3D Numerical Simulation on Bypass Flow in Pebble-Bed High-Temperature Gas-Cooled Reactor

针对球床式高温气冷堆中散体布置的石墨砖等结构带来的旁流问题,数值模拟了高温气冷堆满功率稳态运行时卸料管、控制棒通道及窄缝中的旁流特征。通过结合华能集团自主研发的HN-750型球床式高温气冷堆的结构特点和流道特征,建立了包含窄缝、顶反射层、堆芯球床、底反射层及底部球腔的反应堆三维几何模型和近真实物理数学模型,生成了网格数为2.6亿的混合网格。结果表明,总旁流占总流量比例为29.25%,窄缝旁流占总流量比例为24.43%,并且呈现出回流特性,卸料管旁流占比3.87%,控制棒通道旁流占比0.95%。该研究考虑了非轴对称的进出口结构,是对现有的球床式高温气冷堆二维轴对称模型的补充和提升;该研究针对球床式高温气冷堆的大规模三维数值计算,为球床式高温气冷堆的热工水力优化和安全分析提供了丰富的数据支撑。

Experiments on two-phase flow in hydraulic jump on pebbled rough bed:Part 1–Turbulence properties and particle chord time and length

This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time and length and their probability density functions(PDFs),was investigated.The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length,whereas further downstream,the decay rate was higher.In addition,the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles.Triple decomposition analysis(TDA)was performed to determine the contributions of slow and fast turbulent components.The TDA results indicated that,regardless of bed type and inflow conditions,the sum of the band-pass(T'_(u))and high-pass(T″_(u))filtered turbulence intensities was equal to the turbulence intensity of the raw signal data(T_(u)).T″_(u) highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number.Additional TDA results were presented in terms of the interfacial velocity,auto-and cross-correlation time scales,and longitudinal advection length scale,with the effects of low-and high-frequency signal components on each highlighted parameter.The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream.The second part of this research focused on the basic properties of particle grouping and clustering.

Experiments on two-phase flow in hydraulic jump on pebbled rough bed:Part 2–Bubble clustering

A survey on bubble clustering in air–water flow processes may provide significant insights into turbulent two-phaseflow.These processes have been studied in plunging jets,dropshafts,and hydraulic jumps on a smooth bed.As a first attempt,this study examined the bubble clustering process in hydraulic jumps on a pebbled rough bed using experimental data for 1.70<Fr_(1)<2.84(with Fr_(1) denoting the inflow Froude number).The basic properties of particle grouping and clustering,including the number of clusters,the dimensionless number of clusters per second,the percentage of clustered bubbles,and the number of bubbles per cluster,were analyzed based on two criteria.For both criteria,the maximum cluster count rate was greater on the rough bed than on the smooth bed,suggesting greater interactions between turbulence and bubbly flow on the rough bed.The results were consistent with the longitudinal distribution of the interfacial velocity using one of the criteria.In addition,the clustering process was analyzed using a different approach:the interparticle arrival time of bubbles.The comparison showed that the bubbly flow structure had a greater density of bubbles per unitflux on the rough bed than on the smooth bed.Bed roughness was the dominant parameter close to the jump toe.Further downstream,Fr_(1) predominated.Thus,the rate of bubble density decreased more rapidly for the hydraulic jump with the lowest Fr_(1).

纳米级PEBBLE传感器研究进展

介绍了纳米量级 PEBBLE 传感器的特点、制备方法、当前的应用及发展趋势,重点阐述了基于对细胞内氧成分探测的比例参量 PEBBLE 传感器。

Current Status of the Fabrication of Li_4SiO_4and Beryllium Pebbles for CN HCCB TBM in SWIP

Tritium breeder and neutron multiplier as functional materials play an important role not only in ITER test blanket module （TBM） but also in fusion reactor. The paper describes the status of the fabrication of the two materials in Southwestern Institute of Physics （SWIP）. Li4SiO4 pebbles were fabricated by melt-spraying method. Most of the pebbles with the diazneter of 1.0 mm are well spherically shaped. The properties of the pebbles have been investigated. The results show that the pebbles produced by this method have a high density of 93% TD （theoretical density）. It was also found that the open/closed porosity will be decreased after thermal treatment, but the average crush load will be increased to 7 N. The rotating electrode process （REP） has been adopted to produce beryllium pebble for impurity control and mass production. The pebbles with the diameter of 1.0 mm were produced by REP. The beryllium pebbles produced by REP look almost perfectly spherical with a very smooth surface and a high density of 98% TD. The test results indicate that REP method has excellent prospects for the fabrication of beryllium pebbles and the attractiveness of their properties.

Study of heat transfer by using DEM–CFD method in a randomly packed pebble-bed reactor

The pebble-bed reactor is one of the most promising designs for the nuclear energy industry. In this paper,a discrete element method-computational fluid dynamics(DEM-CFD) approach that includes thermal conduction, radiation, and natural convection mechanisms was proposed to simulate the thermal-fluid phenomena after the failure of forced circulation cooling system in a pebble-bed core. The whole large-scale packed bed was created using the DEM technique, and the calculated radial porosity of the bed was validated with empirical correlations reported by researchers. To reduce computational costs, a segment of the bed was extracted, which served as a good representative of the large-scale packed bed for CFD calculation. The temperature distributions simulated with two different fluids in this DEM-CFD approach were in good agreement with SANA experimental data. The influence of the natural convection mechanism on heat transfer must be taken into account for coolants with strong convective capacity. The proposed DEM-CFD methodology offers a computationally efficient and widely applied method for understanding the heat transfer process in a pebble-bed core. The method can also be easily extended to assess the passive safety features of newly designed fluoride-salt-cooled pebble-bed reactors.

Thermal-Hydraulic System Study of the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) for ITER Using System Code RELAP5

The HCPB concept has been a European DEMO reference concept for nearly one decade. Detailed thermal-hydraulic study on the control behavior of the whole system is one of the important parts of this development. The thermal-hydraulic effect of the TBM-combined cooling circuit during a cyclic operation in ITER has been studied using the system code RELAP5. The RELAP5 is based on an one-dimensional, transient two-fluid model for the flow of a two-phase steam-water mixture that can contain noncondensable components like Helium. The RELAP5models are modified to take the cyclic operation of the circulator, heat, exchanger, bypass, valves etc in to account. A sequence of operational phases is investigated, starting from the cold state through the heating phase that brings the system to a stand-by condition, followed by typical power cycles applied in ITER. The results show that the implemented control mechanisms keep the inlet temperature to the TBM and the total mass flow rate at the required values through all phases.

美国佛罗里达pebble磷矿浮选流程试验

本文对美国佛罗里达pebble磷矿进行了浮选流程试验,试验采用了3种流程,即硅浮选—镁浮选流程,镁浮选—硅浮选流程和镁浮选—脱泥—硅浮选流程。试验结果表明:镁浮选—脱泥—硅浮选流程得到的精矿不但质量较好,而且有较高的P2O5回收率,其综合精矿P2O5品位为30.45%,MgO质量分数为0.98%,P2O5回收率为80.13%。镁浮选—脱泥—硅浮选流程具有流程及药剂制度简单,药剂用量少,试验指标高等优点,是美国佛罗里达pebble磷矿综合利用的有效方法。

Experimental and Numerical Analysis of High-Strength Concrete Beams Including Steel Fibers and Large-Particle Recycled Coarse Aggregates

In order to study the performances of high-strength concrete beams including steel fibers and large-particle recycled aggregates,four different beams have been designed,tested experimentally and simulated numerically.As varying parameters,the replacement rates of recycled coarse aggregates and CFRP(carbon fiber reinforced polymer)sheets have been considered.The failure mode of these beams,related load deflection curves,stirrup strain and shear capacity have been determined through monotonic loading tests.The simulations have been conducted using the ABAQUS finite element software.The results show that the shear failure mode of recycled concrete beams is similar to that of ordinary concrete beams.The shear carrying capacity of high-strength concrete beams including steel fibers and large-particle recycled coarse aggregates grows with an increase in the replacement rate of recycled coarse aggregates.Reinforcement with CFRP sheets can significantly improve the beam’s shear carrying capacity and overall resistance to deformation.

Evolution of the Late Cretaceous Yongfeng-Chongren Basin in Jiangxi Province,southeast China: insights from sedimentary facies analysis and pebble counting

The Gan-Hang Belt in Southeast China is characterized by several igneous and siliciclastic basins associated with crustal extension during Late Mesozoic.The sedimentary evolution of the red basins is still poorly understood.In this study,sedimentary facies analysis and pebble counting were performed on outcrop sections of the Late Cretaceous Guifeng Group in the Yongfeng-Chongren Basin in central Jiangxi Province.Thirty-five conglomerate outcrops were chosen to measure pebble lithology,size,roundness,weathering degree and preferred orientation.Results show that gravels are mostly fine to coarse pebbles and comprise dominantly quartzites,metamorphic rocks,granitoids and sandstones.Rose diagrams based on imbricated pebbles indicate variable paleocurrent directions.Combining with typical sedimentary structures and vertical successions,we suggest that the Guifeng Group were deposited in alluvial fan,river and playa lake depositional systems.The proposed depositional model indicates that the Hekou Formation represents the start-up stage of the faulted basin,accompanied by sedimentation in alluvial fan and braided river environments.Then this basin turned into a stable expansion stage during the deposition of the Tangbian Formation.Except for minor coarse sediments at the basin margin,the other area iscovered with fine-grained sediments of lake and river environments.The Lianhe Formation,however,is once again featured by conglomerates,suggesting a probable tectonic event.Therefore,the study region possibly suffered two tectonic events represented by the conglomerates of the Hekou and Lianhe formations in the context of the crustal extension in Southeast China.

Study on neutronics design of ordered-pebble-bed fluoride-salt- cooled high-temperature experimental reactor

This paper presents a neutronics design of a 10 MW ordered-pebble-bed fluoride-salt-cooled high-temperature experimental reactor. Through delicate layout, a core with ordered arranged pebble bed can be formed,which can keep core stability and meet the space requirements for thermal hydraulics and neutronics measurements.Overall, objectives of the core include inherent safety and sufficient excess reactivity providing 120 effective full power days for experiments. Considering the requirements above, the reactive control system is designed to consist of 16 control rods distributed in the graphite reflector. Combining the large control rods worth about 18000–20000 pcm, molten salt drain supplementary means(-6980 to -3651 pcm) and negative temperature coefficient(-6.32 to -3.80 pcm/K) feedback of the whole core, the reactor can realize sufficient shutdown margin and safety under steady state. Besides, some main physical properties, such as reactivity control, neutron spectrum and flux, power density distribution, and reactivity coefficient,have been calculated and analyzed in this study. In addition, some special problems in molten salt coolant are also considered, including ~6Li depletion and tritium production.

Modeling of Fuel Elements Cycling System in Pebble Bed Reactor Based on Timed Places Control Petri Nets

Pebble bed reactors use cycling scheme of spherical fuel elements relying on fuel elements cycling system (FECS). The structure and control logic of FECS are very complex. Each control link has strict requirements on time and sequence. This increases the difficulties of description and analysis. In this paper, timed places control Petri nets (TPCPN) is applied for the modeling of FECS. On this basis the simulation of two important processes, namely uploading fuel elements into the core for the first time and emptying the core is finished by simulation software Arena. The results show that as TPCPN is able to describe different kinds of logic relationship and has time properties and control properties, it’s very suitable for the modeling and analysis of FECS.

Development of an innovative detection system for pebble bed kinematic studies

Pebble bed reactors enable the circulation of pebble fuel elements when the reactors are in operation.This unique design helps to optimize the burnup and power distribution, reduces the excessive reactivity of the reactor,and provides a mean to identify and segregate damaged fuel elements during operation. The movement of the pebbles in the core, or the kinematics of the pebble bed,significantly affect the above features and is not fully understood. We designed and built a detection system that can measure 3-axis acceleration, 3-axis angular velocity,3-axis rotation angles, and vibration and temperature of multiple pebbles anywhere in the pebble bed. This system uses pebble-shaped detectors that can flow with other pebbles and does not disturb the pebble movement. We used new technologies to enable instant response, precise measurement, and simultaneous collection of data from a large number of detectors. Our tests show that the detection system has a negligible zero drift and the accuracy is better than the designed value. The residence time of the pebbles in a moving pebble bed was also measured using the system.

Intracolonic multiple pebbles in young adults:Radiographic imaging and conventional approach to a case

Most of the foreign bodies detected in adult gastroin- testinal systems are accidentally swallowed pins. In this study, we presented a case with intracolonic multiple pebbles. A 20-year-old man was admitted to emergency surgery policlinic for abdominal pain for 2 d without any alleviation or aggravation. His upright plain abdominal radiographic imaging revealed about 30-40 overt dense opacities in lumen of colonic segments, with oval and well shaped contours, each approximately 1 cm x 1 cm in size. The multiplanar reconstructions and three- dimensional images combined with sectional screening showed that all pebbles had passed completely into the colon and no foreign bodies had remained in the ileal segments. On psychiatric assessment, he was found to have immature personality features, difficulty in over- coming stressors and adaptation disorder. He recovered by conservative management and radiographic monitor- ing applied during his follow-up. Thus, it can be con- cluded that, in differential diagnosis of abdominal pain in adult ages, though less frequently seen than in children, gastrointestinal system foreign bodies should always be kept in mind and it should be considered that ingestion of pebbles may be one of the factors contributing to ab- dominal pain particularly in young adults with psychiatric problems. In such cases suspected of having foreign bodies which cannot be detected by plain f ilms, abdominal tomography can be an alternative for diagnostic imaging.

成都地区卵石地层深基坑开挖的土压力计算方法

[目的]现有土压力理论计算方法未考虑卵石地层孔隙度大、结构松散等离散性特点,计算结果与实际土压力有所偏差,需要研究适用于成都地区卵石地层的土压力计算方法。[方法]以成都轨道交通7号线为依托,分析卵石地层深基坑土压力与朗肯土压力理论值的差别,并建立深基坑开挖土压力计算方法。采用离散元数值模拟和数据统计分析,获取围护结构平动、围护结构绕墙顶转动和围护结构绕墙底转动三种基本变位模式下静止土压力、被动土压力和主动土压力的分布特征。与朗肯土压力理论计算结果进行比较,得到不同变位模式下三种土压力的修正系数,并建立深基坑土压力修正计算方法。进一步与现场实测数据比较,对比验证所提出的土压力计算方法。[结果及结论]主动土压力和被动土压力分布形式具有强烈的非线性,可采用双折线进行描述,交点分别位于埋深8 m和9 m处。静止土压力修正系数分布在0.91~0.96之间,在使用时不需要修正;主动土压力修正系数分布在0.33~0.78之间,被动土压力修正系数分布在0.52~0.91之间,在使用时应予以修正。所提出的卵石地层深基坑土压力计算结果与现场实测结果吻合较好,可为类似轨道交通工程提供参考。

不均匀卵石持力层桩端后注浆效果试验研究

我国东南沿海尤其是温州地区广泛存在上覆深厚软土下覆不均匀卵石的地层。该区域的钻孔灌注桩常采用后注浆技术改善其承载性能。为了评价后注浆技术对这类地层中灌注桩承载力改善效果,开展了相应的模型试验,对比了不同注浆量对桩承载力的影响程度;并结合扫描电镜(scanning electron microscope,简称SEM)试验分析了浆液分布特点,探讨了浆液在卵石层中的扩散范围,研究了浆液扩散范围与桩承载力之间的关系。结果表明:浆液能够有效地填充桩端卵石层,注浆量的增加使得填充范围扩大,填充范围为3~4倍桩径时,桩的承载力改善最显著。在不均匀卵石持力层中存在一个最优注浆量,最优归一化注浆量约为2.8,若超过该最优注浆量归一化值,桩的承载力不再显著提高。单桩模型试验确定的最优注浆量与刘金砺公式[1]的预测结果接近。扫描电镜技术有助于评价桩的后注浆技术在上覆深厚软土下覆不均匀卵石的土层中的效果。

氦冷固态包层氚增殖球床气体和粉末流动特性的数值研究

基于计算流体力学和离散元耦合分析,研究了氦冷固态增殖包层球床中吹扫氦气的速度分布和破碎的正硅酸锂粉末速度随时间的变化及粉末数量随氦气入口流速变化。模拟结果表明,在吹扫氦气流动方向上,用入口流速归一化的氦气速度分布与入口流速无关,在靠近球床边缘速度变化较大,在球床中部速度变化较小;用入口流速归一化的粉末平均速度与入口流速关系不大,会随吹扫时间逐渐趋于稳定;对小粒径粉末,吹扫气体流速越大,越容易被吹出球床,对大粒径粉末,因其本身体积过大,易在球床中形成堵塞。

圈的中间图pebbling数和Graham猜想

图G的一个pebbling移动是从一个顶点移走2个pebble,而把其中的1个pebble移到与其相邻的一个顶点上.图G的pebbling数f(G)是最小的正整数n,使得不论n个pebble如何放置在G的顶点上,总可以通过一系列的pebbling移动,把1个pebble移到图G的任意一个顶点上.图G的中间图M(G)就是在G的每一条边上插入一个新点,再把G上相邻边上的新点用一条边连接起来的图.对于任意两个连通图G和H,Graham猜测f(G×H)≤f(G)f(H).首先研究了圈的中间图的pebbling数,然后讨论了一些圈的中间图满足Graham猜想.

广义友谊图乘积上的Graham pebbling猜想

连通图G的pebbling数f(G)是最小的正整数n,使得不管n个pebble如何放置在G的顶点上,总可以通过一系列的pebbling移动把一个pebble移到图G的任意一个顶点上.Graham猜测对于任意的连通图G和H有f(G×H)≤f(G)f(H).文中证明了当H为友谊图或广义友谊图,G是一个具有2-pebbling性质的图时,Graham猜想成立.作为一个推论,文中也证明了当G和H是友谊图或广义友谊图时,Graham猜想成立.

几类二部图的pebbling数

Chung定义了图G上的一个pebbling移动是从一个顶点移走两个pebble而把其中的一个移到与其相邻的一个顶点上.连通图G的pebbling数f(G)是最小的正整数n,使得不管n个pebble如何放置在G的顶点上,总可以通过一系列的pebbling移动把一个pebble移到G的任意一个顶点上.Graham猜测对于任意的连通图G和H有f(G×H)≤f(G)f(H).作者们验证了三类二部图的2-pebbling性质以及当H为此类二部图,G为一个2-pebbling性质的图时,Graham猜想成立.