• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.190-202
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• 2018

Maintaining the integrity of the major equipment in nuclear power plants is critical to the safety of the structures. In particular, the soundness of the piping is a critical matter that is directly linked to the safety of nuclear power plants. Currently, the limit state of the piping design standard is plastic collapse, and the actual pipe failure is leakage due to a penetration crack. Actual pipe failure, however, cannot be applied to the analysis of seismic fragility because it is difficult to quantify. This paper proposes methods of measuring the failure strain and deformation angle, which are necessary for evaluating the quantitative failure criteria of the steel pipe elbow using an image measurement system. Furthermore, the failure strain and deformation angle, which cannot be measured using the conventional sensors, were efficiently measured using the proposed methods.

• Nuclear Engineering and Technology
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• v.51 no.2
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• pp.561-572
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• 2019

In the design criterion for the nuclear power plant piping system, the limit state of the piping against an earthquake is assumed to be plastic collapse. The failure of a common piping system, however, means the leakage caused by the cracks. Therefore, for the seismic fragility analysis of a nuclear power plant, a method capable of quantitatively expressing the failure of an actual piping system is required. In this study, it was conducted to propose a quantitative failure criterion for piping system, which is required for the seismic fragility analysis of nuclear power plants against critical accidents. The in-plane cyclic loading test was conducted to propose a quantitative failure criterion for steel pipe elbows in the nuclear power plant piping system. Nonlinear analysis was conducted using a finite element model, and the results were compared with the test results to verify the effectiveness of the finite element model. The collapse load point derived from the experiment and analysis results and the damage index based on the stress-strain relationship were defined as failure criteria, and seismic fragility analysis was conducted for the piping system of the BNL (Brookhaven National Laboratory) - NRC (Nuclear Regulatory Commission) benchmark model.

• Journal of the Korean Society of Safety
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• v.32 no.6
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• pp.46-53
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• 2017

The risk is expressed as consequence of damage multiplied by likelihood of failure. The installation of a protective system reduces the risk by reducing the likelihood of failure at the facility. Also, the protective system has different effects on the likelihood of failure according to the proof test cycle. However, when assessing risks in the Off-site Risk Assessment (ORA) system, the variation in risk was not reflected according to the proof test cycle of protective system. This study was conducted to examine the need for proof test and the importance of cycle setting by applying periodic proof test of the protective system to ORA. The results showed that the likelihood of failure and the risk increased with longer proof test cycle. The risk of a two-yearly proof test was eight times greater than that of a three-month cycle. From the results, the protective system needs periodic proof test. Untested protective system for a long term cannot be reliable because it is more likely to be failed state when it is called upon to operate. In order to reduce the risk to an acceptable level, it is effective to differently set the proof test cycle according to the priority. This study suggested a more systematic and accurate risk analysis standard than ORA. This standard is expected to enable an acceptable level of risk management by systematically setting the priority and proof test cycle of the protective system. It is also expected to contribute to securing the safety of chemical facilities and at the same time, will lead to the development of the ORA system.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.24 no.63
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• pp.89-99
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• 2001

This paper proposes assessment of quality management activities based on cost of quality. Cost of quality is considered prevention cost, appraisal cost, internal failure cost, external failure cost in this paper. This paper shows quality cost magement system in thermal power site devision according to activity analysis. Cost of quality in power industries provides a valuable method of both proving the need for improvement and giving a starting point for projects.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.04a
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• pp.161-168
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• 2004

This study describes the behavior and failure probability of basic structural member in case of fire for the research of safety assessment on onshore structure. Fire safety assessment can be done by comparing fire resistance of members with fire severity of heat load For more Practical applications, the commercial structural analysis program is linked with the in-house code and gets the limiting temperature by analyzing structural strength of member with elasto-plastic analysis and large deflection analysis. AFOSM method is utilized to obtain the failure probability against the fire. The examples of rather simple structures such as beams and plates are applied to explain and verify the procedure of fire safety assessment.

• Journal of the Korean Society of Industry Convergence
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• v.10 no.3
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• pp.149-155
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• 2007

Damage assessment and Damage index for RC members failed in flexure was investigated by using the nonlinear finite element analysis, included with nonlocal constitutive law, which is analyzed for the localization of the failure on the post-peak region. In the nonlcal constitutive law, The local strains obtained at gauss points were averaged over a particular length, i.e. characteristic length and it was used to evaluate the damage of RC column member. As the analysis results, The value of nonlocal strain shows less mesh sensibility. In the damage assessment, It was confirmed that evaluations of damage of RC member were able to use nonlocal compressive strain on a cover concrete and a core concrete of the member. Moreover it was confirmed that damage process for the statically indeterminate structure was able to evaluate the damage context of the component members of the structure.

• Proceedings of the Safety Management and Science Conference
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• 2007.11a
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• pp.275-298
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• 2007

Recently, all kind of 21C-typed electronic goods show the tendency of hightechnology and digital convergence rapidly. Also, failure mechanism which differs from original goods concept presents. Today, failure mechanism which differs from one that was happened by restricted harmful environment material before adapted the raw of environment material is changing the paradigm of reliability engineering. Thus, when applied the environment matter of original and secondary material at the electronic goods were removed, reliability assessment method and prediction stay into low level. This study suggests as solution to overcome these phenomenon. The study on the management method of environmental restriction substances which is recognized as important element in the reliability assessment about environment material of electronic goods and the study on reliability assessment method of PWB without environment material are progressed.

• Journal of the Korea Safety Management & Science
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• v.9 no.6
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• pp.55-68
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• 2007

Recently, all kind of 21C-typed electronic goods show the tendency of hightechnology and digital convergence rapidly. Also, failure mechanism which differs from original goods concept presents. Today, failure mechanism which differs from one that was happened by restricted harmful environment material before adapted the raw of environment material is changing the paradigm of reliability engineering. Thus, when applied the environment matter of original and secondary material at the electronic goods were removed, reliability assessment method and prediction stay into low level. This study suggests as solution to overcome these phenomenon. The study on the management method of environmental restriction substances which is recognized as important element in the reliability assessment about environment material of electronic goods and the study on reliability assessment method of PWB without environment material are progressed.

• International journal of steel structures
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• v.18 no.4
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• pp.1242-1251
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• 2018

Not all loads contribute to fatigue crack propagation in the welded detail of steel bridges when they are subjected to variable amplitude loading. For fatigue assessment, therefore, non-contributing stress cycles should be truncated. However, stress range truncation is not considered during typical fatigue reliability assessment. When applying the first order reliability method, stress range truncation occurs mismatch between the expected number of cycles to failure and the number of cycles obtained at the time of evaluation, because the expected number of cycles only counts the stress cycles that contribute to fatigue crack growth. Herein, we introduce a calibration factor to coordinate the expected number of cycles to failure to the equivalent value which includes both contributing and non-contributing stress cycles. The effectiveness of stress range truncation and the proposed calibration factor was validated via case studies.

• Proceedings of the Safety Management and Science Conference
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• 2004.05a
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• pp.271-276
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• 2004

The risk assessment model is an important subsystem for effective establishment and operation of EMS (environment management system). In case of poor risk assessment long-term and large-scale failure expense might be brought. Managing policy, target and other indices based on risk assessment can guarantee successful EMS. In this paper, we aim at comparative analysis of various risk methods and propose an alternative risk assessment model for EMS.