强流相对论电子束传输过程中的电荷中和理论

讨论了有外加磁场情况下,强流相对论电子束传输过程中的电荷中和理论,着重讨论了二次电子逃逸时间和外加磁场对空间电荷中和的影响。得知当电子束半径大于2.0 cm 时,在计算空间电荷中和时间时就得考虑二次电子逃逸时间的影响。在一定条件下,外加磁场对空间电荷中和有阻碍作用,对于长漂移室,存在空间电荷中和允许的磁感应强度上限。     

电子束3D打印动力学模拟计算

正电子束3D打印光路仅由1个螺线管和1个偏转磁铁构成,虽然其结构简单,但是要求束斑尺寸达到0.1mm左右,这对于10mA/60kV的强流低能电子束的难度很大,特别是光路还要求大角度偏转。对于无偏转光路,采用Trace3D对光路进行动力学计算的结果如图1所示,螺线管场强为103G。电子束传输过程中的电荷中和率为0.1%,即电流实际流强为10 mA,电荷中和后的流强为0.01mA,所得束斑半径为0.09mm。     

强流相对论性电子束在中性气体中传输时电流中的过程的研究

研究强流相对论性电子束(660kV,40kA,100ns)在中性气体氢(13—2600Pa)中传输时电流中和特性。实验发现:随着本底气体压强自低到高的过渡,电流中和效应先是由弱到强,继而由强到弱,当压强在133.3Pa左右,测得的最小电流中和比～15%。基于对束流传输时气体电离和带电粒子运动的分析所做的电流中和过程的数值模拟,较好地解释了实验结果,且对束流传输时内部的电流、电磁场和带电粒子密度分布等的变化作了相应研究。     

加工等离子体中的尘埃现象

本文从等离子体中材料产生的新观点评述了加工等离子体中的尘埃现象，已对ＳｉＨ，ＲＦ等离子体广泛地研究了粒子的气体生长，Ｓｉ粒子通常通过三个不同的阶段生长，厚约１０ｎｍ之前的初始生长阶段，其大小是在由等离子体性能及其电子亲合力支配的大小范围内：快速生长阶段和生长饱和阶段，在第一阶段，尽管大部分是中性粒子，但是粒子定域在等离子体／鞘边界附近，在第二阶段，出闰子间极快凝结，这种凝结可用由于高能电子而产生带     

铀表面腐蚀初始阶段的理论模型

本文使用数值模拟方法讨论了铀表面腐蚀初始阶段的氧化物形成过程.这个阶段发生在从清洁的铀表面吸附反应气体后到整个表面被一层氧化物所覆盖的过程之间.对储存在含有腐蚀气体气氛中的铀和铀合金材料,准确了解铀最初开始反应到表面被氧化物完全覆盖的反应速率是非常重要的.本文对该氧化物形成的过程进行了数学推导,讨论了等温情况下的近似分析数学表达式,得到了动力学方程,并与实验结果进行比较,表明理论模型是合理的.     

液滴法制备空心玻璃微球的过程分析

将液滴法制备空心玻璃微球（HGM）的过程划分为液滴的形成、凝胶球壳的形成与干燥、干凝胶球壳的熔炼等阶段,分析了各阶段的物理过程,提出了控制液滴大小、初始速度和液滴中玻璃形成物含量的定量方法,阐述了炉体轴向温度分布、抽气速率和吹扫气体组成对形成HGM的影响。     

低真空中高能电子束传输特性的MC模拟

基于Geant4蒙特卡罗程序包建立了低真空条件下高能电子束的输运模型,并用该模型详细研究了电子束在低真空条件的传输特性。结果表明,低真空条件下电子束传输特性与高真空下的有较大差异,环境气体对电子束有散射作用,而磁场可有效约束高能电子的传输轨迹,最终轨迹是磁场约束作用与环境气体散射作用竞争的结果。对于确定的磁场分布,电子束能量存在一个最佳范围,从而保证电子束的传输特性。     

低压多丝正比室的位置分辨研究

低压多丝正比室为放射性束核反应的靶前粒子提供位置和时间信号。本工作用²⁴¹Amα源研究电压、工作气体压强等因素对低压多丝正比室位置分辨的影响。实验结果表明：在不同的气体压强条件下，低压多丝正比室的位置分辨均可达到1mm，但考虑到时间、效率等因素，实验中需尽可能提高气压。     

安全壳压力试验中多元混合可燃性气体的爆炸极限研究

在核电站安全壳压力试验过程中,由于涂层油漆及维修化学药品挥发而产生的可燃气体易发生扩散、富集现象,加之于高温高压的试验环境,进一步增加了火灾发生的风险。为提高压力试验的安全性和可靠性,本文基于爆炸极限试验模拟及理论模型计算,对压力试验环境下7种常见的可燃性气体及其混合可燃物的爆炸极限变化规律展开研究。研究结果表明：安全壳内混合可燃物中苯、二甲苯、乙酸乙酯、甲苯等爆炸下限较低的可燃性气体所占的体积分数越大,压力试验过程中发生火灾的风险越高;初始压力的增加增大而造成爆炸的可能性较小;爆炸极限范围随着初始温度的升高而增大,尤其是爆炸下限的降低增加了安全壳内可燃气体爆炸的风险性。     

用于短寿命核素研究的简单的气体传输系统

气体传输系统是研究短寿命核衰变的一种重要的实验技术。由于周期表中大多数元素具有高的粘滞系数,这些元素的传输需用气体喷咀技术,特别是氦喷咀技术。对于气体元素或某些能形成稳定气体的化合物元素,由于它们的粘滞系数比较低,运用一般的气体(空气)能把它们从高辐射场位置有效地传输到低本底区。气体的传输速度在亚声速范围以内,对于10     

Collective Acceleration with Intense Electron Beams

Collective acceleration methods that employ an intense relativistic electron beam (IREB) are discussed. A brief history and a classification of collective acceleration methods are given. Methods examined include IREB injection into neutral gas; IREB injection into vacuum; plasma-filled IREB diodes; and vacuum-filled IREB diodes. Accelerating fields of order 106 V/cm have been observed experimentally. The collective acceleration processes for IREB injection into neutral gas and vacuum are discussed. It is noted that the collective acceleration processes for IREB diodes have not been elucidated yet. A summary of present collective ion acceleration research areas that involve IREB's is given.     

Sorption-Extraction Processes in Uranium Hydrometallurgy: Processing of Monometallic Uranium Ores

The method used to develop sorption-extraction processes in uranium hydrometallurgy over the last 50 years is examined. The first-generation sorption-extraction processes, ionites, and apparatus are described. Data for the second-generation sorption-extraction technology and improvement of apparatus are generalized.The third generation of these processes is characterized by the adoption of porous anionites AM-p and AMP-p in order to make the kinetic characteristics of the sorption and extraction processes closer to one another, by sorption leaching of uranium ores, and by adoption of double synergetic mixtures of extracting agents at the stage of repurification of the commercial reclaim and by the development of fast sorption processes for extracting uranium from productive solutions used in mound and underground leaching. The fourth-generation processes are characterized by the use of high-volume vinyl pyridine ionites, tertiary synergetic mixtures at the extraction stage, combined extraction-desorption processes, solid-phase regeneration of saturated ionites, and conversion of absorbed anions of uranyl-trisulfate into nitrate and chloride complexes. 1 figure.     

Investigation of bounds on particle packing in pebble-bed high temperature reactors

Models and methods are presented for determining practical limits of the packing density of TRISO particles in fuel pebbles for a pebble-bed reactor (PBR). These models are devised for designing and interpreting fuel testing experiments. Two processes for particle failure are accounted for: failure of touching particles at the pressing stage in the pebble manufacturing process and failure due to inner pressure buildup during irradiation. The second process gains importance with increasing fuel temperature, which limits the particle packing density and the corresponding fuel enrichment. Suggestions for improvements to the models are presented.     

Magnet stage optimization of 5 kW multi-cusped field thruster

The multi-cusped field thruster is a unique electric thruster device, which has many advantages such as long lifetime, large-range thrust throttling ability, high thrust density, and low mass. The thruster employs several alternating polarity permanent magnets to create a periodic magnetic field with several cusps. Previous studies have indicated that the basic ionization and acceleration processes are directly related to the electron motion behavior, which mainly depends on the magnetic field characteristics. The magnet number and magnet stage length are two key magnetic field parameters that have important effects on the thruster performances. In this paper, both the magnet number and magnet stage length parameters are studied for the optimization of a 5 k W multi-cusped field thruster. The results indicate that the three-stage thruster has a better electron confinement than the two-stage thruster. It has lower ion energy loss at the wall, and shows a higher ionization rate. Therefore, the three-stage magnetic field is a superior magnetic field configuration. Besides, the three-stage magnetic field simulation results indicate that an optimal accelerating electric field distribution and ionization region distribution could be obtained when the magnet length ratio is 78:25:20.     

Matrix-assisted pulsed laser evaporation of polymeric materials: a molecular dynamics study

Matrix-assisted pulsed laser evaporation (MAPLE) has been recently developed to deposit high-quality thin films for a wide range of polymeric materials. To analyze the evaporation of polymer molecules in MAPLE, we present a molecular dynamics (MD) simulation of laser ablation where the target material is modeled as a solution of polymer molecules in a molecular matrix. The breathing sphere model is used for MD simulations of laser ablation of the molecular matrix. Polymer molecules are described using a bead-spring model, where each bead represents one or several polymer groups. The initial stage of polymer ejection is investigated at different laser fluences and pulse durations. The influence of polymer molecules on the stability of clusters formed in the plume and the processes that can lead to polymer decomposition are discussed.     

Applicability of small-scale integral test data to the 4500 MWt ESBWR loss-of-coolant accidents

This paper discusses the scaling methodology used by GE Hitachi Nuclear Energy (GEH) to show that the data obtained from the small-scale integral test facilities, namely, GIST and GIRAFFE-SIT, are relevant to the postulated loss-of-coolant accident (LOCA) of the 4500 MWt ESBWR. The conservation of mass and energy equations for the steam-water mixture in the reactor pressure vessel (RPV) are transformed to the equations for the rates of pressure change and water mass or inventory change. These equations are non-dimensionalized based on the most dominant physical processes of the individual stages of a LOCA, namely, the late blowdown stage, the GDCS (gravity driven cooling system) transition stage and the full GDCS stage. The magnitudes of the non-dimensional Pi-groups, obtained from these equations, for the 4500 MWt ESBWR are compared with those obtained for the small-scale integral tests mentioned earlier. In addition, simplified analyses were conducted for the first two stages by integrating the non-dimensional RPV depressurization rate and the water inventory change rate equations. The results of the 4500 MWt ESBWR are very similar to the test data obtained from the GIST and the GIRAFFE-SIT test facilities. Therefore, based on both the Pi-group magnitudes and the simplified analyses, it is concluded that the small-scale integral test data mentioned above are applicable to the 4500 MWt ESBWR LOCA applications.     

Prediction Method in Numerical Simulation of Dynamics Based on Prompt and Delayed Neutrons in Multiplying Systems

The basic elements of a method of numerical simulation of processes based on prompt and delayed neutrons in multiplying systems are presented. The method is based on predicting the contribution of the instantaneous state of the system to its state at subsequent definite times and summing the predicted contribution as a systematic transition is made to a new moment in time. The key element of the method is determining the initiation functions – the probabilities that a neutron emitted by a source in a prescribed volume of the system initiates a prompt fission neutron in a definite volume of the system sometime after emission. A procedure is proposed for determining the initiation functions; this procedure is based on the first-collision probability method and uses the standard stationary computer codes. The material presented in this paper comprises the basic results of the first stage in the development of the numerical model for full-scale simulation of the dynamics of the subcritical blanket of an experimental accelerator-driven subcritical system under construction at the Institute of Theoretical and Experimental Physics. It is noted that the model being developed can be used to analyze many important processes in other types of multiplying systems.     

Performance of the IAEA transport regulations in controlling doses and risks from a large-scale radioactive waste transport system

Abstract

The role of United Kingdom Nirex Ltd is to provide the UK with safe, environmentally sound and publicly acceptable options for the long-term management of radioactive materials generated by the UK's commercial, medical, research and defence activities. An important part of this role is to set standards and specifications for waste packaging. Waste producers in the UK are currently developing processes for packaging many different types of intermediate-level waste (ILW), and also those forms of low-level waste that will require similar management to ILW. When packaging processes are at the proposal stage, the waste producers consult Nirex about the suitability of the resulting packages for all future aspects of waste management. The response that Nirex provides is based on detailed assessments of the proposed packages, their compliance with Nirex standards and specifications, and their predicted performance through the successive phases of waste management. One of those phases is transport through the public domain. This paper draws on experience gained from more than 200 separate transport safety assessments which have cumulatively covered a wide range of waste types, waste packages and transport packages.     

Nuclear plant life expectancy indicators

The good management of the life potential of nuclear plants requires the availability of life indicators which the operators have to keep under control. The best indicators are these prepared and developed for the early stage of the equipments design. Due to the progress accomplished in the 2 or 3 past decades, the design by analysis of the resistance of main components to various mechanical damages supplies several such indicators which can be followed in service by convenient processes. Further progresses are still strongly wished for damages and equipments which are not still covered by such analysis.