适用于大压降小间距管道的节流件设计及分析

节流件广泛应用于核电站各类管道系统中,对于大压降和短距离的管道系统,节流孔板设置不合理将导致管道振动程度加剧并伴随节流件的孔径、厚度、偏心度和倒角等关键结构参数对节流效果的敏感性进行分析和计算,在此基础上,提出适用于大压降小间距管道的节流件为多级偏心节流孔板。计算表明:多级偏心节流孔板可有效抑制汽蚀和闪蒸的发生,节流效果较好,适用于大压降小间距管道节流。     

孔板汽蚀诱发管道振动问题研究

针对核电厂安全壳喷淋系统(EAS)出现的强烈管道振动问题,采用现场振动试验和数值计算相结合的方法进行研究。研究发现,管道节流孔板过度节流,导致在孔板下游出现汽蚀是诱发管道强烈振动的根本原因;通过数值计算方法对孔板压降、级数、孔径和结构形式等进行一系列优化设计,给出采用三级孔板消除气蚀的减振改造方案,并对改造方案开展完整性评估。通过对改造后的管道进行再鉴定试验表明,采用本文的优化设计分析方法设计的工程改造方案很好地解决了孔板汽蚀诱发的管道强烈振动问题,管道振动和噪声均大幅降低,可以确保EAS管道系统的长期安全运行。     

多级节流孔板在核级管道中的应用

针对大亚湾核电站安全壳喷淋系统(EAS)试验管线节流孔板气蚀引起的管道剧烈振动和噪音,以及支管疲劳破坏这一事例,研究了气蚀引起管道振动的分析方法,以及采用多级节流孔板减小气蚀的设计方法.对气蚀引起的管道振动,采用计算流体动力学(CFD)方法分析孔板附近的流动特性和压力分布,确定节流孔板下游是否发生气蚀现象;对于发生气蚀现象的节流孔板,提出采用多级节流孔板来减弱气蚀,并采用各级节流孔板气蚀数相近的原则确定节流孔径.通过对改造后的EAS试验管线的试验证实,采用本文的设计分析方法设计的多级节流孔板能够有效地减小节流孔板气蚀引起的管道系统振动和噪音.     

核电厂小支管裂纹泄漏原因分析和改造

采取试验与理论分析相结合的方法,分析诊断了核电厂安全壳喷淋系统小支管裂纹泄漏的根本原因,确定根本原因是主管道上的节流孔板设计不合理导致了小支管振动疲劳失效。设计多级节流孔板代替单级节流孔板,改造方案实施后,小支管振动大幅度降低,消除了影响核电机组安全运行的缺陷。     

核电站除氧系统孔板后管道减薄机理分析与改进措施研究

田湾核电站1号机组除氧系统某节流孔板后方的直管段在一个换料周期内壁厚由6.6 mm减薄至2.5 mm,极易造成管道泄漏,为机组安全运行带来潜在的隐患。本文就除氧系统孔板后管道减薄磨损位置、汽蚀原理进行分析,对除氧系统孔板设计存在的缺陷、采用多级节流孔板代替单级节流孔板优势及管道减薄改进措施进行综合论述。通过改造,满足了除氧系统给水管线的运行要求,且有效降低了管道腐蚀速率。     

某核电厂低压安注泵小流量管线振动原因研究

由于小支管振动超标的敏感管问题是困扰所有核电站的难题。国内外投入了大量的人力和物力来解决敏感管问题。分析判断振动原因是解决敏感管问题的首要因素。本文用综合的技术手段对某核电厂安注系统低压安注泵小流量管线中的敏感管振动原因进行了分析研究。通过在管线上布置加速度计进行现场振动实测获得了管线的振动分布,通过振动加速度的时程的RMS值分布获得了节流孔板后方是振动最大的位置,通过对节流孔板后方的加速度进行频谱分析初步判断为节流孔板过分节流导致通过孔板的流体汽化而出现了汽蚀现象。通过对节流孔板的理论分析获得了节流孔板前后的压差并与阻塞压差进行比较进一步验证了节流孔板的过分节流现象。最后用CFD进行了三维流场分析获得了整个管线的详细流场分布,并得到了经过节流孔板后出现了流场中低于流体饱和蒸汽压的区域,该区域是流体汽化区。通过综合的手段最后确定导致该小流量管线振动高的主要原因是节流孔板的汽蚀。本文所用的方法对其他具有类似的振动现象的振动原因分析具有借鉴的意义。     

基于CFD和结构有限元双向耦合方法的载流管路流致振动特性研究

基于计算流体力学(CFD)和结构有限元双向耦合方法建立了典型载流管路双向耦合数值分析模型,获得了管路流致振动基本特性,并分析了流速、管路吊架刚度及位置等因素对其流致振动特性的影响。结果表明,流体载荷可激发出管路低频振动特性,且低频线谱明显;载流管路流致振动特性与管内流速、管路吊架刚度及位置分布等因素相关;管内流体流速与管路流致振动总体响应水平成正相关关系;吊架刚度及位置对结构振动频谱分布特性的影响显著,可通过优化管路吊架参数避开设备、阀门等振源的共振频率。     

核电厂高压安注系统再循环管线节流孔板的分析与改进

某在役运行VVER核电厂高压安注系统（JND）在进行小流量再循环试验时发现再循环流量出现异常波动,导致试验不合格。经过分析认为再循环管线节流孔板发生空化是导致流量波动的主要原因。本文通过相关理论和软件,主要介绍了对再循环节流孔板进行改进设计计算的过程,包括孔板流量、压差、级数、孔径和厚度等参数的计算,重点讨论了如何控制多级孔板的压降以避免孔板发生空化。该项改进已在核电厂中得到实施,实施后再循环流量波动问题得到了明显改善。     

辅助给水系统超流量分析及改进

采用k-ε湍流模型模拟辅助给水系统(ASG)孔板的三维流动状态,获得孔板流速分布、压降分布及流量与压降关系等特性。建立一维的系统仿真模型并验证了模型的有效性,结合数值模拟得到的孔板特性参数,对ASG役前调试期间除氧器超流量报警问题进行仿真验证和分析,提出报警信号延迟的改进方案,有效地解决了除氧器超流量报警的问题。     

孔板管道下游流动加速腐蚀速率数值模拟研究

采用计算流体力学方法中的k-ε模型模拟了孔板管道下游管壁与流体间的传质系数分布,并利用Sanchez-Caldera流动加速速率预测模型计算了孔板管道下游的流动加速腐蚀速率分布。结果表明,孔径比的减小会导致流动加速腐蚀敏感部位向孔板下游移动,入口流速的增大对孔板下游流动加速腐蚀敏感部位的位置无明显影响,pH值的增大能有效减小流动加速腐蚀速率。     

基于改进BP神经网络的节流孔板空化特性预测

为高效地获取核级管道中节流孔板附近的空化特性,构建了可靠的改进反向传播（BP）神经网络预测模型。首先提取了节流孔板的几何特征参数,并使用拉丁超立方抽样（LHS）方法生成了上述几何特征参数的样本库;然后通过计算流体力学（CFD）方法得到了各个样本对应的最小空化数,以该无量纲参数作为输出响应;最后针对原始BP神经网络预测模型的不足,结合遗传算法建立了节流孔板空化特性的改进预测模型。结果表明,孔板开孔直径和前开角度对最小空化数具有较强的全局敏感度;通过遗传算法优化后的BP神经网络预测模型的预测精度得到了大幅提升,误差均方根降低约36.4%。      

CAP1400反应堆吊篮与围筒旁通流特性实验研究

对CAP1400反应堆的吊篮与围筒旁通流量进行实验研究,研究了不同直径的围筒底板开孔下旁流腔的阻力特性及对应原型堆堆芯压降下的旁流份额。研究结果表明,当围筒底板开孔直径大于等于1.2倍的最小实验测量直径时,旁流腔的流量份额超过了对应原型堆堆芯压降下总流量的0.5%,其余孔径下旁流腔的流量份额均小于对应原型堆堆芯压降下总流量的0.5%。     

基于CFD的汽水分离再热器分析计算研究

通过三维数值模拟研究了实际运行工况下汽水分离再热器（MSR）内部流场细节,并对比了2种不同孔板开孔方式对波形板前气流均匀性的影响。采用标准k-ε湍流模型结合标准壁面函数对MSR内部进行了CFD气相流场三维模拟,其中孔板、波形板和管束采用多孔介质模型,通过UDF调整孔板开孔率,防冲板简化为多孔跃升边界。结果表明：分析计算结果与空气动力学试验结果数据绝对值或数据增减幅度较好符合;在保持平均开孔率与均匀开孔相同的基础上,非均匀开孔的波形板前气流速度更为均匀;蒸汽通过孔板和分离器的总压降不大于14 kPa,满足分离装置的压损设计要求,其中蒸汽的再热器管束的压降占整个流线压降的比例较大。     

输流管网流致振动特性数值模拟研究

为研究管路系统流质振动特性以优化管路设计,本文以典型输液管网系统为对象,基于Ansys Workbench平台开展了不同流体激励下的管路双向流固耦合模拟计算,获得了管路结构流致振动特性,分析讨论了激励类型、介质温度、流场结构及结构固有频率对管内流致振动特性的影响。结果表明,脉动流量激励下的管路结构振幅显著大于恒定流量激励下的结构振幅,当流体激励频率较接近管路结构固有频率时,结构和流体将趋于共振,导致结构振动加剧。通过在管道适当位置施加约束支撑,使结构固有频率远离流体激励频率,可有效减小管道的振动。此外,介质温度和流速对结构振幅有较大影响。      

蒸汽发生器流量分配板及横向流局部压力损失系数计算

为计算得到蒸汽发生器流量分配板及横向流的局部压力损失系数,应用三维稳态热工水力软件GENEPI,在无重力、单相条件下,对管束区入口到第2块管子支撑板下游进行三维流场模拟,计算得到了给定出口压力下入口静压,进而求出进出口压降,并通过沿程摩擦以及局部压力损失关系式等,减去两块管子支撑板的压力损失及沿程阻力,推导求出蒸汽发生器流量分配板及横向流的局部压力损失系数。为验证方法的正确性及可行性,以CPR1000-SG和EPR-SG为对象,计算这两个型号蒸汽发生器流量分配板及横向流的局部压力损失系数,并将计算结果与国外经验系数进行对比,结果表明:计算结果与国外经验系数接近,误差在可接受范围内。     

Experimental qualification of subassembly design for Prototype Fast Breeder Reactor

The Prototype Fast Breeder Reactor (PFBR) which is under construction at Kalpakkam, India, is a 500 MWe sodium cooled pool type reactor. The core of the PFBR consists of 1758 free standing subassemblies supported on the grid plate. The entire core is divided into 15 different flow zones and the flow rate required through each zone is calculated based on the fission heat generation. The coolant sodium flows from the bottom of the subassembly to top and the design of the subassembly for each flow zone is quite complex. There are 181 fuel subassemblies in PFBR core with 217 fuel pins in each subassembly, vertically held in the form of bundle within a hexagonal wrapper tube. The pins are separated by spacer wires wound around the pins helically. Analytical prediction of subassembly pressure drop, vibration and determination of inception of cavitation for this complex geometry is very difficult. So experiments were conducted extensively to get a more accurate evaluation of the design and for its qualification for the use in PFBR, which is designed for 40 years of operation.Pressure drop and cavitation experiments were carried out in water on full scale (1:1) subassemblies of all flow zones. The overall pressure drop of the subassembly determines the ratings of the pump. Cavitation of the pressure drop devices lead to erosion damage of fuelpins and may also result in reactivity fluctuation due to sodium-void effect. So it is essential to confirm that the subassembly is not cavitating in the operating regime of the reactor. Subassembly can vibrate in cantilever mode due to the turbulence in the flow and can result in reactivity fluctuation, reactor control problem and can even lead to the failure of the fuel pins. So vibration measurements were carried out in water on the maximum rated subassembly. This paper discusses various experiments carried out on PFBR subassembly, the similarity criteria followed, instrumentation, results and conclusion.     

Laminar flow induced deflections of stacked plates

Some research and power reactors such as the Engineering Test Reactor (ETR), the Materials Test Reactor (MTR) and the Shippingport Reactor have core designs which consist of parallel, flat or curved plate fuel assemblies. The fuel is contained in the thin plates which are separated by narrow channels through which coolant flows to remove heat generated within the plates. Since the plates are flexible, the coolant flowing through the channels causes the plates to deflect. At high coolant velocities large deflections have been observed causing the plates to deform plastically leading to structural failure or plate collapse. This work examines a single plate bounded by two channels and determines the static plate deflection as a function of plate, channel and flow parameters. The deflection is due to differences in pressure and flow velocity in the channels bounding the plate and also due to different channel dimensions caused by tolerance effects. The classical thin plate equations are used with a nonlinear hydrodynamic loading function expressing the external fluid forces on the plate surfaces.     

Large eddy simulation of unsteady flow in gas-liquid separator applied in thorium molten salt reactor

Axial gas-liquid separators have been adopted in fission gas removal systems for the development of thorium molten salt reactors. In our previous study, we observed an unsteady flow phenomenon in which the flow pattern is directly dependent on the backpressure in a gas-liquid separator; however, the underlying flow mechanism is still unknown. In order to move a step further in clarifying how the flow pattern evolves with a variation in backpressure, a large eddy simulation(LES) was adopted to study the flow field evolution. In the simulation, an artificial boundary was applied at the separator outlet under the assumption that the backpressure increases linearly. The numerical results indicate that the unsteady flow feature is captured by the LES approach, and the flow transition is mainly due to the axial velocity profile redistribution induced by the backpressure variation. With the increase in backpressure,the axial velocity near the downstream orifice transits from negative to positive. This change in the axial velocity sign forces the unstable spiral vortex to become a stable rectilinear vortex.     

Evaluation of Delayed Neutron Fraction β for Thermal Fission of U-235 Based on Integral Experiments Using SHE

Countercurrent gas-liquid flow is theoretically and experimentally evaluated for a boiling system simulating a BWR core. In a single channel, flow patterns are determined from the mass balance equations and pressure drop under steady state conditions is calculated for each flow pattern using a drift flux model, where the distribution parameter and drift velocity are correlated as functions of void fraction and hydraulic diameter from void fraction data. The calculated pressure drop shows a similar trend to that of the data for the effects of bypass leak flow rate and heater power. Countercurrent behavior in three boiling channels under slow transient conditions is also predicted from the single channel characteristics and close agreement is obtained between the predicted and experimental results. The results show that steam up-flow or cocurrent up-flow easily occurs in a channel with low pressure drop, namely, with a large entry orifice, high power or low bypass leak flow rate.