Properties of intermediate-frequency vacuum arc in sinusoidal curved contact and butt contact

In this report,two new contact structures of a vacuum interrupter with a sinusoidal curved surface are proposed to improve the capability by increasing the surface area.The experimental investigation of vacuum arc at intermediate frequency(360-800 Hz)was conducted and the results were compared with a butt contact with the same contact diameter(41 mm)and the same material.By analyzing the arc behavior,arc voltage characteristics,arc energy,current interrupting capacity,ablation of the anode contact and condensation of the arc products at a 3 mm gap,the differences in their vacuum arc characteristics were determined.The correlations of their arc energy with the amplitude and the frequency of the current were also achieved.Analysis suggests that the ruled curved contact has strong application potentiality because of its low arc energy,low arc voltage noise and arc voltage peak,light ablation on the surface of the anode contact and high interrupting capacity.     

Measurement of thermal properties of a ceramic/metal joint by laser flash method

This work describes the measurement of thermal diffusivity and the subsequent calculation of thermal conductivity and thermal contact resistance (from room temperature to 800 °C in N₂ atmosphere) at the material interface for carbon/carbon composites (C/C) joined to copper by using the laser flash method. According to these measurements, the thermal resistance at the interface, that is related to the heat transfer through the solid, is <10⁻⁶ m² K W⁻¹ up to 800 °C, indicating a high quality of the joint and no limitations for the thermal heat transfer during operation, e.g. in a nuclear fusion reactor. This measurement is proposed as an innovative non-contact and qualitative investigation technique to assess the ceramic/metal joint integrity.     

Characteristics of a prototype CdZnTe detector

Cadmium zinc telluride(CZT)is a preferred material for X-ray and gamma-ray detector.Thanks to the relatively high atomic number,high density and wide band-gap,CZT detector possesses sharp energy resolution and high detection efficiency without cryogenic cooling.We have developed a CdZnTe detector with an energy resolution of 3.45%(FWHM)at 59.54 keV at room temperature,and it is used for X-ray fluorescence analysis.In this paper, leakage current,energy resolution and long term stability of the CZT detector are discussed.     

High temperature superconductors for the ITER magnet system and beyond

The use of high temperature superconductor (HTS) materials in future fusion machines could increase the efficiency drastically, but strong boundary conditions exist. To outline the prospects, challenges and problems, first the benefit of using HTS materials is estimated considering the saving in cryogenic power. Next, it is demonstrated that industrial available HTS materials can be used for fusion today. For this purpose, we give a short summary of results that have been obtained from an ITER conform 70 kA HTS current lead that was designed, built and tested by the Forschungszentrum Karlsruhe and the CRPP Villigen in the frame of the European Fusion Technology Programme and in cooperation with industry. This current lead consists of an HTS part that covered the temperature range from 4.5 to 70 K and a conventional part, making the connection to room temperature. Because the HTS part had no ohmic losses and poor thermal conduction, the refrigerator power necessary for cooling the current lead was reduced drastically. The saving factor could be calculated to be 5.4 at zero current and 3.7 at 68 kA. The current lead could even be operated at 80 kA and with respect to safety criteria of ITER, a complete loss of He flow was simulated showing that the HTS current lead could hold a current of 68 kA for 6 min without active cooling. These results demonstrate that today existing HTS materials can be used in ITER for current leads or bus bar systems.For fusion machines beyond ITER, the development of an HTS fusion conductor would be the key to operate the complete magnet system at higher temperatures. The option of developing fusion conductors based on Bi-2223 and YBCO are briefly discussed. For a success of such conductors, the AC loss optimisation is crucial.     

Convection effect on an arc plasma evolution process in a two parallel contact system

A low voltage circuit breaker(LVCB) is an important piece of protection equipment which will switch off the fault current in a power system. The moving contact of a low voltage circuit breaker with a higher rated current consists of two parallel contacts. Therefore, the convection effect on the air arc evolution process in a two parallel contact system is analyzed. A threedimensional(3 D) magneto–hydro–dynamic(MHD) model of arc simulation is built. In this model, the anode consists of two parallel contacts and a bonding conductor. A nonlinear voltage–current density characteristic is employed to represent the near-anode and near-cathode voltage. The current density, arc voltage and currents through every contact are obtained. The influence of convection and conduction on the arc evolution process are quantitatively calculated. The displacements of the arc roots are obtained and the asymmetry of the arc root motion is analyzed. The arc evolution process of a two parallel contact system is preliminarily revealed.     

ITER10kA电流引线高温超导段研究

国际热核实验反应堆(ITER)高温超导电流引线（HTSCL）的特点是不仅电流容量大,且安全性要求非常高,高温超导段是HTSCL的关键部件。本文论述了ITER10kA电流引线高温超导叠和超导组件的真空钎焊工艺,分析了高温超导段漏热,并对高温超导段漏热和电流引线在10kA下的安全性参数进行了测试。结果表明,电流引线不仅漏热小,且安全裕度大,满足ITER设计要求。     

Room temperature, high-resolution X-ray spectroscopy with silicondrift chambers

The development of detectors for high resolution room temperature X-ray spectroscopy represents a relevant progress in many fields of application, mainly in out-of-laboratory environments. A new type of silicon detector, the semiconductor drift chamber (SDC), allows one to obtain at room temperature, or with a moderate cooling, a resolution comparable to that obtained at liquid nitrogen temperature with traditional detectors of the same active area. The key feature of the SDC's is the very low output capacitance (about 100 fF) independent of the active area of the device. This feature, together with a good capacitive matching between the detector and the first stage of amplification, leads to high values of the resolution at short shaping times. We tested a simple 6-mm² cylindrical SDC at room temperature and at -20°C (easily obtainable with electrical cooling), by using a specifically designed, low capacitance, JFET as the input transistor of the preamplifier. With a ⁵⁵Fe source, we measured an equivalent noise charge (ENC) of 34 e^- RMS and 27 e^- RMS at room temperature and at -20°C respectively. To our knowledge these are presently the best values obtained for the same active area near room temperature     

Si含量对9%Cr铁素体马氏体钢微观结构和力学性能的影响

铁素体马氏体（F/M）钢是铅冷快堆堆芯的主要候选材料之一,提高Si含量可提高其抗腐蚀性能,但影响其微观结构和力学性能。为研发兼顾力学性能和抗腐蚀性能的高Si含量F/M钢,本文对Si含量（质量分数为034%、061%、080%、098%和120%）对9%Cr F/M钢微观结构和力学性能的影响进行了研究。结果显示,室温下通过正火（1 050 ℃,05 h,空冷）+回火（760 ℃,15 h,空冷）热处理制备的F/M钢均为全马氏体组织。钢的屈服强度和抗拉强度均随Si含量的增加而增加。Si含量对钢的组织及冲击性能的影响可分为两个阶段,当F/M钢中Si含量为034%~080%时,其组织、冲击性能变化很小;Si含量为098%~120%时,F/M钢中的第二相尺寸、数量增加,沿马氏体板条界面析出少量的Laves相,F/M钢的冲击韧性降低。本研究9%Cr F/M钢中Si元素的最优添加量应低于08%,使钢在保持较高强度的同时兼具良好的韧性。     

Energy Loss in Liquid Metal MHD Induction Converter due to Discrete Tooth-Slot Arrangements

In this paper, the performance characteristics of a linear channel LM-MHD induction converter operated in both constant current and constant voltage mode are obtained analytically, appling the slit channel approximation but taking account of variations in the traveling magnetic field intensity in the direction of the fluid flow according to differences in the disposition of the teeth and slots in the stators. The analytically obtained solutions were verified with the experimental converter with and without copper side bars operated in constant voltage mode at room temperature using NaK-78 as the electrically conducting working fluid. The experimental results obtained with the converter with copper side bars agreed with the analytically obtained solutions, though the plots of power output shifted toward greater values of negative slip compared with the theoretical curves, due to the additional ohrnic losses in both the side walls of channel and the copper side bars, which were not taken into account in the present analysis.     

Characteristic evaluation of electromagnetic flow couplers using a liquid metal MHD analysis code

It is known that electromagnetic flow couplers have high efficiency. In fact, an experiment using a small-scale annulus model shows that it has the maximum efficiency of 60%. However, another experiment using a middle-scale sector model exhibits that the maximum efficiency is less than 20%. In order to analyze this discrepancy, a computer code for solving magnetohydrodynamic flows is developed and is applied to the evaluation of these experiments. The obtained results show that the efficiency of the small-scale annulus model is high as observed in the experiment and the low efficiency observed in the middle-scale sector model is ascribed to the energy loss due to the eddy current arising in the ends of the magnetic region and the electric contact resistance between the stainless steel duct and the copper bus bar.     

Effects of temperature and contact stress on the sliding wear of Ni-base Deloro 50 hardfacing alloy

The sliding wear behavior of Ni-base Deloro 50 hardfacing alloy was investigated in air in the temperature range from room temperature to 350°C under contact stresses of 55, 103 and 207 MPa. At temperatures below 100°C, Deloro 50 showed severe adhesive wear and as a result the amount of wear loss was very large regardless of contact stress. With increasing temperature over 100°C, however, the amount of wear loss decreased and reached eventually to near zero value at temperatures of 200°C, 225°C and 250°C under the corresponding contact stresses of 55, 103 and 207 MPa, respectively. It was found that the decrease of the amount of wear loss was due to the wear transition from severe adhesive to mild oxidative wear which was caused by the formation of wear protective oxide layers on wear surfaces. It was considered that if the temperature was high enough to meet the oxidative wear condition, Deloro 50 could be used as hardfacing material for nuclear power plants valves even under the high contact stress of 207 MPa.     

Optimization of contact conditions between iron base alloys and mercury at room temperature

The intimate contact or wetting of iron-base alloys by mercury is obtained at room temperature by varying the environmental conditions, quasi immediately for Armco iron and a high purity Fe-25Ni alloy, after ∼30 min of contact for the 316L/Hg couple, after one week of contact for the T91/Hg couple. Careful mechanical polishing allows for wetting the notches of CCT specimens made in T91 steel with Hg, whereas chemical etching in 4%HCl is required to wet 316L SS identical specimens. Using ICP-OES measurements, values of solubility limit are given for both Fe (45.5 ± 0.4 wt ppm) and Cr (0.56 ± 0.07 wt ppm) in mercury at room temperature, the one of nickel (2.6 ± 0.39 wt ppm) being in agreement with the literature data.     

Design and Fabrication of a Hybrid HTS Magnet for 150 kJ SMES

This paper describes design and fabrication of a hybrid high temperature superconducting (HTS) magnet for a 150 kJ superconducting magnetic energy system. The hybrid HTS magnet, which employs both BSCCO taps and YBCO taps, is composed of 18 double pancake coils (DPC). Six DPC made of BSCCO are respectively installed on the top and bottom with an inner diameter of 240 mm, an outer diameter of 396 mm, and height of 11.5 mm. Six YBCO coils are mounted in the middle of the magnet with the inner and outer diameters of 264, 396 mm and height of 12.1 mm. Copper plates with thickness of 1 mm are arranged between DPC for the cooling of the heat, and epoxy resin plates with thickness of 0.2 mm are arranged between coil and copper plate for the insulation. The inductance of the magnet is about 11.06 H and the resistance is 169.5 Ω at the room temperature. In order to evaluation the performance of the hybrid magnet, each solidified DPC and the assembled magnet were tested in a bath of liquid nitrogen at 77 K. The resistances of 17 joints were also measured and evaluated by the standard four-probe method.     

低温永磁波荡器过冷液氮冷却系统的设计

低温永磁波荡器(Cryogenic Permanent Magnet Undulator,CPMU)是目前插入件技术发展的主要方向之一,其利用一些永磁材料,如钕铁硼(Nd Fe B)或镨铁棚(Pr Fe B)的磁场性能在低温下明显高于室温的特性来提高波荡器性能和光源束流品质,工作温区为50-150 K,需要冷却系统的冷却。CPMU冷却系统主要包括过冷液氮冷却系统和磁体阵列冷却回路。本文介绍了上海光源(Shanghai Synchrotron Radiation Facility,SSRF)CPMU过冷液氮冷却系统的设计方案和设计参数,进行了系统主要热负载的分析;对冷却系统中关键设备之一的过冷换热器进行了设计,并计算分析了过冷氮流经CPMU冷却系统的全程阻力损失,为系统另一关键设备液氮泵的选型提供依据。对CPMU过冷液氮冷却系统进行的在线测试表明,该设计满足CPMU样机的冷却需求。     

Steady state and transient temperature profiles in a multishell spherical system heated internally by reactor-grade plutonium

Steady state and transient temperature distributions are analysed for multishell spherical systems which are heated in their inner part by the alpha-particle heat power of reactor-grade plutonium. Different geometrical thickness of the spherical shells and temperature dependent thermal material properties are assumed. Boundary conditions at the surface of the multishell system are natural convection by air and thermal radiation or cooling by cryogenic liquids. In addition, cooling by internal thermally conducting structures in outer shells is investigated by applying an approximate heat conduction model. The steady state and transient temperature distributions allow defining limits for alpha-particle heat power at different outer boundary conditions for which e.g. the melting points or other temperature limits of different materials are exceeded.     

Finite element analysis of copper–Nb3Sn contact performance under transverse compression

It turns out from recent researches on Nb₃Sn conductor that contact strain is important for Nb₃Sn conductor, as it could cause the degradation of the conductor itself. Few experimental results describing the behavior of Nb₃Sn sub cables under transverse load are available. Numerical modeling is one method to investigate the contact strain inside the cable. In this paper, finite element method was used to analyze the two- and three strand contact strains under two pressing configurations: flat and concave plates. From the finite element analysis, it is found that the average von-Mises strain of bottom Nb₃Sn in Nb₃Sn–Nb₃Sn–Nb₃Sn contact model and copper–Nb₃Sn–Nb₃Sn contact model is the same under flat or concave plates; the average von-Mises strain of bottom Nb₃Sn in two strand contact model is also the same. It is also verified that the shape of the top copper press has no more influence on the strain distribution in Nb₃Sn strand under the transverse compression.     

Boiling heat transfer behavior of lead–bismuth–steam–water direct contact two-phase flow

The boiling heat transfer behavior of lead–bismuth (Pb–Bi)–steam–water direct contact two-phase flow was experimentally investigated. Experimental study was performed using Pb–Bi–steam–water direct contact boiling two-phase flow loop. The heat transfer rate was estimated from data of one-dimensional flow direct contact boiling of water in Pb–Bi. It is assumed in the analysis that film boiling occurs at the surfaces of a small water droplet after water is injected into hot Pb–Bi flow, because of the large temperature difference between water and Pb–Bi (i.e. 493 K and 733 K for injection water and Pb–Bi temperature, respectively). The heat transfer occurs between Pb–Bi and steam without phase change after all water completely evaporates. The overall heat transfer coefficient decreased with the superheat at low injection flow rate and was nearly constant for high injection flow rate. The local heat transfer coefficient was higher than average one in the whole tube, which means that the direct contact boiling heat transfer coefficient was high and it decreased in the downstream direction. Almost all the water vaporized in the test tube at high pressure according to the local and total heat transfer rate.     

Investigation of the sensitivity to EAC of steel T91 in contact with liquid LBE

The ferritic-martensitic steel T91 is one of the most promising material for application in the generation IV type reactors. However, there are critical issues, such as the susceptibility to damage of the steel in contact with the heavy liquid metals and their effect on the mechanical properties of structural materials. In this context, it was initiated a study of the boundary conditions, necessary to ascertain the sensitivity of the T91 to environmentally assisted cracking when loaded in contact with the liquid lead-bismuth eutectic. A series of tensile tests were carried out in a cell where the specimens were immersed in static LBE. Results showed that at high temperature the steel in contact with the liquid metal had a slight decrease of yield and UTS value and a marked increase in the elongation to rupture. However, at low temperature the elongation to rupture and the reduction of area decreased, indicating the sensitivity to EAC.     

多孔注入冷冻靶快速降温过程瞬态特性研究

高度均匀光滑的燃料冰层是惯性约束聚变冷冻靶成功点火的物质前提,其制备关键是在靶丸外建立均匀的球形温度场并进行精确控制。本文针对多孔注入冷冻靶系统,建立了三维仿真模型,数值研究了冷冻靶温度场稳态分布与瞬态降温特性,并分析了接触热阻、氦气压力等因素的影响。结果表明：冷臂温度恒定时,靶丸与充气管接触位置为低温区,激光入射口正对处为高温区,最大温差为003 mK;硅臂加热块功率突降后,靶丸表面最大温差在025 s内急剧上升至8788 mK,温度场均匀性显著恶化;与硅爪 套筒完美接触相比,低温胶层的存在可有效改善降温过程中温度场的恶化,但降温响应时间明显增加;1～10 kPa氦气压力范围内,快速降温过程中靶丸温度响应迅速,且最大温差峰值较小,有利于维持靶丸表面的温度均匀性。     

Controlling and cooling core melts outside the pressure vessel

For future reactors, the control and cooling of ex-vessel corium melts is under consideration to increase the passive safety features even for very unlikely severe accidents. In this context, different research activities are studying ex-vessel corium behaviour and control, including the implementation of a core cooling device outside the reactor pressure vessel in order to prevent basement erosion and to maintain the integrity of the containment. This paper describes current research on key phenomena which must be understood and quantified to be finally controlled by the cooling device. These are the release of corium melt from the pressure vessel, the temporary retention of the melt in the reactor cavity until melt through of the gate, spreading of the melt on a large surface, and finally the cooling and solidification of the melt by direct water contact. The experiments use high temperature melts which are similar to corium melts. Where necessary, models are developed to transfer the results to reactor scale.