地震危险性分析得到的一致概率反应谱,与建筑抗震设计规范给出的设计反应谱常常不一致,特别是在长周期部分,一致概率谱一般均低于相应的规范谱。为解决地震安全性评价得到的一致概率谱在抗震设计中的应用,本文通过比较、分析一致概率谱和规范谱,针对一致概率谱标定得到的衰减指数γ较规范谱明显偏大的特点,提出了一致概率谱衰减指数的取值方法。     

THE EFFECT OF HARD INTERLAYER THICKNESS ONTHE SITE SEISMIC RESPONSE

Studies on the effect of near-surface overburden soil layers on seismic motion have shown that the overburden soil layers have a significant impact on the seismic effect of the site due to the formation age, genetic type, thickness difference, structure, and dynamic characteristics of the soil layers. In this paper, the one-dimensional seismic response analysis of a nuclear power plant site containing a thick hard interlayer was conducted to discuss the influence of the hard interlayer thickness on the site seismic response, so as to provide a basis for determining the seismic motion parameters for seismic design of similar sites. Based on the engineering geological data of a nuclear power plant site, five models of one-dimensional soil-layer seismic response analysis were built, and the equivalent linear method of the one-dimensional site seismic response was applied to analyze the effect of the interlayer thickness on the peak acceleration and the acceleration response spectra of the site seismic response. The seismic response characteristics of the site and influence rules of the hard interlayer thickness are summarized as follows:1)Under different input seismic motion levels, the peak acceleration at the top of the hard interlayer was less than the input peak acceleration, and the peak acceleration at the ground surface of site was greater than the input peak acceleration. 2)Under the same input seismic motion, the ratios of the peak accelerations at the top of hard interlayer to the input peak accelerations were smaller than the ratios of the peak accelerations at the ground surface to the input peak acceleration, and these ratios first decreased and then increased gradually with the increase of the hard interlayer thickness; while for the same hard interlayer thickness, these ratios gradually decreased as the input peak acceleration increasing. 3)For the same input seismic motion, the ratios of the peak accelerations at the ground surface of site to those at the top of the hard interlayer increased gradually as the hard interlayer thickness increased; however, corresponding to different hard interlayer thicknesses, the variation characteristics of ratios which are the peak accelerations at the ground surface of site to those at the top of the hard interlayer were inconsistent with the increase of the input peak acceleration. 4)The hard interlayer had a significant influence on the short-period acceleration response spectrum and the thicker the hard interlayer was, the wider the influence frequency band would be; while for a special hard interlayer thickness, the influence frequency band is certain, and the hard interlayer had little effect on the acceleration response spectrum coordinates outside this frequency band, the longer the period is, the less the influence of the hard interlayer on the acceleration response spectrum coordinates. The seismic response characteristics of the site and influence rules of the hard interlayer thickness indicate that the hard interlayer thickness has a significant impact on the peak acceleration and the acceleration response spectra of the site seismic response, and the hard interlayer has obvious isolation effect at the seismic motion, and the increase of its thickness reduces the nonlinear effect of the site and leads to the wider influence frequency band. Meanwhile, the higher the input peak acceleration is, the stronger the nonlinear effect of the site, and it's remarkable that the soft layer overlying the hard interlayer has a significant amplification effect on the seismic motion.     

施甸5.9级地震强震观测资料的时-频反应谱分析

通过对施甸5．9级地震在太平等观测点的强震记录进行时一频反应谱计算,给出了三个方向的时一频反应谱图,根据时一频反应谱的特点,结合场地条件,对这些场点的震害情况进行了分析,指出了在结构抗震方面应注意的环节,并对时一频反应谱的应用进行了探讨。     

基于强震记录的核电厂抗震标准反应谱研究

依据基岩场地上的汶川地震强震记录,分析了地震动地面峰值和核电站抗震标准反应谱的特性,证明了在推导和使用标准反应谱时所考虑的地面峰值加速度与地面峰值速度之比(PGA/PGV)受地面峰值加速度和震中距的影响,将对标准反应谱形状产生明显的影响.另外还发现了基岩场地的竖向峰值加速度可能要远比通常认为水平向峰值加速度的2/3大....     

Earthquake Response Analysis of Soil-reactor Plant-nuclear power Auxiliary Plant Interaction System

土-结构相互作用分析是核电结构抗震设计的重要环节,考虑到附属厂房可能导致反应堆厂房处于最不利工况状态,对地基土-反应堆厂房-核电辅助厂房结构相互作用体系地震响应进行研究。基于PASSI算法,提出显-隐式单元层计算方法,实现显、隐式交替计算,保持高效性的同时,提高计算稳定性。通过场地分析算例和土-结构相互作用分析算例,与ABAQUS软件计算结果进行对比,验证计算方法的可行性。以某核电站为对象,分析同一基础上相邻厂房对反应堆厂房地震响应的影响。研究结果表明,在基岩场地上,安全厂房通过基础和场地对反应堆厂房的作用较小,对反应堆厂房地震响应的影响较小;地震动输入下,燃料厂房和电器厂房加大了反应堆厂房位移峰值,减小了反应堆厂房加速度反应谱峰值,并使反应堆厂房顶部点加速度反应谱峰值向高频移动;与反应堆厂房共用同一基础的辅助厂房,应与反应堆厂房作为整体进行地震响应分析,至少应将与反应堆厂房相连的辅助厂房作为整体进行分析。     

Characteristics of response spectra for long-periods of main-shock recordings of the Chi-Chi earthquake

Current practice uses predictive models to extrapolate long-period response spectra based on far-field recordings in moderate and weak earthquakes. However, the spectra are not long enough and the data are often not reliable, which means that the seismic design code cannot accurately define seismic design requirements for long-period structures. The near-field recordings in the main-shock of the Chi-Chi earthquake have a large signal-to-noise ratio (SNR), which makes them suitable for studying the long-period acceleration response spectrum up to 20 sec. The acceleration response spectra from 246 stations within 120 km of the causative fault are statistically analyzed in this paper. The influence of distance and site conditions on long-period response spectrum is discussed, and the shapes of the amplification spectra are compared with the standard spectra specified in the seismic design code of China. Finally, suggestions for future revisions to the code are proposed.     

Introducing new design spectra derived from Italian recorded ground motions 1972 to 2017

The shape of design spectra, traditionally based on regions characterized by constant displacement, constant velocity, and constant acceleration, has been discussed from a conceptual point of view by Calvi (2018). In the same study, a formulation for the definition of the design spectra relying on four parameters was proposed. Predictive models are proposed herein to calculate these four parameters, conditional on magnitude and distance. These models were developed using a large number of recorded ground motions in Italy, and they allow defining combined spectral acceleration versus spectral displacement plots. Such design spectra are shown to reasonably interpolate the experimental data, resulting in acceleration and displacement demand that approximate the response spectra resulting from +1σ results obtained from recorded ground motions. While it is recognized that numerous additional parameter should be considered (eg, focal depth and fault distance, site amplification), it is also concluded that this approach to define the seismic demand is promising toward a rationalization of seismic design. A thorough application of the approach developed and preliminary tested in this work may result in a re‐visitation of seismic design approaches and, ultimately, in a more efficient use of the available resources.     

波速原位测试结果标准差对较深软场地地震反应谱影响初探

波速测试结果在工程上的应用越来越重要,但波速测试结果的不确定性一直影响着抗震设计。为了准确地描述这一不确定性,对较深软场地的地震响应进行了计算。采用Shake 2000程序,通过输入不同类型的多种强度的地震波,研究了较深软场地的多种工况下剪切波速测试标准差对地表加速度反应谱和峰值加速度的影响。结果表明,较深软场地上的波速测试标准差对场地的加速度反应谱和峰值加速度基本没有影响;不同地震强度下的反应谱和峰值加速度的变化,基本可以忽略。随着波速测试数据量的增加,本文研究结果还有待进一步的深入与完善。     

弹性能量半径演化谱及其在多自由度体系地震反应计算中的应用

目前用于结构抗震设计的反应谱仅能反映峰值反应,无法体现反应值随时间的变化。文中提出一种弹性能量半径演化谱,可反映线性单自由度体系弹性能量(即动能与弹性势能之和)随地震持时的变化,且其峰值近似等于结构峰值位移。文中给出了利用地震动演化功率谱得到该演化谱的方法并进一步发展了一种计算线性多自由度体系地震位移反应的新方法。通过两座框架结构的地震反应计算,将新方法与传统振型组合法及时程分析法的计算结果进行对比,发现对于振型稀疏结构,新方法计算结果与SRSS法接近;而对于振型密集结构,新方法计算结果较CQC法更精确,且避免了CQC法相关系数的复杂计算。     

某高温气冷堆核电厂结构地震反应分析

以某高温气冷堆核电厂结构为原型,利用有限元软件建立三维结构实体模型,开展了模态分析和弹性动力时程分析的数值计算,以探讨某高温气冷堆核电厂的结构特性和抗震性能,并重点分析了在三向地震动作用下高温气冷堆核电厂的加速度、位移反应时程和楼层反应谱.总体上看,高温气冷堆核电厂在两个水平向的刚度比较均匀,楼层反应接近,布局较为合理;在三向地震动作用下,顶层中心点的竖向楼层反应均明显大于两水平方向楼层反应,因此在高温气冷堆核电厂结构设计中,应关注竖向地震动对核电厂地震反应带来的不利影响.