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。     

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。     

随机填充球床通道内氦气流动特性实验研究

在聚变堆氦冷固态包层氚增殖区,球床通道内氦气流动压降特性对泵功率的设计具有重要意义。以氦冷固态包层氚增殖区为背景,研究了氦气流速、球床颗粒直径及球床通道长度对球床通道内氦气流动压降特性的影响。实验段采用20 mm×20 mm×500 mm的矩形通道,实验中氦气流速为0.1～0.6 m/s,球床颗粒直径为0.5、0.8、1.0、1.5、2.0 mm。实验结果表明,压降与氦气流速以及球床通道长度呈正相关,与球床颗粒直径呈负相关。对比Ergun关系式发现,在球床颗粒直径较小时,Ergun关系式预测值低于实验值,这主要是由于氦气可压缩性的影响。通过动量方程,理论推导出经可压缩性修正的Ergun关系式,结果发现修正后的Ergun关系式预测值与实验值符合良好。本研究为氦冷固态包层氚增殖区设计提供了数据支撑,为球床通道内流动特性的数值模拟提供了验证手段。     

高氚增殖比包层的设计及热工水力分析

本文设计了一种高氚增殖比包层(HBRB),该包层采用多孔U-10Zr合金作为中子倍增剂,Li4SiO4球床作为增殖剂,低活化马氏体(RAFM)钢作为结构材料。在详细研究包层加工工艺、流量分配、中子性能等问题的基础上,完成了包层内部详细结构设计。利用中子学软件分析计算了包层的氚增殖比(TBR)和热沉积分布,并根据计算结果对包层进行热力耦合分析。结果表明:包层TBR较高,且核性能稳定;冷却剂的流量分配情况和压降合理;包层内各组件冷却充分,温度和结构材料热应力不超过限值。     

ITER中国氦冷固体实验包层模块温度场和氦气流场三维数值分析

采用通用计算流体力学软件Fluent对应用于国际热核实验堆(ITER)的实验包层模块(TBM)的第一壁Be、Be球床中子增殖区、Li4SiO4陶瓷球床氚增殖区、以及结构材料的温度场和氦气流道内流场进行了三维数值模拟,研究了TBM的温度场及冷却管道内的氦气流场的分布.结果表明,除极小区域外,材料的温度在该材料所允许的工作范围之内;氦气表现出很好的流动和换热特性.     

堆内辐照在线产氚氦冷陶瓷氚增殖剂包层球床组件热工流体力学计算分析

在研究堆内进行辐照在线产氚试验是ITER计划专项国内配套研究项目之一。本工作主要针对研究堆内辐照氦冷陶瓷氚增殖剂包层（简称陶瓷）球床组件的试验技术要求，评估辐照陶瓷球床组件设计方案的可行性。通过对不同的陶瓷球床组件结构参数和组件在堆内的不同辐照位置，进行热工流体力学设计计算，得到满足要求的入堆辐照陶瓷球床组件设计方案。     

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。     

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。     

多工况下CFETR包层背板及流道热工分析

根据中国聚变工程实验堆(China Fusion Engineering Test Reactor,CFETR)包层背板的设计方案及具体的包层模块内部工况,分别完成了对高场侧包层背板和低场侧包层背板的流道的设计。背板的内部流道具体包括两根吹扫气体流道、三根冷却剂冷流道、三根冷却剂热流道。通过ANSYS软件中的FLUENT模块来初步模拟仿真包层背板的固体和流体热工基本情况,分别得到了背板在200 MW、500 MW、1 GW和1.5 GW工况下的温度场分布及各流道内部流体的热交换情况。结果表明:高场侧背板和低场侧背板的最高温度均小于结构材料的许用温度;高场侧和低场侧内部流道的冷却剂平均温度变化均符合包层端入口和出口的设计要求。     

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.     

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.     

Status and progress of Indian LLCB test blanket systems for ITER

The lead–lithium ceramic breeder (LLCB) TBM and its auxiliary systems are being developed by India for testing in ITER machine. The LLCB TBM consists of lithium titanate as ceramic breeder (CB) material in the form of packed pebble beds. The FW structural material is ferritic martensitic steel cooled by high-pressure helium gas and lead–lithium eutectic (Pb–Li) flowing separately around the ceramic breeder pebble bed to extract the nuclear heat from the CB zones. Low-pressure helium is purged inside the CB zone for in situ extraction of bred tritium. Currently the LLCB blanket design optimization is under progress. The performance of tritium breeding and high-grade heat extraction is being evaluated by neutronic analysis and thermal–hydraulic calculations for different LLCB cooling configurations and geometrical design variants. The LLCB TBM auxiliary systems such as, helium cooling system (HCS), lead–lithium cooling system (LLCS), tritium extraction system (TES) process design are under progress. Safety analysis of the LLCB test blanket system (TBS) is under progress for the contribution to preliminary safety report of ITER-TBMs. This paper will present the status of the LLCB TBM design, process integration design (PID) of the auxiliary systems and preliminary safety analysis results.     

Experimental study and analysis of the purge gas pressure drop across the pebble beds for the fusion HCPB blanket

The lithium ceramic and beryllium pebble beds of the breeder units (BU), in the fusion breeding blanket, are purged by helium to extract the bred tritium. Therefore, the objective of this study is to support the design of the BU purge gas system by studying the effect of pebbles diameter, packing factor, pebble bed length, and flow inlet pressure on the purge gas pressure drop. The pebble bed was formed by packing glass pebbles in a rectangular container (56 mm × 206 mm × 396 mm) and was integrated into a gas loop to be purged by helium at BU-relevant pressures (1.1–3.8 bar). To determine the pressure drop across the pebble bed, the static pressure was measured at four locations along the pebble bed as well as at the inlet and outlet locations. The results show: (i) the pressure drop significantly increases with decreasing the pebbles diameter and slightly increases with increasing the packing factor, (ii) for a constant inlet flow velocity, the pressure drop is directly proportional to the pebble bed length and inlet pressure, and (iii) predictions of Ergun's equation agree well with the experimental values of the pressure drop.     

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.     

Solid breeder thermal transient under purge-line-break accidents

The breeder thermal performances under a purge line break have been analyzed for two blanket design options: a blanket design using a packed breeder bed and a blanket design using a sintered breeder product. Under a purge line break open to a vacuum environment, the packed bed breeder temperature exceeds its operating temperature limit at a faster rate than that of the sintered breeder blanket design for the same breeder temperature gradient. Depending on the breeder material and nominal operating conditions, the breeder reaches its maximum operating temperature in time ranging from 32 seconds to 125 seconds for a break area of 10 cm² in packed bed designs. However for the sintered product design, the consequence of this transient might not result in the breeder exceeding its maximum operating temperature if a reasonable contact pressure could be established at the interface. To reduce the safety hazards, the tritium concentration build up in the vacuum vessel in conjunction with the purge gas pressure inside the blanket module should be used as a measure for initiating the reactor shutdown for this type of accident. The consequence of the purge line break outside the vacuum vessel on the breeder transient thermal performance is less significant because of a longer transient time involved.     

聚变堆混和球床包层中子学和热工水力特性研究

在聚变堆初步概念设计的基础上，针对固态包层设计路线，提出了一个先进的氦冷固态包层概念。设计采用Be₁₂Ti和Li₂TiO₃陶瓷小球混和球床，物理和化学相容性好；采用SiC作为结构材料，提高耐高温性能及氦气出口温度。计算结果表明：选择Be₁₂Ti和Li^₂TiO₃球体积比在2和4之间较合理；在Be₁₂Ti和Li₂TiO₃球体积比为3时，⁶Li富集度取30％~80％较适宜；球床的最高温度低于材料的温度限值，温度分布合理均匀。该方案可较大程度提高热效率和改善中子学以及氚增殖性能。