Spent nuclear fuels released from the reactor are stored in cooling pools and then stored in dry storage casks. During the transition from the wet storage to dry storage cask, a vacuum drying process is used to remove residual water in the cask. During the vacuum drying process, gas pressure is reduced to below 400 Pa to promote evaporation and water removal. KAERI is developing a PWR single assembly (PLUS7) test equipment to simulate the thermal flow in spent fuel assembly. In this study, the thermal conductivity of air at low pressure was derived to perform the thermal analysis of the canister in vacuum. In addition, thermal analyses were performed for the canister with backfill gases of helium, air, and a vacuum in the vertical orientation using the COBRA-SFS code. At low pressure, the thermal conductivity of air depends on pressure and temperature. The reduced thermal conductivity, kr (W/m-K) was calculated using the curve fit for air at reduced pressure in thin gaps presented in the General Electric Fluid Flow Handbook. / = / Where, k0 is the thermal conductivity at atmospheric pressure (W/m-K), P is the reduced (vacuum) pressure (Pa), δ is the gap size (m), T is the temperature (K), and C is the Lasance constant (7.657E-5 N/m-K). The thermal conductivity of air decreases as the pressure decreases. The reduced thermal conductivity of air at pressures of 400 Pa and 40 Pa was calculated to be 0.97 and 0.77, respectively. For the analysis in vacuum, no enhancement of the convective heat transfer was assumed (Nu=1.0). For the helium backfill, the peak cladding temperature was the lowest and the axial temperature profile was the flattest due to the higher thermal conductivity and lower density of the helium. For the vacuum backfill, the peak cladding temperature was the highest and temperature gradient was the sharpest due to the only radiative heat transfer effect in the fuel assembly.
This study deals with the maximum thermal load analysis and optimal capacity determination method of tank culture system for applying seawater source heat pump to save energy and realize zero energy. The location of the fish farm was divided into four sea areas, and the heat load in summer and winter was analyzed, respectively. In addition, two representative methods, the flow-through aquaculture system and the recirculation aquaculture system were reviewed as water treatment methods for fish farms. In addition, the concept of the exchange rate was introduced to obtain the maximum heat load of the fish farms. Finally, power consumption for heat pumps was analyzed in the view point of sea areas, tank capacity, and exchange rate based on the calculated maximum thermal load.
In this study, we performed thermal safety design of the electric module of a heat-loaded equipment with consideration of its heat dissipation performance. Initially, we calculated the heat dissipation of natural convection to choose a cooling method. Based on this, we found that some modules required forced convection and selected an air-cooling method with an outdoor temperature of 43 degrees Celsius, which is the maximum temperature in Korea. Prior to module production, we performed thermal analysis of each module and proceeded with a design to increase the thermal conductivity of the module as a primary step, and subsequently proceeded with Heat Sink design to maximize the heat dissipation performance. After considering various constraints according to the system requirements and designing the cooling path, we experimentally and analytically secured thermal safety at the operating temperature of the equipment.
The shell & tube-type heat exchanger has been frequently used because it shows simple structure, easy manufacturing and wide operation conditions among many heat exchangers. This study aims to investigate the characteristics for thermal flow of coolant and the possibility of damage for tube equipped with shell due to thermal stress. For these purposes, The thermal flow of coolant in tube was simulated using ANSYS-CFX program and thus the behaviors of coolant were evaluated with standard k-ε turbulence model. As the results, as the flow rate of coolant in tube was increased, the mean relative pressure was also increased with quadratic curve, however, as the surface temperature of tube was increased, mean temperature difference was linearly increased. Finally it showed that the damage of tube could be predicted, that is, which tube was the most weak due to thermal stress.
Numerical analysis has been carried out to predict the thermal characteristics for a LED lens in mold core system. These thermal characteristics inside the lens are largely affected by geometry, material, and initial conditions of the mold core and lens system. Local temperature and heat flux variation inside the lens are compared for several initial temperatures. Maximum temperature inside the lens was decreased rapidly from the beginning of cooling process up to about 10 seconds. There was also large variation of the heat flux at the upper and lower surfaces of the lens with initial temperature distribution. And the heat flux from the thin lower surface of the lens was relatively higher than the opposite-side thick region. In addition, overall heat transfer rate from the lens through the mold core has similar transient distribution from the beginning. These results can be applied as basic heat transfer data for the LED lens design and manufacturing process in the mold core system.
본 연구는 정확한 열환경 평가를 위해 옥외 공간에서 체감하는 열쾌적성과 미기후 모델링을 통해 산출된 열쾌적지수의 차이점을 확인하는 것을 목적으로 한다. 이를 위해 대구광역시에 위치한 대학 캠퍼스 두 곳을 대상으로 하여 열쾌적성을 평가하는 두 가지 방법론을 적용하고 분석 결과를 비교하였다. 첫 번째 방법은 현장 설문조사를 기반으로 하여 시민들의 열쾌적성 정보를 수집하는 것이며, 두 번째 방법은 미기후 모델인 ENVI-met을 활용하여 열쾌적지수(PMV)를 수집하는 것이다. 또한, 열쾌적성에 영향을 미치는 요인을 파악하고자 그늘의 특성과 토지피복 특성을 기준으로 캠퍼스 내 상세 대상지를 선정하고 이러한 요인이 열쾌적성에 미치는 영향을 분석하였다. 분석 결과, 두 대학의 분석 일시와 장소가 달랐으나 방법론별 유사한 양상이 나타났다. 먼저, 설문조사 결과 그늘의 양이 증가할수록 쾌적한 것으로 나타났으며, 토지피복의 종류별 특성과는 다른 결과가 나타났다. 다음으로 모델링 결과 전반적으로 설문조사 결과와 비슷한 양상이 나타나지만 동일한 그늘의 특성을 가지는 세부 대상지에서 토지피복이 열환경에 부정적인 영향을 미치는 피복일 경우 열쾌적지수가 더 높게 나타났다. 결론적으로 설문조사 결과와 미기후 모델링 결과 간에 차이가 존재하며, 정책 반영을 위한 열쾌적성 정보의 수집 시 현장 기반의 체감 더위 정보의 수집을 통해 정확한 정보를 활용할 필요가 있을 것으로 판단된다.
The Alkali-Metal Thermal to Electric Converter (AMTEC) can be used as a next-generation power generation technology related with a large thermal energy storage. In particular, this technology is expected for the higher efficiency by a cascade power generation with the thermoelectric generator(TEG), and the temperature distribution becomes a very important design parameter in this case. In this study, the temperature distribution of the AMTEC unit was analyzed through CFD analysis, and design points were discussed based on the results.
This study is to investigate fuel cladding temperature in a transport system for the purpose of developing a methodology for evaluating the thermal performance of spent fuel. Detailed temperature analysis in the transport system is important because the degradation mechanism of the fuel cladding is generally sensitive to temperature and temperature history. In such a system, the magnitude of the temperature change is determined by examining the temperature sensitivity of fuel assemblies and system components including fuel cladding temperature, considering the material properties, component specifications, component aging mechanism, and heat transfer mechanism. The sensitivity analysis is performed using heat transfer models by computational fluid dynamics for the horizontal transport system. The heat transfer within the system by convection, conduction and thermal radiation is calculated by thermal-hydraulic analysis code FLUENT. The calculation region is divided into a basket cell and a transport cask. The thermal analysis of the basket cell is for predicting the fuel cladding temperature. And the reason for analyzing the transport cask is to provide the boundary condition for the basket cell by reflecting the external environmental conditions. Here, the basket cell containing the spent fuel assembly is modeled on the homogeneous effective thermal conductivity. The purpose of this analysis is to evaluate fuel cladding temperatures for the following four main items. That is the effect of surface emissivity changes in basket due to the oxide layer of the fuel cladding, the effect of degradation of the canister backfill helium gas, the effect of fuel assembly position in basket cell on fuel cladding and basket temperatures in canister, and the effect of using the homogeneous effective thermal conductivity model instead of the fuel assembly in basket cell. As a result of the analysis, the maximum temperatures in basket cells are evaluated for the above four items. Thermal margins for each item are investigated for thermal performance requirements (e.g., peak clad temperature below 400oC).
Thermal analysis and safety assessment of spent fuel transport cask are mainly conducted using commercial Computational Fluid Dynamics (CFD) codes based on Finite Volume Method (FVM). The reliability and predictability of CFD codes have greatly been improved by the development in the computer systems, and are widely used to calculate heat flow in complex structures that cannot be analyzed theoretically. In the field of thermal analysis using the CFD code, it is important to clearly reflect the physical model of the transport cask, and a grid configuration suitable for the physical model is essential for accurate analysis. However, since there are no clear standard and guidelines for grid configuration and size, it is highly dependent on the user’s insight. Spatial discretization errors result from the use of finite-width grids and the approximation of the differential terms in the model equations by difference operators. Since the user usually cannot change the truncation error order of a given discretization scheme, spatial discretization errors can only be influenced by the provision of optimal grids. Therefore, it is necessary to quantify the spatial discretization errors caused by the grid. In the case of Orano TN’s NUHOMS® MP197 transport cask, considering four grids for two sets, the temperature uncertainty of the neutron shield, which has the lowest margin at the limit temperature among transport cask components, was quantified by applying 5-step procedure of the Grid Convergence Index (GCI) method for the uncertainty estimation presented in ASME V&V 20-2009. In the case of domestic spent nuclear fuel transport cask (KORAD21), neutron shield among the transport cask components has the lowest margin at the limited temperature. Accordingly, in this study, the temperature uncertainty of the neutron shield was quantified by applying GCI to three sets considering seven grids. As a result of the calculation, the uncertainty was less than ± 1°C, and the temperature of the neutron shield including the uncertainty was evaluated to be maintained below the limit temperature of 148°C.
In this study, for thermal neutron absorption, an aluminum metal composite in which B4C particles were uniformly dispersed was prepared using stirring casting and hot rolling processes. The microstructure, thermal neutron absorption rate, mechanical properties and dispersibility of the reinforcement of the prepared B4C/Al composite were analyzed. The composite in which the 40 μm sized B4C particles were uniformly dispersed increased the tensile strength as the volume ratio of the reinforcement increased.
Dry storage is a predominantly used method as a spent nuclear fuel storage system after spent nuclear fuel is cooled in the spent fuel pool. Spent nuclear fuel is highly radioactive and it generates heat called decay heat originated by fission products and radiation. Therefore, temperature of spent nuclear fuel should be predicted whether its cladding temperature is maintained under 400°C, which is the allowable temperature limit of cladding in a dry storage. ANSYS Fluent and COBRA-SFS are predominantly used computational method to investigate the temperature of spent nuclear fuels in a dry storage. Herein, thermal analysis results with the methods were compared based on a Single Assembly Heat Transfer Test, which is a heat test with an electrically heated model of a single PWR fuel assembly in a dry cask performed at the Pacific Northwest Laboratory. Decay heat was 1kW and backfill gas was air. Fix temperature boundary condition is applied to inner shell according to measured temperature. In case of peak cladding temperature (PCT), Fluent predicted 240–284°C, while COBRA-SFS gave 243–292°C. The discrepancy between the codes is under 2.5%. The location where PCT took place was 3.65 m from the bottom of the assembly in both results. However, temperature difference between the upper and lower region of the assembly based on the Fluent was smaller than the temperature difference based on the COBRA-SFS. It means the heat was well transferred in an axial direction with Fluent compared to COBRA-SFS. In lower plenum region where air was naturally circulated, COBRASFS had disadvantages compared to Fluent because it modeled the lower plenum by single node, so it was hard to simulate convection heat transfer by natural circulation. natural circulation speed of air in a center region of the assembly was 0.07–0.1 m·s−1 in both cases.
The fabrication of waste forms with high thermal and structural stability is an essential technology for the safe management and disposal of radioactive wastes. In particular, the thermal characteristics of waste forms containing high heat-generating nuclides such as Cs and Sr can be used for the optimized design of the waste form to secure its thermal safety, and they also provide basic design data for the safe management of canisters, storage systems, and repositories. The Korea Atomic Energy Research Institute is actively developing processes and equipment for fabricating various types of high-level wastes into a stable glass or ceramic waste form. In previous research related to the thermal analysis of the waste form, a relatively simple analysis was performed by using the analytic solution of the one-dimensional steady-state heat conduction equation considering the decay heat properties of the waste. As a specific application study, the optimized diameter of the cylindrical glass waste form was proposed by evaluating the centerline temperature of the waste form. In this study, we extended previous research by introducing a more complicated model, and the main results are summarized as follows. First, an analytical solution was derived by applying the temperaturedependent thermal conductivity expressed in the general form of polynomial function to the onedimensional heat conduction problem previously studied. Second, the two-dimensional axisymmetric steady-state heat conduction problem with a more realistic cylinder model with finite length was modeled and solved by using the finite element method via Matlab’s PDE (partial differential equation) toolbox. Third, thermal analysis was performed on the SrTiO3 waste form, selected as a stable form of strontium nuclide, using the developed analytical and numerical methods. The differences in the temperature distribution and computation time were evaluated through a comparative study of both solutions. Although the problem considered in this study could easily be solved by using commercial CFD software such as ANSYS or SolidWorks, a code-based program was developed to facilitate parametric design study in conjunction with optimization algorithms. The analysis results could be used to evaluate the thermal stability of waste form and to optimize the shape and size of the waste form in consideration of the design constraints of storage systems or repositories.
Experimental analysis has been carried out on double glazed glass of a commercial vehicle to analyze thermal characteristics for various air flow conditions. This double glazed glass has an important effect on the blocking performance of heat transfer with the vehicle's moving speed and ambient thermodynamic conditions. Calculated thermal resistances and heat transmission coefficient through the glass were compared with measured air indoor and outdoor temperatures including the glass surfaces using an experimental apparatus. The thermal resistance through the glass was increased with the indoor air temperature while overall heat transmission coefficient was decreased due to the convective heat transfer effect. As indoor air became warmer, the effect of air flow velocity on the heat transmission coefficient was reduced significantly. It is expected that these results can be used as applicable design data for the development of the double glazed glass system for many commercial vehicles.
PURPOSES : Steel deck bridges are the preferred structural type for reducing dead load, and the use of thin-layer asphalt concrete with excellent adhesion to the steel deck and excellent deformation followability is increasing for bridge pavements. However, because these materials are constructed at a high temperature of 240 °C or higher to maintain high fluidity during construction, excessive thermal deformation and stress may be temporarily induced in the steel deck. Therefore, the stability of the structure must be assessed by considering the environmental conditions of the site during pavement construction. Herein, a method is presented for estimating the heat source equation, in which conduction and convection effects are removed using temperature measurement data, for modeling U-rib using plate elements. The validity of the study is assessed by deriving the equivalent heat source equation using the temperature data measured from the underside of the steel deck while constructing a 40-mm-thick goose asphalt concrete pavement layer on a 12-mm-thick steel deck. In addition, the practicality is verified by performing heat transfer and thermal stress analyses. METHODS : By comparing the temperature data measured during the construction of high-fluidity asphalt concrete with the results of repeated heat transfer numerical analysis, heat source data without field conduction and convection conditions are obtained. Subsequently, a heat source equation suitable for the heat source data is derived using the least-squares method. RESULTS : The results of the heat transfer analysis using the equivalent heat source equation calculated using the presented method are almost consistent with the measured temperature data. In addition, the behavioral characteristics of the structure that matches the behavior of the actual structure can be derived through thermal stress analysis, which considers heat conduction and convection to adjacent members. CONCLUSIONS : Even when the steel deck and U-rib member are modeled as plate elements, thermal effect analysis can be performed reasonably while considering field conditions.
A 1.8 μm thick polycrystalline diamond (PCD) thin film layer is prepared on a Si(100) substrate using hot-filament chemical vapor deposition. Thereafter, its thermal conductivity is measured using the conventional laser flash analysis (LFA) method, a LaserPIT-M2 instrument, and the newly proposed light source thermal analysis (LSTA) method. The LSTA method measures the thermal conductivity of the prepared PCD thin film layer using an ultraviolet (UV) lamp with a wavelength of 395 nm as the heat source and a thermocouple installed at a specific distance. In addition, the microstructure and quality of the prepared PCD thin films are evaluated using an optical microscope, a field emission scanning electron microscope, and a micro-Raman spectroscope. The LFA, LaserPIT-M2, and LSTA determine the thermal conductivities of the PCD thin films, which are 1.7, 1430, and 213.43 W/(m·K), respectively, indicating that the LFA method and LaserPIT-M2 are prone to errors. Considering the grain size of PCD, we conclude that the LSTA method is the most reliable one for determining the thermal conductivity of the fabricated PCD thin film layers. Therefore, the proposed LSTA method presents significant potential for the accurate and reliable measurement of the thermal conductivity of PCD thin films.
본 연구는 부산광역시를 대상으로 열환경을 개선하기 위한 바람길 관리 방안 제안을 목적으로 한다. 이를 위해, Landsat-7 위성 열영상 자료와 공간통계 분석을 실시하여 부산광역시의 Hot spot과 Cool spot 지역 특성을 파악하였으며, WRF 기상모의를 통해 주요 바람길을 분석하였다. 그 결과, Hot spot 지역 중 열환경 개선이 요구되는 지역은 부산진구, 동래구, 연제구와 사상구 공업지역, 대규모 시설지역에는 부산항 부두로 나타났으며 주요 바람길에는 금정산~백양산~ 구덕산 계곡부로서 확인되었다. 이를 바탕으로 바람길 관리 전략을 제시하면 다음과 같다. 공업시설과 부산항 일대는 대기 온도 상승 요인으로서 주변 지역의 열환경을 악화시키므로 시설의 온도저감 및 바람길을 고려한 도시·건축계획이 요구된다. 바람길 관리가 필요한 지역으로 만덕동, 사직동 일대 산림에 대한 추가적인 훼손이 일어나지 않도록 하여야 하며, 산림과 인접한 지역의 대규모 고층아파트는 산림에서 생성된 차고 신선한 공기의 흐름을 방해하므로 금정산과 접해있는 제3종 일반주거지역의 신규·재개발에 따른 고층아파트 단지 조성은 지양해야 한다. 본 연구 결과는 부산광역시의 기후변화에 대응한 도시계획 및 환경계획수립 시 기초자료로 활용할 수 있을 것으로 기대한다.