• 한국지반환경공학회 논문집
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• 제15권11호
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• pp.53-59
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• 2014

낙석방지망에 대한 기존 연구 결과에 의하면 종래의 낙석방지망에서 발생되는 대표적인 문제점으로 이완성이 없는 횡방향 와이어로프에 의해 발생되는 낙석 중량의 누적현상, 지반과 낙석방지망의 결합지점 부족으로 인한 인발지지력 부족, 낙석의 과도한 충격으로 인한 철망의 빈번한 파손, 낙석방지망의 유지관리 시 철망의 재사용의 어려움 등이 보고되고 있다. 선행 연구를 통해 실내에서의 인장력과 현장실험이 실시되어 새로운 낙석방지망의 효과를 검증한 바 있다. 선행연구에 이어 본 연구에서는 기존의 사각낙석방지망과 비교하여 충격 완화형 육각 낙석방지망의 전체적인 구조적 안정성과 성능을 수치해석적 방법을 통해 점검하는 것에 그 목적이 있으며, 이를 충분히 검토하고 결과를 얻을 수 있도록 수치해석 프로그램이 설정되었다. 수치해석 결과를 종합해볼 때 동일한 단일 셀 간격 뿐만 아니라 동일한 면적비로 비교하더라도 육각 낙석방지망이 사각 낙석방지망에 비해 하중분배 효과가 우수한 것으로 나타났으며, 육각 낙석방지망은 낙석하중이 작용할 경우 이를 효율적으로 분산시킴으로써 과도한 하중 집중이 발생하는 것을 피할 수 있어 장기적인 안정성 확보에 유리할 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.772-784
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• 2024

The hexagonal nodal code RENUS has been enhanced to handle irregularly deformed hexagonal assemblies. The underlying RENUS methods involving triangle-based polynomial expansion nodal (T-PEN) and corner point balance (CPB) were extended in a way to use line and surface integrals of polynomials in a deformed hexagonal geometry. The nodal calculation is accelerated by the coarse mesh finite difference (CMFD) formulation extended to unstructured geometry. The accuracy of the unstructured nodal solution was evaluated for a group of 2D SFR core problems in which the assembly corner points are arbitrarily displaced. The RENUS results for the change in nuclear characteristics resulting from fuel deformation were compared with those of the reference McCARD Monte Carlo code. It turned out that the two solutions agree within 18 pcm in reactivity change and 0.46% in assembly power distribution change. These results demonstrate that the proposed unstructured nodal method can accurately model heterogeneous thermal expansion in hexagonal fueled cores.

• 한국지반환경공학회 논문집
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• 제15권9호
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• pp.69-75
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• 2014

기존에 사용되던 사각형 낙석방지망은 낙석에 의한 충격 완화를 위한 장치가 없어 적층 현상 등을 해결할 수 없으며 과도한 충격으로 철망이 파괴되는 문제 등이 지적되고 있었다. 여러 문제점이 복합적으로 발생하면서 매년 낙석 방지망 자체의 파괴에 의해 많은 피해가 발생하고 있다. 따라서 본 연구에서는 기존의 표준형 낙석방지망의 낙석방호 실패 원인을 고찰하고 설계 시 예상 낙석에너지를 파악하여 적정한 흡수에너지를 가진 육각 낙석방지망을 개발하였다. 또한 실내실험과 실대형실험을 통해 기존 낙석 방지망과의 성능차를 파악하여 육각 낙석방지망의 적용 가능성을 파악하고자 하였다. 실내실험과 실대형실험결과 낙석과 같은 하중 재하 시 육각 낙석방지망에 작용하는 응력은 스프링형 지지 장치에 의해 응력이 완화되어 충격에 의한 소성파괴에 대한 저항성이 우수한 반면 사각 낙석방지망의 경우 작용하는 응력이 직접적으로 낙석방지망에 작용함으로써 하중에 대한 저항력이 육각 낙석방지망보다 효율이 적은 것으로 판단된다.

• Nuclear Engineering and Technology
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• 제52권11호
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• pp.2422-2430
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• 2020

In order to improve calculational efficiency of the CAPP code in the analysis of the hexagonal reactor core, we have tried to implement a refined AFEN method with transverse gradient basis functions and interface flux moments in the hexagonal geometry. The numerical scheme for the refined AFEN method adopted here is the response matrix method that uses the interface partial currents as nodal unknowns instead of the interface fluxes used in the original AFEN method. Since the response matrix method is single-node based, it has good properties such as good calculational efficiency and parallel computing affinity. Because a refined AFEN method equivalent nonlinear FDM response matrix method tried first could not provide a numerically stable solution, a direct formulation of the refined AFEN response matrix were developed. To show the numerical performance of this response matrix method against the original AFEN method, the numerical error analyses were performed for several benchmark problems including the VVER-440 LWR benchmark problem and the MHTGR-350 HTGR benchmark problem. The results showed a more than three times speedup in computing time for the LWR and HTGR benchmark problems due to good convergence and excellent calculational efficiency of the refined AFEN response matrix method.

• 센서학회지
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• 제26권6호
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• pp.379-385
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• 2017

In this study, an amperometric non-enzymatic glucose sensor was developed on the surface of a glassy carbon electrode by simply drop-casting the synthesized homogeneous suspension of hexagonal boron nitride (h-BN) nanosheets with a copper metal-organic framework (Cu-MOF) composite. Comprehensive analytical methods, including field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), cyclic voltammetry, electrochemical impedance spectroscopy, and amperometry, were used to investigate the surface and electrochemical characteristics of the h-BN-Cu-MOF composite. The FE-SEM, FT-IR, and XRD results showed that the h-BN-Cu-MOF composite was formed successfully and exhibited a good porous structure. The electrochemical results showed a sensor sensitivity of $18.1{\mu}A{\mu}M^{-1}cm^{-2}$ with a dynamic linearity range of $10-900{\mu}M$ glucose and a detection limit of $5.5{\mu}M$ glucose with a rapid turnaround time (less than 2 min). Additionally, the developed sensor exhibited satisfactory anti-interference ability against dopamine, ascorbic acid, uric acid, urea, and nitrate, and thus, can be applied to the design and development of non-enzymatic glucose sensors.

• Nuclear Engineering and Technology
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• 제51권1호
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• pp.31-44
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• 2019

This study simulated a control rod assembly (CRA), which is a part of reactor shutdown systems, in immersed and fluid flow conditions. The CRA was inserted into the reactor core within a predetermined time limit under normal and abnormal operating conditions, and the CRA (which consists of complex geometric shapes) drop behavior is numerically modeled for simulation. A full-scale prototype CRA drop test is established under room temperature and water-fluid conditions for verification and validation. This paper describes the details of the numerical modeling and analysis results of the several conditions. Results from the developed numerical simulation code are compared with the test results to verify the numerical model and developed computer code. The developed code is in very good agreement with the test results and this numerical analysis model and method may replace the experimental and CFD method to predict the drop behavior of CRA.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.793-802
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• 2024

In the framework of the European project SAMOSAFER, this numerical study focuses on some thermal aspects of the Emergency Draining Tank (EDT) located underneath the core of a Molten Salt Reactor. In case of an emergency, this tank passively receives the liquid fuel salt and is designed to ensure a subcritical state. An important requirement is that the fuel does not overheat to maintain the EDT Hastelloy container integrity. The present EDT is based upon a group of hexagonal cooling assemblies arranged in a hexagonal grid and cooled down thanks to conduction through the inert salt layer up to an air flow in charge of removing the heat. This numerical thermal study relies on a conjugated heat transfer analysis coupling a Finite Element solid thermal code (SYRTHES) and two instances of a Finite Volume CFD codes (Code_Saturne). Calculations on an initial design suggest that a simple center airpipe flow is likely to not sufficiently cool the device. Alternative solutions have been evaluated. Introduction of fins to enhance the heat transfer do not bring a noticeable improvement regarding maximum temperature reached. However, a solution in which the central pipe air flow is replaced by several cooling channels located closer to the fuel is investigated and suggests a better cooling.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1125-1134
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• 2024

This paper presents a validation study of the subchannel analysis code SLTHEN used for the core thermal-hydraulic design of the Prototype Gen-IV sodium-cooled fast reactor (PGSFR). To assess the performance of the ENERGY model of SLTHEN, four liquid metal heating experiments conducted by ORNL, WARD, and KIT with hexagonal assemblies of wire-wrapped rod bundles were analyzed. These experiments were performed with 19-and 61-pin bundles and varying power distributions of axial and radial peaking factors up to 1.4 and 3.0, respectively. The coolant subchannel temperatures measured at different axial locations were compared with the SLTHEN predictions with the Novendstern, Chiu-Rohsenow-Todreas (CRT), and Cheng-Todreas (CT) correlations for flow split and mixing in wire-wrapped pin bundles. The results showed that the SLTHEN predicts the measured subchannel temperatures reasonably well with root-mean-square errors of ~10 % and maximum errors of ~20 %. It was also observed that the CRT and CT correlations consistently outperform the Novendstern correlation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제12권4호
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• pp.1638-1654
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• 2018

The heterogeneous network (HetNet) has been one of the key technologies in Long Term Evolution-Advanced (LTE-A) with growing capacity and coverage demands. However, the introduction of femtocells has brought serious co-layer interference and cross-layer interference, which has been a major factor affecting system throughput. It is generally acknowledged that the resource allocation has significant impact on suppressing interference and improving the system performance. In this paper, we propose a hybrid-clustering algorithm based on the $Mat{\acute{e}}rn$ hard-core process (MHP) to restrain two kinds of co-channel interference in the HetNet. As the impracticality of the hexagonal grid model and the homogeneous Poisson point process model whose points distribute completely randomly to establish the system model. The HetNet model based on the MHP is adopted to satisfy the negative correlation distribution of base stations in this paper. Base on the system model, the spectrum sharing problem with restricted spectrum resources is further analyzed. On the basis of location information and the interference relation of base stations, a hybrid clustering method, which takes into accounts the fairness of two types of base stations is firstly proposed. Then, auction mechanism is discussed to achieve the spectrum sharing inside each cluster, avoiding the spectrum resource waste. Through combining the clustering theory and auction mechanism, the proposed novel algorithm can be applied to restrain the cross-layer interference and co-layer interference of HetNet, which has a high density of base stations. Simulation results show that spectral efficiency and system throughput increase to a certain degree.

• 소성∙가공
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• 제21권4호
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• pp.240-245
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• 2012

With the increasing demand for light-weight materials to reduce fuel consumption, the automobile industry has extensively studied magnesium alloys which are light weight metals. The intrinsic poor formability and poor ductility at ambient temperature due to the hexagonal close-packed (HCP) crystal structure and the associated insufficient number of independent slip systems restricts the practical usage of these alloys. Hot working of magnesium alloys using a forging or extrusion enables net-shape manufacturing with enhanced formability and ductility since there are several operative non-basal slip systems in addition to basal slip plane, which increases the workability. In this research, the thermomechanical properties of AZ80 Mg alloy were obtained by compression testing at the various temperatures and strain rates. Optical microscopy and EBSD were used to study the microstructural behavior such as misorientation distribution and dynamic recrystallization. The results were correlated to the hardening and the softening of the alloy. The experimental data in conjunction with a physical explanation provide the optimal conditions for net-shape forging under hot or warm temperatures through control of the grain refinement and the working conditions.