원자력발전소의 부지감시시스템의 운영과 활용

박동희(Dong hee Park),조성일(Sung il Cho),이용희(Yong Hee Lee),최원학(Weon Hack Choi),이동훈(Dong Hun Lee),김학성(Hak sung Kim) 대한자원환경지질학회 2018 자원환경지질 Vol.51 No.2

원자력발전소는 부지선정, 부지조사, 설계, 건설 및 운영의 전 과정에 걸쳐 지질조사, 단층 및 지진 특성 분석, 탄성파 탐사, 시추조사, 지반특성 분석 등 모든 가능한 지질학적, 지진학적, 지구물리학적 조사와 자료 분석을 통하여 자연재해 및 인위적 재해에 대하여 건전성을 확보할 수 있도록 견고하게 건설, 운영되고 있다. 본 단보에서는 한국수력원자력(주)에서 자연재해에 대해 원자력발전소 부지의 안전성을 평가하기 위하여 구축하여 운영 중인 지진관측시스템, 단층감시시스템, 사면감시시스템 등 일련의 부지감시시스템의 현황 및 주요 관측 자료에 대한 분석결과를 소개하고자한다. 원자력발전소에는 발전소의 구조물 및 자유장에 여러 대의 가속도계와 지진 트리거로 구성된 지진감시계통을 구성하여 내진설계의 적절성 평가, 지진으로 인한 운전기준 초과 판정, 지진 신속 대응에 활용하고 있다. 이와는 별도로 단층과 지진과의 상관성 분석, 지진발생 특성 연구, 지진재해도 평가 등 원전 부지의 지진안전성 확보를 위하여 1999년부터 원자력 발전소 부지 내 및 인근 지역에 총 13개소의 지진관측소를 운영하고 있으며, 2017년 최신의 지진관측 장비로 교체 설치하였다. 또한 원전 인근의 단층의 활동성을 감시하기 위하여 국내에서 처음으로 체계적으로 단층감시 기반을 확립한 읍천단층 감시시스템(Eupcheon Fault Monitoring System, EFMS)을 2012년 1월부터 운영하고 있다. EFMS는 시추공 변형률계 및 지진계, 지표변위계, GPS, 지하수위계 등으로 구성되며, 상기 계측기의 자료분석 결과 읍천단층은 한반도 동남부 일대에서 발생된 지진에 의해서도 영향을 받지 않는 안정된 단층임을 입증할 수 있었으며, 단층의 지진 안전성 해석과 지진예측 연구에도 단층 감시시스템이 매우 유용하게 활용될 수 있음을 확인하였다. 추가적으로, 2016년부터는 원전 부지 내 사면의 안전성 평가를 위하여 한울원전 배후사면을 대상으로 지중경사계, 지표경사계, 사면변위계, 강우량계 등을 설치하고 K-SLOPE 시스템을 구축하여 사면 거동을 감시하고 있으며, 전체 사면의 거시적 변형거동 평가를 위해 지상 LiDAR를 활용한 분석을 실시하였다. 상기와 같이 한국수력원자력(주)에서는 원자력발전소의 지진 등 자연재해에 대한 부지 안전성 평가를 위하여 실시간 부지 감시기반을 구축, 운영하고 있으며 지속적인 관측자료의 분석기법 고도화, 지진 및 단층과의 상관성 분석, 단층 장기 거통특성예측 기술개발을 통하여 보다 견고하게 원자력발전소의 지진안전성 확보에 기여할 수 있을 것으로 기대된다. Nuclear power plants(NPP) are constructed and operated to ensure safety against natural disasters and man-made disasters in all processes including site selection, site survey, design, construction, and operation. This paper will introduce a series of efforts conducted in Korea Hydro and Nuclear Power Co. Ltd., to assure the safety of nuclear power plant against earthquakes and other natural hazards. In particular, the present status of the earthquake, fault, and slope safety monitoring system for nuclear power plants is introduced. A earthquake observatory network for the NPP sites has been built up for nuclear safety and providing adequate seismic design standards for NPP sites by monitoring seismicity in and around NPPs since 1999. The Eupcheon Fault Monitoring System, composed of a strainmeter, seismometer, creepmeter, Global Positioning System, and groundwater meter, was installed to assess the safety of the Wolsung Nuclear Power Plant against earthquakes by monitoring the short- and long-term behavioral characteristics of the Eupcheon fault. Through the analysis of measured data, it was verified that the Eupcheon fault is a relatively stable fault that is not affected by earthquakes occurring around the southeastern part of the Korean peninsula. In addition, it was confirmed that the fault monitoring system could be very useful for seismic safety analysis and earthquake prediction study on the fault. K-SLOPE System for systematic slope monitoring was successfully developed for monitoring of the slope at nuclear power plants. Several kinds of monitoring devices including an inclinometer, tiltmeter, tension-wire, and precipitation gauge were installed on the NPP slope. A macro deformation analysis using terrestrial LiDAR (Light Detection And Ranging) was performed for overall slope deformation evaluation.

New Approach for Slope Deformation Measurement Using Terrestrial LiDAR in Nuclear Power Plant Site

( Yonghee Lee ),( Weon-hack Choi ),( Hak-sung Kim ),( Seok-chul Kim ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Recently, slope failures are frequently occurred in Korea due to localized torrential rainfalls induced by the world climate change. Therefore, the stability of slopes in nuclear power plant sites has become a major geotechnical issue in the nuclear industry. The slope monitoring using slope-mounted sensors (e.g., inclinometer, tension-wire, and precipitation gauge) are the most accurate and reliable motioning method for slopes. However, slope-mounted sensor systems are ineffective to evaluate the overall deformation of large slopes because measured data from the each slope-mounted sensor represent the single cross-area of the slope. In this study, terrestrial light detection and ranging system (LiDAR) was used to evaluate the overall slope deformation without slope-mounted sensor system. The testbed slope is located in ○○ nuclear power plant site. The length, height, and slope angle of the slope is 1,700 m, 80 m and 34°, respectively. The measurement and analysis procedure are as follows: (1) point cloud data acquisition using terrestrial LiDAR, (2) station adjustment using global navigation satellite system (GNSS), (3) noise filtering to remove unnecessary data (e.g., trees and transmission towers), and (4) slope digital elevation model (DEM) generation. The terrestrial LiDAR data that obtained in 2015 (53 scan positions) and in 2016 (91 scan positions) were compared in this study. There was no significant deformation on the testbed slope, however, slight sediment-scouring which has no impact on the slope stability was observed. Deformation analysis using terrestrial LiDAR data obtained periodically is cost-effective and reliable to monitor the overall deformation of the large slopes.

Influence of Tunnel Excavation on the Stability of a Bedded Rock Slope: A Case Study on the Mountainous Area in Southern Anhui, China

Danqing Song,Xiaoli Liu,Zhuo Chen,Jundong Chen,Jianhua Cai 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.1

Tunnel excavation has a substantial effect on the stability of rock slopes. The influence of tunnel excavation on the deformation and mechanical characteristics of a bedded slope is investigated by analysing the cumulative displacement, stress, and strain of the slope using the finite-element method (FEM) and field monitoring method. The deformation characteristics of the surrounding rock of the tunnel and slope with a supporting structure were analysed using the FEM under the conditions of support or without support. The results show that the deformation characteristics of the slope are controlled by its discontinuities. The deformation of the slope is mainly concentrated in the area above the second discontinuity; in particular, the deformation above the first discontinuity is the largest. In addition, the deformation and mechanical characteristics of the support structure are analysed. The supporting structure has influence on the deformation of the slope, which reduces the cumulative displacement, stress and strain. The shear strains of the second and third discontinuities are greatly influenced by the supporting structure. The mechanical properties of the tunnel support structure are controlled by the first discontinuity, and a stress concentration occurs near the first discontinuity. Moreover, based on the combination of the numerical and field test results, the deformation of the rock slope is closely related to the distance from the slope surface. Tunnel excavation mainly has a significant impact on the deformation of surface slope within a certain range, especially the slope deformation within the range of 4 m, which is the largest.

지상라이다를 이용한 사면파괴 거동분석

유창호,최윤수,김재명 대한공간정보학회 2008 Spatial Information Research Vol.16 No.3

Landslide, one of the serious natural disasters, has incurred a large loss of human and material resources. Recently, many forecasting or alarm systems based on various kinds of measuring equipment have been developed to reduce the damage of landslide. However, only a few of these equipments are guaranteed to evaluate the safety of whole side of land slope with their accessibility to the slope. In this study, we performed some experiments to evaluate the applicability of a terrestrial LiDAR as a surveying tool to measure the displacement of a land slope surface for a slope collapsing protection system. In the experiments, we had applied a slope stability method to a land slope and then forced to this slope with a load increasing step by step. In each step, we measured the slope surface with both a total station and a terrestrial LiDAR simultaneously. As the result of Slope Fracturing analysis using all targets, the LiDAR system showed that three was 1cm RMSE on X-axis, irregularity errors on Y-axis and few errors on Z-axis compare with Total Station. As the result of Slope Fracturing analysis using continuous targets, the pattern of Slope Fracturing was different according to the location of continuous targets and we could detect a continuous change which couldn’t be found using Total station. The accuracy of the LiDAR data was evaluated to be comparable to that of the total station data. We found that a LiDAR system was appropriate to measuring the behaviour of land slope. The LiDAR data can cover the whole surface of the land slope, whereas the total station data are available on a small number of targets. Moreover, we extracted more detail information about the behavior of land slope such as the volume and profile changes using the LiDAR data. 자연재해로 인한 수많은 피해 중 특히 산사태 등 사면붕괴로 인한 피해는 인간에게 많은 인적/물적 자원의 손실을 가져왔다. 이런 사면붕괴로 인한 피해를 줄이고자 사면붕괴 예방을 위해 다양한 계측장비를 이용하여 사면붕괴 예·경보 시스템을 구축하였다. 하지만 대상사면에 접근성 문제를 해결하고 위험 사면 전체에 대한 안전성 평가를 실시할 수 있는 효율적인 계측장비는 많지 않은 실정이다. 이에 사면붕괴예방을 위한 효율적인 계측장비로서 측량학적인 접근 방법으로 사면거동의 정확한 계측을 위해 지상라이다시스템을 이용하여 사면붕괴 예방을 위한 시스템의 활용가능성 판단을 위한 실험을 실시하였다. 본 연구에서는 인공으로 조성되어 사면안정화 공법이 적용된 토사사면에 사면상부에서 단계별로 실물 하중을 가하여 하중에 따른 사면의 거동을 Total Station과 지상라이다시스템을 이용하여 계측하였다. 두 시스템을 이용하여 계측한 성과의 정확한 비교 분석을 위해 두 시스템의 계측 결과를 동일한 좌표계로 일치시키는 3D Similarity Transformation을 통해 서로 다른 좌표계를 가지고 있는 두 좌표계를 하나의 좌표계로 통일시켜 사면이 실물하중에 어떤 거동이 일어나는지를 분석하였다. 타켓중심의 사면거동 분석결과, 지상라이다 시스템은 Total Station과 비교해 X축으로는 1cm이내의 차이가, Y축으로는 규칙적이지 않는 거동의 경향이 발생하고, Z축으로는 서로 유사한 경향을 보였다. 연속된 점에 대한 사면거동 분석결과, Y축의 위치에 따라 사면 하부에서 상부의 방향으로 사면거동의 경향이 다르게 나타나 Total Station에서 분석하기 어려웠던 사면의 연속적인 변화를 관찰할 수 있었다. 따라서 지상라이다 시스템은 Total Station에 버금가는 측량성과를 획득 하여 효율적인 사면모니터링을 위한 계측장비로 판단되었으며 기존의 사면모니터링기법의 한계를 대체 할 수 있는 측량학적 분석방법으로 많은 활용이 기대된다.

논문 : 계측결과 분석을 통한 석탄폐석 적치장 사면의 변형 특성

조용찬 ( Yong Chan Cho ),송영석 ( Young Suk Song ) 대한지질공학회 2013 지질공학 Vol.23 No.1

본 연구에서는 강원도 삼척시에 위치한 도계 석탄폐석 적치장 사면과 적치장 하부늬 자연사면에서의 변형을 조사하고, 이를 분석하였다. 석탄폐석 적치장 사면과 하부 자연사면의 거동을 조사하기 위하여 폐석적치장 상부에 신축변위계와 강우계를 설치하고, 폐식적치장 하부 자연사면에 지중경사계를 설치하였다. 신축변위계를 이용하여 폐석적치장 상부의 변위를 측정한 결과 누적강우량이 증가함에 따라 석탄폐석 적치장 사면 정상부에서 변위는 증가하는 것으로 나타났다. 한펴, 지중경사계를 이용하여 폐석적치장 하부 자연사면의 변위를 측정한 결과 누적강우량이 증가함에 따라 적치장 하부 자연사면의 최대수평변위는 증가하는 것으로 나타났다. 그러나 폐석적치장 하부 자연사면에서 지하수위는 강우에 따른 변화가 없는 것으로 측정되었다. 계측결과에 따르면, 석탄폐석 적치장의 변형은 강우와 밀접한 관계가 있음을 확일 할 수 있다. 석탄폐석 적치장 사면은 강우침투로 인하여 단위증량이 증가하게 되고, 이는 석탄폐석 적치장 사면의 변형을 유발하였다. 그리고 적치장 하부 자연사면의 변형은 강우침투로 위한 석탄폐석 적치장의 하중증가에 의해 발생된 것으로 판단된다. Deformation of a slope at a coal waste depot and the natural slope under the depot was surveyed and investigated at Dogye village in Samcheock city. Gangwon Province. To investigate the behaviors of the slopes, wire sensors and a rain gauge were installed on the erest of the waste depot slope and inclinometers were installed in the natural slope. The results of deformation monitoring at the crest of the waste depot slope sing wire sensors revealed increased deformation with increasing cumulative rainfall. The results of monitoring horizontal deformation of the natural slope revealed that maximum horizontal deformation was also affected by cumulative precipitation. However, the ground-water level at the natural slope showed no change with rainfall. These measurements confirm that deformation at coal mine waste deposte depots is closely related to precipitation, indicating that self-loading at such depots increases with rainfall infiltration, thus causing deformation of the waste depot slope. In addition, increasing the self-load of the coal mine waste depot may cause deformation of the underlying natural slope.

논문 : 터널출입구 시공에 따른 석회암 사면의 안정성 및 거동 분석

송영석 ( Young Suk Song ),윤중만 ( Jung Mann Yun ) 대한지질공학회 2013 지질공학 Vol.23 No.3

석회암 사면에서 터널 출입구를 시공하기 위하여 진입로를 개설하던 중 사면붕괴가 발생되었다. 사면의 붕괴원인을 조사하기 위하여 현장조사, 실내시험 및 수치해석을 수행하였다. 수치해석결과에 따르면 터널 출입구 진입로 개설이전 사면안전율은 1.0이하이며, 진입로 개설이후 사면안전율은 더 저하되는 것으로 나타났다. 그리고 진입로 개설이후 전단변형률 및 소성영역은 사면상부에서 하부로 전이되므로 사면활동영역이 증가되어 사면안정성을 저하시키는 것으로 해석되었다. 터널 출입구 시공을 위해서는 해당사면에 대한 안정성을 확보하여야 하므로, 대상현장의 조건을 고려하여 록볼트, 록앵커 및 FRP 그라우팅을 사면에 보강하는 것으로 결정하였다. 적용된 사면보강공법의 효과를 확인하기 위하여 현장계측을 수행하였다. 현장계측결과 사면지반의 수평변위는 매우 미소하며, 대부분 발생된 이후 다시 회복되는 탄성거동을 보였다. 그리고 록볼트 및 앵커축력은 터널굴착작업 및 장마기간에 의한 영향보다는 사면굴착작업시 영향을 가장 크게 받으며, 터널굴착작업이후 수렴하는 경향을 보이므로 대상사면은 안정한 상태임을 확인할 수 있다. A calcareous rock slope failed during excavation of the slope for construction of a tunnel entrance. The slope is located at the construction site for widening highway in Yeongwol, Korea, Field surveys, laboratory tests, and numerical analyses were performed to determine the reason for the slope failure. The numerical analysis revealed that the safety factor of the slope before construction of the entrance was less than I, and that this decreased after construction. After construction of the entrance, the sliding zone of the slope increased and slope stability decreased because the shear strain and plastic zone in the slope over the tunnel entrance showed an increase relative to the lower part of the slope. To enhance the stability of the slope for construction of the tunnel entrance. countermeasures such as rock bolts, rock anchors, and FRP (Fiber glass Reinforced Plastic) grouting were adopted in light of the field conditions. Serial field monitoring performed to confirm the reinforcing effects of the adopted countermeasures revealed a small amount of horizontal deformation of the slope soils, most of the elastic deformation that can regain its former value. In addition, the axial forces of the rock bolt and anchor were more strongly affected by slope excavation during construction or the tunnel entrance than by tunnel excavation or the rainy season, and the axial forces tended to converge after excavation of the tunnel. Therefore, we can confirm that the slope is currently safe.

현장 모니터링 결과를 이용한 광미 적치사면 안정성의 수치해석적 연구

송영석 ( Young-suk Song ) 대한지질공학회 2017 지질공학 Vol.27 No.1

광미 적치사면에서 측정된 모니터링 결과와 현장조건을 고려한 수치해석결과를 이용하여 강우시 불포화 토층내 모관흡수력 변화를 비교하고 이를 토대로 사면안정해석을 수행하였다. 이를 위하여 계측기간 동안 강우강도가 가장 크게 발생된 기간(72시간)을 선정하고, 대상기간 동안의 모관흡수력과 강우자료를 분석하였다. 그리고 현장에서 측정된 강우자료를 적용하여 침투 및 사면안정해석을 수행하였다. 강우에 따른 사면내 침투거동을 해석하기 위하여 SEEP/W를 활용하고 사면내 침투깊이를 고려한 사면안정해석을 위하여 SLOPE/W를 활용하였다. 먼저 현장에서 측정된 강우자료를 적용하여 SEEP/W를 이용한 침투해석을 수행하였다. 침투해석으로 계산된 모관흡수력과 현장계측으로 측정된 모관흡수력을 비교한 결과 모관흡수력의 크기에서는 다소 차이가 있으나 시간에 따른 변화양상은 유사한 것으로 나타났다. 그리고 침투해석결과와 연동하여 SLOPE/W를 이용한 사면안정해석을 수행한 결과 강우강도가 급속하게 증가되는 시점에서 사면안전율은 크게 감소하였으며, 이후 강우가 발생되지 않는 경우 사면안전율이 회복되는 것으로 해석되었다. Variations in matric suction were compared between field measurements and numerical analysis for a tailings dump slope. We performed an analysis of slope stability using precipitation records measured in the field, selecting the period (72 hours) of highest rainfall intensity during the field monitoring, for which the matric suction and rainfall records measured in the field were analyzed. In addition, we applied the precipitation records of this period to the numerical analysis. SEEP/W and SLOPE/W were used to analyze the seepage flow in the slope due to rainfall and to investigate the slope stability considering the wetting front depth from the ground surface, respectively. The seepage analysis, using SEEP/W, was carried out on the rainfall data obtained in the field. Comparisons between the field monitoring data and simulation results for matric suction show some quantitative difference but similar patterns of temporal variation. According to the results of slope stability analysis using SLOPE/W and the results of seepage analysis, the safety factor of the slope showed a sudden increase at the point of rapid increase in rainfall intensity. It then recovered because subsequent rainfall was scarce. Therefore, the stability of the tailings dump slope can be reasonably estimated if seepage and slope stability analyses, based on precipitation records, have been carried out.

흙사면의 체적함수비 계측을 통한 사면파괴 예측기법 개발

김만일 ( Man Il Kim ),( Makoto Nishigaki ) 대한지질공학회 2006 지질공학 Vol.16 No.2

강우에 의한 사면파괴의 초기단계 및 과정을 규명하기 위하여 실내 사면모델 시험결과를 분석하였다. 이 파괴 초기단계와 관련된 수리학적 상호관계를 파악하기 위해 인공강우 살포동안 사면모델 내 체적함수비 변화를 측정하는데 목적을 두었다. 사면파괴의 과정은 인공강우동안 사면 하단부의 유출면 발달에 의해 파괴를 발생시키는 요인으로 작용하였다. 따라서 국부적인 사면파괴를 예측하기 위해서는 강우에 의해 발생된 침투수의 침투특성에 대한 장기적인 계측이 매우 중요하다. 사면 내에서 강우에 의한 침윤선의 침투 및 지하수위 상승과 밀접한 연관성을 갖는 체적함수비 변화를 3가지의 침투변화(phase I, phase II, phase III)로 나누어 사면파괴를 계측할 수 있는 수리학적 측면으로 접근하였다. 따라서 체적함수비가 급격히 증가하는 phase III 단계부터는 사면파괴 발생 가능성이 매우 증가함을 파악하였다. 그러므로 사면 내체적함수비 변화를 연속적으로 계측함으로써 강우에 의한 사면파괴의 발생을 효율적이고 실질적으로 예측할 수 있을 것으로 판단된다. This study presents the results of a series of laboratory scale slope failure experiments aimed at clarifying the process and the condition leading to the initiation of rainfall-induced slope failures. For the evaluation of hydrologic response of the model slopes in relation the process of failure initiation, measurements were focused on the changes in volumetric water content during the initiation process. The process leading to failure initiation commences by the development of a seepage face. It appears reasonable to conclude that slope failures are a consequence of the instability of seepage area formed at the slope surface during rainfall period. Therefore, this demonstrates the importance of monitoring the development seepage area for useful prediction about the timing of a particular failure event. The hydrologic response of soil slopes leading to failure initiation is characterized by three phases (phase I, II and III) of significant increase in volumetric water content in association with the ingress of wetting front and the rise of groundwater level within the slope. The period of phase III increase in volumetric water content can be used to initiate advance warning towards a failure initiation event. Therefore, for the concept outlined above, direct and continuous monitoring of the change in volumetric water content is likely to provide the possibility for the development of a reliable and effective means of predicting the occurrence of rainfall-induced slope failures.

Applications of New Remote Sensing Technology to Natural Rock Slope Stability Analysis

( D Jean Hutchinson ),( David Bonneau ),( Dave Gauthier ),( Ioannis Farmakis ),( Kurri Reich ),( Paul-mark Difrancesco ),( Alex Graham ),( Melanie Coombs ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Assessment of stability of natural rock slopes located above infrastructure corridors, such as railways, and highways is required in order to evaluate potential for failure, loss of infrastructure capacity, and threats to public safety. As these slopes are not engineered, natural failure processes dominate. These are difficult to assess as direct physical access is generally not possible, and monitoring data is rarely available. A variety of remote sensing techniques from several vantage points and platforms have been deployed to evaluate rock slope stability, including LiDAR, photogrammetry, and Gigapan photography, from terrestrial and a variety of airborne platforms. Techniques have been developed to utilize both single data acquisitions as well as time sequential data sets. Analysis of data sets from different sources has proven to be useful in order to reduce loss of data due to occlusion and to provide different data types which are useful for different applications. A number of case histories of large rock slopes in the mountainous areas of western Canada will be used to demonstrate the integration of engineering geology into the remote sensing analysis of the rock slopes. Research products include assessment of the rockmass characteristics, an assessment of block volume, analysis of slope deformation and failures leading to forecasting of potential future events, dependent on the failure mechanism. As the database of rock slope case histories continues to build, we are moving ever closer to a more detailed understanding of rock slope failure modes, precursor events, deformation thresholds and the effect of triggering events.

A New Measure for Monitoring Intraoperative Somatosensory Evoked Potentials

Jin, Seung-Hyun,Chung, Chun Kee,Kim, Jeong Eun,Choi, Young Doo The Korean Neurosurgical Society 2014 Journal of Korean neurosurgical society Vol.56 No.6

Objective : To propose a new measure for effective monitoring of intraoperative somatosensory evoked potentials (SEP) and to validate the feasibility of this measure for evoked potentials (EP) and single trials with a retrospective data analysis study. Methods : The proposed new measure (hereafter, a slope-measure) was defined as the relative slope of the amplitude and latency at each EP peak compared to the baseline value, which is sensitive to the change in the amplitude and latency simultaneously. We used the slope-measure for EP and single trials and compared the significant change detection time with that of the conventional peak-to-peak method. When applied to single trials, each single trial signal was processed with optimal filters before using the slope-measure. In this retrospective data analysis, 7 patients who underwent cerebral aneurysm clipping surgery for unruptured aneurysm middle cerebral artery (MCA) bifurcation were included. Results : We found that this simple slope-measure has a detection time that is as early or earlier than that of the conventional method; furthermore, using the slope-measure in optimally filtered single trials provides warning signs earlier than that of the conventional method during MCA clipping surgery. Conclusion : Our results have confirmed the feasibility of the slope-measure for intraoperative SEP monitoring. This is a novel study that provides a useful measure for either EP or single trials in intraoperative SEP monitoring.