高温气冷堆备用停堆装置新型供料器分析与试验

吸收球停堆装置参与球床型高温气冷堆的堆芯反应性调节控制,实现反应堆冷停堆,供料器是数百万个6 mm吸收球从堆芯反射层被气力输送回到贮球罐的起点,吸收球在供料器中被气流悬浮、加速,需研究不同结构型式的供料器的输送性能及可靠性.利用Fluent软件对新型流化管式供料器进行了数值模拟分析,获得速度、压力分布场,同时进行了空气介质常温流动供料器试验研究.模拟计算得到供料器局部阻力系数约为5.1,试验测得供料器局部阻力系数为5.7,结果在工程应用可接受的范围内.     

先进的规则床模块式高温气冷堆概念

规则床模块堆是燃料球呈规则堆积的一种先进的模块式高温气冷堆设计。燃料球在平面上成正方形排列,四个球的中心是次一层球的位置,形成正四棱锥堆积。当燃料球落入被做成一定几何形状的堆芯空腔时,就自动形成规则堆积。燃料球可以从反应堆顶部装入和卸出,能够在较短的停堆时间内完成换料操作。规则床堆芯是一种密实体,具有很强的结构适应性和稳定性。在模块化设计中,保持非能动冷却和限制最高燃料温度的条件下,它能够提高输出功率和降低堆芯压降,同时还兼有球形燃料堆和柱状燃料堆的主要优点。本文介绍规则堆积床特性和预测规则床模块堆的设计性能。     

模块式球床反应堆内颗粒流动特性二维数值模拟

采用颗粒离散元方法(PDEM),对模块式球床反应堆内球形燃料元件循环流动的流动特性进行数值模拟,分析了反应堆堆芯内速度场、球体混合情况和球体摩擦系数、壁面摩擦系数对流动特性的影响.计算结果表明,在圆柱结构区域内,颗粒以稳定质量流形式向下移动,颗粒径向偏移很小无混合现象发生;在倒锥形区域,颗粒受器壁结构的影响而向中心会聚流动,颗粒径向偏移增大;颗粒摩擦系数和壁面摩擦系数对颗粒流动的轨迹和滞留时间均有影响,降低摩擦系数有利于均衡燃料球和石墨球的停留时间.     

TMSR-SF球床随机堆积结构的离散元模拟

中国科学院上海应用物理研究所设计的10 MW固态燃料钍基熔盐实验堆(Thorium-based Molten Salt experimental Reactor with Solid Fuel,TMSR-SF)是一种球床型氟盐冷却高温堆,其三维球床随机堆积结构对于堆芯反应性变化和换料分区方案以及热工水力分析中的流动传热都具有重要的影响。为了研究TMSR-SF堆芯球床随机堆积规律,基于PFC3D(Particle Flow Code 3 Dimensional)程序,分别计算并分析了填充颗粒球大小、颗粒间摩擦系数以及填充颗粒球数对球床稳态堆积结构的影响。结果表明:填充直径小的颗粒球,可使球床孔隙率振荡减弱,有利于堆芯功率密度分布的展平;通过减小颗粒间摩擦系数能较好地模拟振动压实效果,压实过程中颗粒间摩擦系数与稳态堆积球床孔隙率和配位数满足负指数关系。当填充颗粒球数超过约8 000个后,球床平均孔隙率和配位数变化趋于恒定,分别稳定在0.43和5.6左右;此时颗粒球数量对球床稳态堆积结构的影响降至最低,可被用来代替满装堆时的球床用于TMSR-SF自然循环的热工水力数值分析,达到节省计算资源的目的。本研究对理解TMSR-SF堆芯球床结构特性与堆积规律具有参考价值。     

球床型氟盐冷却高温堆的初步中子学分析

为分析球床型氟盐冷却高温堆(PB-FHR)堆芯的关键中子学参数,建立了显式随机模型,基于随机填充方法计算了燃料球石墨基质内所有三层各向同性包覆颗粒(TRISO)颗粒的空间坐标,并采用离散元方法计算出堆芯活性区内全部燃料球的空间坐标。最后采用蒙特卡罗程序开展中子输运计算,分析燃料颗粒随机分布对堆芯中子学参数的影响。研究结果表明,TRISO颗粒的随机分布对栅元增殖系数、栅元群截面、活性区燃料球功率的影响较小,本文研究可为简化PB-FHR设计提供理论依据。     

高温气冷堆模拟机的堆芯热工建模研究

为完成核电厂操纵员的培训和考试,需开展适用于高温气冷堆的模拟机研究。根据球床堆芯的特点,利用流体网络与传热网络建立了可实时计算的热工水力模型,讨论了球床中氦气沿径向的流动及换热对堆芯热工水力性能的影响。结果表明,在正常运行工况下,径向流动与换热对轴向流动的影响较小,模拟结果差别不大;而在失流不失压工况下,径向流动与换热对堆芯自然对流的形成、余热导出及整个瞬态过程的影响均较为明显,考虑径向流动与换热的仿真结果与设计软件的结果符合更好。考虑到模拟机仿真范围和逼真度的要求,在高温堆模拟机堆芯建模中需加入径向流动及换热模块。     

局部非热平衡条件下含内热源多孔介质方腔内自然对流数值研究

在流体与固体骨架有效导热系数比一定的条件下,采用局部非热平衡模型与非达西流动模型,研究Ra和Da对含内热源多孔介质的方腔内自然对流流动换热特性的影响。计算结果表明:当Ra取定值,流体平均Nu随Da的增大而增大;当Da取定值,流体平均Nu随Ra的增大而增大。在文中参数的变化范围内,固体相与方腔4个壁面的换热强度相当,且变化较小。方腔左右两壁面流体相换热强度相同,但均弱于上壁面换热强度,下壁面流体相换热强度最低。无量纲容积换热系数较小时,非热平衡效应影响较大。     

氟盐冷却球床高温堆燃料管理程序的开发与分析

基于确定论的中子学分析程序在计算氟盐冷却球床高温堆（PB-FHR）时需解决双重非均匀性的燃料球均匀化、燃料球均匀化时出现的泄漏效应及燃料球在堆芯内连续移动与多次通过堆芯的燃料循环模式问题。本文基于DRAGON5与DONJON5程序开发了PB-FHR的燃料管理程序PBMSR，并进行了验证。使用PBMSR对PB-FHR在不同燃料循环模式下进行计算与初步分析，结果显示在多次通过的燃料管理模式下，燃料球的通过次数对最深卸料燃耗影响较小，但对轴向功率分布影响较大。     

氟盐冷却球床高温堆燃料管理程序的开发与分析

基于确定论的中子学分析程序在计算氟盐冷却球床高温堆(PB-FHR)时需解决双重非均匀性的燃料球均匀化、燃料球均匀化时出现的泄漏效应及燃料球在堆芯内连续移动与多次通过堆芯的燃料循环模式问题。本文基于DRAGON5与DONJON5程序开发了PB-FHR的燃料管理程序PBMSR,并进行了验证。使用PBMSR对PB-FHR在不同燃料循环模式下进行计算与初步分析,结果显示在多次通过的燃料管理模式下,燃料球的通过次数对最深卸料燃耗影响较小,但对轴向功率分布影响较大。     

随机球床模拟方法对氟盐冷却高温堆中子学参数的影响分析

氟盐冷却高温堆（FHR）采用氟盐冷却球形燃料元件,其中子物理计算面临双重不均匀性问题：燃料球在堆芯内的随机排布和包覆燃料颗粒在燃料球中的随机排布。此问题是该堆型设计中面临的主要挑战之一。本文基于MCNP程序和固态燃料钍基熔盐堆（TMSR-SF1）模型完成了不同燃料球床与燃料球描述对关键中子学参数（如k_eff、堆芯能谱、控制棒价值和温度系数等）的影响分析。燃料球床描述使用随机序列添加（RSA）方法建立了随机球床模型与体心立方（BCC）结构的等效规则模型。包覆燃料颗粒描述则基于简立方（SC）等效模型利用MCNP程序中的URAN卡实现随机扰动。结果表明,包覆燃料颗粒随机分布的影响远小于燃料球随机分布的影响;尽管具有相同的总堆积密度,等效规则模型相比于随机球床模型会增加堆芯中子的泄漏,低估冷态满装载反应性约0.5%,高估控制棒价值约5%。     

Natural convection heat transfer of water on a horizontal downward facing stainless steel disk in a gap under atmospheric pressure conditions

An experimental study on natural convection heat transfer on a horizontal downward facing heated surface in a water gap has been carried out under atmospheric pressure conditions. A total of 7204 experimental data points are correlated using Rayleigh versus Nusselt number correlations in various forms, based on different independent variables. The effects of different characteristic lengths and film temperatures are discussed. The buoyancy force acts as a resistance force for natural convection heat transfer on a downward facing horizontal heated surface in a confined space. For the estimation of the natural convection heat transfer under the present conditions, empirical correlations in which Nusselt number is expressed as a function of Rayleigh number, or Rayleigh and Prandtl numbers both, may be used. However, the best accuracy is provided by an empirical correlation which expresses the Nusselt number as a function of the Rayleigh and Prandtl numbers, as well as the gap width-to-heated surface diameter ratio; and uses the temperature difference between the heated surface and the ambient fluid in the definition of Rayleigh number. The characteristic length is the gap size and the film temperature is the average fluid temperature.     

大功率先进压水堆IVR有效性评价中熔池换热研究

熔融物堆内滞留-压力容器外部冷却（IVR-ERVC）是一种重要的核电厂严重事故缓解措施。当前针对IVR有效性评价的方法主要是基于集总参数模型对下封头熔池换热进行分析。在大功率先进压水堆熔池集总参数法计算中,堆芯重量变大、压力容器尺寸增加会导致熔池自然对流换热中的瑞利数Ra ′增大。通过使用集总参数分析程序,对比研究熔池氧化层各换热模型的适用范围,计算大功率先进压水堆高瑞利数条件下稳态熔池的自然对流换热,模拟两层稳态熔池模型中压力容器外壁面的热流密度分布,对其进行选定严重事故序列下的IVR-ERVC有效性评价,并对堆内构件设计提出建议。     

Heat Transfer by Slug Flow in Annulus

This paper deals with an analysis of heat transfer by slug flow in an annulus with different heat fluxes at the two wall surfaces. The local Nusselt numbers at each wall surface are calculated upon analyzing the radial distribution of the fluid temperature.

The local Nusselt number varies with the ratios of the radii as well as of the wall heat fluxes. The heat transfer in a circular tube and between two parallel plates are also discussed. As a special case, the present results agree very well with Dwyer's obtained for the heat transfer between two wall surfaces.     

Natural convection heat transfer from a horizontal cylinder in liquid sodium: Part 2: generalized correlation for laminar natural convection heat transfer

Rigorous numerical solution of natural convection heat transfer, from a horizontal cylinder with uniform surface heat flux or with uniform surface temperature, to liquid sodium was derived by solving the fundamental equations for laminar natural convection heat transfer without the boundary layer approximation. It was made clear that the local and average Nusselt numbers experimentally obtained and reported in part 1 of this paper were described well by the numerical solutions for uniform surface heat fluxes, but that those for uniform surface temperatures could not describe the angular distribution of the local Nusselt numbers and about 10% underpredicted the average Nusselt numbers. Generalized correlation for natural convection heat transfer from a horizontal cylinder with a uniform surface heat flux in liquid metals was presented based on the rigorous theoretical values for a wide range of Rayleigh numbers. It was confirmed that the correlation can describe the authors’ and other workers’ experimental data on horizontal cylinders in various kinds of liquid metals for a wide range of Rayleigh numbers. Another correlation for a horizontal cylinder with a uniform surface temperature in liquid metals, which may be applicable for special cases such as natural convection heat transfer in a sodium-to-sodium heat exchanger etc. was also presented based on the rigorous theoretical values for a wide range of Rayleigh numbers. These correlations can also describe the rigorous numerical solutions for non-metallic liquids and gases for the Prandtl numbers up to 10.     

Liquid solidification in laminar tube flow with internal heat sources

The effect of liquid solidification (freezing) on the heat transfer characteristics for laminar flow of a heat-generating fluid in a cooled circular tube is investigated analytically. Steady-state conditions and a uniform wall temperature, which is lower than the liquid freezing temperature, are assumed. The radius of the liquid-solid interface and local Nusselt number are determined as a function of position along the tube for several different values of the wall temperature and internal heat-generating rate. The thickness of the solid-phase shell increases with distance down the tube and approaches to its fully developed value depending upon a single dimensionless freezing parameter which measures the relative rate of external cooling and internal heating. The local Nusselt number, however, first decreases rapidly, attains a minimum and then increases toward its fully developed value, which is identical with 6.     

Natural convection thermo fluid dynamics in a volumetrically heated rectangular pool

During a severe accident the nuclear reactor core may melt and, further, relocate to the lower plenum in the reactor vessel. Should there be no effective cooling mechanism, the core debris may heat up on account of the volumetric decay heat generation to form a molten pool in natural convection. The Simulant Internal Gravitated Material Apparatus Rectangular Pool (SIGMA RP) tests were performed to study high modified Rayleigh number (Ra′) natural convection in a rectangular pool. The test apparatus was 500 mm long, 500 mm high and 160 mm wide. Forty thin cartridge heaters, with a sheath diameter of 4.2 mm and a length of 600 mm, were used to simulate internal heating in the pool. They were uniformly distributed in the rectangular pool so as to supply a maximum of 2.5 kW power to the pool. Ra′ based on the power input was varied from 10⁹ to 10¹⁴. The working fluid Prandtl number (Pr) ranged from 4 to 8 for water, and 0.7 for air. Particular attention was paid to the Pr influence on natural convection heat transfer in the pool. The relation between the Nusselt number (Nu) and Ra′ was determined for different boundary conditions in the rectangular pool. In one case the upper wall was cooled isothermally, while the lower wall was kept adiabatic. In the other case both the upper and lower walls were cooled isothermally. The experimental results indicated that both the upward and downward natural convection heat transfer rates were affected by Pr. The resultant engineering correlations were applied to simulation of a spectrum of loss-of-coolant accidents to determine the reactor vessel failure time.     

Effect of fluid Prandtl number on heat transfer characteristics in internally heated liquid pools with Rayleigh numbers up to 10

This paper presents an analysis of effects of the fluid Prandtl number (Pr) on natural convection heat transfer in volumetrically heated liquid pools. Experimental and computational studies performed in the past are reviewed, with particular emphasis on the analysis of Pr number effects. As a practical exercise, numerical analysis is performed for two-dimensional square, semicircular and elliptical enclosures, and for three-dimensional semicircular and hemispherical cavities, to investigate the physics of the effect of the Pr number on heat transfer in internally heated liquid pools with Rayleigh numbers up to 10¹². It was found that the fluid Prandtl number has a small effect on heat transfer in the convection-dominated regions (near the top surface and side walls) of the enclosures. The decrease of the Pr number leads to the decrease of the top and side wall Nusselt (Nu) numbers. The effects of the Pr number on the Nu number at the bottom surface of the enclosures are found to be significant and they become larger with increasing Rayleigh numbers. Two physical mechanisms, i.e. thermal diffusivity and kinematic viscosity phenomena, have been proposed to explain the fluid Prandtl number effects. Calculational results have been used to quantify the significance and the area of influence for each mechanism. Also, strong dependence on the geometry (curvilinearity) of the downward cooled pool surface has been found.     

不凝性气体对高温锂热管传热特性的影响研究

热管作为一种具有高热导率的传热装置,工作核心在于其内部工作流体的蒸发和冷凝。若热管工作过程中气腔内存在不凝性气体,主流区中蒸气和不凝性气体在对流运动的作用下将一起移动到气-液分界面,不凝性气体的存在阻碍了工作流体在气-液交界面处的正常冷凝。本文基于热阻网络法添加了不凝性气体区域传热模型,研究了不凝性气体对高温锂热管稳态传热特性的影响。结果表明,热管达到稳态时不凝性气体的存在缩短了热管的有效传热长度,破坏了热管的等温性和良好的传热效率。此外随着不凝性气体体积份额的增大,不凝性气体区域温度降低幅度越大;随着热管蒸发段输入功率的增大,热管正常工作区域整体温度越高,相同质量的不凝性气体占据的体积份额越小,热管壁面温度出现明显温度梯度降低的位置随着功率升高而向下游移动。     

Experimental research on heat transfer to liquid sodium and its incipient boiling wall superheat in an annulus

Liquid sodium is mainly used as a cooling fluid in the liquid metal fast breeder reactor （LMFBR）, whose heat transfer, whether convective heat transfer or boiling heat transfer, is different from that of water. So it is important for both normal and accidental operations of LMFBR to perform experimental research on heat transfer to liquid sodium and its boiling heat transfer. This study deals with heat transfer with high temperature （300-700℃） and low Pe number （20-70） and heat transfer with low temperature （250-270℃） and high Pe number （125-860）, and its incipient boiling wall superheat in an annulus. Research on heat transfer involves theoretical research and experiments on heat transfer to liquid sodium. It also focuses on the theoretical analysis and experimental research on its incipient boiling wall superheat at positive pressure in an annulus. Semiempirical correlations were obtained and they were well coincident with the experimental data.     

A numerical investigation of natural convection heat transfer in horizontal spent-fuel storage cask

Natural convection heat transfer in a horizontally placed dry spent-fuel storage cask is numerical investigated. The commercial computational fluid dynamics (CFD) code, -3.2 is used and the laminar and turbulent model are employed. The numerical predictions obtained are compared with the experimental data reported by Nishimura et al. [J. Nucl. Sci. Technol. 33 (1996) 821]. The computational results corresponding to laminar model agree well with the experimental data, but the calculated results of turbulent model are higher. The velocity pattern and the isotherms are drawn. With the increasing of Rayleigh number, the heat transfer in the cask changes from conduction dominant mode to convection dominant mode. In the condition of Ra_m=1.3×10⁹, turbulent model prevails. The convective heat transfer is so strong that almost all temperature changes take place in the region near the wall of the cask. The Rayleigh number Ra_m and the Nusselt number Nu_m characterized by maximum temperature difference are defined to depict the heat transfer characteristics. It is found laminar and turbulent models predict the same trend but different value. The flow patterns in the cask can be divided to three regimes. In these three regimes, modified Nusselt numbers are proportional to the 0.7, 0.25 and 0 power of the modified Rayleigh number, respectively.