池式鼓泡条件下气溶胶沉降效率研究

放射性气溶胶是核反应堆严重事故中最重要的产物之一，来源于固体裂变产物外漏和气体裂变产物的凝聚成核。池式鼓泡水洗是去除放射性气溶胶的有效途径，准确掌握其过滤效率，对于事故后源项控制和事故分析评价都具有重要意义。本文针对池式鼓泡条件下的气溶胶沉降特性展开深入的基础研究，借助先进的粒径谱分析技术，研究液相淹没深度、气相表观流速等参数对亚微米级气溶胶沉降效率的影响，探究气溶胶在上升气泡群内的沉降机理。本项目的研究成果可用于气溶胶沉降效率模型验证。     

鼓泡过滤可溶性气溶胶特性实验研究

池式鼓泡过滤是核电厂严重事故条件下一种重要的放射性气溶胶滞留过程。本文针对可溶性气溶胶在鼓泡过滤条件下的去除特性开展实验研究。结果表明,可溶性气溶胶会在鼓泡过滤过程中吸湿增长,尺寸增大,因此在评价可溶性气溶胶的去除效率时,必须保证上下游气溶胶处于干燥状态;另外,可溶性气溶胶的吸湿增长使得气溶胶的沉降特性发生改变,主要表现为原处于布朗扩散主导区的小粒径气溶胶会进入最易穿透区,效率降低,而原处于最易穿透区的气溶胶会进入惯性主导区,效率增加;气体流量的变化对气溶胶去除效率的影响不是单调的,与气-液两相流型以及气泡行为密切相关。实验结果可为验证和完善池式过滤气溶胶模型提供数据支撑。     

气泡尺寸对气溶胶水洗效果计算的影响

气溶胶水洗是核电厂严重事故下放射性源项分析的重要环节,气泡尺寸的确定对于合理评估气溶胶水洗效果非常关键。通过构建气溶胶水洗计算模型,选用气泡平均直径关系式预测水洗过程上升区的稳定气泡尺寸,对采用不同注气装置的LACE-Espana以及ACE(Abnormal Conditions and Events)水洗实验典型工况进行模拟分析,探究气泡尺寸对气溶胶水洗净化系数(Decontamination Factor,DF)计算的影响。对比结果表明:采用Akita关系式预测的气泡直径计算所获得的DF更接近实验结果,DF随气泡尺寸的减小而显著增大。     

严重事故下裂变产物气溶胶自然沉积现象研究

以600 MW压水堆核电厂为研究对象,在一体化安全分析模型的基础上建立重力沉降、扩散电泳、惯性碰撞和热电泳4种裂变产物气溶胶的自然沉积模型,选取典型的严重事故序列,分析严重事故下裂变产物气溶胶的自然沉积现象。将MELCOR程序的重力沉降模型植入本文的一体化分析模型,对重力沉降份额进行比较。研究表明,重力沉降对气溶胶沉积的贡献最大;本文采用的重力沉降模型比MELCOR程序重力沉降模型的沉降效应稍强。     

不同流型下气溶胶水洗效果影响因素实验研究

在核电厂严重事故下，安全壳内混合气体通过喷射器注入到乏燃料水池中以降低安全壳超压失效的风险，同时减少放射性向环境的释放。本文建立了气溶胶水洗去除实验装置，研究水池对气溶胶的去除机制。开展了不同流型下通过喷射器的混合气体质量流率对气溶胶水洗净化系数(DF)的影响以及蒸汽冷凝对气溶胶去除效果的影响。结果表明：在注入流型为射流的情况下，由于射流注入区液滴拦截和惯性碰撞去除机制的增强，导致DF随着质量流率的增大而增大；在注入流型为气泡流的情况下，上升区气溶胶去除占主要作用，随着质量流率增大，气泡上升速度增快，导致气泡在水池内运动时间减少，DF降低。同时，在蒸汽存在的情况下，气溶胶去除效果明显增强，蒸汽冷凝是气溶胶去除的主要机制。     

鼓泡过滤多分散气溶胶特性的矩估计分析

池式鼓泡过滤是核电站严重事故场景以及缓解措施中一种典型的放射性气溶胶滞留过程,评估气溶胶在该条件下的去除特性对事故后期的源项评估和制定相应的缓解措施具有重要意义。针对鼓泡过滤多分散气溶胶这一背景,本文假设气溶胶的尺度分布满足对数正态分布,考虑布朗扩散、重力沉降以及惯性碰撞3种机制对气溶胶在气泡内沉降的影响,利用矩方法得到了气溶胶尺度分布的3个分布参数（N、d_pg、σ_g）与其初始值、气泡上升高度以及沉降系数之间的解析关系。通过与精确解对比,对数正态矩方法推导的解析解表现出良好的预测精度。本文得到的解析解可在不需要气溶胶尺度分布具体信息而仅需要一些初始分布参数的情况下对气溶胶的去除特性进行快速评估。     

低流速排放下气溶胶水洗模型

在发生核电厂严重事故时，乏池水洗作为放射性气溶胶去除的手段之一，应用于先进非能动压水堆中。为评估气溶胶水洗效果，本文建立了蒸汽冷凝、惯性碰撞、重力沉降、离心沉积和布朗扩散等典型气溶胶去除机制模型，同时考虑了可溶性气溶胶颗粒增大现象，采用FORTRAN语言实现了气溶胶水洗效果分析程序。通过构建LACE Espana实验装置分析模型，模拟了3种典型低流速工况，并开展了气溶胶粒径、蒸汽份额以及淹没深度等关键因素的影响分析。结果表明：水洗净化系数（DF）计算值与实验结果的符合程度合理，模型有效性得到初步验证；DF随气溶胶粒径、蒸汽份额以及淹没深度的增大而增大，可溶性气溶胶颗粒增大将显著提高DF。     

MCCI过程模型开发及验证

概述了严重事故下堆芯熔融物与混凝土相互作用（MCCI）过程的机理性模型,并给出了大亚湾核电厂全厂断电及大破口叠加安注失效等典型初因事故导致的严重事故下的MCCI过程的计算分析结果,并与相同事故序列下的MELCOR计算结果进行对比。计算结果表明,所给出的严重事故下的MCCI过程模型正确合理,计算速度快,能满足在模拟机上应用的要求。     

SCDAP/RELAP5与MELCOR程序对堆芯损伤过程预测的比较

SCDAP／RELAP5与MELCOR程序是目前得到广泛使用的两个严重事故分析程序．它们在模拟堆芯溶化及压力容器下封头失效过程中采用了基于不同理论的计算模型。本文利用两个程序分别对秦山二期核电厂发生假想的全厂断电事故下的堆芯损伤过程进行预测．并对比分析了这2个严重事故分析程序的优点及相应的计算结果．     

严重事故下吸湿性气溶胶的自然去除研究

反应堆发生严重事故时，堆芯释放出的吸湿性气溶胶会在潮湿的安全壳内增大，从而影响其自然去除过程。本文理论推导了吸湿性气溶胶的增大模型并通过多种方法对其进行了验证。模型计算结果表明，气溶胶的增大过程由于受到溶解度的限制而存在临界湿度值，在该临界值以下时气溶胶不发生吸湿，但这未被其他严重事故分析程序所考虑。同时，基于某三代先进压水堆的特定严重事故工况，本文分析了干颗粒半径及湿度对气溶胶的平衡半径和自然去除系数的影响。结果表明:气溶胶的自然去除系数随干颗粒半径的增大将先减小后增加，并在1 μm时达到最小值；相同湿度下，干颗粒半径对气溶胶半径的最大增大比例的影响不大；湿度的增加对不同干颗粒半径气溶胶去除系数的影响不同。      

Research on Aerosol Deposition Efficiency under Bubbly Scrubbing Condition

Radioactive aerosols as one of the most important products in serious nuclear reactor accidents are generated from leakage of solid fission products and condensation of gaseous fission products. Bubbly scrubbing is an effective way to deposite radioactive aerosols. It is of great significance for post-accident source term control and accident analysis and evaluation to accurately grasp its filtration efficiency. In this paper, an in-depth basic research was carried out on the aerosol deposition characteristics in rising bubbles. With the help of advanced particle size spectrum analysis technology, the influence of parameters such as liquid submersion depth and apparent gas phase velocity on the deposition efficiency of submicron aerosols was studied to explore the deposition mechanism of aerosols in rising bubbles. The research results of this project can be used to verify the aerosol deposition efficiency model, so as to improve the uncertainty of the analysis results of source term concentration under severe accident conditions.     

液池内气溶胶对孔板鼓泡体积影响的实验研究

液池内的孔板鼓泡是安全壳内气体过滤排放过程中的重要现象。过滤过程中,孔板鼓泡体积直接影响气泡的上升速度与气液接触面积,因此是影响过滤器过滤效率的重要参数之一。随着过滤的进行,液池内滞留的气溶胶可能成为孔板鼓泡体积的影响因素之一。本文采用可视化实验,对含BaSO₄和TiO₂气溶胶液池内的孔板鼓泡过程进行研究,观察和分析孔板鼓泡体积的变化规律,进而获取气溶胶对孔板鼓泡体积的影响机制。研究表明,高温液池和TiO₂会使得生成气泡体积增加,添加BaSO₄的影响并不明显,实验还发现了生成气泡顶部含“小气腔”的情况,表面张力及“小气腔”的变化是气泡体积改变的主要机制。      

基于扩散界面法的较大气泡上升过程数值模拟

基于扩散界面法和有限元法,对较大气泡在上升阶段的形态和速度进行了模拟,结果与实验吻合较好,说明该方法能准确地模拟气泡的运动特性。利用该模型,对初始直径不同的较大气泡上升过程中的形态、速度和振荡随时间变化的规律进行了分析。并分析了14mm直径的气泡在不同尺寸通道中上升过程的形态、速度的变化规律。结果表明:气泡的稳定形态随着气泡初始直径的增大由椭球形变为球帽形,且达到稳定形状的时间更长。气泡初始直径越大,气泡的顶端速度越快,并稍有波动。而气泡的底端速度开始快速增大使气泡向内凹陷,随后回落并在气泡顶端速度上下振荡。气泡上升通道越窄,气泡达到稳定形态的时间越长,顶端速度越小,气泡的高宽比越大。     

Analysis of Control Rod Effect on Neutronics in FBR by Three-Dimensional Calculation

Experiments were carried out to study the mass transfer of iodine from a xenon-iodine mixed gas bubble to a liquid sodium pool. The bubble was generated in the pool by cracking a quartz glass ball which contains the xenon-iodine mixed gas. The mixed gas released into the argon cover gas was collected to determine the transferred iodine mass into the sodium pool. A rising velocity of the bubble was measured by Chen-type sensors arranged vertically in the pool. From the measured rising velocity and another observation of bubble behavior in simulated water experiments, it is found that the generated bubble breaks up into several smaller bubbles of spherical cap type during the rising period. Transferred iodine mass per the unit initial bubble volume from the bubbles to the sodium pool shows increases with increasing time and the initial iodine concentration. A mass transfer rate obtained by differentiating the transferred iodine mass with respect to the time indicates a rapid decrease just after the bubble generation and a slow decrease for the successive period. Measured decontamination factors are described as a function of the time and the iodine concentration.     

基于图像法的气液两相稀疏泡状流气泡参数分析

采用图像法对垂直上升管气液两相流中稀疏上升气泡进行实验测量研究。该方法使用高速摄像机拍摄气泡运动图像,经图像处理后,提取气泡的特征参数,分别绘制稀疏气泡上升过程中速度变化曲线和单个气泡上升过程中面积变化及形心位置变化曲线,分析气泡参数,总结运动规律。实验结果表明,采用图像法可以很好地完成对气泡参数的分析。     

窄缝通道内过冷条件下单蒸汽泡尾流特性实验研究

单蒸汽泡尾流特性是影响窄缝通道内蒸汽-水两相流流型形成与演变的关键因素，本文采用粒子图像测速仪PIV和Insight3G后处理软件，对窄缝通道内过冷条件下单蒸汽泡的尾流特性进行研究，获得窄缝通道内单蒸汽泡的尾流特性。实验结果表明，单蒸汽泡冷凝上升过程中，其尾流均为涡交替脱落的不对称尾流结构；汽泡直径越大，涡越细长，涡强度越大，大直径蒸汽泡的尾流对周围汽泡的作用更强；流道间隙减小，则尾流中涡强度降低，流体速度减小，尾流对周围汽泡的影响会相应减弱。单蒸汽泡尾流特性为构建窄缝通道内蒸汽-水两相流模型提供基础支持。      

Isotopic separation of Lithium using Inorganic Ion Exchangers

The authors have been investigating geysering, which may appear during start-up of a natural circulation boiling reactor. From the results, it became clear that a large slug bubble covering the entire channel and its condensation in the upper plenum were indispensable for geysering to occur. In this work, an image processing unit has been developed in order to measure the coalescence process of multiple slug bubbles. The proposed system was used to measure the coalescence process of multiple slug bubbles flow in vertical circular channel on air-water system. It was shown that a following slug bubble was influenced by the preceding slug bubble as the distance between the slug bubbles became 5 times inner channel diameter. The rise velocity of the following slug bubble increased due to the pressure drop induced by the wake behind the preceding slug bubble. The bubbles coalesced together in a fraction of a second.     

生长和浮升过程中气泡形状振荡特性研究

气泡形状变化对两相流动和热质传递过程有着重要影响。本文利用高速摄像仪和粒子图像测速（PIV）技术对生长和浮升过程中气泡的形状振荡特性进行了实验研究,分析了不同注气流量下气泡形状及其周围流场的变化规律。实验结果表明,气流量对脱离后气泡的形状有着明显影响,在低流量下,脱离气泡逐渐由长椭球形转变为扁椭球形,而在高流量下,脱离气泡与生长气泡的聚合将导致气液界面大幅振荡。此外,振荡气泡对其尾流区内生长气泡形状的影响同样不容忽视,其会引起生长气泡所受惯性作用增强,进而导致气泡形状波动。     

New Interfacial Drag Force Model Including Effect of Bubble Wake, (I) Model Development for Steam-Water Bubbly Flow in Large-Diameter Pipes

Several experimental results show that bubbles can easily be captured in the wake formed by leading bubbles when multiple bubbles are rising in a liquid. It is suggested from this experimental result that the effect of bubble wake should be included in the constitutive relationships representing the interfacial drag force. In the present study, steam-water bubbly flow experiments were performed to develop a new interfacial drag force model including the effect of bubble wake. Since the validity of the existing constitutive equations have been tested mainly for two-phase flow in small-diameter pipes, our study focused on two-phase flow in a large-diameter pipe. Using a one-dimensional two-fluid model, the applicability of the new interfacial drag force model to our experimental conditions was investigated. As a result, it was shown that the present model markedly improves the accuracy of the predicted results. It was therefore demonstrated that the present bubble wake model is effective at least for the conditions which were used for model development. Its applicability to different conditions will be discussed in a subsequent study.