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For seismic safety evaluation of piping system with local thinning surface by liquid droplet impingement erosion (LDI), hybrid seismic tests were conducted to the piping with a locally-thinned elbow. In this paper, a method for predicting the thinning shape by LDI on the elbow is developed. To determine the thinning shape by LDI, droplet behavior at the elbow is calculated for various flow conditions and geometries. With the calculation of the collision point and velocity for each droplet, collision frequency and average collision velocity on the elbow are estimated. Then, the thinning shape on the elbow is determined with the relationship between the flow conditions and thinning rate. Finally, the evaluated thinning shape is compared with an actual LDI case for the validation of the method.Copyright © 2011 by ASME

It is well known that the wetness of steam flow sometimes causes measurement errors of the steam flow meter. However, it is difficult to clarify a particular error quantitatively in actual plants and factories, and thus far, there has been no established method for estimating the error caused by the wetness of steam flow. Therefore, wet steam flow rate measurement experiments were conducted to clarify the measurement error caused by the wetness of steam flow in a plant and a factory. In this study, as the first step, the orifice flow meter was applied because it is the main flow meter in actual plants. Experiments were conducted with the steam flow apparatus by changing the flow rate, pressure and wetness. As a result, the correlation between the measurement error and the flow condition was clarified. Moreover, for the correction of the error, a new correction method was applied and was confirmed to be better than existing methods now being used.Copyright © 2011 by ASME

Newly developed wet steam flowrate calibration facility is introduced. It has a closed loop in which boilers generate a steam flow up to 800 kg/h. Steam flow of known wetness up to 12% is generated by cooling down a dry steam flow by a heat exchanger. The wetness is calculated from the enthalpy the heat exchanger draws from the dry steam flow. Analysis of the facility performance, calibration results of an orifice flowmeter calibration, and uncertainty analysis are described.Copyright © 2011 by ASME

The power uprating of the nuclear power plant is conducted in United States, EU countries and so on, and also is planned in Japan. However, the degradation phenomena such as flow-induced vibration and wall thinning may increase or expose in the power uprate condition. In U.S. NPP, the dryer had been damaged by high cycle fatigue due to acoustic-induced vibration. This is caused by acoustic resonance at the stub pipes of safety relief valves (SRVs) in the main steam lines (MSL). Increased velocity by uprating excites the pressure fluctuations and makes large amplitude resonance. We have started to develop the evaluation methods of pressure fluctuations at the dryer in BWR-5, which are the main type of BWR in Japan. In this study, to investigate the fluctuating pressure at rated power condition, we conducted steam flow simulations in actual main steam piping geometry and conditions. As a result, small amplitude resonance was observed in rated power condition.Copyright © 2010 by ASME

During operation, the BWR-3 steam dryer in the Quad Cities Unit 2 Nuclear Power Plant was damaged by high cycle fatigue. The dryer failure was attributed to flow-induced acoustic resonance at the stub pipes of safety relief valves (SRVs) in the main steam lines (MSLs). The acoustic resonance was considered to be generated by interaction between the sound field and an unstable shear layer across the closed side branches with SRV stub pipes. We HITACHI and CRIEPI have started a research program on BWR dryers to develop their loading evaluation methods. Moreover, it has become necessary to evaluate the dryer integrity of BWR-5 plants in particular which are the main type of BWR in Japan. In the present study, we used 1/10-scale BWR tests and analyses to investigate the flow-induced acoustic resonance and characteristics of fluctuating pressure in MSLs. The test apparatus consisted of a steam dryer, a steam dome and 4 MSLs with 20 SRV stub pipes. A finite element method (FEM) was applied for the calculation of three-dimensional wave equations in acoustic analysis. We demonstrated that remarkable fluctuating pressures occurred in high and low frequency regions. Intensity of three peaks observed in the spectrum of fluctuating pressure in MSLs was increased with St. High frequency fluctuating pressures were generated by the flow-induced acoustic resonance in the SRV stub pipes. Low frequency fluctuating pressures were excited by the acoustic resonance in the dead leg. Frequency of fluctuating pressure generating in the SRV stub pipe was changed with St. On the other hand, frequency of fluctuating pressure excited by dead leg was almost constant. Fluctuating pressure in low frequency range increased gradually with flow velocity and its intensity was roughly proportional to the square of flow velocity. The flow-induced acoustic resonance did not occur for St larger than 0.6 in the BWR MSLs for both low and high frequency ranges. Operating conditions of the BWR-5 from 100 to 115% were in the range of St larger than 0.6, so intense acoustic resonance would not occur in the BWR MSLs.Copyright © 2010 by ASME

Control valves of the main steam flow for power plants are operated under wide range of valve openings and pressure ratios. In the present paper, experimental and numerical investigations are described in order to clarify mechanisms of the valve head vibration. Experiments are conducted with two types of the valve head support. One is a flexible support and the other one is with an exciter. Results show that valve head vibrations with large amplitude appear with the flexibly supported valve head under certain range of valve openings and the pressure ratio. With the valve head exciter, dynamic fluid forces are measured. Results show that the added damping force becomes negative around the condition where the valve head oscillation is observed with flexible support. Numerical analyses are carried out in order to observe the flow field. In the simulations, forced vibrations of valve head are assumed. Results show that the pressure distribution on the valve head surface changes depending on the excitation frequencies, and as a result, the negative damping force occurs.Copyright © 2010 by ASME

A pressure fluctuations at a blanch pipe are investigated for an evaluation of pressure fluctuations at a steam dryer, where had been damaged by high cycle fatigue due to acoustic-induced vibration in uprated condition at U.S. NPP. In this study, numerical simulations of the airflow around the branch pipe are conducted to clarify the basic characteristics of the resonance. The excitation of the pressure fluctuations at the branch is observed under various inlet velocity conditions. These fluctuations and inlet conditions are normalized, and the results show that the range and the peak of the amplitude are almost the same as those obtained in experiments.Copyright © 2009 by ASME

Flow Accelerated Corrosion (FAC) is well known as a complex phenomana of hyraulics and electro-chemicals. Among the two, this study focused on the hydraulic factors affecting FAC. FAC experiments with small rectangular flow duct were conducted in PWR condensate condition. Flow field for the experiment was calculated with numerical simulation using LES (Large Eddy Simulation) turbulence model. From both experimental and numerical results, new model of mass transfer coefficient, as the essential parameters of hydraulics, was proposed considering local turbulent velocity, so as to evaluate the effect of eccentric flow on FAC. To verify the applicability of the model, FAC plant data of actual PWR (Pressurized Water Reactor) condensate line (146 degC) and BWR (Boiling Water Reactor) condensate line (35 degC) were referred. Mass transfer coefficients for each pipe lines were calculated from flow numerical analysis. The new proposed model showed good correlation with the data of FAC thinnng rate, and its applicability was confirmed. In addtion, comparing the two plant cases, electro-chemical effect could be estimated as a similar level, which suggests the possibility of low-temperature FAC in BWR condensate lines.Copyright © 2009 by ASME

Liquid droplet impediment erosion (LDI) is a pipe wall thinning phenomena that a droplet accelerated by steam flow attacks pipe surface. It is difficult to evaluate LDI behavior in the system of NPP. Therefore, in current pipe wall thinning management, the pipe element is replaced conservatively when it is recognized to become thinner by pipe wall thinning measurement result. If LDI behavior at each point of the system can be estimated, it is possible to measure the pipe wall thickness and replace the pipe element at an appropriate time, in accordance with reasonable pipe wall measurement schedule. CRIEPI has constructed the evaluation system for LDI by using flow dynamics. This paper is concerned with the following items: • the applicability of the LDI evaluation system by a comparative verification between pipe wall thinning rate calculated by LDI system and that by actual measurement result; • establishment of remaining life assessment method of pipe in LDI environment by using LDI model.Copyright © 2009 by ASME

In measurement of an ultrasonic flowmeter, the flow rate in piping is obtained using some measurement signals along the “chord” of the circular cross section of the piping. As for the “Chordal type ultrasonic flowmeter”, the flow rate is obtained by four (or eight) “chords”. The wall roughness influences the velocity profile. To evaluate the influences of roughness change on the measurement using four velocity points, a water test was performed. The Reynolds (Re) number of the test ranges from 4×105 to 3×106 . It was suggested that high precision measurement in the range of high Re number can be expected in the smooth pipe. In the wall where sand of 0.1mm diameter was pasted, no difference in the velocity profile with the smooth wall was observed. A change in the velocity profiles appeared in the rough surface pipe where sands of 0.6mm and 0.2mm diameter has been pasted. Bias error (ESL ) was used to estimate the uncertainty of the flow rate measurements using four velocity points. The difference of each ESL value based on the influence of roughness tended to diminish as the Re number increased. And the Re number dependency of ESL is small, especially in the high Re number side. It suggests that an actual flow rate test for the high Re number to confirm the influence of roughness would not be necessary.Copyright © 2009 by ASME

The stability of thin plate able to execute translational or rotational vibration in a one dimensional narrow passage is studied, and critical flow rates are obtained theoretically. The effect of pivot point of rotational system is considered. In the case of single-degree-of-freedom rotational system, the pivot position greatly influences stability. Instability can occur when the passage is divergent in the case of translational vibration. When the pivot of rotational vibration is at the entrance of the passage, the region of negative fluid-dynamic damping can become very small, and flutter can hardly occur. When the pivot is at the slightly behind the center of the passage, the instability region can become large, and even if the passage shape is convergent, instability can occur.Copyright © 2009 by ASME

An evaluation system for liquid droplet impingement erosion (LDI) has been developed to predict the LDI location and the wall thinning rate. The results from previous studies and knowledge are organized and the LDI evaluation system that involves the “1. Flow Evaluation Step” and “2. LDI Evaluation Step” is suggested. The flow evaluation step includes the mass flow rate evaluation, flow distribution evaluation and droplet behavior evaluation. The LDI evaluation is conducted with LDI sensitivity function. The LDI sensitivity was test-evaluated in the steam piping model. The results show that the 1st and last elbows have higher LDI sensitivity because of the velocity condition. We also found that the droplet collision frequency is important when evaluating the LDI sensitivity.Copyright © 2009 by ASME

In some cases, a steam control valve (figure 1) in a power plant causes large vibrations in piping systems that can be attributed to pressure fluctuations generated in the valve under the partial-valve-opening (middle-opening) condition. For the maintenance and the management of the plant, the valve system needs to be improved to prevent the onset of hydrodynamic instabilities. However, in the case of the steam control valve, it is difficult to understand the flow characteristics in detail experimentally because the flow around the valve has a complex 3D structure and becomes supersonic (M>1). For these reasons, the details of the flow around the valve are not fully understood before, and CFD simulations are required to understand the underlying complex flow structure associated with the valve. In our previous researches, a mechanism of the pressure fluctuations in the middle opening condition, named “rotating pressure fluctuations”, were clarified and a suppression shape were developed by experiments and CFD calculations. However, as we used air as a working fluid in our previous researches instead of steam that is used in the power plant, we couldn’t consider effects of condensation and difference of change of the state quantities between air and steam. In this report, we have conducted steam experiments and CFD calculations by original code to clarify the effects of the difference of the fluids. As a result, in the middle opening condition, we have observed spike-type pressure fluctuations and their rotation in the experiment, and valve-attached flow and local high-pressure region in the CFD result. These results indicate the pressure fluctuations observed in steam experiments and CFDs are the same as rotating pressure fluctuations observced in air researches.

A cross-shaped control rod guide tube bundle is proposed for the lower plenum structure in the next-generation LWR, ABWR-II. In our previous studies, we measured the local fluid excitation forces acting on a cross-shaped tube bundle as well as the self-excited vibration characteristics in pure cross flow in water tunnel tests. In the reactor conditions, the flow field around the tube bundles contains mixed cross and parallel flow components. In this study, water tunnel tests under mixed cross and parallel flow conditions were preformed to understand the influence of the balance of parallel and cross flow components on vibration response. The distributions of the flow direction and flow velocity in the gap between the adjacent tubes were measured with circular Pilot tubes in detail. It was found that the critical flow velocity of self-excited vibration was not influenced by the parallel flow component, but depended only on the cross flow component.Copyright © 2006 by ASME

In some cases, a steam control valve in a power plant causes a large vibration of the piping system under partial valve opening. For rationalization of maintenance and management of a plant, it is favorable to optimize the valve geometry to prevent such vibration. However, it is difficult to understand the flow characteristics in detail only from experiments because the flow around a valve has a complex 3D structure and becomes supersonic (M>1). Therefore, it is useful to combine experiments and CFD (Computational Fluid Dynamics) for the clarification of the cause of vibration and optimization of valve geometry. In previous researches involving experiment and CFD calculation using “MATIS” code, we found that an asymmetric flow attached to the valve body (named “valve-attached flow”) occurs and pressure increases where the valve-attached flow collides with the flow from the opposite side under the middle opening condition. This high-pressure region rotates circumferentially (named “rotating pressure fluctuation”) and causes cyclic side load on the valve body. However, because we assumed the valve support is rigid, we cannot clarify the interaction between the rotating pressure fluctuation and the valve vibration when the valve stiffness is small. Thus, in this paper, we conducted flow-induced vibration experiments on a valve with a very weak support and investigated the characteristics of the vibration mode under the middle-opening condition. As a result, under the specific lift condition of the region where rotating pressure fluctuation occurs, lock-in phenomena between the rotating pressure fluctuation and the valve vibration occur and large-amplitude vibration can be seen.Copyright © 2005 by ASME

A steam control valve causes vibrations of piping when the opening is in the middle condition. For the rationalization of maintenance and management in a plant, valves should be improved, but it is difficult to understand the flow characteristics in detail experimentally because the flow around the valve has a complex 3D structure and becomes supersonic (M>1). Therefore, it is necessary to clarify the cause of vibration and to develop improvements both experimentally and through CFD (Computational Fluid Dynamics) calculation. First, small-scale air experiments are performed. In this experiment, a spike-type pressure fluctuation that rotates circumferentially is observed in a middle valve opening. This fluctuation sometimes changes its rotation direction suddenly, or sometimes stays at the same position. Because of this randomness, FFT analysis cannot reproduce this peak frequency. However, another peak caused by the 1st-mode resonance in the pipe-diameter direction can be seen. After some experiments, a high-precision 3D CFD code for compressible flow, “MATIS”, was developed. This code can calculate an unsteady 3D compressible flow steadily and accurately, with TVD scheme, LU-SGS implicit scheme and inner iterative calculation. This code also includes LES turbulence model for compressible fluid in order to reproduce turbulence flow accurately. To validate this code, first, some benchmark tests such as karman vortex calculation and the calculation of a detached shock position on a sphere are performed. After benchmark tests, CFD calculation of the valve is performed under several valve opening conditions. The mesh number is about 600 thousand and y+ is about 3. CFD results agree well with those of the experiment qualitatively and quantitatively. Therefore, the validation of MATIS is confirmed. Detailed flow characteristics around the valve in a middle valve opening are investigated. Under this condition, the jet after the throat travels the valve (named “attached flow”) and strikes the jet coming from the opposite side. This phenomenon generates a high-pressure region and a pair of vortices; this region rotates circumferentially and causes cyclic side load on the valve body. CFD calculation clarifies that a circumferentially propagating spike-type pressure fluctuation is caused by attached flow along the valve, and this is though to be the cause of vibration.

A cross-shaped tube bundle is proposed for the lower plenum structure in the next-generation LWR. The effect of tube bundle arrangement on the flow-induced vibration characteristics of the cross-shaped tube bundle in cross flow was considered experimentally. Regarding random vibration, the power spectral density of the fluid force of the staggered arrangement as well as the correlation length was measured and those of the normal arrangement were compared with those of the staggered arrangement. Regarding self-excited vibration, vibration response was compared. The trend of the power spectral densities, correlation length, and the critical velocity of the normal arrangement were similar to those of the staggered arrangement.Copyright © 2003 by ASME

A cross-shaped tube bundle with dense arrangement may be designed for a lower plenum structure in a next generation LWR, though the characteristics of flow-induced vibration of this type of tube bundle remain virtually unknown. In this study, turbulence-induced fluid dynamic forces acting on a cross-shaped tube bundle with a dense arrangement subject to cross flow were measured by water tunnel tests with two types of scale models. One is a small-scale model to measure local fluid dynamic forces and their correlation length in the lift and drag direction. The other is a large-scale model to investigate the effect of the Reynolds number on fluid dynamic forces in the lift, drag and torsional directions. Free oscillation tests with another small-scale model were also conducted to measure vibration amplitude by random excitation force. In conclusion, the following results were obtained. Vortex-induced vibration cannot arise in the cross-shaped tube bundle, since a typical peak corresponding to periodic vortex shedding was not observed in power spectral density for fluid excitation force. Power spectral densities of fluid dynamic forces in the drag, lift and torsional directions have mutually similar properties and they are hardly dependent on the Reynolds number. The experimental results were compiled into dimensionless correlation equations composed of the power spectral density for the local fluid excitation force and its correlation length. They are useful for evaluating the random vibration amplitude. The estimated amplitudes of turbulence-induced vibration by the correlation equation coincide with those of the experimental results obtained by the free-oscillation tests.Copyright © 2002 by ASME

Cross-shaped tube bundle is proposed for a lower plenum structure in a next generation LWR. Vibration response of cross-shaped tube bundle in cross flow has been measured in water tunnel tests. First, small-scale test was conducted. Tests were conducted with 3×3 flexible tubes as well as single flexible tube in rigid tube bundle. The flexible tubes could vibrate in lift, drag, and torsional direction. The effect of arrangements of tube bundle and the natural frequency ratio of bending and torsional vibrations were considered. Second, a large-scale test was conducted for only one case to check the effect of Reynolds number, in which Reynolds number was 10 times larger than that of small-scale test. In all the cases, large amplitude vibration could appear when the flow velocity became larger than a critical value, and a self-excited vibration was found to occur. The nondimensional critical gap velocity of the large-scale test agreed well with that of the small-scale test, which suggested that the effect of Reynolds number was not so large. A design guideline to prevent self-excited vibration was proposed for cross-shaped tube bundle.Copyright © 2002 by ASME