• Nuclear Engineering and Technology
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• v.15 no.1
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• pp.11-22
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• 1983

The reliability of the Chemical and Volume Control System has been analyzed in a pressurized water reactor. The boration failure was taken to be the top event for this reliability analysis. A detailed fault tree was constructed and the minimal cut sets were derived. It was computed that the unavailability of the Chemical and Volume Control System due to boration failure was 1.497$\times$10$^{-5}$ during plant operation. It was found that the reliability of boric acid transfer pumps were the most important factors in the availability of the Chemical and Volume Control System. As expected, human errors also introduce the high system unavilability.

• Information and Communications Magazine
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• v.25 no.6
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• pp.3-11
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• 2008

사용 편의나 안전 서비스를 위해 자동차에 내장되는 전자장치(ECU: Electronic Control Unit)는 증가하고 분산 네트워크 구조에서 운영되도록 네트워크 기반 응용 SW는 더욱 복잡해진다. 복잡해지고 분산화되는 ECU에 적용 가능한 응용서비스 개발을 위해 운영체제에서부터 플랫폼 및 응용 SW에 이르기까지 다양한 분야의 산업 표준화가 진행되고 있다. 운영체제 분야에서는 OSEK/VDX, SW 플랫폼 및 응용서비스 분야에서는 AUTOSAR, 응용서비스의 안전과 신뢰성 검증을 위하여 IEC-61508등에 근거하는 FTA(Fault Tree Analysis) 및 FMEA(Failure Mode and Effect Analysis) 등을 SW 분야에서도 반영하는 추세이다. 본 논문에서는 자동차 전자장치에 사용되는 IT기술의 접목 분야별 표준화 동향과 각 국가 및 지역별 추진방향을 살펴본다.

• Proceedings of the Korea Information Processing Society Conference
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• 2020.11a
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• pp.1097-1100
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• 2020

챗봇(Chatbot)은 자연어처리기술 등 인공지능 기술을 기반으로 한 사용자 친화적인 대화 방식 인터페이스를 제공하는 장점이 있어, 금융, 상담, 주문 등 다양한 산업 분야에서 적용되고 있다. 그러나, 챗봇의 응답이 사용자의 정신 모형과 불일치하는 경우, 다음 대화를 이어가는데 어려움을 야기하게 된다. 그러므로, 챗봇의 사용성을 확보하기 위해서는 응답 오류의 제거 또는 완화가 필수적이다. 기존의 챗봇의 사용성 개선과 관련된 연구들은 설문조사와 인터뷰 등 사용성 평가를 통해 상위 수준의 개선 방향만을 제안하고 있다. 따라서, 챗봇 개발 시, 실무자들이 응답 오류의 문제점을 분석하고, 이를 해결하기 위한 구체적인 개선 방안을 제시하는 데 한계가 있었다. 본 논문에서는 FMEA(Failure Modes and Effects Analysis) 기법을 활용해, 응답 오류의 치명도를 파악하고, 치명적인 오류들에 대해서는 FTA(Fault Tree Analysis) 기법을 기반으로 원인 분석을 실시하여 구체적으로 문제를 해결하기 위한 프로세스를 제안한다. 본 프로세스의 효용성을 검증하기 위해 주문 도메인의 챗봇에 적용해 보았다.

• Proceedings of the KIPE Conference
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• 2020.08a
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• pp.449-450
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• 2020

본 논문에서는 부스트 컨버터와 벅-부스트 컨버터의 동작 특성을 고려하여 Fault Tree Analysis(FTA)를 작성하고 같은 용량으로 설계하여 동작 온도에 따른 고장률의 차이를 비교 및 분석한다. 승압용 컨버터로 사용되는 부스트 컨버터와 벅-부스트 컨버터의 파라미터 설정에 따른 인덕터의 고장률과 커패시터의 고장률을 계산한다. 또한 두 컨버터의 설계 파라미터에 의해 달라지는 커패시터 고장률과 정격전압 차이에 의해 달라지는 다이오드의 고장률을 구한다. 각 소자의 부품 고장률은 MIL-HDBK-217F를 이용하여 구한다. 작성한 FTA에 부품 고장률을 적용하여 고장률과 평균고장시간을 예측한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.4 no.1
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• pp.7-12
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• 2003

The purpose of testability analysis is to estimate the difficulty of testing a stuck-at fault in logic circuits. A good testability measurement can give an early warning about the testing problem so as to provide guidance in improving the testability of a circuit. There have been researches attempting to efficiently compute the testability analysis. Conventional testability measurements, such as COP and SCOAP, can calculate the testability value of a stuck-at fault efficiently in a tree-structured circuit but may be very inaccurate for a general circuit. The inaccuracy is due to the ignorance of signal correlations for making the testability analysis linear to a circuit size. This paper proposes an efficient method for computing testability analysis, which takes into account signal correlation to obtain more accurate testability. The proposed method includes the algorithm for identifying all reconvergent fanouts in a given n circuit and the gates reachable from them, by which information related to signal correlation is gathered.

• Journal of Digital Convergence
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• v.15 no.8
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• pp.69-83
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• 2017

This study aims to analyze the causes of a new product failure by using system safety methods, focusing on the case of Samsung Galaxy Note7. However, when analyzing the causes of a product failure, if only technical problems are too emphasized, it is likely to miss other more meaningful causes of a failure. Thus, we claim that the root causes of a product failure should be identified in a broad perspective of integrated systems that include non-technical as well as technical elements. With this viewpoint, we investigated the failure of Samsung Galaxy Note7, by using Root Cause Analysis(RCA) and Fault Tree Analysis (FTA). The results showed that it is necessary to address not only the technical issues but also other non-technical issues, such as a very impetuous launch of a new product due to a very tough competition in the market. Additionally, we also found that RCA and FTA could be a useful tool for analyzing the causes of a new product failure from the viewpoint of an integrated system comprising technical and management elements.

• Nuclear Engineering and Technology
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• v.30 no.6
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• pp.531-540
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• 1998

The DYLAM-3 code which overcomes the limitation of event tree/fault tree was applied to LOOP (Loss of Off-site Power) in the mid-loop operation employing HEPs (Human Error Probabilities) supplied by the ASEP (Accident Sequence Evaluation Program) and the SEPLOT (Systematic Evaluation Procedure for Low power/shutdown Operation Task) procedure in this study. Thus the time history of core uncovery frequency during the mid-loop operation was obtained. The sensitivity calculations in the operator's actions to prevent core uncovery under LOOP in the mid-loop operation were carried out. The analysis using the time dependent HEP was performed on the primary feed & bleed which has the most significant effect on core uncovery frequency. As the result, the increment of frequency is shown after 200 minutes duration of simulation conditions. This signifies the possibility of increment in risk after 200 minutes. The primary feed & bleed showed the greatest impact on core uncovery frequency and the recovery of the SCS (Shutdown Cooling System) showed the least impact. Therefore the efforts should be taken on the primary feed & bleed to reduce the core uncovery frequency in the mid-loop operation. And the capability of DYLAM-3 in applying to the time dependent concerns could be demonstrated.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.981-988
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• 2023

A seismic event caused an accident at the Fukushima Nuclear Power Plant, which further resulted in simultaneous accidents at several units. Consequently, this incident has aroused great interest in the safety of nuclear power plants worldwide. A reasonable safety evaluation of such an external event should appropriately consider the correlation between SSCs (structures, systems, and components) and the probability of failure. However, a probabilistic safety assessment in current nuclear industries is performed conservatively, assuming that the failure correlation between SSCs is independent or completely dependent. This is an extreme assumption; a reasonable risk can be calculated, or risk-based decision-making can be conducted only when the appropriate failure correlation between SSCs is considered. Thus, this study analyzed the effect of the failure correlation of SSCs on the safety of the system to realize rational safety assessment and decision-making. Consequently, the impact on the system differs according to the size of the failure probability of the SSCs and the AND and OR conditions.

• Korean Chemical Engineering Research
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• v.52 no.6
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• pp.750-754
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• 2014

Quantitative risk analysis has been performed for a pervaporation process for production of high test peroxide. Potential main accidents are explosion and fire caused by a decomposition reaction. As the target process has a laboratory scale, the consequence is considered to belong to Category 3. An event tree has been developed as a model for occurrence of a decomposition reaction in the target process. The probability functions of the accident causes have been established based on the frequency data of similar events. Using the constructed model, the failure rate has been calculated. The result indicates that additional safety devices are required in order to achieve an acceptable risk level, i.e. an accident frequency less than $10^{-4}/yr$. Therefore, a layer of protection analysis has been applied. As a result, it is suggested to introduce inherently safer design to avoid catalytic reaction, a safety instrumented function to prevent overheating, and a relief system that prevents explosion even if a decomposition reaction occurs. The proposed method is expected to contribute to developing safety management systems for various chemical processes including concentration of hydrogen peroxide.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.339-345
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• 2012

RMembrane LNG storage tanks have been recently investigated to replace full-containment LNG storage tanks because of safety and cost aspects. Quantitative Risk Analysis (QRA) and Finite Element Method (FEM) were used to evaluate safety of membrane LNG storage tanks. In this study, structural safety evaluation results via FEM analysis showed that both membrane type and full-containment type cryogenic LNG storage tanks with 140,000 $m^3$ capacity were equivalently safe in terms of strength safety and leakage safety of a storage tank system. Also, Fault Tree Analysis (FTA) was used to improve the safety of membrane LNG storage tanks and membrane LNG tanks were modified by adding three safety equipments: impact absorber structure for the low part of the membrane, the secondary barrier to diminish the thermal stress of the corner part of the outer tank, and a pump catcher in case of falling of a pump. Consequently, the safety of the modified membrane LNG storage tanks were proved to be equivalent to that of full-containment LNG storage tanks.