用化学气相反应法在石墨基体上制备SiC涂层

石墨是建造高温气冷堆的主要材料,提高其抗氧化性能可以进一步改善高温气冷堆安全性.本文对利用化学气相反应法(CVR)在高温气冷堆燃料元件基体石墨上制备SiC涂层的工艺进行了探讨,利用XRD、Raman谱及SEM对制备的SiC涂层进行了分析.结果表明,可以获得单一β-SiC相的SiC涂层,涂层与基体之间具有良好的梯度过渡;但由于在涂层中存在一定的孔隙,仅用CVR制备的SiC涂层不能很好地改善石墨的抗氧化性能,将此方法和其他方法结合起来可以获得低成本的、均匀的SiC抗氧化涂层.     

新型柔性中子屏蔽复合材料研制及性能研究

为满足形状复杂核设备外围防护以及辐射防护服对于柔性中子屏蔽材料的需求,研制了一种新型B4C/SEBS中子屏蔽复合材料,重点研究了不同B4C含量对SEBS基复合材料力学性能、热学性能及中子屏蔽性能的影响。实验结果表明:复合材料拉伸强度、扯断伸长率均随着B4C含量的增加而减小;增加B4C含量,复合材料撕裂强度呈现出先增大后减小的趋势,而复合材料邵氏硬度则不断增大;该材料热导率随着B4C含量的增加而不断升高;利用镅-铍中子源进行材料中子屏蔽测试,同厚度材料中子屏蔽性能随着B4C含量的增加而不断提高。综合考虑该新型柔性中子屏蔽材料良好的中子屏蔽性能、抗撕裂性能及柔韧性能等特性,其在形状复杂核设备外围防护及辐射防护服领域具有较大的应用前景。     

聚变堆第一壁涂层材料

由于使用低Z涂层材料可使传统的结构材料和技术保持不变并能降低等离子体杂质,因而为设计提供了灵活性。低Z涂层可由元素Be,B,C,Al,Ti,V及其化合物中选择。文中介绍了涂层工艺和评价方法。添加约10wt%SiC的热解碳几乎能完全抑制化学溅射。60块C+SiC涂层石墨砖在DoubletⅢ托卡马克的整个照射期间性能令人满意。     

316L不锈钢基材功能梯度Al涂层残余热应力分析

涂层材料的功能性和可靠性在很大程度上受残余热应力的影响,为降低残余热应力防止涂层开裂以及提高其热机械性能,利用有限元方法对Al/316L系梯度功能材料在制备过程中产生的残余热应力分布进行分析,详细讨论了成分分布指数、涂层厚度和梯度层数目对应力大小和分布的影响.分析结果表明成分分布指数的增大不但影响涂层和基体界面的应力大小,还影响涂层中热应力峰值所处位置;涂层残余应力随着梯度层厚度的增加而减小;梯度层数的增多,有利于涂层中残余热应力的缓和,但当梯度层数达到9时,缓和效果并不明显.     

SiC涂层性能与石墨基体结构的关系

采用料浆烧结法在不同石墨基体上制备了SiC涂层。详细研究了SiC涂层在不同石墨表面上的结构及其对不同石墨的抗氧化防护行为。结果表明：石墨基体的孔隙率和孔径尺寸决定着SiC涂层的结构,形成SiC梯度涂层的必要条件是石墨的孔径尺寸须处于0.1～0.5μm范围内;SiC梯度涂层有利于石墨基体抗氧化性能的提高。     

碳纤维增强B_4C/Al中子吸收材料的优化设计

核电站中乏燃料储存格架用到的中子吸收材料需要兼具结构和功能一体化的要求,本文提出用碳纤维Cf增强B4C/Al中子吸收复合材料。利用Monte Carlo方法对碳纤维增强铝基碳化硼中子吸收材料(Cf/B4C/Al)的中子透射率进行模拟计算,研究B4C含量、Cf含量、不同能量中子入射以及材料厚度变化时对中子透射率的影响,并与B4C/Al材料进行比较。结果表明,在1 e V-0.1 Me V能量范围的中子入射下,当B4C含量小于35%时,加入碳纤维能明显改善B4C/Al材料的中子屏蔽性能;在100 e V中子入射下,材料的中子透射率随B4C含量增加呈现指数下降;且Cf/B4C/Al材料的中子透射率随碳纤维含量增加持续降低;当Cf含量达到10%时,材料中子透射率降至最低,之后趋于平稳。通过模拟计算,得到Cf/B4C/Al材料的各组分的最优配比为35 vol.%B4C和10 vol.%Cf。     

高温气冷堆包覆燃料颗粒SiC涂层的制备与表征

采用化学气相沉积法在包覆燃料颗粒上制得SiC涂层.对SiC涂层的功能、沉积设备、沉积工艺及组织结构进行了较系统的描述.研究表明制得的SiC涂层表面光滑、致密、无明显孔洞;与内、外致密热解碳层的界面清晰,无明显扩散渗透现象.对SiC涂层的组分及晶体结构分析表明涂层主要元素为Si和C,且Si/C的摩尔比接近1∶1,反应生成化学计量比的β-SiC.价键结构分析则表明涂层中主要连接键为Si-C共价键.     

北京同步辐射装置4B7A、4B7B光束线高次谐波抑制系统初步设计

为了提高北京同步辐射装置(BSRF)中4B7B软X射线光束线在45-450 eV能区和4B7A中能光束线在1200-2100 eV能区输出单色光的光谱纯净度,我们分别为两条光束线设计了高次谐波抑制系统.该系统主要由平面反射镜组成.我们确定了所有平面反射镜的镀层和掠入射角,并且对其性能进行了计算,结果以图形的形式呈现.     

B4C控制棒高温氧化研究现状

以B4C为中子吸收材料的反应堆堆芯发生严重损毁时,B4C与高温蒸汽发生氧化反应,从而对堆芯降级和重新定位产生强烈的影响.综述了近十年来高温范围内B4C控制棒行为的研究现状和研究成果,归纳总结出B4C氧化动力学原理及氧化模型,详细介绍了当前先进的B4C控制棒行为计算程序,并指出该领域国内研究的不足之处.     

B_4C/Na/S.S.三元体系的化学相容性Ⅰ.温度效应及B/C比的影响

在堆用不锈钢包壳管内分别填装不同B/C比的B4C芯块及核级钠 ,以模拟快堆控制棒内的B4C/Na/S .S .三元体系 ,在堆外 5 5 0、65 0和 75 0℃下相互作用 82d。试验后的B4C芯块外观完整 ,未见掉角、龟裂或破碎 ;表面变得粗糙 ,失去原有的金属光泽 ,化学反应产物NaB5 O8等在表面沉积和粘附 ,并导致B4C芯块体积增大 ;芯块的微观结构和晶粒度试验前后无明显变化。包壳管内表面渗B、渗Na和渗C ,渗B和渗Na量均随温度升高和B/C比增大而增加 ,渗C则反之。Na和Na中杂质以及B4C与包壳间的化学反应产物为NaBO2 、Cr2 B、Fe2 B和Ni3 B。B化物的形成使包壳管内表面显微硬度显著增大。     

High Heat Flux Testing of B4C／Cu and SiC／Cu Functionally Graded Materials Simulated by Laser and Electron Beam

B4C，SiC and C,Cu functionally graded-materials(FGMs) have been developed by plasma spraying and hot pressing.Their high-heat flux properties have been investigated by high energy laser and electron beam for the simulation of plasma disruption process of the future fusion reactors.And a study on eroded products of B4C/Cu FGM under transient thermal load of electon beam was performed.In the experiment SEM and EDS analysis indicated that B4C and SiC were decomposed.Carbon was preferentially evaporated under high thermal load,and a part of Si and Cu were melted,in addition,the splash of melted metal and the particle emission of brittle destruction were also found.Fifferent erosive behaviors of carbon-based materials(CBMs)caused by laser and electron beam were also discussed.     

Fabrication and Thermal Conductivity of Boron Carbide/Copper Cermet

Studies on fabrication and thermal conductivity of B₄C/Cu cermet were made to obtain high performance neutron absorber materials for Liquid Metal-cooled Fast Breeder Reactor (LMFBR). A mixed powder of B₄C and Cu was mechanically blended at high speed thereby a coating layer of Cu was formed on the surface of B₄C powder. Then the B₄C powder with Cu coating was hot pressed at temperatures from 950 to 1,050°C to form a B₄C cermet. A high density B₄C/CU cermet with 70 vol% of B₄C and relative density higher than 90% was successfully fabricated. In spite of the low volume fraction of Cu. the B₄C/Cu cermet exhibited high thermal conductivity which originated from the existence of continuous metallic phase Cu in B₄C/Cu cermet.     

Thermal response of plasma sprayed tungsten coating to high heat flux

In order to investigate the thermal response of tungsten coating on carbon and copper substrates by vacuum plasma spray (VPS) or inert gas plasma spray (IPS), annealing and cyclic heat load experiments of these coatings were conducted. It is indicated that the multi-layered tungsten and rhenium interface of VPS-W/CFC failed to act as a diffusion barrier at elevated temperature and tungsten carbides were developed after 1 h incubation time when annealing temperature was higher than 1600 °C. IPS-W/Cu and W/C without an intermediate bonding layer were failed by the detachment of the tungsten coating at 900 and 1200 °C annealing for several hours, respectively. Cyclic heat load of electron beam with 35 MW/m² and 3-s pulse duration indicated that IPS-W/Cu samples failed with local detachment of the tungsten coating within 200 cycles and IPS-W/C showed local cracks by 300 cycles, but VPS-W/CFC withstood 1000 cycles without visible damages. However, crack creation and propagation in VPS-W/CFC were also observed under higher heat load.     

Bonding tungsten,W–Cu-alloy and copper with amorphous Fe–W alloy transition

W/Cu graded materials are the leading candidate materials used as the plasma facing components in a fusion reactor. However, tungsten and copper can hardly be jointed together due to their great differences in physical properties such as coefficient of thermal expansion and melting point, and the lack of solid solubility between them. To overcome those difficulties, a new amorphous Fe–W alloy transitional coating and vacuum hot pressing (VHP) method were proposed and introduced in this paper. The morphology, composition and structure of the amorphous Fe–W alloy coating and the sintering interface of the specimens were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The thermal shock resistance of the bonded composite was also tested. The results demonstrated that amorphous structure underwent change from amorphous to nano grains during joining process, and the joined W/Cu composite can endued plasma thermal shock resistance with energy density more than 5.33 MW/m². It provides a new feasible technical to join refractory tungsten to immiscible copper with amorphous Fe–W alloy coating.     

Erosion and Modifications of Tungsten-Coated Carbon and Copper Under High Heat Flux

Tungsten-coated carbon and copper was prepared by vacuum plasma spraying (VPS) and inert gas plasma spraying (IPS), respectively. W/CFC (Tungsten/Carbon Fiber-Enhanced material) coating has a diffusion barrier that consists of W and Re multi-layers pre-deposited by physical vapor deposition on carbon fiber-enhanced materials, while W/Cu coating has a graded transition interface. Different grain growth processes of tungsten coatings under stable and transient heat loads were observed, their experimental results indicated that the recrystallizing temperature of VPS-W coating was about 1400℃ and a recrystallized columnar layer of about 30μm thickness was formed by cyclic heat loads of 4 ms pulse duration. Erosion and modifications of W/CFC and W/Cu coatings under high heat load, such as microstructure changes of interface,surface plastic deformations and cracks, were investigated, and the erosion mechanism (erosion products) of these two kinds of tungsten coatings under high heat flux was also studied.     

Design of copper/carbon-coated fiber Bragg grating acoustic sensor net for integrated health monitoring of nuclear power plant

A nuclear power plant (NPP) is a harsh environment that gives rise to age-related degradation of the plant structures, and eventually leads to radiation leakage that threatens humans. Integrated structural health monitoring (ISHM) technology is a strong candidate for the prevention of the NPP accidents during operation. Prior studies have shown that fiber Bragg gratings (FBGs) and metal-coated fibers have good radiation and high temperature resistance. In this study, a FBG acoustic sensor using a metallic adhesive for installation and a relatively economical copper/carbon (Cu/C)-coated fiber is developed for ISHM of high temperature NPP structures. A chemical method is proposed to remove the Cu/C coating. A 5 mm FBG was successfully inscribed in a Ge-doped silica core through a 7 mm-long silica section with the coating removed. The Cu/C-coated fiber with the same core/clad structure as the standard SMF allowed no-loss fusion splicing, and showed good adaptability to the economical standard fiber, adaptor, connector, and instruments. It showed also good thermal resistance (<345 °C) with no degradation in optical power during the optical transmission. The metallic adhesive used to install the FBG in a one-end-free configuration showed superior bonding reliability during temperature cycles ranging from 25 °C to 345 °C. The FBG reflectivity was stabilized at a 58% drop from the initial reflectivity, and the Cu/C-coated FBG sensor using the metallic adhesive could successfully detect the acousto-ultrasonic waves generated by pencil lead breaking and laser beam excitation.     

Vacuum annealing enhances the properties of a tungsten coating deposited on copper by atmospheric plasma spray

A tungsten (W) coating (～900 μm) was deposited on a copper (Cu) substrate via the atmospheric plasma spray (APS) technique, and then annealed in vacuum. Measurements of microstructure, density, oxygen content, microhardness and thermal conductivity show that an appropriate thermal annealing treatment can dramatically improve the quality of the coating. The oxygen content was found to drop from 0.48 wt.% before annealing to 0.06 wt.% after; microhardness increased by about 50%; and thermal conductivity nearly doubled. These results indicate that a vacuum-annealed APS-W coating can match or even surpass the quality of W coatings deposited by vacuum plasma spray (VPS). Compared with VPS, annealed APS is a more convenient and cheaper method to obtain W coatings suitable for fusion applications.     

Failure modes of vacuum plasma spray tungsten coating created on carbon fibre composites under thermal loads

Vacuum plasma spray tungsten (VPS-W) coating created on a carbon fibre reinforced composite (CFC) was tested under two thermal load schemes in the electron beam facility to examine the operation limits and failure modes. In cyclic ELM-like short transient thermal loads, the VPS-W coating was destroyed sub-layer by sub-layer at 0.33 GW/m² for 1 ms pulse duration. At longer single pulses, simulating steady-state thermal loads, the coating was destroyed at surface temperatures above 2700 °C by melting of the rhenium containing multilayer at the interface between VPS-W and CFC. The operation limits and failure modes of the VPS-W coating in the thermal load schemes are discussed in detail.     

偏滤器物理设计与实验研究

应用B2-code模拟了偏滤器等离子体行为,优化了HL-2A装置偏滤器位形。研究了偏滤器刮削层中等离子体与器壁间过渡鞘层的离子碰撞效应,模拟研究了利用LHCD和NBI控制等离子体剖面分布在HL-2A中建立准稳态的反磁剪切位形。HL-2A装置首次实现了下单零点的偏滤器位形运行,完成了偏滤器初步物理实验,截至2004年底,获得等离子体电流320 kA,等离子体存在时间1 580 ms,环向磁场2.2 T。开展了高功率密度聚变堆偏滤器靶板的设计研究,特别是流动液态锂偏滤器靶板表面的物理过程的研究。探索性研究了用RF有质动力势改善偏滤器排灰效率和减少氚投料量。对FEB- E聚变堆偏滤器进行了优化设计。用电子束模拟对碳基材料及钨进行了高热负荷冲击实验,完成了钨/铜合金的热等静压焊接及热疲劳试验研究。研究了氦在钨中的滞留与热解吸行为。     

含硼石墨中甲烷的热解吸行为研究

研究了含硼石墨ＧＢ１１０（１０ｗｔ．％Ｂ）甲烷（ＣＨ４）的热解吸谱,发现甲烷的解吸谱主要由３个峰构成,估算出了ＣＨ４不同峰值的解吸激活能。为了弄清含硼石墨中甲烷的形成与解吸机理,分别对高纯石墨ＩＳＯ８８０Ｕ和Ｂ４Ｃ涂层进行了热解吸实验,同时对材料的微观结构进行了分析。经过比较,表明甲烷在含硼石墨中的形成与解吸有３个过程：氢离子注入导致甲烷沿气孔内壁形成,并通过石墨内部的微通道向表面自由扩散;被石墨中Ｂ４Ｃ析出物所俘获的氢原子与Ｂ４Ｃ化合物中的碳原子反应,从而生成甲烷并解吸出来;以及石墨晶格俘获的氢原子与碳原子化学反应产生的甲烷,通过体扩散过程解吸。其中前后两个过程起主导作用。