Methodology of seismic-response-correlation-coefficient calculation for seismic probabilistic safety assessment of multi-unit nuclear power plants

Eem, Seunghyun,Choi, In-Kil,Yang, Beomjoo,Kwag, Shinyoung Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.3

In 2011, an earthquake and subsequent tsunami hit the Fukushima Daiichi Nuclear Power Plant, causing simultaneous accidents in several reactors. This accident shows us that if there are several reactors on site, the seismic risk to multiple units is important to consider, in addition to that to single units in isolation. When a seismic event occurs, a seismic-failure correlation exists between the nuclear power plant's structures, systems, and components (SSCs) due to their seismic-response and seismic-capacity correlations. Therefore, it is necessary to evaluate the multi-unit seismic risk by considering the SSCs' seismic-failure-correlation effect. In this study, a methodology is proposed to obtain the seismic-response-correlation coefficient between SSCs to calculate the risk to multi-unit facilities. This coefficient is calculated from a probabilistic multi-unit seismic-response analysis. The seismic-response and seismic-failure-correlation coefficients of the emergency diesel generators installed within the units are successfully derived via the proposed method. In addition, the distribution of the seismic-response-correlation coefficient was observed as a function of the distance between SSCs of various dynamic characteristics. It is demonstrated that the proposed methodology can reasonably derive the seismic-response-correlation coefficient between SSCs, which is the input data for multi-unit seismic probabilistic safety assessment.

납적층고무받침(LRB)으로 지지된 면진 원전 구조물의 수직방향 지진응답 분석

조성국,윤성민,김두기,홍기증 한국지진공학회 2015 한국지진공학회논문집 Vol.19 No.3

It is very important to assure the seismic performance of equipment as well as building structures in seismic design of nuclear power plant(NPP). Seismically isolated structures may be reviewed mainly on the horizontal seismic responses. Considering the equipment installed in the NPP, the vertical earthquake responses of the structure also should be reviewed. This study has investigated the vertical seismic demand of seismically isolated structure by lead rubber bearings(LRBs). For the numerical evaluation of seismic demand of the base isolated NPP, the Korean standard nuclear power plant (APR1400) is modeled as 4 different models, which are supported by LRBs to have 4 different horizontal target periods. Two real earthquake records and artificially generated input motions have been used as inputs for earthquake analyses. For the study, the vertical floor response spectra(FRS) were generated at the major points of the structure. As a results, the vertical seismic responses of horizontally isolated structure have largely increased due to flexibility of elastomeric isolator. The vertical stiffness of the bearings are more carefully considered in the seismic design of the base-isolated NPPs which have the various equipment inside.

300m 단층 래티스 돔의 면진 장치에 대한 지진 반응 해석

박강근,정미자,이동우 한국공간구조학회 2018 한국공간구조학회지 Vol.18 No.3

The objective of this study is to investigate the response reducing effect of a seismic isolation system installed between 300m dome and supports under both horizontal and vertical seismic ground motion. The time history analysis is performed to investigate the dynamic behavior of single layer lattice domes with and without a lead rubber bearing seismic isolation system. In order to ensure the seismic performance of lattice domes against strong earthquakes, it is important to investigate the mechanical characteristics of dynamic response. Horizontal and vertical seismic ground motions cause a large asymmetric vertical response of large span domes. One of the most effective methods to reduce the dynamic response is to install a seismic isolation system for observing seismic ground motion at the base of the dome. This paper discusses the dynamic response characteristics of 300m single layer lattice domes supported on a lead rubber seismic isolation device under horizontal and vertical seismic ground motions.

Shaking Table Tests and Numerical Analysis of the Interaction of a Base-isolated Steel Frame's Responses with a Long-span Roof

Tianyang Zhang,Haoru Guo,Yunlong Zhang,Shuguang Wang,Dong-sheng Du,Wei-zhi Xu 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.8

Seismic isolation technology has been extensively used in long-span spatial structures to alleviate losses caused by earthquake disasters. However, limited experimental studies have been conducted to examine the impact of horizontal and vertical vibrations in long-span roof structures with rubber bearings as isolation layers on the isolation effect. This paper presents a study that carried out shaking table experiments on 1/40 scale long-span steel frames, both with and without base isolation. It explores the interplay of horizontal and vertical vibrations in long-span roof structures equipped with rubber bearings, and its influence on the isolation effect. Three ground motions, including horizontal bidirectional (2D) and bidirectional-plus-vertical (3D) components were used as the seismic excitations. The whole structural dynamic responses of the base-isolation (BI) model and fixed-base (FB) model, the local responses of the grids and isolation bearings were measured. Under 2D seismic excitation, the grid layer in the FB model exhibits a substantial vertical acceleration response. When exposed to 3D seismic activity, the isolation system successfully delivers its expected isolation outcome. Although the isolation bearings could not attenuate the vertical seismic acceleration response induced by vertical ground motion, they effectively reduced the vertical dynamic response generated by the coupling by suppressing the horizontal seismic response.

Seismic Response of Circular Tunnels in Jointed Rock

Jin-Kwon Yoo,Jeong-Seon Park,Duhee Park,Seung-Won Lee 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.4

Although deformation along a weak joint under a strong seismic event can seriously damage the tunnel, the effect of joint has notyet been well understood or quantified. We perform a series of pseudo-static discrete element analyses to evaluate the effect ofdeformation along rock joint on the seismic response of circular tunnels. We also perform parallel continuum analyses to compareand quantify their differences. A comprehensive set of joint parameters are considered in this study. The results illustrate that the jointsignificantly increases the moment demand in the tunnel lining, whereas it has a secondary influence on the thrust. The joint stiffnessand shear strength have critical influence on the tunnel response. Widely spaced joint set produces a larger tunnel response. Thetunnel response is highest for vertical and horizontal joints, and the lowest when the joint dips at an angle of 45°. The moment injointed rock may be 20 times higher than that in intact rock. The pronounced deviation from continuum analyses highlights the needto estimate the influence of discontinuities on the seismic response of underground tunnels from discrete element analyses. This maybe of concern for critical structures such as nuclear facilities.

Design response spectra-compliant real and synthetic GMS for seismic analysis of seismically isolated nuclear reactor containment building

Ahmer Ali,NADIN ABU HAYAH,김두기,조성국 한국원자력학회 2017 Nuclear Engineering and Technology Vol.49 No.4

Due to the severe impacts of recent earthquakes, the use of seismic isolation is paramount for the safetyof nuclear structures. The diversity observed in seismic events demands ongoing research to analyze thedevastating attributes involved, and hence to enhance the sustainability of base-isolated nuclear powerplants. This study reports the seismic performance of a seismically-isolated nuclear reactor containmentbuilding (NRCB) under strong short-period ground motions (SPGMs) and long-period ground motions(LPGMs). The United States Nuclear Regulatory Commission-based design response spectrum for theseismic design of nuclear power plants is stipulated as the reference spectrum for ground motion selection. Within the period range(s) of interest, the spectral matching of selected records with the targetspectrum is ensured using the spectral-compatibility approach. NRC-compliant SPGMs and LPGMs fromthe mega-thrust Tohoku earthquake are used to obtain the structural response of the base-isolated NRCB. To account for the lack of earthquakes in low-to-moderate seismicity zones and the gap in the artificialsynthesis of long-period records, wavelet-decomposition based autoregressive moving average modelingfor artificial generation of real ground motions is performed. Based on analysis results from real andsimulated SPGMs versus LPGMs, the performance of NRCBs is discussed with suggestions for futureresearch and seismic provisions.

납적층고무받침(LRB)으로 지지된 면진 원전 구조물의 수직방향 지진응답 분석

조성국,윤성민,김두기,홍기증 한국지진공학회 2015 한국지진공학회논문집 Vol.19 No.3

It is very important to assure the seismic performance of equipment as well as building structures in seismic design of nuclear power plant(NPP). Seismically isolated structures may be reviewed mainly on the horizontal seismic responses. Considering the equipment installed in the NPP, the vertical earthquake responses of the structure also should be reviewed. This study has investigated the vertical seismic demand of seismically isolated structure by lead rubber bearings(LRBs). For the numerical evaluation of seismic demand of the base isolated NPP, the Korean standard nuclear power plant (APR1400) is modeled as 4 different models, which are supported by LRBs to have 4 different horizontal target periods. Two real earthquake records and artificially generated input motions have been used as inputs for earthquake analyses. For the study, the vertical floor response spectra(FRS) were generated at the major points of the structure. As a results, the vertical seismic responses of horizontally isolated structure have largely increased due to flexibility of elastomeric isolator. The vertical stiffness of the bearings are more carefully considered in the seismic design of the base-isolated NPPs which have the various equipment inside.

터널의 지진응답에 대한 암반 절리의 영향 평가

유진권,장재훈,박두희,사공명 한국지반공학회 2014 한국지반공학회논문집 Vol.30 No.9

In performing seismic analysis of tunnels, it is a common practice to ignore the rock joints and to assume that the rock mass surrounding the tunnel is continuous. The applicability of this assumption has not yet been validated in detail. This study performs a series of pseudo-static discrete element analyses to evaluate the effect of rock joint on the seismic response of tunnels. The parameters considered are joint intersection location, joint spacing, joint stiffness, joint dip, and interface stiffness. The results show that the joint stiffness has the most critical influence on the tunnel response. The tunnel response increases with the spacing, resulting in localized concentration of moment and shear stress. The response of the tunnel is the lowest for joints dipping at 45°. This is because large shear stresses result in rotation of the principal planes by 45°. In summary, the weathered and smooth, vertical or horizontal, and widely spaced joint set will significantly increase the tunnel response under seismic loading. The tunnel linings are shown to be most susceptible to damage due to induced shear stress, and therefore should be checked in the seismic design.

가상고정점기법이 적용된 잔교식 구조물의 응답스펙트 럼해석법 개선사항 도출 연구

윤정원,한진태 한국지진공학회 2018 한국지진공학회논문집 Vol.22 No.6

As a method of seismic-design for pile-supported wharves, equivalent static analysis, response spectrum analysis, and time history analysis method are applied. Among them, the response spectrum analysis is widely used to obtain the maximum response of a structure. Because the ground is not modeled in the response spectrum analysis of pile-supported wharves, the amplified input ground acceleration should be calculated by ground classification or seismic response analysis. However, it is difficult to calculate the input ground acceleration through ground classification because the pile-supported wharf is build on inclined ground, the methods to calculate the input ground acceleration proposed in the standards are different. Therefore, in this study, the dynamic centrifuge model tests and the response spectrum analysis were carried out to calculate the appropriate input ground acceleration. The pile moment in response spectrum analysis and the dynamic centrifuge model tests were compared. As a result of comparison, it was shown that the response spectrum analysis results using the amplified acceleration in the ground surface were appropriate.

Analytical Investigation on Cyclic Response of Buckling-restrained Braces with Short Yielding Core Segments

Muhamed Safeer Pandikkadavath,Dipti Ranjan Sahoo 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.4

Buckling-restrained braced frames (BRBFs) are considered to be one of the efficient lateral force-resisting systems used in buildings located in the seismically active regions. Nearly symmetric hysteretic response of buckling-restrained braces (BRBs) in tension and compression due to the yielding of steel core plates helps the BRBFs to withstand the seismic excitations without causing any extensive damage to the primary frame members. However, BRBFs may exhibit the excessive post-earthquake residual drift response due to the low axial stiffness of BRBs under the strong ground motions. A reduction in the yielding core segments of BRBs results in the improved elastic and post-elastic axial stiffness of BRBs which may help in controlling the excessive residual drift response. This study is focussed on the analytical evaluation of hysteretic response of BRBs of varying lengths using finite element (FE) software. The results of FE study are further used to evaluate the inter-story and residual drift response of a 3-story braced frame fitted with BRBs of short core lengths (referred as SBRBF). Nonlinear dynamic analysis results of SBRBF are compared with the conventional BRBF and concentrically braced frame (CBF). It is concluded that the optimum reduction in yielding core lengths of BRBs can improve the overall seismic response of BRBFs with a reduction in the residual drift response.