钠冷快堆燃料组件热工水力特性数值模拟与分析

利用CFD程序CFX,分别对7、19、37、61根棒组成的三角形排列螺旋绕丝定位的钠冷快堆燃料组件棒束通道进行了热工水力特性的分析研究,并将结果与子通道程序SuperEnergy进行了对比验证。重点考察了棒束通道轴向流动分布、横向流交混效应及子通道轴向温升,分析了定位绕丝的影响。结果表明,绕丝对棒束通道的横向流交混效应、轴向流动分布及子通道温升有着重要影响,且随棒束的增多,通道内的流动趋向复杂化,轴向流动不均匀性有升高趋势。     

铅铋冷却绕丝燃料组件横流特性分析

准确预测绕丝棒束通道内的横向流动特性是开展铅铋冷却快堆热工水力安全分析的基础。本文采用数值模拟的方法分析了液态铅铋工质下单绕丝和多绕丝燃料组件内的横流特性。分析结果表明,单绕丝组件的中心子通道横流流速最大不超过主流流速的19%,且横流方向和二次流中心随着高度周期性变化;单绕丝组件中,当绕丝与子通道交界面重合或垂直时,中心子通道界面横向流量和横流交混指数趋于零或达到峰值;在单绕丝组件结构一定的情况下,横流交混指数在湍流区对Re不敏感,而与组件结构参数存在较大相关性;多绕丝组件中心子通道界面上的横流存在两个相反的流向。     

液态铅铋合金在绕丝燃料棒组件子通道间湍流交混数值模拟

液态铅铋合金（LBE）是第四代液态金属核反应堆候选冷却剂,由于LBE热物性具有一定的特殊性,亟待对LBE在燃料组件子通道中的流动与传热过程开展研究。本文对LBE在带绕丝燃料棒组件中湍流流动进行数值模拟与分析,将燃料棒壁面温度的数值模拟结果与响应的实验数据相比较,2者具有较高的吻合度,说明数学模型及数值结果具有较高的可靠性与准确性;使用湍流交混系数β表征LBE在不同子通道间、不同燃料棒间隙宽度与燃料棒直径比（S/D）结构下的湍流交混情况,结果表明,不同子通道间β波动程度具有差异性,β的大小与S/D呈负相关。基于不同S/D与雷诺数的计算结果,拟合出不同子通道间β关联式,为绕丝燃料棒三角形排列方式的燃料组件子通道分析程序开发提供交混模型。      

基于CFD方法的铅铋冷却燃料棒束的热工水力特性分析

铅铋冷却快堆作为第4代反应堆候选之一具有安全性高等特点,研究其在正常工况下的热工水力特性具有重要意义。本文基于商用计算流体力学（CFD）软件STAR-CCM+,使用流固耦合的方法对带有绕丝结构的19棒束铅铋组件进行数值分析,探究了质量流量、功率等边界条件对组件内部流动传热特性的影响。模拟计算结果表明：CFD方法在子通道中心温度和壁面温度预测上与实验结果取得了较好的一致。同时,绕丝结构的存在使得子通道之间存在周期性的横向交混,并使得棒束表面温度呈现震荡。随质量流量的增加,子通道间横向交混增大。功率变化对通道间的横向交混速度的影响较小,冷却剂温度的横向分布无明显差异。     

基于CFD方法的铅铋冷却燃料棒束的热工水力特性分析

铅铋冷却快堆作为第4代反应堆候选之一具有安全性高等特点,研究其在正常工况下的热工水力特性具有重要意义。本文基于商用计算流体力学(CFD)软件STAR-CCM+,使用流固耦合的方法对带有绕丝结构的19棒束铅铋组件进行数值分析,探究了质量流量、功率等边界条件对组件内部流动传热特性的影响。模拟计算结果表明:CFD方法在子通道中心温度和壁面温度预测上与实验结果取得了较好的一致。同时,绕丝结构的存在使得子通道之间存在周期性的横向交混,并使得棒束表面温度呈现震荡。随质量流量的增加,子通道间横向交混增大。功率变化对通道间的横向交混速度的影响较小,冷却剂温度的横向分布无明显差异。     

铅铋冷却快堆含绕丝燃料组件子通道程序开发与验证

由于铅铋冷却剂流动传热现象的复杂性,准确计算铅铋冷却含绕丝燃料组件的冷却剂和包壳温度是液态金属冷却快堆燃料组件热工分析的重点。本文基于集总参数法对守恒方程进行求解,开发了适用于铅铋冷却快堆的子通道分析程序,对液态铅铋在棒束燃料组件中的摩擦阻力模型、湍流交混模型和对流换热模型进行了适用性分析,并对7棒束大涡模拟和19棒束含绕丝传热实验进行了对比验证。结果表明：包壳和冷却剂温度的最大相对误差低于5%。程序能较好完成铅铋冷却含绕丝燃料组件的热工水力计算,可为铅铋冷却快堆设计提供支持。     

中国铅基研究实验堆绕丝燃料组件热工水力分析

在铅基研究反应堆燃料组件设计中,燃料棒之间的绕丝可减少燃料棒在运行过程的机械振动,并使冷却剂在各子通道间有效混合,对绕丝燃料组件内冷却剂的热工水力分析将对燃料组件的设计与优化具有重要意义。本文通过CFD方法对中国铅基研究实验堆(CLEAR-Ⅰ)燃料组件参考设计内的冷却剂流动换热过程进行数值模拟,并分析绕丝组件的速度场、温度场等流场特征量的分布规律。结果表明:绕丝在流场中起着搅混冷却剂的作用,内通道搅混较外通道相对均匀;组件内横向流强度、摩擦系数在入口段先迅速变化,后在充分发展区呈波浪状在其平均值上下波动,努塞尔数变化规律与之类似;包壳最高温度满足安全设计限值。     

棒束燃料组件特征栅元CFD方法研究

AFA-3G燃料组件中存在典型栅元和控制棒导向管栅元两种特征栅元,定位格架搅混翼的排列也具有一定的规律性.本文采用计算流体力学(CFD)方法,分别针对两种特征栅元,从第一类子通道和第二类子通道的角度,沿程评价其交混性能.质量交混与热交混紧密联系又相互区别,第一类子通道质量交换较强,但从传热角度,二者性能相当.AFA-3...     

紧密排列燃料组件交混系数试验研究

单相及两相工况下的交混系数是燃料组件热工分析、特别是子通道分析的一个关键参数。本文介绍19根棒束绕丝结构紧密排列燃料组件交混系数单相试验的试验本体结构、试验内容、试验方法及试验结果。试验研究获得了燃料组件出口温度分布及紧密排列燃料组件交混系数,最后对试验结果、交混系数值以及热工参数对交混系数的影响等进行分析。     

方形子通道内超临界流体流动传热CFD分析

国际上对超临界水冷堆进行了大量的研究,但对其堆芯内超临界流体流动传热特征的认识还十分欠缺.本研究采用CFX软件对典型超临界反应堆燃料组件子通道内的超临界热工水力特征进行了数值分析.研究了流动参数、边界条件和节径比(P/D)对子通道间交混现象和传热特性的影响.计算结果表明:燃料组件外围壁面子通道比内部子通道的湍流交混强烈;稠密栅格的湍流交混比宽栅格的湍流交混小.当P/D>1.2后,P/D比对湍流交混影响不再明显.研究还发现,在拟临界点附近区域,出现湍流交混系数的突变.     

Local heat transfer and hot-spot factors in wire-wrap tube bundle

Heat transfer coefficients and hot-spot factors have been determined from measured local temperatures and calculated local mass flux in seven adjacent tubes and associated subchannels of a 61 wire-wrap tube bundle characteristic of the blanket of a GCFR (Gas Cooled Fast Reactor). The bundle consisted of 2.11 cm OD stainless steel tubes on a triangular array with a pitch/diameter ratio of P/D = 1.05. The helical wire of 0.1067 cm in diameter was coiled on the tube with a respective initial orientation of 0–120–240°C and 30.48 cm helical pitch. The experiment used water at atmospheric pressure and temperature as coolant. The resulting dimensionless correlation for heat transfer is applicable to gases and all non-metal fluids in one phase flow when the fluid properties at subchannel bulk temperature are used. This correlation is based on local subchannel mass flux and is applicable to all wire-wrap configurations. Local subchannel mass fluxes were determined with a computer program COBRA IV and used to correlate the average Nusselt number for each subchannel in terms of local Reynolds number and fluid Prandtl number. The differences of up to 19% between that correlation and the one presented in earlier work are discussed in the text. The hot-spot factors on the convective heat transfer coefficient for tubes and subchannels are given as a function of Reynolds number based on a bundle average mass flux and a local subchannel hydraulic diameter. These factors are specific to the bundle configuration and are also dependent on the wire-wrap configuration.     

Turbulent flow simulation in a wire-wrap rod bundle of an LMFBR

The pressure drop and heat transfer characteristics of wire-wrapped 19-pin rod bundles in a nuclear reactor subassembly of liquid metal cooled fast breeder reactor (LMFBR) have been investigated through three-dimensional turbulent flow simulations. The predicted results of eddy viscosity based turbulence models (k-?, k-ω) and the Reynolds stress model are compared with those of experimental correlations for friction factor and Nusselt number. The Re is varied between 50,000 and 150,000 and the ratio of helical pitch of wire wrap to the rod diameter is varied from 15 to 45. All the three turbulence models considered yield similar results. The friction factor increases with reduction in the wire-wrap pitch while the heat transfer coefficient remains almost unaltered. However, reduction in the wire-wrap pitch also enhances the transverse flow velocity in the cross-sectional plane as well as the local turbulence intensity, thereby improving the thermal mixing of coolant. Consequently, the presence of wire wrap reduces temperature variation within each section of the subassembly. The associated reduction in differential thermal expansion of rods is expected to improve the structural integrity of the fuel subassembly.     

Laminar convection in wall sub-channels and transport rates for finite rod-bundle assemblies by superposition

Finite rod-clusters in circular, square and hexagonal shells have been divided along the symmetry lines into a number of interior, wall and corner subchannels. Laminar fluid flow and heat transfer results have been generated for these subchannels with varying pitch-to-diameter and wall distance-to-diameter ratios. Wall shear stress and temperature variations for typical wall subchannels are presented. Friction factor values for finite bundles are then obtained by superposing the results of the subchannels that constitute the bundles. The values so generated are in excellent agreement with previous work in the literature obtained by the method of symmetry sectors. Considerable disagreements were, however, observed in the superposed values of Nusselt number, apparently due to conduction effects.     

Effects of wire-spacer shape in LMR on thermal–hydraulic performance

In this work, analyses of three-dimensional flow and convective heat transfer in wire-wrapped fuel assemblies with different shaped wire-spacers have been carried out using Reynolds-averaged Navier–Stokes equations with shear stress transport turbulence model. Three cross-sectional shapes of wire-spacer, circle, hexagon and rhombus have been tested. All the assemblies have been analyzed for single pitch of wire-spacer with periodic boundary conditions applied at inlet and outlet of the calculation domain. It is found that the assemblies exhibit the directional periodicity in radial gradients between the adjacent subchannels due to presence of wire-spacer. The overall pressure drop is highest in case of rhombus shaped wire-spacer assembly followed by hexagonal shaped. Although circular shaped wire-spacer gives lowest peak temperature as well as lowest overall temperature difference in the assembly, the rhombus shaped wire-spacer assembly gives highest Nusselt number on fuel rod surface.     

Calculated heat transfer development in bundles

In many cases heat transfer in rod bundles can be considered as a superposition of several simple heat transports. A number of practical problems can thus be solved if solutions for these elementary transport are available. Two elementary heat transports in rod bundle geometry are investigated, namely the transport from a fuel rod surface into the adjacent subchannel and the transport from one subchannel into the next one. The first transport is characterized in terms of the Nusselt or Stanton numbers, while the latter in terms of the Stanton gap number or mixing factor. Hydraulically developed flow is assumed, with no feedback of heat transport on the flow condition. A three-dimensional numerical calculation by means of the finite difference method is applied to determine the eigenvalue solution of the response on a step change in heating for both cases. The method is tested on an internally heated concentrical annulus. The result is compared with available experimental and theoretical predictions. It is found that the heat transfer between subchannels is developed considerably slower in comparison with the development of the heat transport from fuel rod to subchannel.     

带绕丝2×2棒束超临界水传热实验研究

针对两流程带绕丝定位的2×2棒束实验本体,开展了超临界水的流动传热实验研究。实验结果表明,在带绕丝的2×2棒束中,同一横截面上存在显著的周向温度不均匀现象。在较小的G/q工况下出现传热恶化现象,且存在二次恶化现象。由于绕丝的搅混作用,流道下游的传热恶化得到抑制。实验表明,棒束传热规律与单管类似,对比结果指出Bishop等（1964）的计算公式能较好地预测实验结果。同时与不带格架的2×2棒束相比,绕丝具有强化传热的作用。     

CFD analyses in tight-lattice subchannels and seven-rod bundle geometries of a Super Fast Reactor

This paper presents CFD analyses in heat unsymmetric subchannels and heat symmetric seven-rod bundle geometries of a Super Fast Reactor (Super FR) fuel assembly using STAR-CD. The purpose of CFD analyses in heat unsymmetric subchannels is to evaluate the effect of the power differences on the heat transfer in subchannels of the Super Fast Reactor. For heat symmetric seven-rod bundles, the effects of the gap clearance between the fuel rod and the assembly wall and the displacement of the fuel rod on the circumferential temperature distributions and Maximum Cladding Surface Temperature (MCST) are analyzed. The results show that larger power difference between fuel rods gives larger circumferential temperature difference of the hottest fuel rods. Considering cross flow between edge and ordinary subchannels, 1 mm gap between the fuel rod and the assembly wall is better for small MCST although the circumferential temperature difference in edge subchannel is large. MCST increases exponentially with the displacement. The relative error of displacement should be less than 1% if the allowable increment of MCST due to displacement is less than 6 °C.     

定位绕丝结构对棒束通道热工水力特性影响数值分析

定位绕丝设计广泛应用于金属快堆堆芯设计及气冷快堆堆芯设计中,本文基于三维精细化绕丝定位棒束通道网格模型模拟分析了定位绕丝螺距、定位绕丝数量及定位绕丝形状对超临界二氧化碳在棒束通道中流动换热的影响。模拟结果表明定位绕丝螺距比定位绕丝数量及定位绕丝形状对温场流场的影响更大,定位绕丝螺距小于200 mm时,进出口压降大幅增加,表面换热系数增加,温度不均匀度大幅降低;随着定位绕丝数量增加,进出口压降线性增加,表面换热系数变化不大;圆形定位绕丝可以以较小截面积达到与方形定位绕丝相似的效果,梯形定位绕丝对流场影响不如矩形定位绕丝。     

球床模块堆停堆后自然对流传热特性数值研究

对冷却流体在球床模块堆内燃料颗粒填充区域中的流动和传热过程进行了研究.数值模拟突然停堆后燃料颗粒区在温差作用下的自然对流过程,分析了瑞利数Ra对燃料填充区域内流场、温度场和局部努塞尔数Nu以及壁面摩擦阻力系数的影响.计算结果表明:当球床模块堆突然停堆时燃料填充区域可形成加热壁面流体上升流动、冷却壁面下降流动的自然循环流动;随着Ra数增大,回流中心向上移动;沿轴向壁面局部Nusselt数和摩擦阻力系数存在极值,并且极值点随Ra数增大而向上移动;与氮气相比,氦气作为冷却介质停堆后具有更均匀的堆芯轴向温度分布.     

转运通道中燃料组件自然对流传热特性试验研究

针对燃料组件滞留转运通道期间的自然循环传热过程开展了试验研究。获得了承载器顶角区域加热棒的试验数据,并拟合出传热经验关系式。计算结果与试验结果比较表明,该关系式能较好地计算顶角区域加热棒顶部局部努塞尔数Nu。并通过试验数据证实了在相同的燃料棒热流密度和承载器进口水温条件下,最靠近承载器顶角位置的1号棒的传热能力最差,壁温最高。