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운전원을 포함한 원전계측제어시스템의 정량적 안전성 평가 방법 개발
No full text학위논문(박사) - 한국과학기술원 : 원자력및양자공학과, 2004.8, [ ix, 123 p. ]Conventional PSA (probabilistic safety analysis) is performed in the framework of event tree analysis and fault tree analysis. In conventional PSA, I&C systems and human operators are assumed to be independent for simplicity. But, the dependency of human operators on I&C systems and the dependency of I&C systems on human operators are gradually recognized to be significant. I believe that it is time to consider the interdependency between I&C systems and human operators in the framework of PSA. But, unfortunately it seems that we do not have appropriate methods for incorporating the interdependency between I&C systems and human operators in the framework of PSA. Conventional human reliability analysis (HRA) methods are not developed to consider the interdependecy, and the modeling of the interdependency using conventional event tree analysis and fault tree analysis seem to be, event though is does not seem to be impossible, quite complex. To incorporate the interdependency between I&C systems and human operators, we need a new method for HRA and a new method for modeling the I&C systems, man-machine interface (MMI), and human operators for quantitative safety assessment.
As a new method for modeling the I&C systems, MMI and human operators, I develop a new system reliability analysis method, reliability graph with general gates (RGGG), which can substitute conventional fault tree analysis. RGGG is an intuitive and easy-to-use method for system reliability analysis, while as powerful as conventional fault tree analysis. To demonstrate the usefulness of the RGGG method, it is applied to the reliability analysis of Digital Plant Protection System (DPPS), which is the actual plant protection system of Ulchin 5&6 nuclear power plants located in Republic of Korea. The latest version of the fault tree for DPPS, which is developed by the Integrated Safety Assessment team in Korea Atomic Energy Research Institute (KAERI), consists of 64 pages of fault trees which should...한국과학기술원 : 원자력및양자공학과
Magnetization structure and cluster formation of fept thin film for magnetic recording media
No full text학위논문(박사) - 한국과학기술원 : 신소재공학과, 2008.2, [ ix, 136 p. ]본 논문은 FePt 자성박막의 미세조직 및 자화조직에 대한 전산모사 연구이다. FePt 자성박막의 미세조직 연구를 위해 Monte-Carlo 전산모사법을 사용하였다. 결정립성장과 상변화를 동시에 다룰 수 있도록 수정된 model을 사용하였으며 이 때, 사용된 기본가정은 carbon의 결정립계 편석에 의한 상계면의 이동도가 제한된다는 것이다. 실험적으로 관찰된 300oC에서 증착된 FePt(20nm)/C(4nm)n(n=0,1,4) 자성박막의 열처리에 따른 결정립크기, 결정립크기분포, 결정립성장거동과 일치하였다. n이 증가할수록, 최종결정립크기는 감소하고 결정립크기분포가 좁아질 수 있으며 결정립성장이 크게 억제되어 최종적으로 안정한 2상 구조를 형성하는 것이다. 이로부터 FePt 자성박막에 carbon이 첨가되는 경우, 안정한 2상구조의 형성이 가능하다는 것을 규명하였으며 이러한 영향은 carbon의 상계면으로의 편석현상으로 설명될 수 있음을 보였다.
FePt 자성박막의 자화조직을 전산모사하기 위해 micromagnetics 결과를 이용하여 Fresnel contrast를 계산하는 방식을 사용하였다. 이 방식을 사용하는 경우, 결정립에 의한 contrast가 없는 ideal한 domain wall을 가시화할 수 있다. 계산결과, 자화상태에 따라 극명하게 다른 자화조직을 나타내었으며 ordering 정도에 따라 자화조직은 미세화됨과 동시에 천이되었다. 특히, dc-demag. state에서 다른 자화상태에 비해 가장 조대화된 자화조직을 나타내었으며 Keff값에 따라 vortex-antivortex network 타입의 자화조직에서 elongated reversed domain 구조를 거쳐 ring-type dot 구조로 천이된다. vortex-antivortex network 타입의 자구조직은 자화반전거동시 ‘S``-shape의 ripple로부터 형성된 vortex와 antivortex의 이동에 의해 나타났으며 elongated reversed domain구조는 국부적으로 반전된 자화벡터에 의한 일방향으로의 계속되는 국부적인 vortex의 생성과 소멸과정으로 나타나는 것이었음을 규명하였다. 40vol.% 첨가된 FePt:C박막의 증착온도에 따른 자화조직과 대부분 일치하는 모습을 보였으며 이는 2가지를 의미한다. 첫째 FePt:C 박막의 자화조직은 interacting Stoner-Wohlfarth model로서 이해될 수 있다는 점. 둘째 FePt:C 박막에서 실제로 존재하게 될 2상구조의 자화조직은 effective Ku값을 갖는 단상구조의 자화조직으로 표현될 수 있다는 점이다.
FePt 박막의 자화조직과 media noise관점에서 magnetic cluster size는 그것의 기본을 이루는 단위이다. 따라서 이것의 변화를 감지하는 것은 자화조직과 media noise를 이해하는 데에 큰 도움을 준다. 본 연구에서는 cross-track correlation coefficient값을 이용하여 실제적으로 관찰되는 magnetic cluster size를 측정할 수 있는 방법을 개발하였다. magentic cluster size는 Keff값이 증가할수록, A값이 감소할수록, 특정 범위의 결정립크기 (const. A > 0.5x10-6erg/cm)에서 최소화됨을 보였다. 한편, 10 vol.% 이하의 최소화된 fcc particle이 존재하는 경우, 보자력이방성의 큰 감소없이 magnetic cluster size는 급격히 미세화됨을 알 수 있었다.한국과학기술원 : 신소재공학과
대면적 transformer coupled plasma원에서의 임피던스 정합에 관한 연구
No full text학위논문(석사) - 한국과학기술원 : 원자력공학과, 1999.2, [ vi, 55 p. ]Impedance matching in a large-area Transformer Coupled Plasma source was studied. At first, automatic impedance matching was planned, so some ideas for automatic impedance matching are presented. But, we discovered that in our experimental system there is only one impedance matching condition and it is irrelevant to plasma status. Because the automatic impedance matching in our experimental system is meaningless, we tried to find the only impedance matching condition.
During the impedance matching experiment, a discrepancy between theoretical calculations and experimental results was found. So, we introduced a new way of understanding our system using a modified model which is based on the assumption that inductance and capacitances have a dependency on frequency, and the modified model explained the experimental results well. With this modified model, load impedances of the power supply in various configurations were calculated and used to analyze the data from plasma experiments. In our experimental system, maximum plasma density was found near 500Ω load impedance regardless of the condition of a plasma. Thus, we concluded that the only impedance matching condition is located near 500Ω load impedance. Furthermore, plasma control is possible based on the experimental data.한국과학기술원 : 원자력공학과
Reliability Graph with General Gates: An Intuitive and Practical Method for General System Reliability Analysis
No full textA method for identifying instrument faults in nuclear power plants possibly leading to wrong situation assessment
No full textIn this paper, we propose a method for identifying instrument faults that could potentially affect an operators' situation assessment capability in nuclear power plants (NPPs), an issue which has received a lot of attention recently. In the proposed method, patterns of selected plant parameter trends in selected plant states and NPP operators' patterns of selected plant parameter trends in selected plant states are analyzed, and a comparison between the two kinds of patterns is performed to identify instrument faults which could potentially affect a NPP operators' capability to correctly assess a plant's conditions. An example application is presented to demonstrate how the proposed method can be used to identify the possibilities of operators' developing a wrong situation assessment because of instrument faults and to identify the corresponding safety concerns. We conclude that in order to get more accurate results, an analysis with a full-scope NPP simulator and interviews with NPP operators will be necessary. (c) 2007 Elsevier Ltd. All rights reserved
An Analysis on Possible Effects of Instrument Faults on Situation Assessment of Nuclear Power Plant Operators
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Development of a Situation Assessment Model of a Nuclear Power Plant Operator from Compact Nuclear Simulator Simulations
No full textConsideration of Uncertainties in the Specification of Control Modes in CREAM Using a Probabilistic Approach
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