• 품질경영학회지
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• 제21권1호
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• pp.78-95
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• 1993

The art of designing and analyzing fault-tolerant computers is surveyed with special emphasis on problems of analyzing the behavior of computers that have autonomous repair capability. The survey covers the following topics : (1) general issues in computer reliability, (2) fault-tolerance state relations and requirements, (3) computational hierarchy, (4) fault characteristics, (5) fault diagnosis, (6) fault-tolerance schemes for logic network and machines, (7) fault-coverage effects, and (8) fault-tree analysis of coverage. This paper does not include techniques for verifying nonredundant hardware or system software designs or for verifying the correctness of application programs.

• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2238-2249
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• 2020

In a seismic PSA, dependency among seismic failures of components has not been explicitly modeled in the fault tree or event tree. This dependency is separately identified and assigned with numbers that range from zero to unity that reflect the level of the mutual correlation among seismic failures. Because of complexity and difficulty in calculating combination probabilities of correlated seismic failures in complex seismic event tree and fault tree, there has been a great need of development to explicitly model seismic correlation in terms of seismic common cause failures (CCFs). If seismic correlations are converted into seismic CCFs, it is possible to calculate an accurate value of a top event probability or frequency of a complex seismic fault tree by using the same procedure as for internal, fire, and flooding PSA. This study first proposes a methodology to explicitly model seismic dependency by converting correlated seismic failures into seismic CCFs. As a result, this methodology will allow systems analysts to quantify seismic risk as what they have done with the CCF method in internal, fire, and flooding PSA.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1989년도 한국자동제어학술회의논문집; Seoul, Korea; 27-28 Oct. 1989
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• pp.805-812
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• 1989

An efficient diagnostic approach for real-time operation aiding expert system in chemical process plants is discussed. The approach is based on the hybrid of the simplified symptom tree(SST) and the fault consequence digraph(FCD), representation of propagation patterns of fault states. The SST generates fault hypothesis efficiently and the FCD resolve the real fault accurately. Frame based knowledge representation and object-oriented programming make diagnostic system general and efficient. Truth maintenance system enables robust pattern matching and provides enhanced explain facilities. A prototype expert system for supports operation of naphtha furnaces process, called OASYS, has been built and tested to demonstrate this methodology. Utilization of diversified process symbolic data, produced using dynamic normal standards, overcomes the problem of qualitative Boolean reasoning and enhance the applicability.

• Nuclear Engineering and Technology
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• 제39권2호
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• pp.123-128
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• 2007

In order to apply a static fault-tree (FT) method to a system or a plant whose configuration changes dynamically, condition gates and a post processing method are used to effectively accommodate these changes. An operator's performance change, which can be caused by these configuration changes, should also be considered to assess the risk to a plant in a more realistic manner. This study aims to develop an integrated framework to accommodate various configuration changes and their effect on an operator’s performance by using the FT model. We applied a condition-based human reliability assessment (CBHRA) method to consider various conditions endured by an operator. That is, we integrated the CBHRA method with the conventional post processing method for modeling the system configuration changes. The effect of the condition monitoring systems installed in a plant is also considered. In this study, we show an example application of the integrated framework to a probabilistic safety assessment for the shutdown phase of a nuclear power plant.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 심포지엄 논문집 정보 및 제어부문
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• pp.81-83
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• 2005

The Reactor Protection System (RPS) is a very important system in a nuclear power plant because the system shuts down the reactor to maintain the reactor core integrity and the reactor coolant system pressure boundary if the plant conditions approach the specified safety limits. This paper describes the unavailability assessment of a digital reactor protection system using the fault tree analysis technique. The fault tree technique can be expressed in terms of combinations of the basic event failures. In this paper, a prediction method of the hardware failure rate is suggested for a digital reactor protection system. and applied to the reactor protection system being developed in Korea.

• 한국안전학회지
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• 제12권4호
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• pp.180-190
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• 1997

A new method in the fault tree analysis (FTA) for the reliability calculation is suggested. Two steps are necessary in traditional method in evaluation of the occurrence probability of top event in fault tree (FT). The first step is to find the minimal outsets, and the second one is to substitute the result into the poincare equation. In order to reduce the enormous computing time of this method, lots of rapid algorithms have been developed. Almost of all achievements were, however, based on the partial structural properties of FT. In this paper, the FT is transformed to a non-linear graph G which has the same minimal outsets of original n, and then the reliability is calculated using the domination theory. In this new method, the required number of equation terms are at most $2^n$ (n is node number of graph G), while $2^m$-1 (m is the number of minimal cutsets) calculation terms are required in the poincare equation in traditional method. Since m>>n in general. our new method reduces the calculation time significantly.

• 한국멀티미디어학회논문지
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• 제20권11호
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• pp.1793-1802
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• 2017

In the recent years, IT and Network Technology has rapidly advanced environment in accordance with the needs of the times, the usage of the smart learning service is increasing. Smart learning is extended from e-learning which is limited concept of space and place. This system can be easily exposed to the various security threats due to characteristic of wireless service system. Therefore, this paper proposes the improvement methods of smart learning system security by use of faults analysis methods such as the FTA(Fault Tree Analysis) and FMECA(Failure Mode Effects and Criticality Analysis) utilizing the consolidated analysis method which maximized advantage and minimized disadvantage of each technique.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.671-675
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• 2008

Railway signal system is responsible for the safety operation of railway and performs vital functions as safe space control, route control and etc. These functions prevent collision accidents between trains and derailment accidents of trains. However, these accidents are occurred by some causes. It is necessary to analysis hazards, hazard frequency and risk contribution. And railway signal system must make practical application of the analysis results. This paper includes analysis results of railway accident data by FTA(Fault Tree Analysis) and hazards. Railway signal system must consider these hazards. This paper used the railway accident data of RSSB(Railway Safety & Standard Board) of UK. We will use the FTA result to set up a draft of safety criteria of railway signal system.

• 한국안전학회지
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• 제18권2호
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• pp.64-72
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• 2003

A new reliability assessment methodology is presented and the new method is compared with fault tree analysis. The system is modeled by directed graph at a new methodology, which is composed of nodes and arcs. The directed graph corresponds to the layout of chemical process and is easy to construct. Therefore, the directed graph analysis is applicable to the chemical process that has complex sequence. The example of fault tree analysis and directed graph analysis is given. The directed graph analysis has proved to be a valuable and useful method for the reliability assessment of chemical process.

• Nuclear Engineering and Technology
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• 제54권4호
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• pp.1213-1220
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• 2022

The Emergency Diesel Generator (EDG) is a critical and essential part of the Nuclear Power Plant (NPP). Due to past catastrophic disasters, critical systems of NPP like EDG are designed to meet high dependability requirements. Therefore, we propose a framework for the dynamic reliability assessment using the Fault Tree and the Dynamic Bayesian Network. In this framework, the information of the component's failure probability is updated based on observed data. The framework is powerful to perform qualitative as well as quantitative analysis of the system. The validity of the framework is done by applying it on several NPP systems.