• Nuclear Engineering and Technology
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• 제49권4호
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• pp.710-720
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• 2017

In Korea, many nuclear power plants operate at a single site based on geographical characteristics, but the population density near the sites is higher than that in other countries. Thus, multiunit accidents are a more important consideration than in other countries and should be addressed appropriately. Currently, there are many issues related to a multiunit probabilistic safety assessment (PSA). One of them is the quantification of a multiunit PSA model. A traditional PSA uses a Boolean manipulation of the fault tree in terms of the minimal cut set. However, such methods have some limitations when rare event approximations cannot be used effectively or a very small truncation limit should be applied to identify accident sequence combinations for a multiunit site. In particular, it is well known that seismic risk in terms of core damage frequency can be overestimated because there are many events that have a high failure probability. In this study, we propose a quantification method based on a Monte Carlo approach for a multiunit PSA model. This method can consider all possible accident sequence combinations in a multiunit site and calculate a more exact value for events that have a high failure probability. An example model for six identical units at a site was also developed and quantified to confirm the applicability of the proposed method.

• 대한토목학회논문집
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• 제13권3호
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• pp.59-67
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• 1993

부분구조법(部分構造法)으로 프리스트레스드 콘크리트 원자로격납건물(原子爐格納建物)의 지진에 대한 확률위험도분석이나 내진 안전여유평가시 상부구조에 관한 입력자료(入力資料)가 되는 구조물(構造物)의 고유전동수와 구조물 상부에서의 최대가 속도값의 구조변수(構造變數)에 대한 변동성이 연구되었다. 본 연구는 먼저 구조모델의 고유진동수에 가장 큰 영향을 미치는 구조변수를 결정하기 위하여 각 구조변수(構造變數)의 상대적(相對的) 민감도(敏感度)를 분석(分析)하였고, 각 변수의 결정에 포함될 수 있는 불확실성(不確實性)의 정도를 고려하여 Monte Carlo 수치모형실험을 수행하였다. 최대 가속도값의 변화는 직접적분(直接積分)에 의한 시간이력곡선법으로 분석되었다. 연구결과로 첫번째모드의 고유 진동수와 건물 정상부의 최대가속도값은 각 변수중 탄생계수의 영향을 가장 크게 받으며, 결정론적 방법으로 구한 값과 비교할 때 확률론적 방법으로 구한 값(평균+표준편차)은 (+)12% 정도 변함을 알 수 있다. 또한 휨강성의 불확실성을 고려하면 동적응답은 (-)4%~(+)14% 정도 달라진다.

• Nuclear Engineering and Technology
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• 제49권2호
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• pp.426-433
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• 2017

This paper describes the development process, the innovative techniques used and insights gained from the latest integrated, full scope, multistate Level 2 PSA analysis conducted at the Leibstadt Nuclear Power Plant (KKL), Switzerland. KKL is a modern single-unit General Electric Boiling Water Reactor (BWR/6) with Mark III Containment, and a power output of $3600MW_{th}/1200MW_e$, the highest among the five operating reactors in Switzerland. A Level 2 Probabilistic Safety Assessment (PSA) analyses accident phenomena in nuclear power plants, identifies ways in which radioactive releases from plants can occur and estimates release pathways, magnitude and frequency. This paper attempts to give an overview of the advanced modeling techniques that have been developed and implemented for the recent KKL Level 2 PSA update, with the aim of systematizing the analysis and modeling processes, as well as complying with the relatively prescriptive Swiss requirements for PSA. The analysis provides significant insights into the absolute and relative importances of risk contributors and accident prevention and mitigation measures. Thanks to several newly developed techniques and an integrated approach, the KKL Level 2 PSA report exhibits a high degree of reviewability and maintainability, and transparently highlights the most important risk contributors to Large Early Release Frequency (LERF) with respect to initiating events, components, operator actions or seismic component failure probabilities (fragilities).

• Earthquakes and Structures
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• 제2권3호
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• pp.207-232
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• 2011

The development of reliable earthquake mitigation plans and seismic risk management procedures can only be based on the establishment of comprehensive earthquake hazard and loss scenarios. Two cities, Grevena (Greece) and D$\ddot{u}$zce (Turkey), were used as case studies in order to apply a comprehensive methodology for the vulnerability and loss assessment of lifelines. The methodology has the following distinctive phases: detailed inventory, identification of the typology of each component and system, evaluation of the probabilistic seismic hazard, geotechnical zonation, ground response analysis and estimation of the spatial distribution of seismic motion for different seismic scenarios, vulnerability analysis of the exposed elements at risk. Estimating adequate earthquake scenarios for different mean return periods, and selecting appropriate vulnerability functions, expected damages of the water and waste water systems in D$\ddot{u}$zce and of the roadway network and waste water system of Grevena are estimated and discussed; comparisons with observed earthquake damages are also made in the case of D$\ddot{u}$zce, proving the reliability and the efficiency of the proposed methodology. The results of the present study constitute a sound basis for the development of efficient loss scenarios for lifelines and infrastructure facilities in seismic prone areas. The first part of this paper, concerning the estimation of the seismic ground motions, has been utilized in the companion paper by Kappos et al. (2010) in the same journal.

• Earthquakes and Structures
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• 제22권2호
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• pp.169-184
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• 2022

The importance of seismicity in developing countries and the strengthening of buildings is a topic of major importance. Therefore, the study of several solutions with the development of new technologies is of great importance to investigate the damage on retrofitted structures by using probabilistic methods. The Federal Emergency Management Agency considers three types of performance levels by considering different scenarios, intensity and duration. The selection and scaling of ground motions mainly depends on the aim of the study. Intensity-based assessments are the most common and compute the response of buildings for a specified seismic intensity. Assessments based on scenarios estimate the response of buildings to different earthquake scenarios. A risk-based assessment is considered as one of the most effective. This research represents a practical method for developing countries where exists many active faults, tall buildings and lack of good implementable approaches. Therefore, to achieve the main goal, two high-rise steel buildings have been modeled and assessed. The contribution of buckling-restrained braces in the elastic design of both buildings is firstly verified. In the nonlinear static range, both buildings presented repairable damage at the central top part and some life safety hinges at the bottom. The nonlinear incremental dynamic analysis was applied by 15 representative/scaled accelerograms to obtain levels of performance and fragility curves. The results shown that by using probabilistic methods, it is possible to estimate the probability of collapse of retrofitted buildings by buckling-restrained braces and tuned mass dampers, which are practical retrofitting options to protect existing structures against earthquakes.

• Earthquakes and Structures
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• 제20권1호
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• pp.71-86
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• 2021

This paper focuses on the development and assessment of the expected damage for the rocking response of rigid anchored blocks, with irregular geometry and non-uniform mass distribution, considering the site conditions and the seismicity of Mexico City. The non-linear behavior of the restrainers is incorporated to evaluate the pure tension and tension-shear failure mechanisms. A probabilistic framework is performed covering a wide range of block sizes, slenderness ratios and eccentricities using physics-based ground motion simulation. In order to incorporate the uncertainties related to the propagation of far-field earthquakes with a significant contribution to the seismic hazard at study sites, it was simulated a set of scenarios using a stochastic summation methods of small-earthquakes records, considered as Empirical Green's Function (EGFs). As Engineering Demand Parameter (EDP), the absolute value of the maximum block rotation normalized by the body slenderness, as a function of the peak ground acceleration (PGA) is adopted. The results show that anchorages are more efficient for blocks with slenderness ratio between two and three, while slenderness above four provide a better stability when they are not restrained. Besides, there is a range of peak intensities where anchored blocks located in soft soils are less vulnerable with respect to those located in firm soils. The procedure used in here allows to take decisions about risk, reliability and resilience assessment of different types of contents, and it is easily adaptable to other seismic environments.

• 한국구조물진단유지관리공학회 논문집
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• 제25권5호
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• pp.94-101
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• 2021

현재 국내에서 내진성능관리 실무에 사용되고 있는 내진성능관리-의사결정 지원기술은 개별시설물의 내진성능을 정성적인 지수 값에 근거한 내진보강 우선순위만을 결정하고 있어 내진보강이 되었음에도 불구하고 지진 시 도로가 정상적인 교통통행기능을 수행하지 못하는 상황이 발생하고 있다. 이러한 단점을 극복하고 도로망관점에서 내진성능관리를 수행할 수 있도록 의사결정에 필요한 다양한 판단자료를 제공할 수 있는 새로운 내진성능관리 의사결정지원 기술이 필요하다. 본 논문에서는 교량, 터널, 사면, 옹벽으로 구성된 포항시 도로망을 대상으로 "지진위험도평가"를 적용하여 정량적인 지진 전·후 직·간접 피해규모 산출, 내진보강 전후의 직·간접 피해규모 비교에 의한 내진보강효과 검토, 이를 통해 수행 할 수 있는 내진보강 우선순위 선정, 필요예산 계획, 방재도로선정 등의 다양한 의사결정 사항들을 제시하였다. 또한 지진 위험도평가 방법을 이용한 내진성능평가를 시각적으로 구현하여 의사결정자들이 직관적으로 의사결정을 수행할 수 있도록 지원하기위해 개발된 의사결정지원 소프트웨어를 소개하였다.

• Nuclear Engineering and Technology
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• 제49권7호
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• pp.1414-1422
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• 2017

Remote response technology has advanced to the extent that a robot system, if properly designed and deployed, may greatly help respond to beyond-design-basis accidents at nuclear power plants. Particularly in the aftermath of the Fukushima accident, there is increasing interest in developing disaster robots that can be deployed in lieu of a human operator to the field to perform mitigating actions in the harsh environment caused by extreme natural hazards. The nuclear robotics team of the Korea Atomic Energy Research Institute (KAERI) is also endeavoring to construct disaster robots and, first of all, is interested in finding out to what extent safety benefits can be achieved by such a disaster robotic system. This paper discusses a new approach based on the probabilistic risk assessment (PRA) technique, which can be used to quantify safety benefits associated with disaster robots, along with a case study for seismic-induced station blackout condition. The results indicate that to avoid core damage in this special case a robot system with reliability > 0.65 is needed because otherwise core damage is inevitable. Therefore, considerable efforts are needed to improve the reliability of disaster robots, because without assurance of high reliability, remote response techniques will not be practically used.

• 한국지진공학회논문집
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• 제16권3호
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• pp.35-42
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• 2012

암반지반에 주어진 등재해도 스펙트럼에 상응하는 원전부지 토사지반에서의 등재해도 스펙트럼을 도출하기 위한 확률론적 방법론을 제시하였다. 이를 위해 지진 운동 및 지반의 불확실성을 고려한 지반응답 해석을 통해 토사지반 지표에서의 지진동 증폭계수를 산정하였다. 증폭계수는 가장 상관관계가 높은 지반운동의 스펙트럴 가속도 규모와의 회귀분석을 통해 계산되었다. 이 방법론을 적용하여 국내 KNGR (Korean Next Generation Reactor) 및 APR1400 (Advanced Power Reactor 1400) 원전의 포괄부지 지반 중 B1, B4, C1 및 C3 지반을 대상으로 등재해도 스펙트럼을 도출하였다. 등재해도 스펙트럼을 통해 지진동 발생 빈도 별 위험 주파수 대역을 평가하고 분석하였다. 이 결과는 원전의 종합적 지진리스크 평가 결과를 보다 합리적으로 개선하는 데에 활용될 수 있으며, 향후 다양한 종류의 토사지반에 대한 등재해도 스펙트럼을 평가하는 데에 적용할 수 있을 것으로 기대된다.