气体电离探测器中的陶瓷-金属封接

气体电离探测器目前仍广泛用于核工业、核医学、同位素应用等领域。作为探测器中的电信号引出,电极支撑等则有不少采用陶瓷及陶瓷—金属封接,对于要求机械强度高、绝缘电阻大、高温性能稳定的探测器而言,必须采用陶瓷—金属封接。 气体电离探测器的种类繁多,用途广泛,要求陶瓷—金属封接件具有不同的几何尺寸和相应的结构。以下就在设计封接件中的一些要求,以及北京核仪器厂目前已有的封接件作一简单的介绍。     

显微CT在早期釉砂研究中的应用:以西周倗国出土釉砂珠为例

利用同步辐射显微CT、XRD和EDXRF对西周倗国墓地出土的一枚釉砂开展无损分析,探讨该枚釉砂的制作工艺。结果表明,此釉砂珠的石英胎质较为致密,胎料为研磨很细的石英颗粒,与西方釉砂的内部结构相差较大,暗示该样品不是从西方输入。此釉砂珠的制作工艺为,首先围绕圆柱形内芯制作石英胎,然后施釉,烧制后去除内芯;这种工艺可能受当时青铜器铸造工艺和原始瓷制作工艺的影响。显微CT无损分析釉砂的内部结构的优越性,显示其在釉砂研究中有着广阔的应用前景。     

江西洪州窑古瓷的元素谱及产地特征的SRXRF研究

古陶瓷的元素谱分析是古陶瓷研究中的一项重要内容,它对古陶瓷的产地鉴定及真伪鉴别起看十分重要的作用。我们选用江西丰城洪州窑从东汉晚期直到晚唐五代8个考古化期共32个古瓷碎片,用SRXRF对其胎进行了多点分析和线状区域扫描分析,并对釉面进行了区域扫描分析。初步确定了洪州窑古瓷的化学组成的产地特征为：胎釉中Fe,Tt等着色元素含量较高,釉中钙高钾低,属高钙釉。     

制造UO_2陶瓷微球的一种先进工艺(TGU)

UO_2陶瓷微球是制造高温气冷核反应堆(HTGR)球状燃料元件的最重要的部件。为此,清华大学核能技术设计研究院开发了一种全胶凝工艺(TGU)。它是在传统的溶胶-凝胶工艺,即外胶凝(EGU)和内胶凝(IGU)工艺的基础上发展起来的,现已被选用为10MW高温气冷试验堆燃料芯核的生产工艺。该项研究的目的是从芯核的质量控制(QC)和质量保证(QA)的要求出发,采用批量试验方式,检验工艺参数和产品质量的稳定性。试验结果证明:当工艺参数被控制并固定时,芯核的质量能够满足质量规范的要求,即当胶体流量和喷嘴的振动频率被固定时,芯核的几何尺寸便随之固定;烧结温度和时间固定时,芯核密度亦随之固定;采用纯氢烧结时,O/U比便接近化学计量。对UO_2陶瓷微球的性能和结构也进行了研究。     

制造UO_2陶瓷微球的一种先进工艺(TGU)(英文)

UO_2陶瓷微球是制造高温气冷核反应堆(HTGR)球状燃料元件的最重要的部件。为此,清华大学核能技术设计研究院开发了一种全胶凝工艺(TGU)。它是在传统的溶胶-凝胶工艺,即外胶凝(EGU)和内胶凝(IGU)工艺的基础上发展起来的,现已被选用为10MW高温气冷试验堆燃料芯核的生产工艺。该项研究的目的是从芯核的质量控制(QC)和质量保证(QA)的要求出发,采用批量试验方式,检验工艺参数和产品质量的稳定性。试验结果证明:当工艺参数被控制并固定时,芯核的质量能够满足质量规范的要求,即当胶体流量和喷嘴的振动频率被固定时,芯核的几何尺寸便随之固定;烧结温度和时间固定时,芯核密度亦随之固定;采用纯氢烧结时,O/U比便接近化学计量。对UO_2陶瓷微球的性能和结构也进行了研究。     

Nb-1Zr与1Cr18Ni9Ti高温真空钎焊工艺研究

采用BNi-5钎料,对Nb-1Zr与1Cr18Ni9Ti高温真空钎焊工艺进行试验研究,对试验钎焊的接头进行了密封性能检验、抗热冲击性能试验、接头界面区微观分析以及钎缝拉伸强度试验.通过分析试验结果,确定了Nb-1Zr与1Cr18Ni9Ti高温真空钎焊工艺规范参数.     

涂层裂纹的MHD压降研究

目前的研究已表明,自冷包层中的MHD压降问题可以在与液态金属流体接触的通道壁上涂电绝缘陶瓷涂层或自修复涂层而得到很好的解决。但因热应力等因素引起陶瓷出现裂纹或剥落,在陶瓷涂层出现裂纹或剥落后的MHD压降需要开展相应的实验工作。考虑到低成本和方便的涂层工艺,本研究中的绝缘涂层使用了     

用中子活化分析研究郊坛下官窑与清凉寺汝窑的原料来源

选取11个清凉寺窑古汝瓷、23个郊坛下窑古官瓷、4个现代仿古官瓷的釉和胎等样品进行中子活化分析(NAA),测定每个样品的微量元素含量,将这些测量数据进行模糊聚类分析,分别得到胎和釉的动态模糊聚类分析图,以确定它们的原料来源。结果表明,郊坛下古官瓷胎的原料来源非常集中,清凉寺古汝瓷胎的原料来源稍分散些;古官瓷釉的原料来源比较集中,古汝瓷釉的原料来源分散,古汝瓷釉和古官瓷釉的原料来源明显不同。郊坛下窑官瓷的胎和釉与清凉寺窑汝瓷的胎和釉既有差异又有可比性。     

建窑古瓷胎的产地和年代特征的NAA和WDXRF分析研究

产地研究和断代是古陶瓷科学研究的重要内容,为从化学成分角度判别古陶瓷的产地和年代,须研究不同产地、不同年代的古瓷胎釉元素组成的特征和差异。从庵尾山、大路后门和营长墘3处窑址收集了建窑7个时期的古瓷碎片139片,用NAA和WDXRF分别测定了瓷胎中的微量和主量元素含量。分析结果表明,根据化学成分的不同可将建窑古瓷分为晚唐五代、北宋、南宋和元代4个群组;大路后门和营长墘窑址的黑瓷采用了相似的制瓷原料,庵尾山窑址所用的原料与前两者存在明显差别。     

高温堆嬗变Pu燃料元件的制备

介绍了清华大学在制备高温气冷堆嬗变Pu惰性元件方面的研究进展.分别采用溶胶凝胶工艺和注凝成型工艺制备ZrO2陶瓷微球作为基体,经过低温烧结获得多孔微球;用U代替Pu进行浸渍后,再经过高温烧结获得致密的陶瓷微球;基体中的U含最基本稳定在10%左右.采用与10MW高温气冷堆燃料元件包覆颗粒相同的制备工艺,在ZrO2/U复合微球表面依次沉积疏松热解炭、致密热解炭、SiC和外致密热解炭,制备出包覆型嬗变燃料颗粒.     

Study on the ablation modification effects for EB-PVD ceramic coatings considering the microstructure of the surface

Based on the surface microstructure of EB-PVD ZrO₂ coatings, the ablation effects of a novel method for ceramic modification technique by high-intensity pulsed ion beam irradiation have been studied numerically. Taking the nonlinear depositing energy of ions in the coatings calculated by Monte Carlo methods as the thermal source term in heat transfer equations, the surface melting process and the evolution of temperature of ZrO₂ specimens induced by HIPIB irradiation were obtained. About 1 μm in thickness of ZrO₂ ceramic was re-solidified after melting, a dense modification coat layer formed, and near the top surface an even denser layer formed. During the calculation the latent heat of ZrO₂ is introduced to consider the additional heat due to the phase change between solid-liquid and liquid-gas states. The numerical result about the ablation melted thickness of surface layer is in reasonable agreement with those measured by HIPIB irradiation experiments.     

Progress in core and cermet fuel modelling to calculate severe accidents

The use of cermet type composite fuels leads to an optimised use of plutonium; a good thermomechanical behaviour due to a low operating temperature thanks to a high thermo-conductivity, that favours high burn-up due to the low fission gas release. However, the increase in the metallic mass, an alloy of zircaloy, in the core, as well as the composite nature of the fuel with two very different melting temperature ( 1873 K for the metal, and 2573 K for the ceramic) lead to a behaviour very different from that of the traditional ceramic fuel in the event of an accident.     

A mechanistic model of critical heat flux under subcooled flow boiling conditions for application to one- and three-dimensional computer codes

Based on a review of visual observations at or near critical heat flux (CHF) under subcooled flow boiling conditions and consideration of CHF triggering mechanisms, presented in a companion paper [Le Corre, J.M., Yao, S.C., Amon, C.H., 2010. Two-phase flow regimes and mechanisms of critical heat flux under subcooled flow boiling conditions. Nucl. Eng. Des.], a model using a two-dimensional transient thermal analysis of the heater undergoing nucleation was developed to mechanistically predict CHF in the case of a bubbly flow regime. The model simulates the spatial and temporal heater temperature variations during nucleation at the wall, accounting for the stochastic nature of the boiling phenomena. It is postulated that a high local wall superheat occurring underneath a nucleating bubble at the time of bubble departure can prevent wall rewetting at CHF (Leidenfrost effect). The model has also the potential to evaluate the post-DNB heater temperature up to the point of heater melting.Validation of the proposed model was performed using detailed measured wall boiling parameters near CHF, thereby bypassing most needed constitutive relations. It was found that under limiting nucleation conditions; a peak wall temperature at the time of bubble departure can be reached at CHF preventing wall cooling by quenching. The simulations show that the resulting dry patch can survive the surrounding quenching events, preventing further nucleation and leading to a fast heater temperature increase. The model was applied at CHF conditions in simple geometry coupled with one-dimensional and three-dimensional (CFD) codes. It was found that, within the range where CHF occurs under bubbly flow conditions (as defined in Le Corre et al., 2010), the local wall superheat underneath nucleating bubbles is predicted to reach the Leidenfrost temperature. However, a better knowledge of statistical variations in wall boiling parameters would be necessary to correctly capture the CHF trends with mass flux (or Weber number).     

高温气冷堆环境模拟装置动态传热特性建模分析

清华大学核能与新能源技术研究院研制了模拟高温气冷堆温度、环境氛围的材料测试装置,可进行1 600℃及以下高温碳还原环境下的各类实验。通过对该实验装置的结构进行适当简化,建立了模拟其高温、真空条件下辐射、导热动态传热特性的二维数学模型。仿真结果与实验装置各测点的实测温度变化趋势一致,可解释实验时观察到的多种动态传热现象。此外,该模型可对材料测试区径向温度分布、不同加热功率条件下发热体最高温度等难以直接测量的重要参数进行估计,给出进一步实验的指导性建议。     

The Pelletron Accelerator

A review is given of early development work at the University of Wisconsin on electrostatic accelerators insulated by high pressure gas. This work started in 1933 and led in 1940 to a 4.5MeV accelerator. Starting in 1946 development work was initiated along three lines: 1) Bakeable high strength metal to ceramic bonding, 2) Organic-free pumping, 3) Metal charge carrying devices. In 1951 construction was started at the University of Wisconsin on an accelerator utilizing results of these three development programs. In 1965 much development work was transferred to the National Electrostatics Corp. where the charging chain was developed. It consists of metal cylinders joined by links of solid insulating material. A 1MV column support unit was perfected which is used to construct column modules. A bakeable all metal and ceramic tube, free of organic vapors was developed. It consists of short sections bolted together with three sections per column module. A three-stage accelerator was built and was tested with a beam up to energies of 22MeV. A two-stage accelerator to provide 28MeV protons (14MV on terminal) is under construction. A two-stage accelerator to give 40MeV protons (20MV on terminal) has been designed.     

Interaction of Metal Melt with Zirconium Dioxide Refractories in an External Trap

The results of an investigation of the interaction of metal melt of reactor materials with zirconium dioxide refractories (ceramic, concrete) in an atmosphere with various oxygen contents at temperatures up to 2600 K are presented. The experiments showed that the melt Zr + 2.5% Nb at 2273 K does not give rise to erosion of the ceramic; at 2500–2600 K, it permeates and dissolves the ceramic. Erosion of concrete starts at the melting point of the alloy. A melt of reactor steel does not interact with refractories. Under certain conditions, capillary permeation of steel into refractories occurs. At temperatures above 2500 K, a steel–20% Zr melt gives rise to erosion of zirconium dioxide concrete.The results are used to analyze the operation of a refractory protective layer of an EPR trap.     

Simulation of Filament Heater for Uniform Emission from Dispenser Cathode

This paper presents the design study of toroid shape filament heater for dispenser cathode.The filament heater will be used in cathode assembly of 200 kW 42 GHz gyrotron. A 3 D model of cathode assembly is designed using electromagnetic and thermal simulation software, ANSYS. The simulations are performed for optimizing the input filament heater power with respect to cathode surface temperature. The parametric study shows that the input power and cathode surface temperature depends strongly on the potting material, diameter of filament, number of turns, position and height of the filament heater with respect to cathode pellet. The design analyses are also carried out for two different filament heater materials i.e. tungsten and molybdenum. Further, the thermal, structural and transient analyses are also carried out to study the mechanical strength of the filament heater. It is concluded that the input heater power should be greater than 200 W to achieve cathode surface temperature greater than 1,000°C.     

Interruption Phenomenon in Intermediate-Frequency Vacuum Arc

In the condition of the 3 mm gap, experiments for 360 Hz intermediate-frequency vacuum arc are carried out in interrupters with the diameters being 41 mm and with the contact materials being CuCr50 and Cu-W-WC alloy respectively. The results indicate that the contacts material is closely related to the breaking capacity of the vacuum interrupters and characteristics of an intermediate-frequency vacuum arc. For contacts with the same diameter, the breaking capacity of CuCr50 is better than that of Cu-W-WC. When the current fails to be interrupted, the arcs overflow the gap and present irregular performances in the first half wave. Consequently a voltage spike appears. More macroscopic metal droplets can be seen in the arc column between CuCr50 contacts because of the lower melting point. It is observed that the droplet emission is much more severe during arc reignition than that in the first half wave. It is much more conspicuous that the high frequency arc voltage noises appear in Cu-W-WC contacts when the vacuum arcs reignite, for higher temperature and stronger electronic emission ability of Cu-W-WC contacts.     

EDXRF无损检测青花瓷器的研究

用ＥＤＸＲＦ方法测量青花瓷器中元素含量的研究结果表明：在青花瓷器的烧制过程中，存在色料层元素向釉层的扩散现象，通过对青花瓷器半值厚度的计算，发现瓷胎中有些元素对上述测量也有贡献，实验还发现，同一瓷器，不含青花纹饰的釉层各元素的测量结果与所测部位无关，而含纹饰的釉层有些元素的测量结果随位置而改变。     

熔融物材料扩散系数的从头算分子动力学计算

为获得核反应堆严重事故后期反应堆压力容器(RPV)下腔室内熔融物微观组织的演化规律,需要对熔融物的材料物理性质进行研究。以熔融池中发生熔化过程的实际材料,包括燃料芯块UO₂、包壳管熔融后的U-Zr-O材料以及不锈钢构件熔融后的U-Fe-O材料为研究对象,采用基于第一性原理的从头算分子动力学模拟了熔融物材料高温液态下的原子扩散行为。研究结果表明,在高温液相中的U、Zr、Fe、O的原子扩散系数与原子质量呈负相关,且在相同温度下受组分的影响较小,仍保持相对稳定的比例关系。不同原子扩散系数的差异理论上会导致熔融池形成分层结构,因此,可对比上述3种材料在高温液态下各种原子的扩散系数,确定直接的量化关系,为在大尺度下进一步研究熔融物微观组织的演化奠定基础。