• Transactions of the Korean hydrogen and new energy society
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• v.25 no.6
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• pp.609-619
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• 2014

In the present study, the frequency of the undesired accident was estimated for a quantitative risk assessment of a large-scale hydrogen liquefaction plant. As a representative example, the hydrogen liquefaction plant located in Ingolstadt, Germany was chosen. From the analysis of the liquefaction process and operating conditions, it was found that a $LH_2$ storage tank was one of the most dangerous facilities. Based on the accident scenarios, frequencies of possible accidents were quantitatively evaluated by using both fault tree analysis and event tree analysis. The overall expected frequency of the loss containment of hydrogen from the $LH_2$ storage tank was $6.83{\times}10^{-1}$times/yr (once per 1.5 years). It showed that only 0.1% of the hydrogen release from the $LH_2$ storage tank occurred instantaneously. Also, the incident outcome frequencies were calculated by multiplying the expected frequencies with the conditional probabilities resulting from the event tree diagram for hydrogen release. The results showed that most of the incident outcomes were dominated by fire, which was 71.8% of the entire accident outcome. The rest of the accident (about 27.7%) might have no effect to the population.

• Proceedings of the Korean Reliability Society Conference
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• 2000.04a
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• pp.239-246
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• 2000

This paper presents a new dynamic approach for assessing feasibility associated with the implementation of accident management strategies by the operators. This approach includes the combined use of both the concept of reliability physics and a dynamic event tree generation scheme. The reliability physics is based on the concept of a comparison between two competing variables, i.e., the requirement and the achievement parameter, while the dynamic event tree generation scheme on the continuous generation of the possible event sequences at every branch point up to the desired solution. This approach is applied to a cavity flooding strategy in a reference plant, which is to supply water into the reactor cavity using emergency fire systems in the station blackout sequence. The MAAP code and Latin Hypercube sampling technique are used to determine the uncertainty of the requirement parameter. It has been demonstrated that this combined methodology may contribute to assessing the success likelihood of the operator actions required during accidents and therefore to developing the accident management procedures.

• 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.

• Journal of Navigation and Port Research
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• v.40 no.6
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• pp.391-400
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• 2016

A number of maritime accidents, and accident response activities, including the command and control procedures that were implemented at accident scenes, are analyzed to derive useful information about responding to maritime accidents, and to understand how the chain of events developed after the initial accident. In this research, a new concept of a 'risk based accident response support system' is proposed. In order to identify the event chains and associated hazards related to the accident response activities, this study proposes a 'Brainstorming technique for scenario identification', based on the concept of the HAZID technique. A modified version of Event Tree Analysis was used for quantitative risk analysis of maritime accident response activities. PERT/CPM was used to analyze accident response activities and for calculating overall (expected) response activity completion time. Also, the risk based accident response support system proposed in this paper is explained using a simple case study of risk analysis for oil tanker grounding accident response.

• Journal of the Korean Society of Safety
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• v.31 no.5
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• pp.16-21
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• 2016

The purpose of this paper is to conduct ETA on 15 components of power installations: the DS/LBS, LA, MOF, CT, PT, A/V meter, VCB, OCR, COS, PF, Transformer, Condenser(C), Grounding, Cable and Connector. To achieve that, power installations work flow and its components are categorized. Based on performance, human, environmental, management, and safety, this paper drew Initiation events (IE) and End states (ES). ETA is applied to the main functions of each component, and the end states that may occur in one initiation event are suggested. In addition, detailed classification was performed to induce various end states on the basis of the suggested initiation events. If the suggested IEs and ESs are applied on the basis of power installations event cases, it is expected to prevent the same kinds of accident and operate power installations safely.

• Nuclear Engineering and Technology
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• v.21 no.3
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• pp.205-215
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• 1989

The EVNTREISS code, used as a basis of the present work, is highly complex and versatile in comparison with the previous CET used in the WASH-1400 study. Since the construction of the EVNTREISS code is very complex and has not gone through a thorough validation and review process by an independent referee it is not surprising to find a few areas of improvement and several inherent problems of the code. The present study is thus initiated to identify all the problems and areas of improvement for the EVNTREISS code and modify the code according to the insights gained from the experience of reproducing the Zion containment response analysis performed at the Brookhaven National Laboratory. As a result of this study, several areas of improvement for the EVNTREISS code have been identified and a few problems of the code have been resolved in addition to the reproduction of the Zion results. Finally, the modified code can now be run by a personal computer and can be used in the analysis of a Large Dry PWR containment response for severe accidents.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.5
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• pp.319-325
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• 2021

The 2011 East Japan Earthquake caused accidents at a number of nuclear power plants in Fukushima, highlighting the need for a study on the seismic safety of multiple NPP (Nuclear Power Plant) units. In the case of nuclear power plants built on a site that shows a similar seismic response, there is at least a correlation between the seismic damage of structures, systems, and components (SSCs) of nuclear power plants. In this study, a probabilistic seismic safety assessment was performed for the loss of essential power events of twin units. To derive an appropriate seismic damage correlation coefficient, a probabilistic seismic response analysis was performed. Using the external event mensuration system program, we analyzed the seismic fragility and seismic risk by composing a failure tree of multiple loss of essential power events. Additionally, a comparative analysis was performed considering the seismic damage correlation between SSCs as completely independent and completely dependent.

• Fire Science and Engineering
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• v.22 no.5
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• pp.35-42
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• 2008

With the huge navy projects such KDX-III, LPX, bigger and more complicated vessel constructions are being underway in navy. In this paper, considering these trends, we performed a risk analysis on the navy vessel for the fatality of soldiers on board and presented the risk level with FN curve. Assuming a fire occurs in one of the soldier bedrooms, we established event tree to visualize the possible development scenarios and calculated the fatality for each scenario. The critical condition to survive inside the bedroom was obtained through CFAST program.

• Journal of the Korean Institute of Gas
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• v.7 no.1 s.18
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• pp.10-18
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• 2003

Consequence model has been suggested to evaluate consequence of city gas accident considering actual situation. Through event tree analysis(ETA), probable accidents were summarized and listed. Then release rate was calculated both sonic and subsonic conditions. Among city gas accidents, fire damage is the dominant one and mainly discussed; fatality, burning injury, and damage to building were estimated using the consequence model suggested. With an appropriate conditions, calculating total cost by accident was suggested.

• Journal of Radiation Protection and Research
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• v.29 no.2
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• pp.129-139
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• 2004

Recently, much attentions are paid to the risk associated with increased uses of medium size radiation sources in medical and industrial fields. In this study, radiation risks to the worker and to the general public due to $^{99m}Tc$ generator were assessed for both normal and accident conditions. Based on the event tree technique, exposure scenarios for various situations were derived. Uncertainty analysis based on the Monte-Carlo technique was applied to the risk assessment for workers and members of the public in the vicinity of the work place. In addition, sensitivity analysis was performed on each of the five independent input parameters to identify importance of the parameters with respect to the resulting risk. Because the frequencies of normal tasks are fat higher than those of accidents, the total risk associated with normal tasks were higher than the accident risk. The annual dose due to normal tasks were $0.6mSv\;y^{-1}$ for workers and $0.014mSv\;y^{-1}$ for public, while in accident conditions $3.96mSv\;y^{-1}\;and\;0.0016mSv\;y^{-1}$, respectively. Uncertainty range of accident risk was higher by 10 times than that of normal risk. Sensitivity analysis revealed that source strength, working distance and working time were crucial factors affecting risk. This risk analysis methodology and its results will contribute to establishment of risk-informed regulation for medium and large radioactive sources.