CFD Estimation of the Flow-Induced Vibrations of a Fuel Rod Downstream a Mixing Grid

2009 ◽  
Author(s):  
S. Benhamadouche ◽  
P. Moussou ◽  
C. Le Maitre
Keyword(s):  
Power Plants ◽  
Beam Theory ◽  
Fretting Wear ◽  
Euler Beam ◽  
Local Flow ◽  
Fuel Rod ◽  
Eddy Simulation ◽  
Natural Modes ◽  
Flow Induced Vibrations ◽  
Wear Damage

Turbulent-induced vibrations of fuel assemblies in PWR power plants is a potential cause of deformation and of fretting wear damage. Because of the complexity of a 17 × 17 rod assembly with a length exceeding four meters, the prediction of its vibrations is still a challenging task as regards computer simulation. The Large Eddy Simulation (LES) technique provides the instantaneous pressure and velocity fields inside the fluid as well as the shear stress and the pressure along the walls. EDF inhouse open source CFD tool Code_Saturne is used in the present work with a 8 million cells grid to compute the flow along four sub-channels all around one fuel rod by taking into account only one mixing grid. The computations are carried out on 1024 processors of a BlueGene/L supercomputer. Hence, the overall turbulent excitation upon one single rod is estimated numerically, taking into account the specific influence of the deflectors. As regards the structure, using the forces provided by the CFD computation, a linear model of the rod based on Euler beam theory and simplified boundary conditions is proposed. The first natural modes of the structure are hence obtained, and the modal forces are estimated using the standard techniques of modal projection and joint acceptance. Estimations of the vibration amplitude of rod induced by the local flow are finally obtained, using simplified expressions of the added mass and of the damping coefficient. The amplitudes are significant for the first mode essentially, and reach a value of the order of the μm, with a maximum around 6 μm.

An Evaluation of Fuel Rod Fretting Wear in Spacer Grid With Conformal Shape

2006 ◽  
Author(s):  
Young Ki Jang ◽  
Nam Kyu Park ◽  
Jae Ik Kim ◽  
Kyu Tae Kim ◽  
Chong Chul Lee ◽  
...  
Keyword(s):  
Nuclear Fuel ◽  
Calculation Method ◽  
Power Plants ◽  
Failure Time ◽  
Fretting Wear ◽  
Measuring System ◽  
Wear Volume ◽  
Wear Depth ◽  
Volume Calculation ◽  
Fuel Rod

Turbulent flow-induced vibration in nuclear fuel may cause fretting wear of fuel rod at grid support locations. An advanced nuclear fuel for Korean PWR standard nuclear power plants (KSNPs), has been developed to get higher performance comparing to the current fuel considering the safety and economy. One of the significant features of the advanced fuel is the conformal shape in mid grid springs and dimples, which are developed to diminish the fretting wear failure. Long-term hydraulic tests have been performed to evaluate the fretting wear of the fuel rod with the conformal springs and dimples. Wear volume is a measure to predict the fretting wear performance. The shapes of a lot of scars are non-uniform such as wedge shapes, and axially non-symmetric shapes, etc., depending on the contact angle between fuel rod and springs/dimples. In addition, conformal springs and dimples make wear scars wide and thin comparing to conventional ones with convex shape. It is found that wear volumes of these kinds of non-uniform wear scars are over-predicted when the traditionally used wear depth-dependent volume calculation method is employed. In order to predict wear volume more accurately, therefore, the measuring system with high accuracy has been used and verified by the known wear volumes of standard specimens. The wear volumes of the various wear scars have been generated by the measuring system and used for predicting the fretting wear-induced failure time. Based on new evaluation method, it is considered that the fretting wear-induced fuel failure duration with this conformal grid has increased up to 8 times compared to the traditionally used wear depth-dependent volume calculation method.

Monte Carlo Simulation of Fretting Wear Performance of Fuel Rods

2005 ◽  
Author(s):  
Pablo R. Rubiolo
Keyword(s):  
Monte Carlo ◽  
Fretting Wear ◽  
Fuel Rods ◽  
Wear Performance ◽  
Wear Rates ◽  
Fuel Rod ◽  
Cell Clearance ◽  
Vibration Model ◽  
Support Conditions ◽  
Wear Damage

The effect of the diverse parameters affecting the fretting-wear performance of nuclear fuel rods is investigated by performing Monte Carlo simulations with a fuel rod vibration model. The study is focused on the analysis of the effect of the grid parameters, including the cell clearance and the grid/support misalignments, on the support preload forces distribution, the rod dynamic response and the overall wear damage. In the present approach, the fuel rod and grids are modeled as a beam constrained at a finite number of axial positions and a non-linear vibration model is used to predict the rod motion and the wear rates. The results of the analysis suggest that an important fraction of the variability of the assembly wear damage distribution can be explained by the local variations of the rod-support conditions.

A Numerical Characterization of Flow-Induced Vibration and Fretting Wear Potential in Nuclear Steam Generator Tube Bundles

2011 ◽  
Author(s):  
Marwan Hassan ◽  
Atef Mohany
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Complex Dynamics ◽  
Fretting Wear ◽  
Contact Ratio ◽  
Flow Induced Vibration ◽  
Numerical Characterization ◽  
Wear Damage ◽  
Effect Of Support ◽  
Tube Failure

Nuclear power plants have experienced problems related to tube failures in steam generators. While many of these failures have been attributed to corrosion, it has been recognized that flow-induced vibrations contribute significantly to tube failure. In order to avoid these excessive vibrations, tubes are stiffened by placing supports along their length. Various tube/support geometries have been used, but the majority are either support plates (plates with drilled or broached holes) or flat bars. Unfortunately, clearance is often considered necessary between the tubes and their supports to facilitate tube/support assembly and to allow for thermal expansion of the tubes. A combination of flow-induced turbulence and fluidelastic forces may then lead to unacceptable tube fretting-wear at the supports. The fretting wear damage could ultimately cause tube failure. Such failures may require shut downs resulting in production losses, and pose potential threats to human safety and the environment. Therefore, it is imperative to predict the nonlinear tube response and the associated fretting wear damage to tubes due to fluid excitations. Tubes in loose flat-bar supports have complex dynamics due to the possible combinations of geometry. The understanding of tube dynamics in the presence of this type of support and the associated fretting wear is still incomplete. These issues are addressed in this paper through simulations of the dynamics of tubes subjected to crossflow turbulence and fluidelastic instability forces. The finite element method is utilized to model the vibrations and impact dynamics. The tube model simulates a U-tube supported by 16 flat bars with clearances and axial offset. Results are presented and comparisons are made for the parameters influencing the fretting-wear damage such as contact ratio, impact forces and normal work rate. The effect of support clearance and support axial offset are investigated.

A New Tube/Support Impact Model for Heat Exchanger Tubes in Loose Supports

2003 ◽  
Author(s):  
M. A. Hassan ◽  
D. S. Weaver ◽  
M. A. Dokainish
Keyword(s):  
Heat Exchanger ◽  
Contact Stiffness ◽  
Single Point ◽  
Friction Model ◽  
Fretting Wear ◽  
Analytical Models ◽  
Stick Slip ◽  
Proposed Model ◽  
Flow Induced Vibrations ◽  
Wear Damage

Heat exchanger tubes are usually loosely supported at intermediate points by plates or flat bars. Flow-induced vibrations result in fretting wear tube damage due to impacting and rubbing of tubes against their supports. Prediction of tube response relies on modelling the nonlinear tube/support interaction. The evaluated response is used to predict the resultant wear damage using experimentally measured wear coefficients. An accurate of prediction of impact forces and the work rate is therefore paramount. The analytical models available assume tube/support contact occurs over a single point. In this paper, a computational algorithm is proposed to describe the tube/support impact considering a finite support width. The new model provides a means of representing tube/support contact as a combination of edge and segmental contact. The proposed model utilizes a distributed contact stiffness to describe the segmental contact. The formulation also incorporates a stick/slip friction model. The model developed is utilized to simulate the dynamics of loosely-supported tubes.

Fretting Wear of the Zr Fuel Rod Cladding

2014 ◽  
Author(s):  
Ladislav Pecinka ◽  
Jaroslav Svoboda ◽  
Vladimír Zeman
Keyword(s):  
Nuclear Power ◽  
Nuclear Reactors ◽  
Fretting Wear ◽  
Pressurized Water ◽  
Fuel Rods ◽  
Fuel Rod ◽  
Fuel Assemblies ◽  
Flow Induced Vibrations ◽  
Water Reactors ◽  
Fretting Damage

Fretting wear is a particular type of wear that is expected to occur in fuel assemblies of pressurized water cooled nuclear reactors. Fretting damage of fuel rods may cause Nuclear Power Plant (NPP) operations problems and are very expensive to repair. As utilities and fuel vendors adopt higher utilization of uranium and improved thermal margins plants, burned fuel rods will be loaded at core the periphery as part of the margin mechanisms. Pressurized Water Reactors (PWRs) have experienced fuel rods fretting wear failures due to flow induced vibrations. This study describes basic results of theoretical analysis and describes experiments to predict thinning of the Zr cladding wall thickness performed.

scholarly journals CFD Estimation of the Unsteady Fluid Force Along a Fuel Rod Downstream a Mixing Grid

2011 ◽  
Author(s):  
P. Moussou ◽  
S. Benhamadouche ◽  
Ch. Bodel
Keyword(s):  
Power Plants ◽  
Axial Flow ◽  
Point Of View ◽  
Fretting Wear ◽  
Pressure Force ◽  
Power Spectral ◽  
Water Reactors ◽  
Wear Damage ◽  
Unsteady Fluid ◽  
Few Data

Unsteady flow loading of fuel assemblies in Pressurised Water Reactors power plants is a potential cause of deformation and of fretting wear damage. Inside a fuel assembly, rods are arranged in 17 × 17 bundles. The rod diameter is equal to about 9 mm, and the gap between two rods is equal to about 2 mm. Each rod is several meters long, and mixing grids are arranged every 0.4 m. The axial flow velocity is equal to about 5 m/s, so that the Reynolds number reaches 5 × 105 in the reactor configuration. Due to the complexity of the turbulent flow pattern, an accurate description of the fluid-structure interaction is still a challenging task, and only a few data about this issue are available today in literature. Recent Computational Fluid Dynamics results are revisited from the point of view of classical axial turbulence-induced vibrations. The unsteady pressure force Power Spectral Densities are determined, a convective velocity is derived, and an estimation of the axial correlation length for the pressure force is given. The results agree reasonably well with the scientific literature.

Fluidelastic Instability Modeling of Loosely Supported Multispan U-Tubes in Nuclear Steam Generators

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Marwan Hassan ◽  
Atef Mohany
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Complex Dynamics ◽  
Tube Bundle ◽  
Design Guidelines ◽  
Fretting Wear ◽  
Contact Ratio ◽  
Steam Generators ◽  
Fluidelastic Instability ◽  
Wear Damage

Steam generators in nuclear power plants have experienced tube failures caused by flow-induced vibrations. Two excitation mechanisms are responsible for such failures; random turbulence excitation and fluidelastic instability. The random turbulence excitation mechanism results in long-term failures due to fretting-wear damage at the tube supports, while fluidelastic instability results in short-term failures due to excessive vibration of the tubes. Such failures may require shutdowns, which result in production losses, and pose potential threats to human safety and the environment. Therefore, it is imperative to predict the nonlinear tube response and the associated fretting-wear damage to tubes due to fluid excitation. In this paper, a numerical model is developed to predict the nonlinear dynamic response of a steam generator with multispan U-tubes and anti-vibration bar supports, and the associated fretting wear due to fluid excitation. Both the crossflow turbulence and fluidelastic instability forces are considered in this model. The finite element method is utilized to model the vibrations and impact dynamics. The tube bundle geometry is similar to the geometry used in CANDU steam generators. Eight sets of flat-bar supports are considered. Moreover, the effect of clearances between the tubes and their supports, and axial offset between the supports are investigated. The results are presented and comparisons are made for the parameters influencing the fretting-wear damage, such as contact ratio, impact forces, and normal work rate. It is clear that tubes in loose flat-bar supports have complex dynamics due to a combination of geometry, tube-to-support clearance, offset, and misalignment. However, the results of the numerical simulation along with the developed model provide new insight into the flow-induced vibration mechanism and fretting wear of multispan U-tubes that can be incorporated into future design guidelines for steam generators and large heat exchangers.

The Effect of Coating on the Fretting Wear Between Tubes and Supports in a Nuclear Steam Generator

2007 ◽  
Author(s):  
Joong-Hui Lee ◽  
Jin-Sun Kim ◽  
Jung-Min Park ◽  
Bo-Ra Shin ◽  
Young-Ze Lee
Keyword(s):  
Steam Generator ◽  
Coating Thickness ◽  
Nuclear Power ◽  
Power Plants ◽  
Hard Coatings ◽  
Fretting Wear ◽  
Tube Material ◽  
Flat Type ◽  
Wear Damage ◽  
Wear Tests

The steam generator in the nuclear power plants is a kind of heat exchanger, which is composed of bundles of long and slender pipes. The tubes are supported by anti-vibration bar to reduce the vibration, caused by the water flows for cooling purpose. The wear damage due to this vibration is called as the fretting wear, which should be minimized for the safe operation of plants. The hard coatings are very effective to reduce the amount of wear. In this paper, the coatings of TiN and CrN were deposited on the tube material to protect the fretting surfaces. The tube-on-flat type tester was used for fretting wear tests. The wear amounts of the coated tubes were decreased depending on coating thickness. CrN coating was very effective to reduce the wear. In case of TiN the wear amounts were dependent on the coating thickness. Thick coating of TiN was very effective for wear resistance.

Generic CFD for Vortex Induced Acoustic Resonance in Deep Cavities

2008 ◽  
Author(s):  
Eric Lillberg ◽  
Per Nilsson
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Stokes Equations ◽  
Acoustic Resonance ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Induced Vibrations ◽  
Deep Cavities

Extended power uprates (EPUs) of nuclear power plants result in changes in steam velocity and temperature. These changes increase the risk of flow induced vibrations due to shear layer instabilities and vortex shedding amplified by acoustic resonance. In the present study the possibility to predict vortex induced acoustic resonance is investigated using compressible Navier-Stokes equations (NSE) for viscous fluid flow with focus on generality. For this purpose the NSE are solved using Large Eddy Simulation (LES) technique and the open source solver OpenFOAM which is available under GPL. Validation is made using experiments as well as a other simulation using a pseudo compressible formulation. In the present study several LES models are used including the more recent Implicit LES (ILES) approach.

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