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.

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.

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.

Oil debris monitoring in misaligned spline couplings subjected to fretting wear

2014 ◽  
Vol 229 (12) ◽  
pp. 2261-2269 ◽  
Author(s):  
Vincenzo Cuffaro ◽  
Francesca Curà ◽  
Andrea Mura
Keyword(s):  
Structural Integrity ◽  
Experimental Tests ◽  
Surface Damage ◽  
Point Of View ◽  
Fretting Wear ◽  
Experimental Point ◽  
Spline Coupling ◽  
Wear Damage ◽  
Oil Debris ◽  
Onset Phase

Mechanical components may be subjected to wear damage that may cause the component failure. From the experimental point of view, the wear damage may be detected by analyzing the debris produced by the wear phenomena into the lubrication oil. This technique may be used to monitor the structural integrity of bearings and gear health by means of dedicated sensors. In this work, the oil debris production due to fretting wear in spline couplings has been investigated; in particular, the aim of this work is to identify both entity and onset phase of the surface damage by means of parameters obtained from the oil debris monitoring. Experimental tests have been performed by means of a dedicated test that allows to reproduce the real working conditions on spline coupling specimens, by varying both transmitted torque and misalignment angle. The oil debris production has been monitored by means of an optical sensor, in terms of particles size and numerosity. Results show that the wear damage may be identified by monitoring the variation of both Kurtosis of the particle distribution and amount of the particles production, both for as concerns phenomenon entity and corresponding onset.

Fretting-Wear Damage due to Vibration in Nuclear and Process Equipment

2017 ◽  
Author(s):  
Michel J. Pettigrew ◽  
Metin Yetisir ◽  
Nigel J. Fisher ◽  
Bruce A. W. Smith ◽  
Colette E. Taylor ◽  
...  
Keyword(s):  
Mechanical Energy ◽  
Work Rate ◽  
Point Of View ◽  
Contact Forces ◽  
Fretting Wear ◽  
Process Equipment ◽  
Damage Development ◽  
Simple Formulation ◽  
Piping Systems ◽  
Wear Damage

The problem of fretting-wear damage between a vibrating structure and its supports is discussed in this paper. Typical components of concern are piping systems and pipe-supports, multispan heat exchanger tubes and tube supports, and nuclear fuel bundles and fuel channels. Fretting-wear damage is related to the dynamic interaction between a structure and its supports. This interaction is conveniently formulated in terms of a parameter called “work rate” to predict fretting-wear damage. Work rate is simply the integral of contact force over sliding distance per unit time. Fretting-wear damage may be investigated from an energy point of view. It is essentially the mechanical energy or power dissipated through contact forces and sliding that causes fretting-wear damage. Development of a simple formulation that relates tube vibration response and fretting-wear damage is reviewed in this paper. Some new practical examples and simple calculations are discussed.

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.

Finite Element Analyses of Residual Stresses in Typical Welded Joints Used in Nuclear Power Plants and Comparisons With Experiments

2010 ◽  
Author(s):  
Dean Deng ◽  
Kazuo Ogawa ◽  
Nobuyoshi Yanagida ◽  
Koichi Saito
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Residual Stresses ◽  
Welded Joints ◽  
Nuclear Power ◽  
Power Plants ◽  
Butt Joint ◽  
Welding Residual Stress ◽  
Dissimilar Metal ◽  
Water Reactors

Recent discoveries of stress corrosion cracking (SCC) at nickel-based metals in pressurized water reactors (PWRs) and boiling water reactors (BWRs) have raised concerns about safety and integrity of plant components. It has been recognized that welding residual stress is an important factor causing the issue of SCC in a weldment. In this study, both numerical simulation technology and experimental method were employed to investigate the characteristics of welding residual stress distribution in several typical welded joints, which are used in nuclear power plants. These joints include a thick plate butt-welded Alloy 600 joint, a dissimilar metal J-groove set-in joint and a dissimilar metal girth-butt joint. First of all, numerical simulation technology was used to predict welding residual stresses in these three joints, and the influence of heat source model on welding residual stress was examined. Meanwhile, the influence of other thermal processes such as cladding, buttering and heat treatment on the final residual stresses in the dissimilar metal girth-butt joint was also clarified. Secondly, we also measured the residual stresses in three corresponding mock-ups. Finally, the comparisons of the simulation results and the measured data have shed light on how to effectively simulate welding residual stress in these typical joints.

scholarly journals Tackling Complexity of the Just Transition in the EU: Evidence from Romania

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1509
Author(s):  
Roxana Voicu-Dorobanțu ◽  
Clara Volintiru ◽  
Maria-Floriana Popescu ◽  
Vlad Nerău ◽  
George Ștefan
Keyword(s):  
Environmental Sustainability ◽  
Power Plants ◽  
Point Of View ◽  
Major Power ◽  
Complex Issue ◽  
Energy Mix ◽  
Carbon Neutrality ◽  
Vulnerable Consumers ◽  
The Eu

The process of reaching carbon neutrality by 2050 and cutting CO2 emissions by 2030 by 55% compared to 1990 as per the EU Green Deal is highly complex. The energy mix must be changed to ensure long-term environmental sustainability, mainly by closing down coal sites, while preserving the energy-intensive short-term economic growth, ensuring social equity, and opening opportunities for regions diminishing in population and potential. Romania is currently in the position of deciding the optimal way forward in this challenging societal shift while morphing to evidence-based policy-making and anticipatory governance, mainly in its two coal-mining regions. This article provides possible future scenarios for tackling this complex issue in Romania through a three-pronged, staggered, methodology: (1) clustering Romania with other similar countries from the point of view of the Just Transition efforts (i.e., the energy mix and the socio-economic parameters), (2) analyzing Romania’s potential evolution of the energy mix from the point of the thermal efficiency of two major power plants (CEH and CEO) and the systemic energy losses, and (3) providing insights on the socio-economic context (economic development and labor market transformations, including the component on the effects on vulnerable consumers) of the central coal regions in Romania.

Assessment of Fretting‐Wear Damage in Nuclear and Process Equipment

2021 ◽  
pp. 373-395
Author(s):  
Michel J. Pettigrew ◽  
Metin Yetisir ◽  
Nigel J. Fisher ◽  
Bruce A. W. Smith ◽  
Victor P. Janzen
Keyword(s):  
Fretting Wear ◽  
Process Equipment ◽  
Wear Damage

scholarly journals Investigation of Corrosion Resistance of Alloys with Potential Application in Supercritical Water-cooled Nuclear Reactors

2019 ◽  
Vol 63 (2) ◽  
pp. 328-332 ◽  
Author(s):  
Ákos Horváth ◽  
Attila R. Imre ◽  
György Jákli
Keyword(s):  
Corrosion Resistance ◽  
Supercritical Water ◽  
Power Plants ◽  
Fuel Cladding ◽  
Pressurized Water ◽  
Water Reactors ◽  
Reactor Types ◽  
Materials Used ◽  
Supercritical Water Cooled Reactor ◽  
Nuclear Applications

The Supercritical Water Cooled Reactor (SCWR) is one of the Generation IV reactor types, which has improved safety and economics, compared to the present fleet of pressurized water reactors. For nuclear applications, most of the traditional materials used for power plants are not applicable, therefore new types of materials have to be developed. For this purpose corrosion tests were designed and performed in a supercritical pressure autoclave in order to get data for the design of an in-pile high temperature and high-pressure corrosion loop. Here, we are presenting some results, related to corrosion resistance of some potential structural and fuel cladding materials.

Sign in / Sign up

Export Citation Format

Share Document