Calculation of the Heat Flux on the First Wall During Disruption on Tokamak

Disruptions are the most dangerous instabilities in tokamak plasma. During plasma disruption, the large amounts of energy will be deposited on Plasma Facing Components (PFCs) which is a damaging threat for the divertor target and the first wall materials. Therefore, studying the characteristic of heat deposition on the first wall is very significant. The Infrared (IR) camera is an effective tool to measure the surface temperature profile on the first wall on the Experimental Advanced Superconducting Tokamak (EAST). With a finite difference method, the heat flux arrived to the divertor can be calculated from the surface temperature. However, the surface layer on the divertor has a great influence on the calculation of the heat flux on the divertor. The numerical method for solving heat conduction for semi-infinite model is given in this paper. And the thermal resistance of surface layers is considered in this numerical method. In addition, the distribution of heat flux on the divertor during disruption is also shown.     

Manufacturing of small-scale mock-ups and of a semi-prototype of the ITER Normal Heat Flux First Wall

This paper describes the manufacturing development and fabrication of reduced scale ITER First Wall (FW) mock-ups of the Normal Heat Flux (NHF) design, including a “semi-prototype” with a dimension of 305 mm × 660 mm, corresponding to about 1/6 of a full-scale panel. The activity was carried out in the framework of the pre-qualification of the European Domestic Agency (EU-DA or F4E) for the supply of the European share of the ITER First Wall. The hardware consists of three Upgraded (2 MW/m²) Normal Heat Flux (U-NHF) small-scale mock-ups, bearing 3 beryllium tiles each, and of one Semi-Prototype, representing six full-scale fingers and bearing a total of 84 beryllium tiles.The manufacturing process makes extensive use of Hot Isostatic Pressing, which was developed over more than a decade during ITER Engineering Design Activity phase. The main manufacturing steps for the semi-prototype are described, with special reference to the lessons learned and the implications impacting the future fabrication of the full-scale prototype and the series which consists of 218 panels plus spares.In addition, a “tile-size” mock-up was manufactured in order to assess the performance of larger tiles. The use of larger tiles would be highly beneficial since it would allow a significant reduction of the panel assembly time.     

Thermal Performance Study of VPS-W Coatings on CuCrZr Under High Heat Flux

Three tungsten coatings with a thickness of 250 μm, 600μm and 220 μm, respectively, were deposited on a CuCrZr substrate by the vacuum plasma spraying technology. In order to study the thermal performance of the coatings, heat load limit, thermal fatigue lifetime and thermal response tests were performed by means of the electron beam irradiation with a heat flux from 0 MW/m^2 to 10 MW/m^2. Experimental results indicated that tungsten coatings on CuCrZr with a titanium or tungsten/copper interlayer could expel heat flux timely and had good thermal fatigue properties, titanium was a promising compliant layer which provided a reliable way to join tungsten onto the CuCrZr heat sink, even suffering from a heat flux of 10 MW/m^2 or withstanding 54 cycles of fatigue tests under 5 MW/m^2. However, the better quality of tungsten coating itself was necessary because its surface temperature was higher than that of the sample with a tungsten/copper interlayer.     

超临界压力水冷包层方案第一壁的热与应力分析

针对超临界水冷包层中第一壁的运行工况,利用数值计算软件ANSYS中CFX和Workbench两个模块对第一壁结构中的固体域和流体域进行数值分析研究。对比矩形管道和圆形管道内传热及热应力分布发现,矩形管道四个角域强化了壁面流体和主流流体的动量和热量的交换,使传热性能优于圆形管道,而四个角域的存在也造成了该处的应力集中,使结构材料的最大应力明显高于圆形管道。进一步研究冷却剂流向和冷却管道几何结构参数对第一壁结构温度场和应力场的影响发现,在ITER运行工况下,冷却剂流向影响很小,增大冷却管道直径和减小冷却管道最小壁厚均能改善第一壁结构材料中的最高温度,而这两个几何结构参数对第一壁应力的影响较为复杂。     

卧式V型管管壁温度特性及临界热负荷的研究

本文对卧式Ｖ型管高压汽水两相流的传热特性进行了试验研究。根据试验得到了计算临界热负荷的关系式。该式可用来预测卧式Ｖ型管弯头上、下游部分的传热恶化条件，为沸腾燃烧锅炉中卧式Ｖ型坦管、锅炉炉膛出口凝渣管等的设计与运行提供了可靠依据。     

Evaluation of The Thermal Performance of Multi—Element Doped Graphite under Steady—State High Heat Flux

Multi-element doped graphite,GBST1308 has been developed as a plasma facing material(PFM) for high heat flux components of the HT-7U device.The thermal performance of the material under steady-state(SS) high heat flux was evaluated under actively cooling conditions,the specimens were mechanically joined to copper heat sink with supercarbon sheet as a compliant layer between the interfaces.The experiments have been performed in a facility of ACT (actively cooling test stand) with a 100kW electron gun in order to test the suitability and the loading limit of such materials.The surface temperature and bulk temperature distribtuion of the specimens were investigated.The experimental results are very encouraging that when heat flux is not more than 6 MW/m^2,the surface temperature of GBST1308 is less than 1000℃,which is the lowest,compared with IG-430U and even with CX-2002U(CFC),The primary results indicate that the mechanically-joined material system by such a proper design as thin tile.Super compliant layer,GBST as PFM and copper-alloy heat sink,can be used as divertor plater for HT-7U in the first phase.     

Thermal and mechanical analysis of welded structures

The prediction of the residual state of stress and deformation in a welded structure is one of the most interesting, challenging, and complex problems in structural mechanics. The wide spectrum of physical phenomena provides the interest; economic and safety considerations provide the challenge; and the essential nonlinearity of the analytical models provides the complexity. Even if it is assumed that reasonable prediction of tje transient temperature field in the structure is possible, determining the residual mechanical state is both a difficult and an expensive task. The analysis inevitably involves temperature-dependent mechanical properties and, in addition, the severe thermal gradients and high temperatures generic to the welding process induce irrecoverable inelastic creep and plasticity in the structure.In spite of this, the stress analysis is now considered to be a straightforward application for general purpose, nonlinear finite element structural programs. A few special features of such analyses, however, will be discussed: (1) the legitimacy of time-dependent plasticity theories for treating the residual stress problem; (2) criteria for choosing plane stress, plane strain, generalized plane strain, or fully three-dimensional models; (3) methods for coping with possible floating solid regions during cooling; and (4) the use of linear constraints to treat weld metal deposition and intermittent contact.Since the most important parameters in the welding process that pertain to the stress analysis are the cooling rate and the welding torch efficiency, the heat transfer problem seems to require a critical look. The dominant features of this problem are: (1) source (torch) characterization; (2) radiation from surfaces that are heated to high temperatures; (3) latent heat effects; and (4) subsidiary considerations, such as enforced convection heat transfer modes that are designed to control the cooling rate. Motion of the welding torch, even at low speeds, is not usually a critical factor in determining the residual mechanical state. Again, finite element analysis is applicable, provided that the solution accuracy can be adequately estimated. Several alternative, two-step, implicit time integration schemes will be compared, especially with regard to accuracy and numerical stability for welding-type problems. The efficacy of ‘flux correction’ will also be discussed and the application of these ideas to typical industrial welding problems will then be outlined.     

Thermal and mechanical analysis of the ITER plasma-position reflectometry antennas

The antennas of the ITER plasma-position reflectometer are the components most exposed to the plasma. High thermal loads can cause high temperatures and excessive stress, so the first constrains on the antenna design arise from thermal simulations results. Therefore, the first step of the analysis is to develop a finite element thermal model with ANSYS. Once the temperatures are kept at acceptable levels, structural analysis is performed to know the thermal stress. Simulations performed using different materials and support structure geometries are discussed. Further, it has been checked that the components can withstand the electromagnetic loads expected during disruptions and vertical displacement events. The stress due to these electromagnetic loads is calculated analytically as well as with ANSYS simulations. The proposed antenna arrangement is properly designed against thermal and mechanical loads.     

Radiative Heat Deposition Analysis of Fusion Reactor First Wall by Monte Carlo Transport Code

Heat flux distribution on the first wall of a fusion reactor due to the thermal radiation from high temperature protection wall placed in front of the first wall was analyzed. With necessary modifications, a three-dimensional Monte Carlo transport code developed for neuronics calculation was successfully applied in the analysis. That is, reasonable results with sufficiently small statistical error were obtained with reasonable computational time. The heat flux distribution was found to be insensitive to the reflection characteristic of the radiation at the first wall i. e. diffusive or specular.     

CLAM用作超临界水冷包层第一壁结构材料的热与应力性能分析

在聚变堆超临界水冷固态增殖包层第一壁的运行工况下,采用数值方法对采用中国低活化马氏体钢(CLAM)作为结构材料的第一壁进行单向流固耦合分析,为超临界水冷实验包层模块(TBM)的热工设计提供借鉴。分别采用CLAM和F82H作为第一壁结构材料,对比温度场和应力场,并考察不同冷却管道形状(矩形和圆形)、不同冷却管道直径和最小壁厚对第一壁温度场和应力场的影响。结果表明:CLAM的最高温度及最大应力均高于F82H的;采用CLAM作为结构材料时,矩形冷却管道的角域的换热得到了增强,但同时也造成了应力集中,第一壁设计时应综合权衡;增大冷却管道直径和减小最小壁厚均有利于换热。     

Thermal and mechanical analysis of ITER-relevant LHCD antenna elements

A 20 MW Lower Hybrid Current Drive system using an antenna based on the Passive-Active Multijunction (PAM) concept is envisaged on ITER. This paper gives an overview of the mechanical analysis, modeling and design carried out on two major elements of the antenna: the grill front face, and the RF feed-through or windows. The front face will have to withstand high heat and fast neutrons fluxes directly from the plasma. It will be actively cooled and present a beryllium coating upon ITER requirement. The RF window being a critical safety importance class component (SIC) because of its tritium confinement function, two of them will be put in series on each line to achieve a double barrier. A design of a water cooled 5 GHz CW RF “pillbox” window capable of sustaining 500 kW of transmitted power is proposed. Both studies allow to move forward, and focus on critical issues, such as manufacturing processes and R&D associated programs including tests of mock-ups.     

Thermal Shock Performance of Sintered Pure Tungsten with Various Grain Sizes Under Transient High Heat Flux Test

Pure tungsten samples with multimodal grain size of 1.85 ± 0.84/0.47 ± 0.2 μm (PW1) and grain size of 0.33 ± 0.1 μm (PW2) were prepared by resistance sintering under ultra high pressure. Then the thermal shock performance of both W was evaluated using the electron beam facility with 1 cycle and 5 ms pulse duration at 0.22 GW/m². PW1 exhibited higher relative density, thermal conductivity but lower microhardness and bending strength compared with PW2. Furthermore, PW1 displayed slight higher major crack density (smaller major crack distance) while slight smaller major crack width compared with PW2. Besides, the microcracks that only formed in PW2 have the potential to detach W grains from the matrix. Moreover, both samples showed close major crack depth and surface roughness. Thus it can be concluded that PW1 with large grain size showed better thermal shock performance compared with PW2 with small grain size.     

Thermal and mechanical analysis of Wendelstein 7-X thermal shield

The thermal insulation of Wendelstein 7-X cryostat consists of multi-layer insulation (MLI) and a thermal shield. The shield is cooled by helium gas flowing in pipes which are attached to the shields via copper strips or braids. The paper presents the basic thermal and mechanical layout of the thermal shield. The design is strongly influenced by the tight design space.Main mechanical loads on the shield are electromagnetic forces resulting from rapid shut down of the magnet system and the self weight. Design and calculations were performed iteratively. Copper and brass were checked in combination with different electrical isolation variants. The induced eddy currents will be reduced if the upper and the lower half shells of the cryostat are electrically isolated against each other. The cryostat shield and the port shields are made of brass.The expected heat loads on the shield were estimated. The resulting temperature distribution was then calculated for brass and copper shield panels. The average shield temperature is below 85 K and fulfills the thermal requirements.     

Numerical Investigation of Channel for Helium Cooled China HCCB-TBM First Wall by Application Enhance Heat Transfer Method

To enhance heat transfer efficiency on first wall (FW) of ITER China Helium-Cooled Ceramic Breeder-Test Blanket Module (HCCB-TBM), CFD numerical simulation method is adopted. On the basis of calculating helium gas cooling scheme of FW smooth channel, FW structural temperature gradient, maximum wall temperature, average heat transfer coefficient, and pressure drop of channel are selected as evaluation indexes. Numerical simulation comparison are performed on heat transfer schemes like placing transversal ribs and V-shaped ribs in the flow channel of front wall and the helium gas turbulence intensity and the heat transfer area are improved through optimizing the distance and angle between V-shaped ribs and other parameters to enhance heat transfer. The optimization scheme of helium-cooled FW for HCCB-TBM through the three dimensional numerical simulation is: V-shaped ribs are placed on the inner surface of front wall, the rib cross section is 1 mm × 1 mm, the distance between rib pitches is 10 mm and the rib angle is 60°. Under the same helium cooling condition, compared with the FW smooth channel, the optimized V-shaped rib scheme enhances the average heat transfer efficiency by about 70 % and the FW maximum temperature drops by 349.3 K. The result provides support for further research on FW helium cooling heat transfer enhancement experiment and engineering design optimization for China HCCB-TBM.     

流动不稳定性对CHF的影响

本文成功地训练了一个用于预测流动不稳定性条件下CHF的人工神经网络,利用所训练的人工神经网络,分析了流动不稳定性对无量纲因子F的影响规律.分析结果表明,系统压力对F的影响是非单值的;平均质量流速增大,总体上F也增大.还分析了流动不稳定性条件下系统主要参数对临界热流密度的影响.结果表明:当质量流速的振幅与平均质量流速的比增加时,CHF 减小;质量流速的振幅与平均质量流速的比不变时,随着周期增大,CHF减小.     

偏滤器高热负荷材料研究

用热等静压焊接的方法对两种性能差异很大的金属材料钨和铜进行了成功的焊接。用SEM对断口和焊接界面在各种不同条件下焊接的性能作了对比分析。给出了两种样品的断裂特征和焊接过程中元素的扩散特点。钨和铜合金的结合主要是物理结合 ,是在高温高压下 ,材料表面微观的凹凸不平而产生的犬齿交合结合在一起的 ,扩散结合只占很少的部分。偏滤器靶板的寿命主要决定于靶板材料的热疲劳性能。在真空室中用大功率电子束作为热源进行了热疲劳试验。电子束的功率密度选为 9MW/m2 ,循环周期为 4 0s,冷却水流量为 80mL/s。用直径为 0 .3mm的NiCr NiSi热电偶测量了下材料表面的温度分布。结果发现 ,在冷却充分的情况下 ,表面最高温度约 4 0 0℃ ,钨铜焊缝处的平均最高温度约1 5 0℃。经过 1 0 0 0次的循环加热后 ,没有发现靶板材料出现破坏现象。对试验条件下的材料表面温度分布进行了计算机模拟计算。计算结果和试验测得的结果是相吻合的 ,表明试验结果是真实可靠的     

临界热流密度实验研究进展

临界热流密度是重要的限制性热工参数，它的大小直接影响反应堆的安全性和经济性。本文介绍了我国核电站临界热流密度实验研究进展，比较了国外核电站临界热流密度研究发展状况，文章认为，我国临界热流密度实验研究的发展方向是进行全长棒束非均匀加热临界热流密度的实验研究。     

棒束临界热流密度流体模化研究

在空泡物理和自然循环重点实验室氟里昂热工实验装置上进行了CHF实验 ,实验段为9 5×1 0mm元件管组成的 4× 4棒束 ,并对其开展了 4× 4棒束CHF流体模化研究。在压力 1 5 9～ 2 73MPa、质量流速 4 88～ 2 0 80kg (m2 ·s)、临界含汽率 -0 2 0～ 0 3 0的工况范围内 ,采集了 1 70个 4× 4棒束CHF实验数据 ,并与压力 9 9～ 1 6 2MPa、质量流速 2 74～ 1 4 73kg (m2 ·s)、临界含汽率 -0 2 0～0 3 4工况范围内 ,以水为工质相同棒束实验段内的 2 0 6个棒束CHF实验数据进行比较 ,发现Ahmad补偿失真模型、张振杰模型和Stevens Kirby模型在上述工况范围内不再适用于棒束CHF的模化 ,这些模型的预测偏差均大于 2 0 %以上 ,而且棒束CHF模化的流量模化因子k明显地受压力、质量流量和入口含汽率的影响。据此提出适用于上述工况范围内 4× 4棒束CHF模化的流量模化因子k的关系式 ,其CHF预测偏差在± 1 5 %以内 ,均方根误差为 7 0 5 %。