• Nuclear Engineering and Technology
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• 제48권1호
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• pp.33-42
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• 2016

Spacer grids play an important role in maintaining the proper form of the fuel assembly structure and ensuring the safety of reactor core design. This study applies the Monte Carlo method to the analysis of the neutronics effects of spacer grids in a typical pressurized water reactor (PWR). The core problem used to analyze the neutronics effects of spacer grids is a modified version of Korea Advanced Institute of Science and Technology benchmark problem 1B, based on an Advanced Power Reactor 1400 (APR1400) core model. The spacer grids are modeled and added to this test problem in various ways. Then, by running MCNP5 for all cases of spacer grid modeling, some important numerical results, such as the effective multiplication factor, the spatial distributions of neutron flux, and its energy spectrum are obtained. The numerical results of each case of spacer grid modeling are analyzed and compared to assess which type has more advantages in accuracy of numerical results and effectiveness in terms of geometry building. The conclusion is that the most realistic modeling for Monte Carlo calculation is the "volume-preserving" streamlined heterogeneous spacer grids, but the "banded" dissolution spacer grids modeling is a more practical yet accurate model for routine (deterministic) analysis.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1998년도 춘계학술발표회논문집(1)
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• pp.483-488
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• 1998

A pressure drop model for the PWR grids with and without mixing device is proposed at single phase based on the fluid mechanistic approach. Total pressure loss is expressed in additive way for form and frictional losses. The general friction factor correlations and form drag coefficients available in the open literatures are used to the model. As the results, the model shows better predictions than the existing ones for the non-mixing grids, and reasonable agreements with the available experimental data for mixing grids. Therefore it is concluded that the proposed model for pressure drop can provide sufficiently good approximation for grid optimization and design calculation in advanced grid development.

• 조명전기설비학회논문지
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• 제27권2호
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• pp.45-53
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• 2013

In this paper, we analyze the typical phase voltage and line current waveform characteristics of the distribution system with 3 phase small synchronous generation source in case with load and non-load group, in order to investigate the power quality for end load connected of generation source. As demonstrated by our experimental results, the distortion and power quality of phase voltage and line current waveform were relatively good for low voltage 3 phase model grids connected of 3 phase small synchronous generation source in case with non-load group. However, distortion and power quality of voltage and current waveform was poor for low voltage 3 phase model grids connected to 3 phase small synchronous generation source in the load group with some phase voltage and frequency difference. From the above results, we conclude that the phase voltage and frequency of 3 phase generation source must be identical to that of distribution system source to maximize the power quality. Also, special attention is required in case of having load group or non-load group to 3 phase generation source.

• 한국정보시스템학회지:정보시스템연구
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• 제22권1호
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• pp.225-248
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• 2013

Korean government has been implementing a smart grid testbed in Jeju Island for the low-carbon green growth. As smart grids are in the early stage of their diffusion, strategic guidelines and related measures are needed to spread them successfully. In general, the successful diffusion of new technologies or new products are mostly determined in its early stages. With the introduction of smart grids, the electricity market paradigm will be transformed into user-oriented from provider-oriented. Thus, a study on the diffusion of smart grids from the perspective of users is necessary. This paper examines factors affecting the adoption and diffusion of smart grids from users' perspectives and provide strategic guidelines for diffusing the smart grid. Researchers conducted in-depth interviews with 41 people who have been already using smart grids in the Jeju testbed. Semi-structured interviews were used to collect data. The interviews were recorded on a digital voice recorder memory and subsequently transcribed verbatim. A total of 133 pages of transcripts were obtained from about 10 hours interviews. 97 concepts, 47 sub-categories and 19 categories were identified through open coding of grounded theory. We suggested a paradigm model for diffusing smart grids and total of seven propositions as strategic guidelines.

• 한국구조물진단유지관리공학회 논문집
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• 제3권1호
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• pp.137-146
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• 1999

Analysis of R/C columns requires modeling of the plastic hinge region, as well as nonlinear material characteristics. This becomes a challenging task in view of the nonlinearity of both steel and concrete. Furthermore, formation and progression of plasticity in the hinge is a difficult phenomenan to simulate, especially under reversed cyclic loading and decaying strength conditions. This research provide one analytical model employed in column analysis, including the analysis procedure for establishing inelastic force-deformation relationships. The analytical results show good correlation with experimental data. The employed procedure with the adopted analytical models can be used to compute inelastic displacements of concrete columns with welded reinforcement grids. The inelastic deformability beyond the peak was similar to those indicated by columns with conventional ties. The superior performance of columns with welded grids may be attributed to the improved confinement characteristics of grids associated with increased rigidity of welded ties.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.77-83
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• 2009

In this study, we conducted resistance and propulsion performance test of ship composed of the Resistance Test, Propeller Open Water Test and Self Propulsion Test using the CFD(Computational Fluid Dynamics). We used commercial RANS(Reynolds Averaged Navier Stokes equation) solver, as a calculating tool. The unstructured grids were used in a bow and stern of ship, having complex shape, for a convenience of generating grids, and the structured grids were adopted in a central hull and rest of hull having a relatively simple shape which is called hybrid grid method. In addition, The sliding mesh method was adopted to rotate a propeller directly in the Propeller Open Water and Self Propulsion Test. The Resistance Test and Self Propulsion Test were calculated using Volume of Fluid (VOF) model and considering a free surface. And all The three cases were applied realizable k-epsilon model as the turbulence model. The results of calculations were verified for the suitability of calculations by comparing MOERI's EFD results.

• Nuclear Engineering and Technology
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• 제42권3호
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• pp.279-296
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• 2010

For the analysis of transient two-phase flows in nuclear reactor components, a three-dimensional thermal hydraulics code, named CUPID, has been developed. The CUPID code adopts a two-fluid, three-field model for two-phase flows, and the governing equations were solved over unstructured grids, which are very useful for the analysis of flows in complicated geometries. To obtain numerical solutions, the semi-implicit numerical method for the REALP5 code was modified for an application to unstructured grids, and it has been further improved for enhanced accuracy and fast running. For the verification of the CUPID code, a set of conceptual problems and experiments were simulated. This paper presents the flow model, the numerical solution method, and the results of the preliminary assessment.

• 한국소음진동공학회논문집
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• 제13권5호
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• pp.384-392
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• 2003

The fuel rods in the Pressurized water reactor are continuously supported by a spring system called a spacer grid which is one of the main structural components for the fuel rod cluster(fuel assembly). The fuel rods vibrate within the reactor due to coolant flow. Since the vibration, which is called flow-induced vibration(FIV) can wear away the surface of the fuel rod, it is important to understand it's vibration characteristics. In this paper, the vibration analyses and the tests for the dummy rods supported by New Doublet(ND) spacer grids are described. A new FE model which reflects the contact area between the rod and ND spacer grid spring is developed to replace the previous one by which a good agreement could not be obtained with the vibration test. The natural frequency and mode shape calculated by both the Previous FE model and the new one are compared with those of experiment for a single-spanned rod supported by two ND spacer grids. The results of the new model showed good agreement with the experiment compared with those of previous model. In addition. the new FE model is applied to the vibration analysis for the dummy rod of 2.189 mm tall continuously supported by five ND spacer grids. It is also obtained that the analysis results of the new FE model well agreed to experiment ones as the single-spanned rod.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1216-1221
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• 2002

The fuel rods in the pressurized water reactor are continuously supported by a spring system called a spacer grid which is one of the main structural components for the fuel rod cluster (fuel assembly). The fuel rods are vibrating within the reactor due to coolant flow. Since the vibration, what is called flow-induced vibration(FIV), can wear away the surface of the fuel rod, it is important to understand the vibration characteristics of it. In this paper, the vibration analyses and the tests for the dummy rods supported by New Doublet(ND) spacer grids are described. A new FE model which reflects the contact area between the rod and ND spacer grid spring is developed to replace the previous one by which a good agreement could not be obtained with the vibration test. The natural frequency and mode shape calculated by both the previous FE model and the new one are compared with those of experiment fur a single-spanned rod supported by two ND spacer grids. The results by the new model show good agreement to experiment as compared with the ones by previous model. In addition, the new FE model is applied to the vibration analysis fur the dummy rod of 2.19 m tall continuously supported by five ND spacer grids. It is also obtained that the analysis results by the new FE model well agree to experiment ones as the single-spanned rod.

• 한국수자원학회논문집
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• 제36권4호
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• pp.705-713
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• 2003

본 연구에서는 근해 지진해일에 의한 원형섬 주변에서의 처오름높이를 산정하기 위하여 사면구조(quadtree) 격자기법을 이용한 수치모형을 개발하였다. 비선형 천수방정식을 지배방정식으로 사용하였으며, 적합화된 계층적 사면구조 격자를 이용하여 leap-frog 기법으로 양해적으로 유한차분하였다. 원형섬 주위를 따라 적용된 사면구조 격자는 사각형 및 원형의 형상으로 세밀화 되었다. 계산된 수치해석결과를 검증하기 위해 수리실험결과와 비교하였으며, 본 연구의 결과는 수리실험결과와 양호하게 일치하였다.