The thermal integrity of spent nuclear fuels has to be maintained during their long-term dry storage. The detailed temperature distributions of spent fuel assemblies are essential for evaluating the integrity of their dry storage systems. In this study, a subchannel analysis model was developed for a canister of a single fuel assembly using the COBRA-SFS code. The thermal parameters affecting the peak cladding temperature (PCT) of the spent fuel assembly were identified, and sensitivity analyses were performed based on these parameters. The subchannel analysis results indicated the presence of a recirculation flow, based on natural convection, between the fuel assembly and downcomer region. The sensitivity analysis of the thermal parameters indicated that the PCT was affected by the emissivity of the fuel cladding and basket, convective heat transfer coefficient, and thermal conductivity of the fluid. However, the effects of the wall friction factor of the canister, form loss coefficient of the grid spacers, and thermal conductivities of the solid materials, on the PCT were predominantly ignored.

The measurements from the upper and tailrace reservoirs, and the discharge flow rate, are essential for the optimal operation of the hydraulic power plant. Typically, water level monitoring studies have been carried out, however, the real-time monitoring of the discharge flow rate is not available for most power plants. The present study proposes a method for estimating the discharge flow rate using head loss calculation with differential pressure measurement in the inlet pipeline. The flow rate assessment method was developed using the Bernoulli, Darcy-Weisbach, and Colebrook-White equations. To verify the method, comparative flow measurement tests were performed using the K-water flow meter calibration system. The results confirmed that flow rates calculated with differential pressure measurements are consistent with the measured ones by the standard flow meter, within a specific error range.

Computational Fluid Dynamics (CFD) was performed under low-speed wind tunnel test conditions using a 29.7% scale model of the NASA common research model. A wind tunnel test was conducted to measure the aerodynamic coefficient of the CRM with Belly sting model support configuration at a low Reynolds number of 0.3x10(6) and it was compared with the aerodynamic coefficient of CFD analysis. In order to verify the validation of the analysis, a computational analysis under the conditions of the advance research was performed and compared. The interference effect of the Belly sting model support affected not only the fuselage but also the main and tail wings.

The weight of spent nuclear fuel concrete storage casks usually exceeds 100 tons. Therefore, thermal testing of prototype casks is expensive and time consuming. In this study, thermal testing method using a scaled-down model of a storage cask was developed to perform the thermal testing of large-scale storage casks efficiently. Scaling analyses were performed to derive scale ratios between a prototype cask and the scaled-down model. Additionally, thermal analyses were performed on the prototype cask and half-scale model using the obtained scale ratios. The analysis results showed that scale ratios between the prototype cask and half-scale model were conserved well. Thermal tests were performed on the prototype cask and half-scale model. The analysis and test results were in good agreement. The thermal test results confirmed the thermal-fluid flow similarity between the prototype cask and half-scale model. (C) 2020 Elsevier Ltd. All rights reserved.

A wind tunnel test of 29.7% scaled model of NASA Common Research Model with belly model support was performed in small low speed wind tunnel. The static aerodynamic forces and moments of CRM were measured with belly sting support configuration. Pitching moments of belly sting with various fairings were compared and small interference fairing shape was found. The belly sting model support interference and reducing effect of fairing shapes with CFD analysis.

In advanced small modular reactors, a natural circulation system with liquid metal is preferred, as it offers enhanced safety features, simplicity of reactor design, and is economical with respect to construction. A natural circulation system also provides potential non-proliferation benefits to the international community. To test lead-bismuth eutectic as a liquid metal coolant, we have studied its natural circulation characteristics. We present the results of experiments on natural circulation conducted in a full-height scale test loop for varying core power, heat exchanger coolant oil temperature, and bubble injection rate. The experiments on the liquid metal were conducted under core power source conditions ranging from 2.5 kW to 15 kW. The aim of this experiment was to study natural circulation under various conditions. With our demonstration facility-based technology, we plan to verify small modular reactor cooling system safety and the technology of the bubble injection system that has been developed for liquid metal flow devices.

사용후핵연료 저장용기의 공기 흡입구 및 배기구에는 외부환경으로부터 이물질의 유입을 방지하기 위하여 bird screen이 설치되며, bird screen에서는 공기의 유동 저항이 발생하게 된다. 본 연구에서는 Bird screen mesh의 단순화 모델을 이용한 열해석을 수행하기 위하여 다공성매질 해석모델을 개발하였다. CFD 해석을 ...

Chemical substance Control Act was revised on Jan 2015 to prevent toxic substances leakage accidents such as hydrofluoric acid leakage accident in Gumi city in 2012. According to the revised laws, companies which treat toxic substances more than a certain quantity of chemical substances are obliged to submit off-site impact assessment and risk management plan. BR In this study, we simulated damage distance, influence range in the case of leakage of chlorine and ozone gas in a water treatment plant taking into account characteristics of chlorine and ozone injection system. According to the study result, the damage distance and the number of inhabitants in the influence area were 299 m and 138 under the situation of alternative scenario of chlorine gas leakage, respectively. Also the damage distance and the number of inhabitants in the influence area were 1,224 m and 19,611 under the situation of alternative scenario of ozone gas leakage, respectively. This result shows that the risk of chlorine gas leakage in a water treatment plant was not higher than expected, but appropriate safety measures are required when treating ozone gas.

Sodium hypochlorite, used as water disinfectant, is generated by electrolysis of salt. Compared to chlorine gas disinfection, it is free from high-pressure gas regulation and does not generate toxic gas, so it is increasingly used as a safe disinfectant.BR Despite these advantages, the concentration of sodium hypochlorite decreases with temperature during long-term storage, and the amount of chlorate increases when a large amount is added, it has mainly been applied to small-scale waterworks. To solve this problem, high sodium hypochlorite generation was developed.BR In this study, the changes of concentration and chlorate of sodium hypochlorite with time has been studied. As a result of the test, it was found that the usable period of sodium hypochlorite produced at a certain temperature or less was increased from 1.5 days to 13 days. Overall, sodium hypochlorite can be applied even in large-scale waterworks, which makes operation more stable and also reduces the disinfection byproducts, thus it contributed greatly to securing water quality.

Sodium hypochlorite used in water disinfection processes is generally in the production of chlorine to 0.8%. As the dose of chlorine increases, disinfection by-products (Chlorate) also increase simultaneously and exceed water quality standards. In this study, the electrolytic cell of a sodium hypochlorite generator (12% chlorine) was adjusted to control the production of the disinfection by-products. As a result, it was possible to reduce Chlorate concentrations by more than 95% by adjusting the pH of the electrolytic cell from 1.53 to 4.2 (normal pH of the electrolytic cell). As a low current is required to obtain these results, a 15% improvement in the efficiency of the positive electrode is also observed. For the development of High Sodium Hypochlorite Generation can be used in a safe sodium hypochlorite solution, which is expected to contribute to improvement in the safety of the disinfection process.

The counter diffusion lattice Boltzmann method (LBM) is used to simulate intermediate-sized bubbles in low viscous liquids. Bubbles at high Reynolds numbers ranging from hundreds to thousands are simulated successfully, which cannot be done for the existing LBM versions. The characteristics of the path instability of two rising bubbles are studied for a wide range of Eotvos and Morton numbers. Finally, the study presented how bubble swarms move within the flow and how the flow surrounding the bubbles is affected by the bubble motions. (C) 2016 Elsevier B.V. All rights reserved.

A numerical study was conducted to predict the performance curve of a downscaled model of the main coolant pump for a sodium-cooled fast reactor and to reduce the head loss by the optimization of the diffuser blade. The ANSYS CFX program was utilized to obtain flow characteristics inside the pump as well as the overall pressure rise across the pump operating on- and off-design points. Computational domain was divided into several blocks to achieve high grid quality effectively and 7.5 million nodes were used totally to resolve small leakage flows as well as the flow inside the rotating impeller. The corresponding experiment was conducted to validate CFD computed results. The comparison between the CFD and experimental data shows excellent agreement in terms of mass flow rate and head rise on and near design operating points. The DOE (design of experiments) and RSM (response surface method)[1] were utilized to reduce the head loss by the diffuser blade in the pump. The diffuser blade was defined as four geometric parameters for DOE. The analysis of 25 cases was made to solve the output parameters for all design points which are defined by the DOE. RSM was fitting the output parameter as a function of the input parameters using regression analysis techniques. The optimized model increased the total pump head on the design point and the low mass flow rate point, but total pump head on 130% of operating mass flow rate was reduced than the initial model.

초공동 수중비행체는 수중에서 시속 300 km 이상의 속력을 가진다. 초공동 수중비행체는 로켓추진을 동력으로 사용하기 때문에 초공동 수중비행체의 수치해석은 물과 수증기, 배기가스로 이루어진 다상 유동을 다루게 된다. 배기가스가 수중비행체에 미치는 영향은 초공동 수중 비행체 성능연구에 중요한 부분이다. 본 연구에서는 초공동 수중비행체 주변의 유동장에 대한 수치해석을 통하여 배기가스가 비행체의 항력에 어떠한 영향을 미치는지 알아보았다. 배기가스가 없는 경우, 수중비행체를 둘러싼 초공동으로 물이 유입되는 재유입현상에 의해 수중비행체 항력의 변화가 발생한다. 추진체가 있는 경우 배출되는 가스는 재유입현상에 의한 영향을 감소시킨다. 또한 배기가스는 마하디스크를 생성하며 그 영향을 받아 항력 변화가 발생한다.

A computational study of thermal striping in the upper plenum of the prototype generation-IV sodium-cooled fast reactor (PGSFR) being developed at Korea Atomic Energy Research Institute is presented. First, previous experimental and numerical studies on the thermal striping are briefly discussed. Both Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) approaches are employed for the simulation of thermal striping in the upper plenum of the PGSFR. For the RANS approach, the conventional k − ϵ turbulence model is employed and the LES is performed using the wall-adapting local eddy viscosity model. From the RANS results, the time-averaged velocity components and temperature field in the complicated upper plenum of the PGSFR are calculated. In the LES results, the time history of temperature fluctuation at several locations of upper internal structure (UIS) and intermediate heat exchanger (IHX) are additionally stored. Comparisons of the predicted time-averaged velocity and temperature between the two methods show that the prediction by the LES shows faster thermal mixing than that by the k − ϵ turbulence model. From the computed results of the temporal variation of temperature, it was possible to find the amplitude and frequency of the temperature fluctuation at the several locations of the UIS and IHXs. It was found that the location where the thermal stress is largest in the upper plenum of the PGSFR is the ⊃-shape region of the first grid plate.

In a pressurized water reactor (PWR), control rod assembly (CRA) falls into the guide tubes of a fuel assembly due to gravity for scram. Various theoretical approaches and numerical analyses have been performed because its shape is simple and its design was completely developed several decades ago. A control rod assembly for a sodium-cooled faster reactor (SFR) which is geometrically more complicated is being actively developed in Korea nowadays. Drop time and impact velocity of a CRA are important parameters with respect to reactivity insertion time and the mechanical robustness of a CRA and a guide duct. In this paper, computational method considering simultaneously the equation of motion for rigid body and the Navier-Stokes equations for fluid is suggested and verified by comparison with theoretical analysis results. Through this valuable CFD analysis method, drop time and impact velocity of initially designed SFR CRA are evaluated before performing scram tests with it.

A computational study of a thermal striping in the upper plenum of the PGSFR (Prototype Generation-IV Sodium-cooled Fast Reactor) being developed at KAERI (Korea Atomic Energy Research Institute) is presented. First, previous experimental and numerical studies on the thermal striping are briefly discussed. Both RANS (Reynolds-Averaged Navier-Stokes) and LES (Large Eddy Simulation) approaches are employed for the simulation of thermal striping in the upper plenum of the PGSFR. For the RANS approach, the conventional k–ε turbulence model is employed and the LES is performed using the WALE (Wall-Adapting Local Eddy-viscosity) model. More than 11.8 million unstructured elements are generated in the upper plenum region of the PGSFR using the ICEM commercial code. From the RANS results, the time-averaged velocity components and temperature field in the complicated upper plenum of PGSFR are calculated. In the LES results, the time history of temperature fluctuation at the several locations of solid walls of UIS (Upper Internal Structure) and IHX (Intermediate Heat Exchanger) are additionally stored. Comparisons of the predicted time-averaged velocity components and temperature between the two methods are also presented. From the temporal variation of temperature at the solid walls, one can find the locations where the thermal stress is large and assess whether the solid structures can endure the thermal stress during the reactor life time.

This paper describes the numerical investigations of the influence of the blending method on the combustion characteristics and NOx emission in a 500 MW, tangentially coal-fired boiler. The in-furnace and out-furnace blending methods are simulated with the blend of 60% bituminous and 40% subbituminous coals on a weight basis. The simulation shows the blending method has a great effect on carbon in ash, but a little effect on NOx emission. The in-furnace blending method which burns bituminous coal at lower burners and subbituminous coal at upper burners gives the least carbon in ash. For two blending methods, carbon in ash is mainly attributed to the middle burner sets in the furnace. The field tests at a 500 MW coal-fired power plant showed that the in-furnace blending method substantially reduces in NOx and carbon in ash, compared with the out-furnace blending method. (C) 2014 Published by Elsevier Ltd.

This paper concerns a finite element analysis for a spacer grid support (spring and dimple) design. An accurate prediction of the support characteristics (contact force vs. deflection) is the most crucial in the design by analysis. It is found that the mechanical properties are the key parameter to simulate the characteristics as close as the experimental results after using three different sets of mechanical property data including the actual tensile test results of the present material for a spacer grid of a dual cooled fuel. Besides, the validity of using the characteristics during unloading process is also discussed incorporating a possible overshoot of the support. The coincidence between the present finite element prediction and experimental results is quite good: less than 3.09% at most. (C) 2014 Elsevier B.V. All rights reserved.