AP1000中ADS-4液体夹带实验研究

以AP1000核电厂中自动泄压管线(ADS-4)与热管段形成的T型结构为研究对象,开展缩小比例的T型管夹带实验。实验结果表明:大尺寸支管的夹带与小尺寸支管的夹带有明显差别。分层流情况下的夹带研究中发现两种夹带机理;在较低气相Froude数及较低气腔高度时,容易产生间歇流夹带;在较高气相Froude数情况下,往往出现环状流夹带。此外,实验研究发现,大尺寸支管中回流现象显著。支管形状对起始夹带有重要影响,而液体横流似乎并不影响起始夹带。     

Numerical Analysis of Jet Breakup Behavior Using Particle Method

A continuous jet changes to droplets where jet breakup occurs. In this study, two-dimensional numerical analysis of jet breakup is performed using the MPS method (Moving Particle Semi-implicit Method) which is a particle method for incompressible flows. The continuous fluid surrounding the jet is neglected. Dependencies of the jet breakup length on the Weber number and the Froude number agree with the experiment. The size distribution of droplets is in agreement with the Nukiyama-Tanasawa distribution that has been widely used as an experimental correlation. Effects of the Weber number and the Froude number on the size distribution are also obtained.     

Gravity-driven injection experiments and direct-contact condensation regime map for passive high-pressure injection system

A gravity-driven injection experiment of a passive high-pressure injection system with a pressurizer pressure balance line (PRZ PBL) is conducted by using a small-scale test facility to identify the parameters affecting the gravity-driven injection and the major condensation regimes. It turns out that the larger the water subcooling is, the more the injection initiation is delayed. A sparger and natural circulation of the hot water from the steam generator accelerate the gravity-driven injection. The condensation regimes identified through the experiments are divided into three distinct ones: sonic jet, subsonic jet, and steam cavity. The steam cavity regime is a unique regime of downward injection with the present geometry not previously observed in other experiments. The condensation regime map is constructed using Froude number and Jacob number. It turns out that the buoyancy force has a larger influence on the regime map transition because the regime map using the Froude number better fits data with different geometries than other dimensionless parameters. Simple correlations for the regime boundaries are proposed using the Froude number and the Jacob number.     

Experimental study on scale effect on gas entrainment at free surface

It is necessary to understand effects of scale and fluid properties on gas entrainment phenomena for prediction of gas entrainment in a fast breeder reactor (FBR). In the present study, three models of different scales but of similar geometry were used for water tests to examine the effects of scale and viscosity. The results have shown that the critical Froude (Fr) number, above which gas entrainment appears, drastically decreases as the scale increases. A prediction method using the Fr-Re map is proposed in the present paper for the sodium flow in an FBR.     

A numerical simulation of water jet injection behavior in fuel–coolant interaction

Water injection mode of molten fuel and coolant interaction is a key issue during the steam generator tube rupture accident in liquid metal reactors. The focus of the present study is placed on the numerical simulation of the water jet behavior falling into a pool of a denser fluid in order to get qualitative and quantitative understanding of initial premixing phase of water injection mode. A multi-phase code with the volume of fluid (VOF) method is developed. The simulation results are compared with experimental data to examine the capability of the current approach. Effects of density ratio and Froude number on cavity penetration velocity are quantitatively analyzed. The simulation results show surface waves and breakup behavior occur both at the top of the cavity during cavity collapse and at the cavity boundary. The simulation results are compared with the existing theories. At the top of the cavity, the water jet wavelength is close to the value estimated based on the Rayleigh–Taylor instability. At the cavity boundary, melt wave length is close to the value estimated based on the Kelvin–Helmholtz instability.     

ADS-4空气-硼酸夹带试验研究

为研究真实工况下的ADS-4夹带现象,以CAP1400为原型按1∶1的比例设计搭建了FATE试验台架。硼酸溶液用来模拟反应堆堆芯中真实工况的流体。利用数据采集系统和高速摄像仪记录夹带过程,将所得的试验数据与纯水工况和已有的模型进行比较。结果表明：对于夹带起始和稳态夹带率,硼酸工况和纯水工况的试验结果与之前的模型均不同。硼酸工况和纯水工况的现象基本相似,弗劳德数随夹带起始液位的增加而减小。两者的夹带起始均有回滞效应,且自上而下的夹带起始更易发生。硼酸工况和纯水工况之间也存在着差异,这主要是由于两者的物理特性参数不同而造成的,尤其是密度和黏度的影响。     

大型先进压水堆ADS-4夹带试验研究

针对大型先进压水堆的ADS-4夹带现象,按照实际比例1∶1搭建了全尺寸ADS-4试验台架(FATE),在不同工况下进行了多组夹带试验。将试验数据与不同模型的结果进行对比,并将试验数据进行拟合,得到夹带起始的模型关系式。试验结果显示：拟真实工况与纯水工况的现象较相似,支管弗劳德数随夹带起始气腔高度的增加而增加;在不同工况的组合中均出现了回滞现象;由于黏性和表面张力的作用,拟真实工况的夹带起始相比纯水工况更难发生。无论是纯水工况、硼酸工况还是杂质工况,除少部分试验数据外,大部分稳态夹带率的试验数据与Welter模型存在较大差异,相对误差均大于20%。     

蒸汽夹带作用下高温颗粒表面拖曳力模型研究

高温熔融物在冷却剂中的沉降过程关系到蒸汽爆炸的触发及后续过程的发展,影响严重事故缓解措施的设计与实施。基于高温颗粒表面蒸汽膜的夹带作用,通过理论建模与实验拟合的方法,构建了预测粗混合阶段颗粒在冷却剂中沉降过程的拖曳力系数的半经验关系式,表示为颗粒弗洛德数（Fr_p）与夹带雷诺数（Re_α）的函数。通过与高温钢球下落冷液中沸腾运动过程实验结果的比较,验证了粗混合初期蒸汽的夹带作用是颗粒沉降的主导因素。另外,沉降速度的变化受高温颗粒的直径影响。颗粒的直径越小,其沉降特征越接近于“冷颗粒”,这主要与蒸汽夹带作用的降低有关。      

Hydrodynamic characteristics of a gas blowdown into a two-dimensional liquid pool

Hydrodynamic experiments were performed on transient gas jet discharge into liquid pool. Liquid entrainment, jet development, and the possibility of liquid vaporization by a noncondensible gas were investigated.Liquid entrainment during jet expansion in the plenum was seen to increase with increasing pressure. However, the fraction of the expansion volume which is liquid was not affected by gas pressure. Higher initial entrainment was seen for a more dense fluid. A Taylor instability mechanism for entrainment seems to fairly predict the rate of entrainment. Another entrainment mechanism besides that of Taylor instabilities may exist at higher pressures.     

Entrainment of soluble and non soluble tracers from a boiling water surface

The entrainment of droplets containing solid or soluble fission product simulants from the surface of a boiling water pool into a gas atmosphere was investigated at conditions, which are relevant to a severe core melt scenario. Different air–steam ratios and at pressures (2–6 bar) were considered in the model containment. Measurements carried out far above the air-liquid interface are compared with the predictions of existing correlations. Favorable agreement is obtained with the correlation of Kataoka and Ishii [Int. J. Heat Mass Transf. 27 (1984)] for the entrainment of soluble fission products into an air–steam atmosphere. Results from integral measurements however suggest that improved correlations should be based on the Froude, Weber and Rayleigh numbers, and separate between entrainment and sedimentation.     

Gas entrainment inception at the border of a flow-swollen liquid surface

A rapid liquid flow into a tank may impinge on the free surface, making it swell partially. The returning flow branches off from the free surface and re-submerges at the border of the swollen surface. If the flow velocity along the swollen surface is high enough, gas bubbles are formed at the border and entrained by the liquid flow. The conditions necessary for gas entrainment in a simple system are examined experimentally, using water and air as working fluids. The effect of surface tension is examined by adding a surface active agent to the water. The results show that gas entrainment inception is determined by the flow pattern in the system and the product of the Froude and Weber numbers based on the local velocity at the bubble formation point.     

Large eddy simulation of rough and smooth liquid plunging jet processes

Large eddy simulation based on the Smagorinsky dynamic sub-grid scale model in combination with the multiphase volume of fluid (VOF) model, was used to simulate the flow of two turbulent plunging water jets. The jets were intended to simulate a weakly disturbed jet with low turbulence content and a highly disturbed jet with a profile almost fully-developed at the exit Reynolds number of 9000. The simulation captured successfully the previous experimentally-observed topological phenomena taking place during the transient impact and continuous-entrainment regime. It showed that surface instabilities in the free jet, due to its turbulence content have remarkable effect on submerged interfacial area, air volume, and air-entrainment rate. The simulation predicted an air entrainment rate within the range of semi-empirical correlations. The calculated mean velocity field exhibited almost identical trends for both. The combination of the LES-VOF models achieved a reasonably good level of agreement with experimental and empirical results.     

Experimental and computational study on jet final depth under coolant jet-melt interaction

Pouring coolant into molten material provides an efficient method for cooling molten core debris in light water reactor. This coolant jet-melt interaction mode needs to be studied for proposed application and safety concern. The jet breakup pattern and its final depth are crucial factors for efficient cooling. In the present study, the hydraulic penetration behavior of coolant jet is investigated using experimental and numerical approaches. A series of visual experiments are conducted using low-density gasoline as coolant jet and high-density water as molten fuel. The images of jet behaviors and the data of gasoline jet penetration depth are obtained and analyzed. Based on FLUENT15.0 a 3D axisymmetric model is built and Volume of Fluid (VOF) method is used. The hydraulic penetration behaviors of jet and final penetration depth are correctly simulated and analyzed. The fluctuating phenomenon of penetration depth and the effects of various parameters are discussed. Jet velocity and density ratio are key factors to final penetration depth. The conclusions are helpful to understand the parameter influence and the fluctuation mechanism of final penetration depth and substantiate the understanding of the coolant jet hydraulic penetration behavior during coolant jet-melt interaction.     

Flow transport and mixing induced by horizontal jets impinging on a vertical wall of the multi-compartment PANDA facility

In the frame of the OECD/NEA SETH project an experimental campaign has been carried out in the PANDA facility to investigate gas transport and mixing induced by a plume or a jet in the large-scale multi-compartment PANDA facility. The paper summarizes the results of the horizontal jet test series consisting of eight tests. Horizontal jets impinging on a vertical wall of one of the cylindrical PANDA containment vessels have been generated by changing various parameters, such as: type of injected fluid (steam or a mixture of steam and helium), fluid injection velocity, elevation (with respect to the containment vessel) of the injection exit, initial fluid composition in the vessels, and location of the vent line. The initial jet Froude number has been varied between 17 and 36 and in one of the test condensation occurred. The paper shows the effect of these parameters variation on the test evolution with respect to jet impingement location in the vertical curved wall and variation of impingement location as a function of buoyancy variation. Fluid mixing and stratification, characteristics of gas transport between the compartment and the effect of condensation on the overall phenomena evolution are analyzed in the paper.     

Correlations for the penetration of ECC water in a model of a PWR downcomer annulus

The application of dimensional analysis to the partial penetration data on the Battelle models (1/15 and 2/15 scales) results in a better fit of the penetration data than previous correlations. This analysis predicts the fractional penetration of ECC water into the lower plenum from the water flow rate, liquid subcooling and system pressure, in terms of Froude numbers based on superficial velocities of steam and water.     

Liquid entrainment and off-take through the break at the top of a vessel

In order to determine the bleed capacity of the safety depressurization system (SDS) of Advanced Power Reactor 1400 (APR1400) in the case of total loss of feed water (TLOFW), we performed an experimental study of liquid entrainment and liquid off-take from the swelled two-phase mixture surface in a vessel. A total of 220 experimental data on the entrainment and off-take are obtained using a test vessel with a height of 2.0 m and an inner diameter of 0.3 m and a top break with a diameter of 0.05 m. Two-phase mixture levels are measured by an ultrasonic sensor within ±1.77% with respect to the visual level data. Droplet entrainment data are obtained with and without the top break and are compared with the existing pool entrainment data. The present droplet entrainment data have higher values than the existing pool entrainment data due to (a) the pulling toward the break of the liquid deentrained on the top wall of the vessel and (b) gas acceleration in the vicinity of the break. In the present experiment, droplet entrainment, E_fg, strongly depends upon and is proportional to the seventh power of in the same way as the off-take data. The empirical correlation for the onset of off-take is developed in terms of the Froude number (Fr_g) at the break and the non-dimensional inception height (h_b/d). This correlation shows agreement with the present experimental data within ±15%. The present off-take quality data show agreement with Schrock's off-take quality correlation with the rms error of 15.8%.     

Modeling of bubble shape in horizontal and inclined tubes

An experimental and theoretical study on the bubble shape of intermittent flow in the horizontal and inclined pipes has been carried out. The experiment results show that the bubble shape depends on the Froude number, bubble length and pipe inclination. The bubble with staircase pattern tail is observed at low Froude numbers, which is corresponding to plug flow. A model for the prediction of the bubble shape in horizontal and inclined pipes is proposed. The model is able to predict the bubble shape, flow pattern transition between plug and slug flow regimes as well as nose-tail inversion phenomenon observed in the downwardly inclined pipe. Validation shows the model can well predict the bubble shapes in horizontal and inclined pipes. The model discloses that the transition between plug and slug flow regimes occurs within a region. The Froude number range for plug flow regime in the downwardly inclined pipe is much wider than that in the horizontal or upwardly inclined pipe. The assumption of fully developed liquid film under the long bubbles tends to under-estimate the liquid fraction in this part of the slug structure, especially, for the intermittent flow in the upwardly inclined pipe with high Froude numbers.     

Influences of the inner diameter of the solid shielding tube on the characteristics of the radio-frequency cold atmospheric plasma jet

Active control of the local environment of the cold atmospheric plasma (CAP) jet is of great importance in actual applications since the CAP operates in an open atmosphere with the inevitable entrainment of the surrounding cold air. In this paper, the solid shielding effects of the cylindrical quartz tubes with different inner diameters on the characteristics of the CAP jets driven by a radio-frequency (RF) power supply are studied experimentally. The experimental results show that the total length of the shielded plasma jet can be increased significantly by an appropriate combination of the quartz tube inner diameter and that of the plasma generator nozzle exit with other parameters being unchanged. This phenomenon may be qualitatively attributed to the loss of diffusion of the charged particles in the radial direction under different inner diameters of the quartz tubes. Compared with the plasma free jet, the plasma shielding jet is produced with optimized parameters including longer plasma jet length, higher concentrations of chemically reactive species, higher rotational, vibrational, and electron excitation temperatures when the inner diameters of the solid shielding tube and the generator nozzle exit are the same. A maximum plasma jet length of 52.0 cm is obtained in contrast to that of 5.0 cm of the plasma free jet in this study. The experimental results indicate that the solid shielding effect provides a new method for the active control of the local environment of the RF-CAP jet operating in an open atmosphere.     

Analytical study of coupled neutronic and thermodynamic instabilities in a boiling channel

Linear stability analysis in the frequency domain is performed to reveal the basic mechanism of coupled nuclear-thermal instabilities in a boiling channel. It is found that the Ledinegg instability will not occur due to the coupling of the void-reactivity feedback and the hydrodynamic feedback. Besides the phase-change number N_p and Jacob number Ja, the Froude number Fr and the fuel-time-constant τ_M are found to be the parameters determining the density-wave instability. It is also found that the Froude number effect on the density-wave stability becomes stronger when the void-reactivity feedback is involved, and that the lower the Fr number the less stable the system. The result reveals that there exists a region in which the void-reactivity feedback loop is unstable, and this has a strong effect on the stability of the system. A non-dimensional fuel-time-constant number is proposed, with which the stability boundary is better presented in the range of Froude numbers of interest.     

Experimental simulation of corium dispersion phenomena in direct containment heating

In a direct containment heating (DCH) accident scenario, the degree of corium dispersion is one of the most significant factors responsible for the reactor containment heating and pressurization. To study the mechanisms of the corium dispersion phenomenon, a DCH separate effect test facility of 1:10 linear scale for Zion PWR geometry is constructed. Experiments are carried out with air-water and air-woods metal simulating steam and molten core materials. The physical process of corium dispersion is studied in detail through various instruments, as well as with flow visualization at several locations. The accident transient begins with the liquid jet discharge at the bottom of the reactor pressure vessel. Once the jet impinges on the cavity bottom floor, it immediately spreads out and moves rapidly to the cavity exit as a film flow. Part of the discharged liquid flows out of the cavity before gas blowdown, and the rest is subjected to the entrainment process due to the high speed gas stream. The liquid film and droplet flows from the reactor cavity will then experience subcompartment trapping and re-entrainment. Consequently, the dispersed liquid droplets that follow the gas stream are transported into the containment atmosphere, resulting in containment heating and pressurization in the prototypic condition. Comprehensive measurements are obtained in this study, including the liquid jet velocity, liquid film thickness and velocity transients in the test cavity, gas velocity and velocity profile in the cavity, droplet size distribution and entrainment rate, and the fraction of dispersed liquid in the containment building. These data are of great importance for better understanding of the corium dispersion mechanisms.