• Journal of Navigation and Port Research
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• v.40 no.1
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• pp.21-26
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• 2016

Even in the marine industry was required the looser positioning performance as compared to other application domain, a high-quality positioning performance and reliability are becoming ever more important. The high-quality performance includes not only accuracy but also integrity, continuity, and availability. However, current DGPS service is not satisfying the minimum positioning performance requirements for maritime user proposed by IMO. Especially, no one can guarantee the required integrity performance by DGPS service. This paper presents the advanced monitoring concept to strengthen the performance of current DGPS through the enhanced monitoring, guarantee and notice functions. To this, the limitations of the integrity monitoring function of current DGPS are analyzed, and a countermeasure is prepared to improve the limitations of the current integrity monitoring function. This paper can be applied as basis research to improvement of the DGPS service.

• Proceedings of the Korean Nuclear Society Conference
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• 2003.05a
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• pp.146-146
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• 2003

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.5 no.2
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• pp.13-19
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• 2009

As the operating time in nuclear power plants (NPPs) increases, the integrity of nuclear components may be continually degraded due to aging effects of systems, structures and components. Recently, a number of NPPs are being operated beyond their design life to produce more electricity without shutting down. The critical issue in extending a lifetime is to maintain the level of safety during the extended operation period while satisfying the international regulatory standards. Therefore, it is beneficial to build a monitoring system to measure an aging status. In this paper, the Aging Monitor (AM) based on lots of aging database obtained from the operating plants and research results on the aging effects was developed to monitor, manage and evaluate the aging phenomena systematically and effectively in NPPs. The AM for the CANDU is divided into 6 modules: (1) Aging Alarm/Coloring Monitor, (2) Aging Database, (3) Aging Document, (4) Real-time Integrity Monitor, (5) Surveillance and Inspection Management System, and (6) Continued Operation and Periodic Safety Review (PSR) Safety Evaluation. The proposed system is expected to provide the integrity assessment for the major mechanical components of an NPP under concurrent working environments.

• Nuclear Engineering and Technology
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• v.47 no.6
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• pp.766-775
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• 2015

The integrity assessment of reactor vessel internals should be conducted in the design process to secure the safety of nuclear power plants. Various loads such as self-weight, seismic load, flow-induced load, and preload are applied to the internals. Therefore, the American Society of Mechanical Engineers (ASME) Code, Section III, defines the stress limit for reactor vessel internals. The present study focused on structural response analyses of the upper guide structure upper flange. The distributions of the stress intensity in the flange body were analyzed under various design load cases during normal operation. The allowable stress intensities along the expected sections of stress concentration were derived from the results of the finite element analysis for evaluating the structural integrity of the flange design. Furthermore, seismic analyses of the upper flange were performed to identify dynamic behavior with respect to the seismic and impact input. The mode superposition and full transient methods were used to perform time-history analyses, and the displacement at the lower end of the flange was obtained. The effect of the damping ratio on the response of the flange was also evaluated, and the acceleration was obtained. The results of elastic and seismic analyses in this study will be used as basic information to judge whether a flange design meets the acceptance criteria.

• Journal of the Korean Society of Safety
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• v.33 no.6
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• pp.58-65
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• 2018

The life span of the porcelain insulator was made to be 30 years, but currently many of the 154kV NGK porcelain insulators using in Korea are found to have passed the production life. Accidents caused by aged mechanical breakdown can lead to disruption of power supply in some areas, large economic losses, and casualties. Therefore, ultrasonic method, which is one of the non - destructive test methods, is applied as a method for evaluating the integrity of porcelain insulators. In this study, the experiment on the interface of cap was conducted and the difference between the energy difference and the attenuation coefficient of the reflected wave was derived according to the interface state of the steel - cement. The results of this study are expected to be used as the basic data of the ultrasonic testing to evaluate the interface condition of the porcelain insulator cap.

• Journal of the Korean Society of Safety
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• v.29 no.5
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• pp.160-165
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• 2014

The realistic cases causing severe core damage should be analyzed and arranged systematically for preparing an accident management of the specific nuclear power plant. The objective of this paper is to establish basic technical information for reactor safety and reactor building integrity management strategies in CANDU reactor severe accident. For the development of severe accident management strategies, plant specific features and behaviors must be studied by detailed analysis works. This analysis scope will serve to cover overall methods and analyzing results to understand the reactor building integrity status in the most likely severe accident sequences that could occur at CANDU reactor. Also analysis results could help prevent or mitigate severe accidents for the identification of any plant specific vulnerabilities to severe accidents using the probabilistic safety assessment (PSA) quantified results.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.18 no.spc
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• pp.21-36
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• 2020

With respect to spent nuclear fuels, disposal containers and bentonite buffer blocks in deep geological disposal systems are the primary engineered barrier elements that are required to isolate radioactive toxicity for a long period of time and delay the leakage of radio nuclides such that they do not affect human and natural environments. Therefore, the thermal stability of the bentonite buffer and structural integrity of the disposal container are essential factors for maintaining the safety of a deep geological disposal system. The most important requirement in the design of such a system involves ensuring that the temperature of the buffer does not exceed 100℃ because of the decay heat emitted from high-level wastes loaded in the disposal container. In addition, the disposal containers should maintain structural integrity under loads, such as hydraulic pressure, at an underground depth of 500 m and swelling pressure of the bentonite buffer. In this study, we analyzed the thermal stability and structural integrity in a deep geological disposal environment of the improved deep geological disposal systems for domestic light-water and heavy-water reactor types of spent nuclear fuels, which were considered to be subject to direct disposal. The results of the thermal stability and structural integrity assessments indicated that the improved disposal systems for each type of spent nuclear fuel satisfied the temperature limit requirement (< 100℃) of the disposal system, and the disposal containers were observed to maintain their integrity with a safety ratio of 2.0 or higher in the environment of deep disposal.

• Nuclear Engineering and Technology
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• v.54 no.5
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• pp.1698-1711
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• 2022

A combined safety approach, which uses a best-estimate computer code and adopts conservative assumptions for safety systems availability, is developed and applied to the safety margin evaluation for the Loss of Condenser Vacuum (LOCV) of the 1000 MWe Korean Nuclear Power Plant. The Multi-dimensional Analysis of Reactor Safety-KINS standard (MARS-KS) code is selected as a best-estimate code and the PAPIRUS program is used to obtain different initial operational conditions through random sampling of control variables. During an LOCV event, fuel integrity is not threatened by the increase in Departure from Nuclear Boiling Ratio (DNBR). However, the high pressure in the primary coolant system and the secondary system might affect the system integrity. Thus, the peak pressure becomes a major safety concern. Transient analyses are performed for 124 cases of different initial conditions and the most conservative case, which results in the highest system pressure is selected. It is found the suggested methodology gives similar peak pressures when compared to those predicted from existing methodologies. The proposed approach is expected to minimize the time and efforts required to identify the conservative plant conditions in the existing conservative safety methodologies.

• Journal of the Korean Society of Safety
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• v.22 no.4
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• pp.7-12
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• 2007

In order to evaluate the integrity of Zr-2.5Nb pressure tubes, probabilistic fracture mechanics(PFM) approach was employed. Failure assessment diagram(FAD), plastic collapses, and critical crack lengths(CCL) were used for evaluating the failure probability as failure criteria. The Kr-FAD as failure assessment diagram was used because fracture of pressure tubes occurred in brittle manner due to hydrogen embrittlement of material by deuterium fluence. The probabilistic integrity evaluation observed AECL procedures and used fracture toughness parameters of EPRI and recently announced theory. In conclusion, the probabilistic approach using the Kr-FAD made it possible to determine major failure criterion in the pressure tube integrity evaluation.

• Journal of the Korean Society of Safety
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• v.23 no.4
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• pp.7-12
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• 2008

This study proposes integrity evaluation method of weld zone in titanium using titanium distance amplitude characteristics curve(TDACC) and ultrasonic signals. For these purposes, the ultrasonic signals for porosity defects of weld zone in titanium are acquired in the type of time series data and echo strength. 4 lines in the DACC indicated damage evaluation standard of weld zone in titanium. The acquired ultrasonic signals agree fairly well with the measured results of reference block and sensitivity block(defect location, bean1 propagation distance, echo strength, etc). The proposed TDACC in this study agree fairy well with the measured results of weld zone in titanium(weld defects as porosity). The proposed TDACC in this study can be used for integrity evaluation of weld zone in titanium.