scholarly journals CFD Turbulence Study of PWR Spacer-Grids in a Rod Bundle

2014 ◽  
Vol 2014 ◽  
pp. 1-15 ◽  
Author(s):  
C. Peña-Monferrer ◽  
J. L. Muñoz-Cobo ◽  
S. Chiva
Keyword(s):  
Mechanical Stability ◽  
Turbulence Models ◽  
Cfd Modeling ◽  
Spacer Grid ◽  
Pressurized Water ◽  
Spacer Grids ◽  
Eddy Simulation ◽  
Transient Nature ◽  
Rod Bundle ◽  
Wide Range

Nuclear fuel bundles include spacers essentially for mechanical stability and to influence the flow dynamics and heat transfer phenomena along the fuel rods. This work presents the analysis of the turbulence effects of a split-type and swirl-type spacer-grid geometries on single phase in a PWR (pressurized water reactor) rod bundle. Various computational fluid dynamics (CFD) calculations have been performed and the results validated with the experiments of the OECD/NEA-KAERI rod bundle CFD blind benchmark exercise on turbulent mixing in a rod bundle with spacers at the MATiS-H facility. Simulation of turbulent phenomena downstream of the spacer-grid presents high complexity issues; a wide range of length scales are present in the domain increasing the difficulty of defining in detail the transient nature of turbulent flow with ordinary turbulence models. This paper contains a complete description of the procedure to obtain a validated CFD model for the simulation of the spacer-grids. Calculations were performed with the commercial code ANSYS CFX using large eddy simulation (LES) turbulence model and the CFD modeling procedure validated by comparison with measurements to determine their suitability in the prediction of the turbulence phenomena.

Study of Mixing Characteristics Over a Spacer Grid With Sloping Channels Based on Numerical Simulations in a PWR 5×5 Rod Bundle Using CFD Codes

2013 ◽  
Author(s):  
Xi Chen ◽  
Hong Zhang
Keyword(s):  
Numerical Simulations ◽  
Safety Margin ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Spacer Grid ◽  
Pressurized Water ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Commercial Code ◽  
Water Reactors

Spacer grids are important components of fuel assemblies for Pressurized Water Reactors (PWR). The presence of spacer grid promotes local heat transfer adjacent to the rod wall downstream by inducing swirl and cross flows within and between sub-channels to increase thermal hydraulic safety margin. Recent years, Computational Fluid Dynamics (CFD) methodologies are widely adopted to designs of spacer grids. This paper presents results of numerical simulations with commercial code CFX 12.0 in a PWR 5 × 5 rod bundle including a spacer grid with sloping channels. Based on a combined mesh generation approach of structured and unstructured mesh, distributions of velocity fields, temperature and pressure fields downstream the spacer grid were analyzed. The results indicate that cross flows caused by the spacer grid are uniform in circumference inducing no thermal hydraulic deterioration, but mass exchange between central hot fluid and external cold fluid appears insufficient for the new style grid.

CFD Study on Mixing in VVER-440 Fuel Rod Bundle With Guiding Vanes in Spacer Grids

2009 ◽  
Author(s):  
Tellervo Brandt ◽  
Timo Toppila
Keyword(s):  
Turbulence Models ◽  
Heat Fluxes ◽  
Normal Operation ◽  
Navier Stokes ◽  
Pressurized Water ◽  
Spacer Grids ◽  
Fuel Rod ◽  
Rod Bundle ◽  
Computational Fluid Dynamics Cfd ◽  
Water Reactors

In this article, we study mixing in a fuel rod bundle geometry used in VVER-440 type pressurized water reactors. The flow inside the fuel assembly under normal operation is simulated using the FLUENT 6.3 computational fluid dynamics (CFD) solver. Steady state one phase Reynolds-averaged Navier-Stokes modeling is applied with two-equation turbulence models. In the first part of the article, grid independence is studied using a small submodel of the fuel rod bundle. In the second part, flow across a full-length fuel rod bundle is simulated both with constant temperature and with prescribed heat fluxes at the rod walls. Finally, in the third part of the article, we study how guiding vanes included in the spacer grids would enhance mixing in the hottest subchannels. We propose that having four guiding vanes on each side of the hexagonal spacer grid would produce most mixing in the desired locations of the fuel rod bundle.

Numerical Flow Simulation of Spacer Grids With Mixing Vanes in a 5 × 5 PWR Rod Bundle

2009 ◽  
Author(s):  
Moyse´s Alberto Navarro ◽  
Andre´ Augusto Campagnole dos Santos
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Pressure Loss ◽  
Considerable Increase ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Spacer Grid ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Vane Angle

The spacer grids exert great influence on the thermal hydraulic performance of the PWR fuel assembly. The presence of the spacers has two antagonistic effects on the core: an increase of pressure drop due to constriction on the coolant flow area and increase of the local heat transfer downstream the grids caused by enhanced coolant mixing. The mixing vanes, present in most of the spacer grid designs, cause a cross and swirl flow between and in the subchannels, enhancing even more the local heat transfer at the cost of more pressure loss. Due to this important hydrodynamic feature the spacer grids are often improved aiming to obtain an optimal commitment between pressure drop and enhanced heat transfer. In the present work, the fluid dynamic performance downstream a 5 × 5 rod bundle with spacer grids is analyzed with a commercial CFD code (CFX 11.0). Eleven different split vane spacer grids with angles from 16° to 36° and a spacer without vanes were evaluated. The computational domain extends from ∼10 Dh upstream to ∼50 Dh downstream the spacer grids. The standard k-ε turbulence model with scalable wall functions and the total energy model were used in the simulations. The results show a considerable increase of the average Nusselt number and secondary mixing with the angle of the vane up to ∼20 Dh downstream the spacer, reducing greatly the influence of the vane angle beyond this region. As expected, the pressure loss through the spacer grid also showed considerable increase with the vane angle.

scholarly journals Numerical Investigation on the Flow Characteristics in a 17 × 17 Full-Scale Fuel Assembly

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 397 ◽  
Author(s):  
Zihao Tian ◽  
Lixin Yang ◽  
Shuang Han ◽  
Xiaofei Yuan ◽  
Hongyan Lu ◽  
...  
Keyword(s):  
Fuel Assembly ◽  
Flow Characteristics ◽  
Full Scale ◽  
Pressurized Water Reactor ◽  
Lateral Velocity ◽  
Pressurized Water ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Real Size ◽  
Cfd Method

In a previous study, several computational fluid dynamics (CFD) simulations of fuel assembly thermal-hydraulic problems were presented that contained fewer fuel rods, such as 3 × 3 and 5 × 5, due to limited computer capacity. However, a typical AFA-3G fuel assembly consists of 17 × 17 rods. The pressure drop levels and flow details in the whole fuel assembly, and even in the pressurized water reactor (PWR), are not available. Hence, an appropriate CFD method for a full-scale 17 × 17 fuel assembly was the focus of this study. The spacer grids with mixing vanes, springs, and dimples were considered. The polyhedral and extruded mesh was generated using Star-CCM+ software and the total mesh number was about 200 million. The axial and lateral velocity distribution in the sub-channels was investigated. The pressure distribution downstream of different spacer grids were also obtained. As a result, an appropriate method for full-scale rod bundle simulations was obtained. The CFD analysis of thermal-hydraulic problems in a reactor coolant system can be widely conducted by using real-size fuel assembly models.

Turbulent Flow Through Spacer Grids in Rod Bundles

1998 ◽  
Vol 120 (4) ◽  
pp. 786-791 ◽  
Author(s):  
Sun Kyu Yang ◽  
Moon Ki Chung
Keyword(s):  
Turbulent Flow ◽  
Laser Doppler Velocimetry ◽  
Hydraulic Characteristics ◽  
Rod Bundles ◽  
Spacer Grid ◽  
Spacer Grids ◽  
Rod Bundle ◽  
Turbulence Decay ◽  
Skewness Factor ◽  
Flow Through

The effects of the spacer grids with mixing vanes in rod bundles on the turbulent structure were investigated experimentally. The detailed hydraulic characteristics in subchannels of a 5 × 5 rod bundle with mixing spacer grids were measured upstream and downstream of the spacer grid by using a one component LDV (Laser Doppler Velocimetry). Axial velocity and turbulent intensity, skewness factor, and flatness factor were measured. The turbulence decay behind spacer grids was obtained from measured data. The trend of turbulence decay behaves in a similar way as turbulent flow through mesh grids or screens. Pressure drop measurements were also performed to evaluate the loss coefficient for the spacer grid and the friction factor for a rod bundle.

An Estimation of the Dynamic Buckling Load for the Spacer Grid of Pressurized Water Reactor Fuel Assembly

2006 ◽  
Vol 326-328 ◽  
pp. 1603-1606 ◽  
Author(s):  
Sang Youn Jeon ◽  
Young Shin Lee
Keyword(s):  
Fuel Assembly ◽  
Dynamic Buckling ◽  
Buckling Load ◽  
Estimation Methods ◽  
Pressurized Water Reactor ◽  
Spacer Grid ◽  
Pressurized Water ◽  
Water Reactor ◽  
Spacer Grids ◽  
The Impact

This study contains an estimation of the dynamic buckling load for the spacer grid of fuel assembly in pressurized water reactor. Three different estimation methods were proposed for the calculation of the dynamic buckling loads of spacer grid. The dynamic impact tests and analyses were performed to evaluate the impact characteristics of the spacer grids and to predict the dynamic buckling load of the full size spacer grid. The estimation results were compared with the test results for the verification of the estimation methods.

scholarly journals Experimental Study of Pressure Loss in a 5 × 5–Rod Bundle With the Mixing Vane Spacer Grid

2021 ◽  
Vol 9 ◽  
Author(s):  
Wenhai Qu ◽  
Weiyi Yao ◽  
Jinbiao Xiong ◽  
Xu Cheng
Keyword(s):  
Pressure Loss ◽  
Lateral Pressure ◽  
Reynolds Numbers ◽  
Wall Friction ◽  
Geometrical Parameters ◽  
Strong Correlations ◽  
Pressurized Water Reactor ◽  
Spacer Grid ◽  
Pressurized Water ◽  
Rod Bundle

Axial and lateral pressure loss in a 5 × 5 rod–bundle with a split-type mixing vane spacer grid was experimentally measured using differential pressure transmitters at different sub-channel Reynolds numbers (Re) and orienting angles. The geometrical parameters of the 5 × 5–rod bundle are as follows: they have the same diameter (D = 9.5 mm) and pitch (p = 12.6 mm) as those of real fuel rods of a typical pressurized water reactor (PWR), with a sub-channel hydraulic diameter (Dh) of 11.78 mm. The characteristics and resistance models of pressure loss are discussed. The main axial pressure loss is caused by the spacer grid, and the spacer grid generates additional wall friction pressure loss downstream of the spacer grid. The lateral pressure loss shows strong correlations with orienting angles and distance from the spacer grid. The lateral pressure loss shows a sudden burst in the mixing vanes region and a slight augmentation at z = 3Dh. After 3Dh, the lateral pressure loss decays in an exponential way with distance from the spacer grid, and it becomes constant quickly at z = 20Dh.

Evaluation of Single-Phase CFD Applicability to Estimate Fluid Hot Spot Locations by Comparing Water DNB Data

2004 ◽  
Author(s):  
Kazuo Ikeda ◽  
Yasushi Makino ◽  
Masaya Hoshi
Keyword(s):  
Heat Generation ◽  
Pressure Loss ◽  
Single Phase ◽  
Flow Behavior ◽  
Cfd Modeling ◽  
Spacer Grid ◽  
Flow Measurements ◽  
Fuel Rods ◽  
Spacer Grids ◽  
Grid Design

For development of PWR spacer grids, it is necessary to confirm mechanical strength and thermal-hydraulic characteristics. Mitsubishi has applied Computational Fluid Dynamics (CFD) to thermal-hydraulic design of spacer grids. To satisfy the requirement of high thermal performance spacer grid, the compatibility of low-pressure loss and high Critical Heat Flux (CHF) performance is necessary; therefore, parametric CFD analyses have been carried out for new spacer grid designs. Related to spacer grid design, i.e., strap structures and mixing vane, the parametric analyses have been carried out to estimate pressure-loss of each spacer grid. Moreover, thermal analyses, where heat generation from fuel rods was taken into account, have been carried out to evaluate coolant mixing capability, which is assumed to relate the CHF performance, by comparing fluid peak temperature of each grid design. In our previous study (ICONE11-36087), the rod type Laser Doppler Velocimetry (rod LDV) and Particle Imaging Velocimetry (PIV) technique were applied to cross-flow and axial flow measurements in rod gaps and sub-channels to obtain reference data for verification of CFD estimation. Estimated velocity fields at the downstream of the grid were quantitatively compared with the measurements. As a result, it was confirmed that the CFD modeling estimated flow behavior in the rod bundle appropriately. In this study, CFD under single-phase condition, which took into account heat generation from rods, was performed to simulate flow conditions of water DNB test with the same design grid of the previous study. The correlation between estimated enthalpy distribution around fuel rods by the CFD and the CHF rods in the DNB test was examined. This study was performed in collaboration with Westinghouse Electric Company and Mitsubishi Heavy Industries, Ltd.

scholarly journals CFD Modeling of Hydrocyclones—A Study of Efficiency of Hydrodynamic Reservoirs

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 118 ◽  
Author(s):  
Marvin Durango-Cogollo ◽  
Jose Garcia-Bravo ◽  
Brittany Newell ◽  
Andres Gonzalez-Mancera
Keyword(s):  
Pressure Drop ◽  
Separation Efficiency ◽  
Collection Efficiency ◽  
Saddle Points ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Cfd Modeling ◽  
Eddy Simulation ◽  
Discrete Phase ◽  
Rsm Model

The dynamics of hydrocyclones is complex, because it is a multiphase flow problem that involves interaction between a discrete phase and multiple continuum phases. The performance of hydrocyclones is evaluated by using Computational Fluid Dynamics (CFD), and it is characterized by the pressure drop, split water ratio, and particle collection efficiency. In this paper, a computational model to improve and evaluate hydrocyclone performance is proposed. Four known computational turbulence models (renormalization group (RNG) k- ε , Reynolds stress model (RSM), and large-eddy simulation (LES)) are implemented, and the accuracy of each for predicting the hydrocyclone behavior is assessed. Four hydrocyclone configurations were analyzed using the RSM model. By analyzing the streamlines resulting from those simulations, it was found that the formation of some vortices and saddle points affect the separation efficiency. Furthermore, the effects of inlet width, cone length, and vortex finder diameter were found to be significant. The cut-size diameter was decreased by 33% compared to the Hsieh experimental hydrocyclone. An increase in the pressure drop leads to high values of cut-size and classification sharpness. If the pressure drop increases to twice its original value, the cut-size and the sharpness of classification are reduced to less than 63% and 55% of their initial values, respectively.

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