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Experimental Study and Modelling of Spacer Grid Influence on Flow in Nuclear Fuel Assemblies
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The work is focused on experimental study and modelling of spacer grid influence on single- and two-phase flow. In the experimental study a mock-up of a realistic fuel bundle with five spacer grids of thin plate spring construction was investigated. A special pressure measuring technique was used to measure pressure distribution inside the spacer. Five pressure taps were drilled in one of the rods, which could exchange position with other rods, in this way providing a large degree of freedom. Laser Doppler Velocimetry was used to measure mean local axial velocity and its fluctuating component upstream and downstream of the spacer in several subchannels with differing spacer part. The experimental study revealed an interesting behaviour. Subchannels from the interior part of the bundle display a different effect on the flow downstream of the spacer compared to subchannels close to the box wall, even if the spacer part is the same. This behaviour is not reflected in modern correlations. The modelling part, first, consisted in comparing the present experimental data to Computational Fluid Dynamics calculations. It was shown that stand-alone subchannel models could predict the local velocity, but are unreliable in prediction of turbulence enhancement due to spacer. The second part of the modelling consisted in developing a deposition model for increase due to spacer. In this study Lagrangian Particle Tracking (LPT) coupled to Discrete Random Walk (DRW) technique was used to model droplet movements through turbulent flow. The LPT technique has an advantage to model the influence of turbulence structure effect on droplet deposition, in this way presenting a generalized model in view of spacer geometry change. The verification of the applicability of LPT DRW method to model deposition in annular flow at Boiling Water Reactor conditions proved that the method is unreliable in its present state. The model calculations compare reasonably well to air-water deposition data, but display a wrong trend if the fluids have a different density ratio than air-water.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2009. , 40 p.
Series
Trita-FYS, ISSN 0280-316X ; 2009:02
Keyword [en]
spacer grid influence, annular flow, deposition, Lagrangian Particle Tracking
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-9983ISBN: 978-91-7415-229-6 (print)OAI: oai:DiVA.org:kth-9983DiVA: diva2:173910
Presentation
2009-02-26, FA31, Roslagstullsbacken 21, Albanova University Centre, 10:00 (English)
Opponent
Supervisors
Available from: 2009-02-18 Created: 2009-02-18 Last updated: 2012-11-26Bibliographically approved
List of papers
1.  Detailed pressure drop measurements in single- and two-phase adiabatic air-water turbulent flows in realistic BWR fuel assembly geometry with spacer grids
Open this publication in new window or tab >> Detailed pressure drop measurements in single- and two-phase adiabatic air-water turbulent flows in realistic BWR fuel assembly geometry with spacer grids
2004 (English)In: The 6th International Conference on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-6) Nara, Japan, October 4-8, 2004, 2004Conference paper, Published paper (Refereed)
Abstract [en]

In recent years, advanced numerical simulation tools based on CFD methods have been increasingly used in various multi-phase flow applications. One of these is two-phase flow in fuel assemblies of Boiling Water Reactors. The important and often missing aspect of this development is the validation of CFD codes against proper experimental data. The purpose of the current paper is to present detailed pressure measurements over a spacer grid in adiabatic single- and two-phase flow, which will be used to validate and further develop a CFD code for BWR fuel bundle analysis. The experiments have been carried out in an asymmetric 24-rod sub-bundle, representing ¼ of Westinghouse SVEA-96 nuclear reactor fuel assembly. Single-phase measurements have been performed at superficial velocities comprised between jliq: 0.90 – 4.50 m/s and in the two-phase, which was simulated by air-water mixture, measurements have been performed at void fractions ranging from 4 to 12% and liquid superficial velocity jliq : 4.50 m/s. In order to increase the number of the measured points, five pressure taps were drilled in one of the rods, which was easily moved vertically by a traverse system, covering most of the points in axial direction. The possibility to substitute any of the rods in the fuel bundle by the pressure sensing rod and the possibility to change the pressure taps facing-angle provides more measuring points inside the subchannels. A detailed pressure distribution comparison between single- and two-phase flows for different subchannel positions and different flow conditions was performed over one of the spacers.  In addition, single-phase pressure drop measurements on the upper part of the test section comprising two spacer grids has been carried out.

Keyword
Pressure drop, pressure distribution, fuel bundle, spacer grid, air-water mixture, pressure sensing rod
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-9904 (URN)
Conference
The 6th International Conference on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-6) Nara, Japan, October 4-8, 2004
Note
QC 20101007Available from: 2009-02-18 Created: 2009-01-29 Last updated: 2010-10-07Bibliographically approved
2. Experimental investigation of turbulent flow through spacer grids in fuel rod bundles
Open this publication in new window or tab >>Experimental investigation of turbulent flow through spacer grids in fuel rod bundles
2009 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 239, no 10, 2013-2021 p.Article in journal (Refereed) Published
Abstract [en]

This paper contains experimental data of pressure, velocity and turbulence intensity in a 24‐rod fuel bundle withspacer grids. Detailed pressure measurements inside the spacer grid have been obtained by use of a sliding pressuresensingrod. Laser Doppler Velocimetry technique was used to measure the local axial velocity and its fluctuatingcomponent upstream and downstream of the spacer grid in subchannels with different blockage ratios. Themeasurements show a changing pattern in function of radial position in the cross‐section of the fuel bundle. Forsubchannels close to the box wall, the turbulence intensity suddenly increases just downstream of the spacer andthen gradually decays. In inner subchannels, however, the turbulence intensity downstream of the spacer decreasesbelow its upstream value and then gradually increases until it reaches the maximum value at approximately twospacer heights. The present study reveals that spacer effects, such as local pressure distribution and turbulenceintensity enhancement, do not depend exclusively on the local geometry details, but also on the location in thecross‐section of the rod bundle.

Keyword
Axial velocity, Blockage ratio, Experimental data, Experimental investigations, Fluctuating components, Fuel bundle, Fuel rods, Laser Doppler Velocimetry, Local geometry, Maximum values, Radial position, Rod bundles, Sliding pressure, Spacer effects, Spacer grid, Subchannels, Turbulence intensity
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-9906 (URN)10.1016/j.nucengdes.2009.05.029 (DOI)000270411500032 ()2-s2.0-68449099150 (Scopus ID)
Note

QC 20101007. Uppdaterad från Submitted till Published (20101007).

Available from: 2009-02-18 Created: 2009-01-29 Last updated: 2012-12-07Bibliographically approved
3. Measurements and CFD Predictions of Velocity, Turbulence Intensity and Pressure Development in BWR Fuel Rod Assembly with Spacers
Open this publication in new window or tab >>Measurements and CFD Predictions of Velocity, Turbulence Intensity and Pressure Development in BWR Fuel Rod Assembly with Spacers
2007 (English)In: Proceedings of the 12th International Meeting on Nuclear Reactor Thermal Hydraulics (NURETH12), 2007Conference paper, Published paper (Refereed)
Abstract [en]

The current paper presents measurements of axial velocity and its fluctuating component across a spacer in a rod bundle, using LDV technique. The measurements were performed in single-phase water flow in three subchannels of an asymmetric 24-rod mock-up of SVEA-96 fuel bundle. The subchannels differ in the spacer part. CFD models of the three subchannels were developed using commercial CFX 10.0 code. The flow structure in the spacer region has been predicted with two different turbulence models available in the code. The predictions were compared to the current experiments and additionally to experiments of pressure distribution across the spacer reported previously. The comparison showed that CFX code could predict the pressure drop over the spacer with an accuracy of 20-30%. The axial velocity development in the middle point of the subchannel could be reasonably predicted. However, the turbulence intensity increase downstream the spacer observed in the experiments could not be adequately predicted by the chosen turbulence models.

Keyword
Rod bundle, spacer, experimental flow characteristics, CFD
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-9905 (URN)2-s2.0-44349123025 (Scopus ID)978-089448058-4 (ISBN)
Conference
The 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-12), Sheraton Station Square, Pittsburgh, Pennsylvania, U.S.A. September 30-October 4, 2007.
Note

QC 20101007

Available from: 2009-02-18 Created: 2009-01-29 Last updated: 2014-11-07Bibliographically approved
4. Annular Flow Deposition Model with Obstacle Effect
Open this publication in new window or tab >>Annular Flow Deposition Model with Obstacle Effect
2007 (English)In: Proceedings of the 6th International Conference on Multiphase Flow, ICMF 2007, July 9-13, Leipzig, Germany, 2007Conference paper, Published paper (Refereed)
Abstract [en]

Lagrangian particle simulations were performed in round, square and subchannel-type ducts with obstacle in order to study the influence of the obstacle and the shape of the conduit on deposition. The deposition mass transfer coeffient calculated from these simulations was correlated to the averaged square root of turbulent kinetic energy in the channel upstream and downstream of the obstacle, thus to obtain a new deposition model to be included into a thermal-hydraulic subchannel code for the prediction of CHF phenomenon. The deposition results calculated by the new model were compared to Govan correlation, with the conclusion that round duct data compare good to the correlation, but not the other geometries. Since the correlation itself was developed from round duct experimental data, it can be stated that the new deposition model is able to predict the deposition rate fairly good for this case. The results from other geometries would have to be compared to experimental data to be able to conclude that the model is valid.

Keyword
annular flow, deposition model, obstacle effect, particle tracking
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-9907 (URN)
Conference
The 6th International Conference on Multiphase Flow, ICMF 2007, Leipzig, Germany, July 9-13, 2007
Note
QC 20101007Available from: 2009-02-18 Created: 2009-01-29 Last updated: 2010-10-07Bibliographically approved
5. Verification of Discontinuous Random Walk Lagrangian Particle Tracking as a Tool to Model Deposition in Annular Flow
Open this publication in new window or tab >>Verification of Discontinuous Random Walk Lagrangian Particle Tracking as a Tool to Model Deposition in Annular Flow
2009 (English)In: Proceedings of the 17th International Conference on Nuclear Engineering ICONE17 July 12-16, 2009, Brussels, Belgium ICONE17-75297, Brussels, Belgium, 2009, 311-319 p.Conference paper, Published paper (Refereed)
Abstract [en]

A verification of the applicability of the discontinuous random walk (DWR) Lagrangian Particle Tracking (LPT) model to calculate deposition in annular two-phase flow has been conducted. The comparison of simulation results to experimental data of deposition of mono-sized droplets shows that the model follows the correct trend in inertiamoderated regime, but is un-reliable in diffusion-impaction deposition regime. The comparison to other experimental studies of annular flow of different density ratios between the two phases reveals that the density ratio is incorrectly incorporated into the model, since the experimental trend is reversed. It can be concluded that the applicability of DWR LPT model for deposition calculation in steam-water flow at BWR conditions cannot be validated by solely comparing the simulation results to air-water experimental data.

Place, publisher, year, edition, pages
Brussels, Belgium: , 2009
Series
International Conference on Nuclear Engineering, Proceedings, ICONE, 3
Keyword
Air-water, Annular flows, Annular two-phase flow, Density ratio, Deposition regimes, Experimental data, Experimental studies, In-diffusion, Lagrangian particle tracking, Mono-sized, Random Walk, Simulation result, Steam-water flows, Two phasis
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-9909 (URN)10.1115/ICONE17-75297 (DOI)000282466600038 ()2-s2.0-77952821861 (Scopus ID)978-0-7918-4353-6 (ISBN)
Conference
the 17th International Conference on Nuclear Engineering ICONE17 July 12-16, 2009, Brussels, Belgium ICONE17-75297
Note
QC 20101007. Tidigare titel: "LAGRANGIAN PARTICLE TRACKING AS A TOOL FOR DEPOSITION MODELING IN ANNULAR FLOW".Available from: 2009-02-18 Created: 2009-01-29 Last updated: 2011-01-31Bibliographically approved

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