• Nuclear Engineering and Technology
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• v.36 no.6
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• pp.559-570
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• 2004

A computational fluid dynamics model for predicting moderator circulation inside the Canada deuterium uranium (CANDU) reactor vessel has been developed to estimate the local subcooling of the moderator in the vicinity of the calandria tubes. The buoyancy effect induced by the internal heating is accounted for by the Boussinesq approximation. The standard $k-{\varepsilon}$ turbulence model with logarithmic wall treatment is applied to predict the turbulent jet flows from the inlet nozzles. The matrix of the calandria tubes in the core region is simplified to a porous media in which the anisotropic hydraulic impedance is modeled using an empirical correlation of pressure loss. The governing equations are solved by DFX-4.4, a commercial CFD code developed by AEA technology. The resultant flow patterns of the constant-z slices containing the inlet nozzles and the outlet port are "mined-type", as observed in the former 2-dimensional experimental investigations. With 103% full power for conservatism, the maximum temperature of the moderator is $82.9^{\circ}C$ at the top of the core region. Considering the hydrostatic pressure change, the minimum subcooling is $24.8^{\circ}C$.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1658-1668
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• 2019

Nuclear power generates a large portion of the energy used today and plays an important role in energy development. To ensure safe nuclear power generation, it is essential to conduct an accurate analysis of reactor structural integrity. Accordingly, in this study, a methodology for obtaining accurate structural responses to the combined seismic and reactor coolant loads existing prior to the shutdown of a nuclear reactor is proposed. By applying the proposed analysis method to the reactor vessel internals, it is possible to derive the seismic responses considering the influence of the hydraulic loads present during operation for the first time. The validity of the proposed methodology is confirmed in this research by using the finite element method to conduct seismic and hydraulic load analyses of the advanced APR1400 1400 MWe power reactor, one of the commercial reactors. The structural responses to the combined applied loads are obtained using displacement-based and stress-based superposition methods. The safety of the subject nuclear reactor is then confirmed by analyzing the design margin according to the American Society for Mechanical Engineers (ASME) evaluation criteria, demonstrating the promise of the proposed analysis method.

• Journal of Hydrogen and New Energy
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• v.25 no.6
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• pp.629-635
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• 2014

This paper presents annual energy production (AEP) by a 1.5kW wind turbine due to be installed in Deokjeok-Do island. Local wind data is determined by geometric shape of Deokjeok-Do island and annual wind data from Korea Institute of Energy Research at three places considered to be installed the wind turbine. Numerical simulation using WindSim is performed to obtain flow pattern for the whole island. The length of each computation grid is 40 m, and k-e turbulence model is imposed. AEP is determined by the power curve of the wind turbine and the local wind data obtained from numerical simulation. To capture the more detailed flow pattern at the specific local region, Urumsil-maul inside the island, fine mesh having the grid length of 10m is evaluated. It is noted that the input data for numerical simulation to the local region is used the wind data obtained by the numerical results for the whole island. From the numerical analysis, it is found that a local AEP at the Urumsil-maul has almost same value of 1.72 MWh regardless the grid resolutions used in the present calculation. It is noted that relatively fine mesh used for local region is effective to understand the flow pattern clearly.

• Journal of Hydrogen and New Energy
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• v.31 no.4
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• pp.387-394
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• 2020

A parametric study of a 2.5 kW class propeller type micro hydraulic turbine was performed. In order to analyze the internal flow characteristics in the hydraulic turbine, three dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were used and the hexahedral grid system was used to construct computational domain. To secure the reliability of the numerical analysis, the grid dependency test was performed using the grid convergence index method based on the Richardson extrapolation, and the grid dependency was removed when about 1.7 million nodes were used. For the parametric study, the axial distance at shroud span (L) between the inlet guide vane and the runner, and the inlet and outlet blade angles (β₁, β₂) of the runner were selected as the geometric parameters. The inlet and outlet angles of the runner were defined in the 3 spans from the hub to tip, and a total of 7 geometric parameters were investigated. It was confirmed that the outlet angles of the runner had the most sensitive effect on the power and efficiency of the micro hydraulic turbine.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.941-951
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• 2016

The aim of this work is to simulate the thermohydraulic consequences of a main steam line break and to compare the obtained results with Rossendorf Coolant Mixing Model (ROCOM) 1.1 experimental results. The objective is to utilize data from steady-state mixing experiments and computational fluid dynamics (CFD) calculations to determine the flow distribution and the effect of thermal mixing phenomena in the primary loops for the improvement of normal operation conditions and structural integrity assessment of pressurized water reactors. The numerical model of ROCOM was developed using the FLUENT code. The positions of the inlet and outlet boundary conditions and the distribution of detailed velocity/turbulence parameters were determined by preliminary calculations. The temperature fields of transient calculation were averaged in time and compared with time-averaged experimental data. The perforated barrel under the core inlet homogenizes the flow, and therefore, a uniform temperature distribution is formed in the pressure vessel bottom. The calculated and measured values of lowest temperature were equal. The inlet temperature is an essential parameter for safety assessment. The calculation predicts precisely the experimental results at the core inlet central region. CFD results showed a good agreement (both qualitatively and quantitatively) with experimental results.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.1
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• pp.1-11
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• 2012

The equation of the step-drawdown test "$s_w=BQ+CQ^p$" written by Rorabaugh (1953) is suitable for drawdown increased non-linearly in the fractured rocks. It was found that value of root mean square error (RMSE) between observed and calculated drawdowns was very low. The calculated $C$ (well head loss coefficient) and $P$ (well head loss exponent) value of well head losses ($CQ^p$) ranged $3.689{\times}10^{-19}{\sim}5.825{\times}10^{-7}$ and 3.459~8.290, respectively. It appeared that the deeper depth in pumping well the larger drawdowns due to pumping rate increase. The well head loss in the fractured rocks, unlike that in porous media, is affected by properties of fractures (fractures of aperture, spacing, and connection) around pumping well. The $C$ and $P$ value in the well head loss is very important to interpret turbulence interval and properties of high or low permeability of fractured rock. As a result, regression analysis of $C$ and $P$ value in the well head losses identified the relationship of turbulence interval and hydraulic properties. The relationship between $C$ and $P$ value turned out very useful to interpret hydraulic properties of the fractured rocks.

• Journal of Hydrogen and New Energy
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• v.31 no.3
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• pp.328-336
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• 2020

In the Francis turbine, the leakage flow through the runner gaps which are between the runner and the stator structure influences the internal flow and hydraulic performance. Thus, the investigation for the flow characteristics induced by the runner gaps is important. However, the runner gaps are often disregarded by considering the time and cost of the numerical analysis. Therefore, in this study, the flow characteristics according to runner gaps of the Francis turbine model were investigated including the leakage flow of the runner cone. The three-dimensional unsteady Reynolds-averaged Navier-Stokes analyses were conducted using a scale-adaptive simulation shear stress transport as a turbulence model for observing the influence of the leakage flow on the internal flow and hydraulic performance. The efficiencies were decreased slightly with runner gaps; and the complicated flows were captured in the gaps.

• Nuclear Engineering and Technology
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• v.42 no.6
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• pp.656-661
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• 2010

Lead-alloys are very attractive nuclear coolants due to their thermo-hydraulic, chemical, and neutronic properties. By utilizing the HELIOS (Heavy Eutectic liquid metal Loop for Integral test of Operability and Safety of PEACER$^2$) facility, a thermal hydraulic benchmarking study has been conducted for the prediction of pressure loss in lead-alloy cooled advanced nuclear energy systems (LACANES). The loop has several complex components that cannot be readily characterized with available pressure loss correlations. Among these components is the core, composed of a vessel, a barrel, heaters separated by complex spacers, and the plenum. Due to the complex shape of the core, its pressure loss is comparable to that of the rest of the loop. Detailed CFD simulations employing different CFD codes are used to determine the pressure loss, and it is found that the spacers contribute to nearly 90 percent of the total pressure loss. In the system codes, spacers are usually accounted for; however, due to the lack of correlations for the exact spacer geometry, the accuracy of models relies strongly on assumptions used for modeling spacers. CFD can be used to determine an appropriate correlation. However, application of CFD also requires careful choice of turbulence models and numerical meshes, which are selected based on extensive experience with liquid metal flow simulations for the KALLA lab. In this paper consistent results of CFX and Star-CD are obtained and compared to measured data. Measured data of the pressure loss of the core are obtained with a differential pressure transducer located between the core inlet and outlet at a flow rate of 13.57kg/s.

• Journal of the Korean earth science society
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• v.37 no.7
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• pp.448-464
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• 2016

The purpose of this study is to optimize the parameters related to consensus coherency within the PCL 1300, the operating program of wind profiler, from a validation of wind data between rawinsonde and wind profiler at Chupungryeong ($36^{\circ}13^{\prime}$, $127^{\circ}59^{\prime}$) site in Korea. It is then to analyze the diurnal and seasonal characteristics of the turbulence energy dissipation rate (${\varepsilon}$) in clear and rainy days from March 2009 to February 2010. In comparison of the wind data between wind profiler and rawinsonde during April 22-23, 2010, it was shown in a big error more than $10ms^{-1}$ over the height of 3,000 meters in the zonal (u) and meridional (v) wind components. When removing more than $10ms^{-1}$ in each wind speed difference of u an v components between the two instruments, the correlation coefficients of these wind components were 0.92 and 0.88, respectively, and the root mean square errors were 3.07 and $1.06ms^{-1}$. Based on these results, when the data processing time and the minimum available data within the PCL 1300 program were adjusted as 30 minutes and 60%, respectively, the bias errors were small. In addition, as a result of an analysis of sensitivity to consensus coherency of u and v components within the PCL1300 program, u components were underestimated in radial coherency, instantaneous and winbarbs coherency, whereas v components were overestimated. Finally by optimizing parameters of the PCL1300 program, the diurnal and seasonal means of ${\varepsilon}$ at each height were higher in rainy days than those in clear days because of increasing in the vertical wind speed due to upward and downward motions. The mean ${\varepsilon}$ for clear and rainy days in winter was lower than those of other seasons, due to stronger horizontal wind speed in winter than those in other seasons. Consequently, when the turbulence energy dissipation rates in the vertical wind speed of more than ${\pm}10cm\;s^{-1}$ were excluded for clear and rainy days, the mean ${\varepsilon}$ in rainy days was 6-7 times higher than that in clear days, but when considering them, it was 4-5 times higher.

• The KSFM Journal of Fluid Machinery
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• v.19 no.1
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• pp.11-17
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• 2016

In this paper, a numerical analysis was performed to investigate the effect of the pitch angle of a helical nozzle on the performance characteristics of a vortex tube. Three-dimensional numerical simulation has been performed with standard $k-{\varepsilon}$ turbulence model by using FLUENT 13.0. The effect of the pitch angle of helical nozzle was described in term of ${\beta}$. A CFD analysis was performed on ${\beta}=0^{\circ}$, $5^{\circ}$, $10^{\circ}$, $15^{\circ}$. In order to realize the influence of ${\beta}$ on performances of the vortex tube. Computation results were expressed by the ${\beta}-{\Delta}T_{h,c}$ graph and radial profiles of axial velocity and swirl velocity. The results showed that ${\beta}$ which improves energy separation capacity of vortex tube was $5^{\circ}$ at ${\alpha}=0.33$, 0.5 and $10^{\circ}$ at ${\alpha}=0.33$. Besides, It was confirmed that the results were closely related to axial velocity and swirl velocity.