• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1175-1183
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• 2010

A spacer grid assembly is one of the most important structural components in a Light Water Reactor(LWR) nuclear fuel assembly. In the case of the Zircaloy spacer grid assembly, the primary design consideration is to ensure that lateral dynamic crush strength of the spacer grid assembly is sufficient to resist design basis loads and thereby prevent seismic accidents, without a significant increase in the hydraulic head loss for the reactor coolant in the reactor core. In this study, factors affecting the lateral dynamic crush strength of a spacer grid assembly were analyzed by performing lateral dynamic crush tests and finite element analyses. Further, an effective and economical method to enhance the lateral dynamic crush strength of the spacer grid assembly is proposed.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.590-592
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• 2008

A spacer grid is one of the most important structural components in a LWR nuclear fuel assembly. The primary considerations are to provide a Zircaloy spacer grid with crush strength sufficient to resist design basis loads, without significantly increasing pressure drop across the reactor core. In this study, the dynamic crush strength analysis and test are carried out for the specimens of a spacer grid assembly.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.305-308
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• 2007

The spacer grid assembly is one of the main structural components of the nuclear fuel assembly of a PWR. The spacer grid assembly supports and aligns the fuel rods, guides the fuel assemblies past each other during handling and, if needed, sustains lateral seismic loads. The ability of the spacer grid assembly to resist the lateral loads is usually characterized in terms of its dynamic and static crush strengths, which are acquired from tests. In this study, a finite element analysis on the dynamic crush strength of spacer grid assembly specimens is carried out and compared with test results.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.705-709
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• 2002

The spacer grids in nuclear fuel assembly locate and align the fuel rods with respect to each other. They provide axial and lateral restraint against an excessive rod motion mainly caused by coolant flow. It is understood that each rod Is supported by multiple spacer grid. In such a case, it is important to determine spacer grid span so as to avoid resonance between the natural frequency of the fuel rods and excitation frequency. Actually dynamic characteristics of the fuel rods can be improved by assigning adequate spacer grid locations. When a dynamic performance of the structure is to be improved, design sensitivity analysis plays an important role as like many structural redesign problems. In this work, a shape design concept, different from conventional design, was applied to the problem. According to the theory shape can be a design parameter and optimal shape design can be found. This study concentrates on eigenvalue design sensitivity of the fuel rod supported by multiple spacer grids to determine optimal spacer grids positions.

• Nuclear Engineering and Technology
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• v.33 no.1
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• pp.93-101
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• 2001

The spacer grid is one of the main structural components in the fuel assembly, which supports the fuel rods, guides cooling water, and protects the system from an external impact load, such as earthquakes. Therefore, the mechanical and structural properties of the spacer grids must be extensively examined while designing them. In this paper, a numerical method for predicting the buckling strength of spacer grids is presented. Numerical analyses on the buckling behavior of the spacer grids are performed for a various array of sizes of the grids considering that the spacer grid is an assembled structure with thin-walled plates and imposing proper boundary conditions by nonlinear dynamic finite element method using ABAQUS/Explicit. Buckling tests on several numbers of specimens of the spacer grid were also carried out in order to compare the results between the test and the simulation result. The drop test is accomplished by dropping a carriage on the specimen at a pre-determined position. From this test, the specimens are buckled only at the uppermost and the lowermost layer among the multi-cells, which is similar to the local buckling at the weakest point of the grid structure. The simulated results also similarly predicted the local buckling phenomena and were found to give good correspondence with the experimental values for the thin-walled grid structures.

• Journal of Korean Neurosurgical Society
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• v.58 no.1
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• pp.43-49
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• 2015

Objective : $Dynesys^{(R)}$ is one of the pedicle-based dynamic lumbar stabilization systems and good clinical outcome has been reported. However, the cylindrical spacer between the heads of the screws undergoes deformation during assembly of the system. The pre-strain probably change the angle of instrumented spine with time and oblique-shaped spacer may reduce the pre-strain. We analyzed patients with single-level stabilization with $Dynesys^{(R)}$ and simulated oblique-shaped spacer with finite element (FE) model analysis. Methods : Consecutive 14 patients, who underwent surgery for single-level lumbar spinal stenosis and were followed-up more than 24 months (M : F=6 : 8; age, $58.7{\pm}8.0$ years), were analyzed. Lumbar lordosis and segmental angle at the index level were compared between preoperation and postoperative month 24. The von Mises stresses on the obliquely-cut spacer ($5^{\circ}$, $10^{\circ}$, $15^{\circ}$, $20^{\circ}$, $25^{\circ}$, and $30^{\circ}$) were calculated under the compressive force of 400 N and 10 Nm of moment with validated FE model of the L4-5 spinal motion segment with segmental angle of $16^{\circ}$. Results : Lumbar lordosis was not changed, while segmental angle was changed significantly from $-8.1{\pm}7.2^{\circ}$ to $-5.9{\pm}6.7^{\circ}$ (p<0.01) at postoperative month 24. The maximum von Mises stresses were markedly decreased with increased angle of the spacer up to $20^{\circ}$. The stress on the spacer was uneven with cylindrical spacer but it became even with the $15^{\circ}$ oblique spacer. Conclusion : The decreased segmental lordosis may be partially related to the pre-strain of Dynesys. Further clinical and biomechanical studies are required for relevant use of the system.

• Nuclear Engineering and Technology
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• v.24 no.2
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• pp.111-120
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• 1992

This paper investigates the dynamic characteristics of spacer grid impact loads and the effects of variations in the amplitude and frequency of the core plate motions on the resultant impact loads. A model of the longest row (15 fuel assemblies) across the core is analyzed using the input motions generated from safe shutdown earthquake. Input excitations consist of time history motions applied to the core support plate, fuel alignment plate and core shroud. The responses are determined for a set of four parameter runs with respect to the amplitude and frequency changes. Spacer grid impact loads and normalized input values for all cases are presented. The results show that changing the natural frequency has negligible effect but changing the amplitude of the input motions has a significant effect on the grid impact loads Therefore, time history analysis is not necessary for a shifted case to get the core responses under the seismic excitation.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1948-1952
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• 2012

The paper presents modal testing and analysis in order to obtain the dynamic characteristics of a middle spacer grids of a nuclear fuel rod. A spacer grid is one of the important structural elements supporting nuclear fuel rods. Such a fuel rod can be oscillated by its thermal expansion, neutron irradiation and etc. due to cooling water flow under the operation of a nuclear power plant. When the fuel rod vibrates, fretting wear due to repeated friction motion between the fuel rods and spacer grids can be occurred, and so the fuel rod is damaged. In this paper, through modal analysis and testing, natural frequencies and modes of a middle spacer grid were calculated, and the following conclusions were obtained. Firstly the numerical first-seven natural frequencies for spacer grids of a fuel rod having complicated structures have a small difference within 3.8% with experimental natural frequencies, and so the suitability of simulation results was verified. Secondly, experimental mode shapes for a middle spacer grid of a nuclear fuel rod were verified by obtaining lower non-diagonal terms through MAC(Modal Assurance Criteria), and were confirmed by the simulation modes.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2019.05a
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• pp.88-89
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• 2019

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.4
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• pp.219-224
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• 2010

Recycling issue for the construction wastes is gradually important to future society. Recently, a star screen has been developed to use for this purpose, however some modifications were needed to enhance the separation accuracy. The objective of study is to evaluate and predict separation ability by verifying the effect for the modified shapes of the screen part. Two analysis models of the screen part were established using commercial software ADAMS to simulate the dynamic interaction of waste particles. Results showed that spacer and gear shapes directly affected separation ability. The modified spacer shapes were much higher screening rate with comparison to default shape. Screening ability for the half number of gear type was greater than other types. Therefore, modification of the design of screen part will be required to achieve better separation ability.