高温球床壁面区域有效导热系数模型优化

有效导热系数用来表征高温气冷球床堆堆芯综合传热能力,提高球床有效导热系数的预测精度对于高温气冷球床堆的热工设计和安全分析十分重要。为了优化球床壁面区域有效导热系数模型,本文针对无序石墨球床有效导热系数开展数值研究,分析了无序堆积球床主体区域、近壁面区域以及壁面区域有效导热系数的分布特性。结果表明：壁面区域有效导热系数相对于主体区域和近壁面区域显著降低,其平均降幅约为22%。因此引入了修正系数C_w对ZBS模型在壁面区域进行优化,对于球床主体区域及近壁面区域修正系数C_w=1,对于壁面区域,修正系数C_w=0.78。通过与前期无序球床实验数据和南非HTTU实验数据的对比,验证了优化后的ZBS模型能较好地预测球床壁面区域有效导热系数。     

高温气冷堆球床接触导热计算方法

接触导热是低温条件下高温堆球床堆芯传热的主要方式,接触导热的计算精度决定了低温条件下高温气冷堆球床传热计算的精度。本文建立了类似热离散单元法的球床接触导热的计算模型,通过计算流体力学方法进行模型中两个球之间理想接触的导热量计算,给出了所编写的大规模随机堆积球床接触导热计算程序的详细步骤。通过与计算流体力学方法对球床局部堆积结构接触导热计算结果的比较,验证了该计算程序的准确性。该方法与球床局部结构计算流体力学方法精度接近,并可用于颗粒尺度大规模球床计算。     

高温气冷堆球床有效导热系数的计算模型及其在SANA基准试验分析中的应用

用THERMIX程序计算了石墨球床的温度分布。研究了高温气冷堆球床内部热量传递机制,给出了三种有效导热系数的分析方法和计算模型。以国际原子能机构(IAEA)关于“高温气冷堆在事故工况下的热传输和余热载出”问题的合作研究计划(Coordinated Research Program简称CRP)的SANA基准试验为基础,计算了球床内的温度分布和自然对流对传热的影响。计算结果与实验测量结果作了比较,证实了THERMIX程序和有效导热系数的准确性。     

球床式高温气冷堆球流及球床辐射的理论与实验研究进展

球床堆芯的球流及等效导热系数是直接影响球床式高温气冷堆设计、运行和安全的重要依据,具有重要的意义。清华大学核能与新能源技术研究院近年对球流和球床等效导热系数进行了实验测量、理论研究和数值模拟,全面深入地揭示了球流规律、球流纺及径向内扩散规律、球床几何优化、物性参数影响、球流流态表征及刻画、球床等效导热系数建模等。本文对此进行了回顾总结,并指出了下一步的研究方向。     

堆内辐照氚增殖剂球床有效热导率分析

氘-氚聚变反应堆中,固态氚增殖剂包层能不断为聚变反应提供氚核素,是实现聚变反应堆商用的关键技术之一。由锂陶瓷小球堆积形成的球床形式的固态氚增殖剂包层具有比表面积大、产氚效率高等优点,是我国重点发展的氚增殖剂包层形式。氚增殖剂球床须能支撑在堆内辐照时的高温环境,这就要求氚增殖剂球床有较好的导热特性。球床的有效热导率在球床设计和辐照过程中的安全分析十分重要,因此在中国先进研究堆(CARR)开展了氚增殖剂球床在堆内辐照环境下的有效热导率测量实验。根据MCNP计算得出的球床发热功率,结合实验测量的球床温度分布反推得到氚增殖剂球床的有效热导率,并与广泛应用于球床有效热导率计算的改进型ZBS模型计算结果以及堆外实验结果进行对比分析,理论值与实验值能较好吻合。     

堆内辐照氚增殖剂球床有效热导率分析

氘-氚聚变反应堆中，固态氚增殖剂包层能不断为聚变反应提供氚核素，是实现聚变反应堆商用的关键技术之一。由锂陶瓷小球堆积形成的球床形式的固态氚增殖剂包层具有比表面积大、产氚效率高等优点，是我国重点发展的氚增殖剂包层形式。氚增殖剂球床须能支撑在堆内辐照时的高温环境，这就要求氚增殖剂球床有较好的导热特性。球床的有效热导率在球床设计和辐照过程中的安全分析十分重要，因此在中国先进研究堆（CARR）开展了氚增殖剂球床在堆内辐照环境下的有效热导率测量实验。根据MCNP计算得出的球床发热功率，结合实验测量的球床温度分布反推得到氚增殖剂球床的有效热导率，并与广泛应用于球床有效热导率计算的改进型ZBS模型计算结果以及堆外实验结果进行对比分析，理论值与实验值能较好吻合。     

球床式高温气冷堆球流及球床辐射的理论与实验研究进展

球床堆芯的球流及等效导热系数是直接影响球床式高温气冷堆设计、运行和安全的重要依据，具有重要的意义。清华大学核能与新能源技术研究院近年对球流和球床等效导热系数进行了实验测量、理论研究和数值模拟，全面深入地揭示了球流规律、球流纺及径向内扩散规律、球床几何优化、物性参数影响、球流流态表征及刻画、球床等效导热系数建模等。本文对此进行了回顾总结，并指出了下一步的研究方向。     

高温堆球床等效导热系数实验温度测量系统设计

为解决清华大学核能与新能源技术研究院研制的高温堆示范电站(HTR-PM)堆芯全尺寸球床等效导热系数测量实验装置中温度场的稳定、准确测量问题,本文设计并构建了其测温系统的软硬件系统。该装置中的温度测量涉及高温堆安全分析的全部温度范围(0~1 600℃),并处于石墨球床环境中。根据实验装置的总体构成和测点布置需求,选择了特殊工艺制作的非标准钨铼热电偶作为前端传感器,搭建了基于NI PXI平台的数据采集硬件系统,采用生产者/消费者模式和队列模式结合的方式编写了软件系统。用前期缩小比例的验证装置对材料、结构、设备等关键设计进行先期验证,结果表明,设计的温度测量系统可长期稳定、可靠满足实验的测温需求,为球床等效导热系数实验研究的开展、提升高温气冷堆经济性和安全性奠定了基础。     

球床式高温气冷堆MOX燃料循环优化

与压水堆相比,球床式高温气冷堆能在堆芯结构不做明显改变的情况下采用全堆芯装载混合氧化物（MOX）燃料元件。基于250 MW球床模块式高温气冷堆堆芯结构,设计了4种球床式高温气冷堆下MOX燃料循环方式,包括铀钚混合的燃料球和独立的钚球与铀球混合装载的等效方式,采用高温气冷堆设计程序VSOP进行分析,比较了初装堆的有效增殖因数、燃料元件在堆芯内滞留时间、卸料燃耗、温度系数等主要物理特性。结果表明：采用纯铀和纯钚两种分离燃料球且铀燃料球循环时间更长的方案,平均卸料燃耗较高,总体性能较其他循环方式优越。     

350MW环型球床高温气冷堆失冷失压事故下的热工特性研究

由于环型球床高温气冷堆特殊的堆芯结构，使其在失冷失压事故下堆内最高温度能够明显低于模块式球床高温气冷堆在相同事故下堆内最高温度。当堆芯热功率有较大幅度提高时，环型堆芯仍然能够凭借自身传热机能将衰变热量及时排出，满足失冷失压事故下燃料最高温度限制。这不仅增大了反应堆的安全性能，同时也能够有效地增加反应堆单堆功率，使环型球床高温气冷堆在经济上更具竞争力。本文研究环型球床高温气冷堆在提高功率水平时，反应堆在失冷失压事故下堆内的热工特性，并综合分析了几个重要的结构尺寸热工参数对失冷失压事故下燃料最高温度的影响。     

Experimental measurement of effective thermal conductivity of packed lithium-titanate pebble bed

Lithium titanate is a promising solid breeder material for the fusion reactor blanket. Packed lithium titanate pebble bed is considered for the blanket. The thermal energy; that will be produced in the bed during breeding and the radiated heat from the reactor core absorbed must be removed. So, the experimental thermal property data are important for the blanket design. In past, a significant amount of works were conducted to determine the effective thermal conductivity of packed solid breeder pebble bed, in helium atmosphere, but no flow of gas was considered. With increase in gas flow rate, effective thermal conductivity of pebble bed increases. Particle size and void fraction also affect the thermal properties of the bed significantly. An experimental facility with external heat source was designed and installed. Experiments were carried out with lithium-titanate pebbles of different sizes at variable gas flow rates and at different bed wall temperature. It was observed that effective thermal conductivity of pebble bed is a function of particle Reynolds number and temperature. From the experimental data two correlations have been developed to estimate the effective thermal conductivity of packed lithium-titanate pebble bed for different particle Reynolds number and at different temperatures. The experimental details and results are discussed in this paper.     

Effective Thermal Property Estimation of Unitary Pebble Beds Based on a CFD-DEM Coupled Method for a Fusion Blanket

Lithium ceramic pebble beds have been considered in the solid blanket design for fusion reactors.To characterize the fusion solid blanket thermal performance,studies of the effective thermal properties,i.e.the effective thermal conductivity and heat transfer coefficient,of the pebble beds are necessary.In this paper,a 3D computational fluid dynamics discrete element method(CFD-DEM) coupled numerical model was proposed to simulate heat transfer and thereby estimate the effective thermal properties.The DEM was applied to produce a geometric topology of a prototypical blanket pebble bed by directly simulating the contact state of each individual particle using basic interaction laws.Based on this geometric topology,a CFD model was built to analyze the temperature distribution and obtain the effective thermal properties.The current numerical model was shown to be in good agreement with the existing experimental data for effective thermal conductivity available in the literature.     

A Measurement Platform Scheme and Data Post-processing Method for Thermal Conductivity of Li<Subscript>4</Subscript>SiO<Subscript>4</Subscript> Pebble Bed

The effective thermal conductivity of tritium breeder pebble bed is an important thermal parameter and must be known for the thermo-mechanical design of solid tritium breeder blankets. In order to obtain the parameter, experimental measurement is an effective method. A measurement platform was designed by University of Science and Technology of China for CFETR solid blanket scheme to measure the immediate thermal conductivity data and study the effect of pebble bed temperature, the purge gas pressure and pebble deformation on the thermal conductivity of pebble bed. Measurements were performed based on about 1 mm diameter Li₄SiO₄ pebbles in the temperature range between 100 and 800 °C, with purge gas pressure ranging from 0.1 to 0.3 MPa. This paper described a measurement platform scheme by thermal probe method. On the other hand, for the sake of increasing the precision of thermal conductivity data transformed from temperature data, some improvements for the data post-processing using Monte Carlo inversion method were made in this paper too.     

高温气冷堆热工分析模型改进与堆芯温度场分析

更准确地模拟球床式高温气冷堆堆芯温度分布,是反应堆安全分析尤其是超高温运行研究中的关键问题之一。由于堆芯球流运动具有不确定性,石墨块和碳砖等结构材料采用散体布置,堆内冷却剂流道复杂,对热工水力准确模拟造成困难,可进一步优化。本文结合HTR 10的结构特点和流道特征,简要分析了堆芯传热过程,说明了在热工模拟中准确划分结构和流道对获取更精确的堆芯温度分布的重要意义。详细梳理了冷却剂流动路径,改进了在THERMIX程序下建立的HTR 10原有热工分析模型,更合理地模拟了堆芯冷却剂漏流行为,使得模型对堆芯冷却剂流动和传热过程的描述更准确。与试验数据对比,改进后的模型对堆芯外围系统的温度分布模拟准确性显著提升。计算结果表明,反应堆在额定设计工况下满功率稳态运行时,燃料和反射层最高温度均未超过材料的耐热限值。     

真空石墨加热器温度场数值模拟与分析

石墨加热器是测量球床堆芯等效导热系数实验的关键部件,加热器温度场对系统安全及数据准确性有重要影响。本文基于Fluent计算平台,分别采用DTRM模型、P1模型、ROSSELAND模型、DO模型对真空保护环境下的石墨加热器温度场进行数值模拟,确定适合真空保护石墨加热器温度场的计算方法并讨论石墨导热系数、表面发射率对温度场分布的影响。比较分析表明：DO模型计算得到的温度分布较为接近真实情况,导热系数小于35W/(m•K)时,最高温度对其敏感;导热系数大于35W/(m•K)时,其对加热体最高温度影响较小,最高温度较为稳定。     

氚增殖剂球床组件堆内辐照物理热工计算分析

为验证在中国先进研究堆(CARR)内进行国际热核聚变实验堆(ITER)氚增殖包层模块(TBM)辐照实验的可行性和安全性,进行了氚增殖剂球床组件堆内辐照物理及热工计算分析。氚增殖剂包层模块主要是固态氚增殖剂陶瓷球床。本文采用Monte Carlo粒子输运模拟程序对氚增殖剂球床进行堆内建模,计算球床的中子注量率、能量沉积和产额,得到不同功率下球床的中子注量率、发热功率和产氚速率以及球床组件引入反应堆的反应性。根据物理计算得到的组件各部件发热情况建立热工计算一维模型,通过更改反应堆功率得到满足实验要求的工况并采用三维程序进行验证。物理与热工计算分析的结果表明,在反应堆运行功率为20 MW的工况下球床组件各部件的温度均不超过限值。     

Void fraction and effective thermal conductivity of binary particulate bed

In many industrial processes, solid particles of different sizes are mixed in different volume or mass fractions for various applications, primarily to reduce void volume or to increase the density of the mixture. A few of these processes include; production of high density ceramics, mortar, concrete, graphite, bricks and carbon blocks. Experiments were carried out with alumina and lithium titanate pebbles (size ≥ 1 mm) and particles (size < 1 mm) of different sizes and volume fractions in cylindrical and rectangular vessels to study the variation of void fraction with volume fraction of component pebbles and with large pebble to small pebble or pebble to particle size ratio. It was observed that the variation of void fraction with volume fraction of smaller pebbles or particles is ‘V-shaped’. Thus there exists a minimum void fraction and two different volume fractions of smaller pebbles or particles which can give same void fraction. The effect of void fraction on the effective thermal conductivity of binary bed of lithium titanate and alumina pebbles and particles of different sizes and volume fractions was investigated. From the experimental results it was found that the binary particulate bed has higher effective thermal conductivity that that of a unary particulate bed. Effective thermal conductivity of binary particulate bed is the maximum when its void fraction is the minimum. The binary particulate bed with less volume fraction of small particles has higher conductivity than that of the binary bed of higher volume fraction of small particles and having same void fraction. This is due to the fact that with increase in volume fraction of small pebbles or particles, the number of small-to-small and large-to-small pebbles and or particles contact point increases resulting in higher resistance to heat transfers. The experimental details and results are discussed in this paper.