密集颗粒流动的连续性方法应用研究

颗粒流动广泛存在于自然现象和工程应用中,无论是山体坍塌还是工程上球床模块式高温气冷堆和中国科学院近代物理研究所提出的新型流态固体颗粒靶概念。本文基于适用于处理大变形问题的物质点法(MPM),采用μ(I)流变模型,实现了用连续性方法模拟密集颗粒流动的计算框架,并模拟了颗粒坍塌实验和漏斗流动现象,数值模拟结果与实验结果、DEM计算结果均吻合较好。本文采用的连续性本构和MPM能有效模拟密集颗粒流动。可在本文探究的连续性方法模拟密集颗粒流动的框架基础上,完善边界条件和本构模型,为用连续性方法处理大量颗粒的工程问题提供借鉴。     

基于DEM的重金属颗粒流靶区输运过程研究

基于固体和液体散裂靶,近期国内外研究学者提出了一种新概念重金属颗粒流散裂靶。加速器驱动次临界系统(ADS)中重金属散裂靶在高能质子轰击作用下,出现能量沉积现象,而这些热量必须进行有效冷却以保证ADS的安全性。本文针对这种新概念颗粒流靶对靶区产生的高额热量的导出效果进行了模拟分析。首先采用蒙特卡罗程序计算450 Me V质子束轰击钨靶后能量沉积的空间分布,并将此作为颗粒流的体热源输入,基于计算流体力学-离散单元法(CFD-DEM)耦合方法对ADS靶区两种不同直径颗粒流的输运过程进行了模拟研究。结果表明,随颗粒直径的减小,靶区内温度分布更为均匀,颗粒流的流动特性更接近流体,颗粒导热性能增强;颗粒流靶中热应力可局限在单个颗粒内部而承受更高的能量沉积,具有更高的安全限值以及更广阔的应用前景。     

颗粒流散裂靶缩比模型流态实验研究

散裂靶是加速器驱动次临界系统（ADS）的重要组成部分,颗粒流散裂靶是最新提出并经理论计算的一种高功率散裂靶,研究其颗粒流的流动特性对散裂靶的设计优化有重要意义。本文以螺旋提升机为颗粒流驱动装置,搭建一套颗粒流循环回路系统,研究了倾斜段管道的倾斜角度对三维颗粒流从堵塞流向密集流转变的影响。研究发现,随着螺旋提升机提升频率的增加（即颗粒流量的增加）,在散裂靶靶区存在颗粒稀疏流-密集流转变,在靶区附近能形成稳定的密集流。     

基于FOCUS程序的ADS颗粒流靶熔化事故分析

针对ADS颗粒流靶熔化事故,采用基于移动粒子半隐式（MPS）方法开发的FOCUS程序模拟了颗粒靶在靶区出口堵塞时的流动、传热过程和熔融物的迁徙过程。结果表明,颗粒靶尺寸越小,整个系统的换热能力越强,颗粒熔化的速率越快。在颗粒的传热方式中,颗粒接触导热的作用最为显著,是颗粒间主要的换热过程。     

3D Simulation of Solid-Melt Mixture Flow with Melt Solidification Using a Finite Volume Particle Method

Relocation and freezing of molten core materials mixed with solid phases are among the important thermal-hydraulic phenomena in core disruptive accidents of a liquid-metal-cooled reactor (LMR). To simulate such behavior of molten metal mixed with solid particles flowing onto cold structures, a computational framework was investigated using two moving particle methods, namely, the finite volume particle (FVP) method and the distinct element method (DEM). In FVP, the fluid movement and phase changes are modeled through neighboring fluid particle interactions. For mixed-flow calculations, FVP was coupled with DEM to represent interactions between solid particles and between solid particles and the wall. A 3D computer code developed for solid-liquid mixture flows was validated by a series of pure-and mixed-melt freezing experiments using a low-melting-point alloy. A comparison between the results of experiments and simulations demonstrates that the present computational framework based on FVP and DEM is applicable to numerical simulations of solid-liquid mixture flows with freezing process under solid particle influences.     

Modeling strategies for unsteady turbulent flows in the lower plenum of the VHTR

Validation simulations are presented for turbulent flow in a staggered tube bank, geometry similar to the lower plenum of a gas-cooled high temperature reactor. Steady 2D RANS results are compared to unsteady 2D RANS results and experiment. The unsteady calculations account for the fact that nonturbulent fluctuations (due to vortex-shedding) are present in the flow. The unsteady computations are shown to predict the mean variables and the total shear stress quite well. Previous workers’ results indicate that 3D simulations are needed to obtain reasonable agreement; present results indicate 2D is sufficient. Best practices are based on requirements for the ASME Journal of Fluids Engineering.     

Application of Nuclear Recoil to Radioisotope Enrichment of Copper-64

A new target material has been proposed for nuclear recoil enrichment of ⁶⁴Cu. This radionuclide was hitherto produced by tedious chemical processing using concentrated sulfuric acid solution of neutron irradiated copper phthalocyanine. Simplified chemical processes using a water-soluble copper phthalocyanine derivative, octacarboxyphthalocyanato copper (II), have been adopted in this work. Two methods of separation involving solvent ex-traction and precipitation have been tested. Higher specific activity of ⁶⁴Cuhas been obtained for the extraction method than for the precipitation method. Feasibility of the extraction method in ⁶⁴Cu enrichment is discussed.     

Safety analysis of the IAEA reference research reactor during loss of flow accident using the code MERSAT

Using the thermal hydraulic code MERSAT detailed model including primary and secondary loop was developed for the IAEA's reference research reactor MTR 10 MW. The developed model enables the simulation of expected neutronic and thermal hydraulic phenomena during normal operation, reactivity and loss of flow accidents.Two different loss of flow accident (LOFA) have been simulated using slow and fast decrease time of core mass flow. In both cases the expected flow reversal from downward forced to upward natural circulation has been successfully simulated. The results indicate that in both accidents the limit of onset of subcooled boiling was not arrived and consequently no exceed of design limits in term of thermal hydraulic instability or DNB is observed. Finally, the simulation results show good agreement with previous international benchmark analyses accomplished with other qualified channel and thermal hydraulic system codes.