• Nuclear Engineering and Technology
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• 제49권8호
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• pp.1617-1628
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• 2017

In the passive residual heat removal system of a molten salt reactor, one of the residual heat removal methods is to use the thimble-type heat transfer elements of the drain salt tank to remove the residual heat of fuel salts. An experimental loop is designed and built with a single heat transfer element to analyze the heat transfer and flow characteristics. In this research, the influence of the size of a three-layer thimble-type heat transfer element on the heat transfer rate is analyzed. Two methods are used to obtain the heat transfer rate, and a difference of results between methods is approximately 5%. The gas gap width between the thimble and the bayonet has a large effect on the heat transfer rate. As the gas gap width increases from 1.0 mm to 11.0 mm, the heat transfer rate decreases from 5.2 kW to 1.6 kW. In addition, a natural circulation startup process is described in this paper. Finally, flashing natural circulation instability has been observed in this thimble-type heat transfer element.

• Computers and Concrete
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• 제23권4호
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• pp.281-294
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• 2019

The post-fire behavior of structural elements and the cooling process has always been one of the main concerns of the structural engineers. The structures can be cooled at different rates, where they affect the structure's behavior. In the present study, a numerical model has been developed using the Abaqus program to investigate the effect of cooling rate on the post-fire behavior of the CFST column. To verify the model, results of an experimental study performed on CFST columns within a full heating and cooling cycle have been used. In this model, coMParison of the residual strength has been employed in order to examine the behavior of CFST column under different cooling rates. Furthermore, a parametric study was carried out on the strength of steel and concrete, the height of the specimens, the axial load ratio and the cross-sectional shape of the specimen through the proposed model. It was observed that the cooling rate affects the behavior of the column after the fire, and thus the higher the specimen's temperature is, the more effect it has on the behavior. It was also noticed that water cooling had slightly more residual strength than natural cooling. Furthermore, it was recognized from the parametric study, that by increasing the strength of steel and concrete and the load ratio, as well as modifying the cross-sectional shape from circular to square, residual strength of column at the cooling phase was less than that of the heating phase. In addition, with reducing column height, no change was witnessed in the column behavior after the cooling phase.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2088-2095
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• 2023

The safety of nuclear installations is largely determined by the tightness of fuel elements cladding. As the Fukushima nuclear accident showed, the main task in case of loss of power supply is to ensure reliable removal of residual heat release from spent fuel pool (SFP) with irradiated fuel assemblies (IFAs). The paper presents the results of calculated-experimental studies and thermal-hydraulic modeling of temperature storage modes of IFAs in SFP. Experimental studies of SFP's temperature regime and calculated evaluation of residual heat removal due to the thermal conductivity of building structures surrounding the SFP were performed. To ensure the safe operation of research reactors, it's necessary to know the IFA's residual heat power (RHP) in the reactor and SFP, which is determined depending on the operating time of fuel assemblies (FAs) and the IFAs calculated holding time. The FAs operating time depends on the reactor energy output. The IFAs calculated holding time is determined by the fuel burnup, U-235 mass in the fuel, and reactor utilization factor. The IFAs fuel burnup was calculated using the MCU-PTR program. Also presented are the RHP's calculation results using some of the empirical dependencies. The concept of a passive heat removal system (PHRS) based on thermosyphon's operating principle was proposed.

• Corrosion Science and Technology
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• 제17권4호
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• pp.193-201
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• 2018

In order to suppress $CO_2$ emission and protect passengers in case of vehicle collision, continuous efforts are being made to increase the application ratio and tensile strength of advanced high strength steels used in the manufacturing of automotive body. Simultaneously, hydrogen embrittlement which was not a concern in the past has currently become a major issue due to microstructure that is sensitive to hydrogen uptake. The sensitivity increases with residual stress and hydrogen uptake content. Many automotive OEM companies and mill makers are setting specifications to control hydrogen embrittlement. The factors which lead to hydrogen embrittlement are material sensitivity, residual stress, and hydrogen concentration; researches are in progress to develop countermeasures. To reduce material sensitivity, mill makers add high energy trap elements or microstructure refinement elements. Automotive OEM companies design the car parts not to concentrate local stress. And they manage the levels to not to exceed critical hydrogen concentration. In this article, we have reviewed hydrogen embrittlement evaluation methods and corresponding solutions that are being studied in automobile manufacturing industries and mill makers.

• 한국전산구조공학회논문집
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• 제19권1호
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• pp.39-46
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• 2006

본 연구는 파 해석에 있어서 공간-시간 분할 개념을 도입하여 켈러킨 방법으로 해석하였다. 공간-시간 유한요소법은 오직 공간에 대해서만 분할하는 일반적인 유한요소법보다 간편하다. 비교적 큰 시간간격에 대해서 공간과 시간을 동시에 분할하는 방법을 제시하며 가중잔차법이 공간-시간 영역에서 유한요소 정식화에 이용되었다. 큰 시간 간격으로 인하여 문제의 해가 발산하는 경우가 동적인 문제에서 흔히 발생한다. 이러한 결점을 보완한 사각형 공간-시간 요소를 취하여 문제를 해석하고 해의 안정에 대해 기술하였다. 다수의 수치해석을 통하여 이 방법이 효과적 임을 알 수 있었다.

• Computers and Concrete
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• 제8권5호
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• pp.541-561
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• 2011

The Finite Element Method (FEM) was employed to demonstrate that accurate simulations of seismically repaired and retrofitted reinforced concrete shear walls can be achieved provided a good analysis program with comprehensive models for material and structural behaviour is used. Furthermore, the analysis tool should have the capability to retain residual damage experienced by the original structure and carry it forward in the repaired and retrofitted structure. The focus herein is to provide quick, simple, but reliable modelling procedures for repair and retrofitting strategies such as concrete replacement, addition of diagonal reinforcing bars, bolting of external steel plates, and bonding of external steel plates and fibre reinforced polymer sheets, thus illustrating versatility in the modelling. Slender, squat, and slender-squat shear walls were investigated. The modelling utilized simple rectangular membrane elements for the concrete, truss bar elements for the steel and FRP retrofitting materials, and bond-link elements for the bonding interface between steel or FRP to concrete. The analyses satisfactorily simulated seismic behaviour, including lateral load capacity, displacement capacity, energy dissipation, hysteretic response, and failure mode.

• Steel and Composite Structures
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• 제29권1호
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• pp.139-149
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• 2018

In this paper a new multi-step damage detection approach is provided. In the first step, condensed modal residual vector based indicator (CMRVBI) has been proposed to locate the suspected damaged elements of structures that have rotational degrees of freedom (DOFs). The CMRVBI is a new indicator that uses only translational DOFs of the structures to localize damaged elements. In the next step, salp swarm algorithm is applied to quantify damage severity of the suspected damaged elements. In order to assess the performance of the proposed approach, a numerical example including a three-layer square laminated composite plate is studied. The numerical results demonstrated that the proposed CMRVBI is effective for locating damage, regardless of the effect of noise. The efficiency of proposed approach is also compared during both steps. The results demonstrate that in noisy condition, the damage identification approach is capable for the studied structure.

• 한국주조공학회지
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• 제15권6호
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• pp.546-557
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• 1995

This study was undertaken to obtain an improved understanding of the effects of alloying elements on the residual amounts of Mg in the melt and on the resultant microstructure of compacted vermicular graphite cast irons, and the influence of alloying elements and cooling rates during solidification on the formation of phosphide eutectics, and on the mechanical properties of compacted vermicular graphite cast irons containing copper, tin, molybdenum for producing pearlitic matrix, and also containing phosphorus and boron for increasing wear resistance were evaluated.

• 한국공작기계학회논문집
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• 제11권6호
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• pp.68-74
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• 2002

This research covers the development of axi-symmetric plastic elements for injection molding with insert steel such as high stiffness Sabot. The functional requirements of sabot are concentricity and fracture resistance about vertical and horizontal forces. For these, an analysis of characteristics of PEI(polyetherimide) polymer is performed by standard test specimen with accordance of ASTM test guidance. Moldflow analysis and simulation of injection molding process are carried out in order not only to estimate of the warpage but also to predict the characteristics of residual stresses which both product and structure of mold may have. A new vertical side injection machine and transverse mold have been constructed. Results of the measuring concentricity and fracture test after molding of sabot are satisfied to design specification over Cp $ratio{\geq}1.33$. Finally, this technique needs more research application to others axi-symmetric elements having different radius with insert steel md structure analysis from now on.

• 한국가스학회지
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• 제17권1호
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• pp.56-66
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• 2013

가스제조 시설들은 불활성 가스공급을 통하여 제조업 시설의 안전한 운영 및 유지하는 역할을 하며, 폭발성, 가연성 및 독성가스를 공급하여 화학제품 제조에 필요한 기초 원료의 공급을 담당하는 역할을 한다. 또한 가스의 제조과정에서 고온, 고압, 초저온 및 촉매반응 등의 운전조건 하에서 시설이 운전되기 때문에 안전하고 신뢰성 있는 운영이 반드시 필요하다. 이러한 공장들은 공정관리가 복잡하며 제조물질의 누출로 인한 화재, 폭발 및 독성가스 누출로 인한 중대산업사고의 위험성이 있고, 불활성가스로 인한 질식재해, 고온 및 초저온으로 인한 화상 등 잠재적인 위험요소를 많이 가지고 있다. 본 연구는 신뢰성 있는 준 정량적 위험성평가 기법인 GRA(Generic Risk Analysis) 모델을 공기분리시설(ASU)에 적용하여 초기위험도(Initial Risk) 산정, 안전방벽(Safety Barriers) 적용, 잔여위험도(Residual Risk) 산정 및 중요안전요소(EIS, Elements Important for Safety)를 도출 하였으며, 위험성 평가 결과로 도출된 중요안전요소에 대한 효과적인 안전관리 및 시행절차의 구축을 제안하였다.