Use of Neural Network for the Simulation of a Gas Centrifuge

The prediction by a mathematical model of the separation of uranium isotopes using a gas centrifuge process is a hard task. The gas motion can be described by analytical or numerical solutions of the system of equations defined by the equation of continuity, the Navier-Stokes equation and the equation of energy. However, these calculations cannot be performed for actual centrifuges.

Neural networks are an alternative for modelling complex problems that show too many difficulties to be solved by phenomenological models.

The authors propose the use of neural networks for the simulation and prevision of the separative and operational parameters of a gas centrifuge separating uranium isotopes. The results from the uranium separation experiments (Zippe data) are compiled and presented to the neural network in the learning and testing processes. The prediction using the neural network model shows good agreement with the experimental data.     

Flow in Rotating Cylinder of a Gas Centrifuge

Thermal convection and weak forced flows in a rotating cylinder were studied theoretically to find the mass velocity distributions in a gas centrifuge. Compressibility of the gas is taken into account in the form of a density stratification in the radial direction. First of all, a scaling analysis was made to verify the dominance of Coriolis force in the field of flow. The result of this analysis indicated that the body of the fluid in the centrifuge is composed of inviscid cores separated by a viscous layer concentric to the axis of rotation, and enveloped by other viscous layers lining the side and end faces of the cylinder. The transport of the gas from the feed ports to the discharge ports is made through these viscous layers.

The thermal convection has its largest component near the side wall in the form of a recirculating flow, and its pattern is controlled by the temperature distribution of the wall. These theoretical results were verified in part by an experiment devised to permit visual observation of the air flow in a rotating cylinder.     

Thermally Induced Flow in Gas Centrifuge, (I)

Centrifugally driven thermal convection near the cooled rotor conver of a centrifuge is treated.

Boundary layer equations are reduced to ordinary differential equations by the Lees-Levy transformation, and solved numerically by applying the quasilinearization method.

Sample solutions for radial and azimuthal velocity profiles are presented. The values of the axial velocity at the rotor center are calculated as a function of the temperature difference between the rotor cover and the contained gas.     

Numerical Investigation of Gas Flow Distribution and Thermal Mixing in Helically Coiled Tube Bundle

In this study, we carried out the numerical simulation of gas flow across a helically coiled tube bundle, which is fitted in the annular space between a central spine and an outer casing. We focused on the effect of clearances at the inner and outer radial boundaries on the gas flow distribution and thermal mixing in the tube bundle. The conservation equations of mass, momentum and energy were numerically solved by computational fluid dynamics. It was demonstrated from the numerical simulation results that (i) the gas flow distribution in the tube bundle is very sensitive to clearances at the inner and outer radial boundaries, and even a very small variation of clearances would lead to a considerable change in the average velocity profile, which correspondingly leads to a great deviation of the gas flow distribution away from the original one; (ii) the clearance effect on thermal mixing is not as strong as that on gas flow distribution;(iii) the Reynolds number has little effect on the gas flow distribution and thermal mixing, the latter of which is in agreement with the results of Achenbach experiments.     

高温气冷堆热气导管的结构稳定性分析

热气导管是高温气冷堆中氦气循环的重要流道,其在各工况下的结构完整性与稳定性关系到反应堆是否能运行安全。本文详细分析了热气导管在事故工况下所承受的压力载荷,包括绝热纤维对管壁的压力以及一回路失压事故时发生氦气泄漏产生压力;并根据得到的压力载荷计算了热气导管承受外压时的结构稳定性。计算结果表明热气导管在事故工况的压力载荷作用下能够保持结构的完整性并且不会发生失稳。     

螺旋式传热管束流致振动试验研究

对某溶液堆堆芯内呈纵向螺旋状盘绕的传热管束进行了流致振动试验研究,包括结构在空气中和静水中振动特性的计算和试验以及稳态和瞬态运行工况下的流致振动试验.试验结果表明,传热管束入、出口之间的压力差随流速的增加而增加,且上部固定连接端是相对薄弱的部位.在稳态运行时不会发生动力失稳,振动位移不会造成管束各管段之间发生接触碰撞,疲劳分析表明满足规范要求.瞬态响应最大振动位移和应变均比稳态运行时高两个数量级以上.     

Effect of Gas Introduction on Temperature Distribution for Tube Flow with Internal Heat Sources

An experimental study has been conducted to investigate the effect of gas introduction on the heat transfer characteristics for turbulent flow of a heat generating liquid in an adiabatic tube 20 mm in inside diameter. Heat generation within the fluid was brought about by passing an alternating current through the working fluid, which was an aqueous solution of sodium chloride mixed with air bubbles. The superficial liquid Reynolds number ranged 3,700–11,000. The quality was varied from 2.6×10^?5 to 3.3×l0^?3. Measurements were made of the temperature distributions in the fluid as well as on the tube wall. The experimental results were compared with theoretical analyses.

In bubbly flow; the introduction of air into liquid brought forth a flat temperature distribution due to a considerable increase of turbulence and a saddle-shaped void distribution, which had a maximum near the tube wall. In slug flow, however, the void distribution changed to a dome-shaped profile with a maximum at the tube center and the rate of heat generation was higher near the wall than in the center region, resulting in a steep temperature distribution.     

流量波动条件下圆管内流动换热特性数值研究

对流量波动条件下核动力装置系统圆管内流体的流动换热特性进行了数值研究,重点研究了波动周期、波动振幅两个因素对流动换热特性的影响。结果表明:流量波动时,通道内的摩阻系数和壁面换热系数均随时间周期性波动,且波动周期与流量波动周期相同;波动周期增加,摩阻系数波动幅值减小,壁面换热系数波动振幅变化不明显;相对振幅增加,摩阻系数波动幅值增大,壁面换热系数波动振幅增大。     

Flow Profile Measurements of Gas in a Rotating Cylinder

An azimuthal flow of the gas motion in a rotating cylinder induced by the forced source-sink flow was measured using the laser Doppler anemometer in connection with the development of a gas centrifuge for ²³⁵U enrichment. The cylinder, held vertically, was driven in the air at an angular velocity of 10 π rad/sec. The air to which paraffin mist was added as the light scattering particles was fed into the cylinder through the inlet slit provided on the upper end plate at the relative radius of 0.43 and withdrawn through the outlet slit on the lower end plate at the relative radius of 1.0. The Ekman number E was approximately 5.6 × 10^?5 in this experiment. The Ekman layer on the upper end plate was so thin that it was not observed, and that on the lower end plate was not either. The Stewartson E ^1/4 layers on the side wall and at the feed radius were clearly observed and their profiles were quite similar to the result of the linear theory except the inviscid core region. The discrepancy in this region should be attributed to the fact that the Stewartson layers on the side wall and at the feed radius were thick enough to overlap each other.     

Drift-Flux Parameters for Upward Gas Flow in Stagnant Liquid

The drift-flux model is widely used for gas-liquid two phase flow analysis, because it is applicable to various flow patterns and a wide range of void fractions. The drift- flux parameters for upward gas flow in stagnant liquid, however, have not been well examined. In this study, the distribution parameter C_o and the drift velocity V_gj for stagnant liquid were derived from the void fraction correlation and boundary conditions of drift-flux parameters, and then compared with C_o and V_gj for high liquid velocities. Also using the two region model where a circular flow area was divided into an inner region of cocurrent up-flow and an outer annulus region of liquid down flow, C_o and V_gj for stagnant liquid and for high liquid velocity were compared. The results showed that C_o values for stagnant liquid were larger than values for high liquid velocity, while V_gj values were almost the same for both cases.     

Flow Rate Induced Effects on Dynamic Characteristics of BWR Jet Pump Structure

The studies performed on a two-dimensional reactor model with burnup and fuel management simulation prove that the lead cooled fast reactor concept provides the possibility to develop critical equilibrium reactor confining all of the self-produced transuraniums and long-lived fission products in the core. Such inherent safety features of the reference, non-confining lead cooled reactor design as negative void reactivity effect and ‘zero’ burnup reactivity swing may also be provided for equilibrium confining design by implementing the design approaches described in this paper.     

扁管传热与阻力特性的实验研究

以水为工质,对3种不同几何尺寸的扁管进行了传热与流阻的实验研究.相同换热条件下3根扁管的传热系数和管内传热系数均高于圆管,管内传热系数最大可提高到圆管的2.43倍.说明扁管具有很好的强化传热效果,但压降也高于圆管.同时对扁管在套管内水平和竖直2种放置方式的换热情况进行了对比,实验结果表明竖直放置的传热效果优于水平放置.     

内螺纹管中汽-液两相流体摩擦压降特性研究

在压力为9～22MPa,质量流速为600～1200kg/(m2·s),含汽率为0～1的工况范围内,对Φ38.1mm×7.5mm的6头内螺纹管中汽-液两相流体的摩擦压降特性进行了试验研究。试验段采用水平绝热布置。试验结果表明:压力对两相流摩擦压降的影响很大,随压力增加,两相流摩擦压降倍率减小,在临界压力附近,两相流摩擦压降倍率趋近于1;随含汽率增加,两相流摩擦压降倍率先增加,然后有减小的趋势;随质量流速增加,两相流摩擦压降倍率减小。用于计算单相水摩擦压降系数以及用于计算汽-液两相流体摩擦压降的试验关联式被提供。     

U型管高压汽-液两相流动密度波型不稳定性的实验研究

在系统压力P=4～10MPa,质量流速G=450～1200kg／m~2·s,人口过冷度△T_(sub)=10～70℃,热负荷q=O～650kW／m~2的工况范围内,采用φ20×2mm的23Crl8Ni不锈钢U型管,在高压试验台上进行了密度波型脉动的研究;分析了系统压力、质量流速、入口过冷度、热负荷对它的影响。结果表明,随着压力的增加,系统稳定性增加;随着质量流速增加,界限热负荷增加,界限干度下降;进口过冷度对密度波型脉动呈现单值性影响,随着进口过冷度下降,界限热负荷降低。根据实验结果及量纲分析,得出了预测界限热负荷的无因次关联式,与试验值相比,误差在15％以内。     

Hydraulics of Coolant Flow through Control Rod Channel in Very High Temperature Gas Cooled Reactor

Flow rate distribution and total pressure loss of a coolant flow through a control rod channel in the Very High Temperature Gas Cooled Reactor (VHTR) were analytically and experimentally examined. Helium gas of atmospheric temperature was used in the experiment; and the total mass flow rates ranged 0.005～0.05 kg/s and the gas pressures ranged 0.14～0.42 MPa. Pressure losses and flow rates in the control rod channel were measured. An analysis was made by using a one-dimensional flow network model for the inner and outer channels and the gap. The analytical results agreed fairly well with the experimental results on the flow rate distribution and the total pressure loss in the control rod channel.     

高温气冷堆螺旋管蒸汽发生器流量漂移不稳定性研究

建立与氦气对流换热的并联螺旋管蒸汽发生器数值模型,分别采用一维飘移流模型和一维可压缩流动模型描述水侧和氦气侧的流动。在此基础上研究了球床模块式高温气冷堆核电站螺旋管蒸汽发生器内的流量漂移不稳定性。动态计算结果表明,在一定条件下蒸汽发生器内有可能发生流量漂移,不同传热管流量可相差几倍,而出口温度则相差几百度。通过对质量流速-压降曲线的分析,发现热负荷对稳定性起主导作用,热负荷越大越易发生流量漂移,且边界质量流量随热负荷呈线性增长。增大入口节流阻力和过冷度可以在一定程度上避免流量飘移。最后给出了蒸汽发生器流量飘移的稳定边界。     

非稳定流场中的大流量测量

本文介绍了非稳定流场中的大流量测量的一种方法。由于管道布置的限制,只能在φ700的管子弯头后1D的位置采用φ12的五孔球形测针作多点测量,再用等环面面积积分方法来确定其流量。此方法进行了实验室验证,并对反应堆主热交换器流量(2000—4000m~3/h)进行了实测。证明此方法是稳妥可靠的,误差为±5%。测量结果已为工程所采用。     

高温堆热气联箱内部流场分析

以高温堆热气联箱为研究对象,在实验研究的基础上,采用流体力学计算程序CFX5对热气联箱和热气导管内部流场进行了数值模拟,以获得热气联箱和热气导管内的速度场、压力场和温度场,为高温堆热气联箱的设计和实验研究提供参考.数值计算结果表明:热气联箱内气流发生剧烈搅混,加速了不同温度气流间的热传递,有利于高温和低温气流间的温度混合.但存在肋片的区域没有发生剧烈的气流搅混,不利于气流间的热传递.热气导管内温度混合率随其长度的增加逐渐增大,热气导管长度2.5m以上时,温度混合率达到99%以上.     

Application of Neutron Radiography to Visualization and Void Fraction Measurement of Air-Water Two-Phase Flow in a Small Diameter Tube

Abstract

The purpose of this study is to investigate the feasibility of visualization and void fraction measurement of air-water two-phase flow in a small diameter tube (I.D.: 4.08mm) by using the real-time neutron radiography and image processing techniques. Video images of two-phase flow were taken by using the real-time neutron radiography system (thermal neutron radiography facility No. 2) installed at the Japan Research Reactor 3 M of the Japan Atomic Energy Research Institute. The shape of bubbles and its moving behavior were clearly observed from the video images. The image corrections for dark current, shading, field intensity fluctuation and electrical system drift were examined in order to measure the void fraction from the video images. Though, generally speaking, the effect of the scattered neutron could not be ignored for quantification of the images taken by the neutron radiography, the scattered neutron could not affect the final results of void fraction in the case of a small diameter tube. The void fraction calculated from the corrected images was correlated well with the drift flux equation, indicating that the existing drift flux equation could be applied to predict the void fraction of two-phase flow in a small diameter tube. It was demonstrated that the real-time neutron radiography technique could be useful for measuring the void fraction of two-phase flow in a small diameter tube.