Calculation of a square cascade with losses of the working material in the steps and pipelines during separation of multicomponent isotopic mixtures

A method is proposed for calculating the stationary mass transfer of a multicomponent isotopic mixture in a square cascade with arbitrary enrichment and losses at the separation steps and in the pipelines of the cascade. The method, which is based on successive approximation of the cascade separation factor, makes it possible to reduce computational time substantially compared with the conventional method of quasilinearization. __________ Translated from Atomnaya énergiya, Vol. 104, No. 1, pp. 17–23, January, 2008.     

装机量圆整对刚性级联流体性能影响初步理论分析

建立刚性级联在投资回报率、稳定运行等方面具有一定优势。刚性级联更接近理想级联形式,理想级联对各级的供料流量有着严格的要求,因此在组成级联的单个分离设备供料流量一致的情况下,就对级联各级的装机量有严格的要求。而实际生产级联中无法完全满足理想级联对装机量的要求,装机量往往需要圆整,因此研究装机量圆整对级联性能的影响具有实际意义。本文提出一个圆整参数,并通过对级联流体性能分析得出:任一个级联只要给出运行边界条件,就能获得在保证级联安全运行前提下所允许的圆整范围。本文还确定一种能使实际级联性能更接近理想级联的装机量圆整方法。     

Kinetics of Periodic Cascade Boosters from the Standpoint of Their Speed of Operation and Safety

A system of equations is formulated governing the kinetics of a reactor that is adequate for the purpose of describing transient neutron phenomena in a periodic cascade booster and includes all groups of delayed neutrons. An analytical solution of these equations for the case of constant neutron multiplication coefficient k _eff (booster with no reactivity modulation) is used. The calculations show that periodic cascade boosters have substantial advantages over single-section boosters. The main advantage is that cascade boosters make it possible to increase the depth of subcriticality of the setup, intensify the fast pulse sharply, and decrease the background fission intensity manyfold. In principle, pulse parameters acceptable for practice can be achieved in a cascade periodic booster even without including the reactivity modulation factor. This means that using the cascade principle in periodic boosters will make them safer and improve their pulse parameters.     

单机运行工况对多组分同位素分离级联结构参数的影响

大分离系数情况下的多组分同位素级联的设计和优化可以准理想级联为模型。已知目标组分的精料、贫料丰度及基本参量,可确定准理想级联的结构。除级联本身的参数外,组成级联的单机运行工况也是影响级联分离性能的重要因素。通过利用基本全分离系数作为中间量,理论推导了在分离多组分同位素时,单机运行工况对级联结构及分离性能的影响。同时针对Xe中间组分的分离,采用单纯形法对其优化,研究了单机运行工况对最佳级联的结构参数及最小装机量的影响,进而确定了级联分离Xe中间组分的最佳单机运行工况。     

级联中部设置净化级的可行性研究

级联分离同位素的过程中,不可避免的存在轻杂质,需要在级联的中间设置净化级。如果工质中轻杂质含量较多,运行级联较长时,轻杂质的存在会影响级联的正常运行。为探索在级联中部设置净化级的可行性,采用非定常态法计算求解级联分离方程组,研究净化级的位置、净化比和级联分流比对产品中轻杂质和目标组分丰度的影响。结果表明,在级联中部设置净化级,通过选取合适的级联参数,可以提高目标组分丰度,同时去除轻杂质,实现分离和净化。     

Special features of the enrichment of components with intermediate mass in a quasi-ideal cascade

An approximate approach is described, making it possible to estimate without solving nonlinear equations describing the mass transfer of a multicomponent mixture in a quasi-ideal cascade, the maximum concentration of the intermediate target component which can be obtained in the product flux from the cascade. Asymptotic formulas are obtained for the range of existence of the solutions of the system of equations which relates the external and internal parameters of the cascade. The approach developed is illustrated by examples of a process of separation of a natural mixture of krypton isotopes in a quasi-ideal cascade for admissible concentrations of the target intermediate component in the product and waste flows. __________ Translated from Atomnaya énergiya,Vol. 100, No. 1, pp. 51–56, January, 2005.     

Analytical calculation of the content of uranium isotopes in a cascade with two feed flows,two product flows,and one waste flow

The problem of estimating the ^232,234,236U content in the product flows of an optimal cascade is examined. Relations are found for studying the characteristics of the concentration variations along the cascade for various ratios of the feed flows. It is shown that an effective procedure is to obtain from the intermediate product of the cascade a diluent for high-enrichment uranium. __________ Translated from Atomnaya énergiya, Vol. 102, No. 4, pp. 241–244, April, 2007.     

双通道滤波器组与小波变换

从信号处理和工程应用的角度出发,避开了复杂的数学公式推导．阐述了双通道滤波器组与小波变换的关系．并讨论了母小波函数的选择可归结为正交镜像滤波器的设计。     

针对不锈钢表面60Co污染的电化学去污研究

核设施退役与三废治理过程中会产生大量表面被沾污的不锈钢金属部件,作业环境和人员将面临潜在的放射性污染和受照剂量问题。针对不锈钢金属表面的60Co污染问题,设计了手持式电化学试验装置对不锈钢表面污染进行合理有效的原位去污;采用正交实验法优化电解液浓度、电流密度和电极间距等电化学工艺参数,并对不锈钢表面60Co污染进行去污验证。研究结果表明,本文建立的电化学原位去污方法具有去污时间短、效率高等优点;在电解时间为30 s、电解液为10 mol/L硝酸、电流密度为0.3 A/cm2、电极间距为0.4 cm的条件下,此方法对不锈钢表面60Co污染的去污效率可达99.9%以上,腐蚀深度大于10 μm,可使污染降低至环境本底辐射水平。      

Experiments on cascade-reactor models

There is great interest in our and other contries in cascade blankets. Theoretical and design work has been done on cascade blankets but up to now no experimental work has been done. The first experiments in the world were performed at the All-Russia Reserach Institute of Experimental Physics in 2003–2004 on deeply subcritical uranium— neptunium assemblies. Three series of experiments on cascade and the corresponding single-section blanket models have been peformed. The experiments have confirmed the theoretical conclusions that cascade blankets have positive properties and that ²³⁷Np is effective in them; they have provided valuable experience in operating cascade setups with an electron accelerator. The good agreement between the measurements and the calculations has increased confidence in the computational results obtained for cascade blankets with real values of k_eff. The results of the second and third experiments and a general conclusion concerninig all three series of experiments are presented in this paper. __________ Translated from Atomnaya énergiya, Vol. 100, No. 2, pp. 107–116, February, 2006.     

Gas Separation Performance of Tapered Cascade with Membrane

Membrane gas separation cascades are analyzed at steady state. The methods of calculating the flow rate and concentration profiles in the cascade are examined, using formulas expressing the various membrane separation cell characteristics. The method adopted is applicable to relatively high concentrations and separation factors. Considerations are further given on the steady state performance of four theoretical forms of cascade : (a) with common value of cut for all stages, (b) with symmetric separation cells, (c) with no mixing at the junction at each stage, and (d) ideal cascade.

The analysis showed that, with membrane cells, the ideal cascade would have a pressure ratio varying from stage to stage. The symmetric separation cascade would provide a separation performance lower than the ideal cascade on account of the mixing at the junctions of streams possessing different concentrations, whereas the cut and separation factor of the no-mixing cascade requiring minimum membrane area exhibits zig-zag curves when plotted against stage number. Both these circumstances contribute to the lower separation performance obtained with these two forms as compared with the ideal cascade, and results in larger total membrane area; but these semi-ideal forms retain the advantage of easy practical treatment with their pressure ratio common to all stages.     

富集中间组分同位素的级联—— “T”级联

除了常规矩形级联和阶梯级联等模型外,还有一些其他的级联模型,使用这些特殊级联可以达到特殊分离目的。本文提出一种用于中间组分同位素分离的特殊级联“T”级联。该级联模型可以通过一点供料三点取料的模式,直接提取中间组分同位素。以氙同位素为例,进行理论计算,“T”级联可以一遍分离直接获取丰度90%以上的¹³¹Xe同位素,略高于双级联分离能力。结果表明,“T”级联适合进行中间组分同位素的一遍提取分离。     

Assessment of the MDNBR enhancement methodologies for the SMART control rods banks withdrawal event

For an electricity generation and seawater desalination, a 330 MW System-integrated Modular Advanced ReacTor (SMART) was developed by KAERI. The safety level of the SMART is enhanced when compared to that of the typical commercial reactors, with the aid of an elimination of a large break loss of coolant accident by placing the major components of the primary system in a reactor vessel and the adoption of a new technology and a passive design concept into the safety system. However, the events related to reactivity and power distribution anomalies have been evaluated as vulnerable points when compared to the other initiating events in the SMART, since the reactivity worth of the control rods (CR) banks is quite large due to the boron free core concept. Especially, safety margins, i.e., minimum departure from nucleate boiling ratio (MDNBR), are significantly threatened during the CR banks withdrawal event. Therefore, MDNBR enhancement methodology for the CR banks withdrawal event should be considered to further enhance the safety level of the SMART design. Two methodologies have been suggested to enhance the MDNBR during the CR banks withdrawal event: the application of a DNBR trip function into a core protection system and a turbine trip delay methodology. Sensitivity studies are performed to evaluate the two MDNBR enhancement methodologies and show that the suggested methodologies could enhance the MDNBR during the CR banks withdrawal event of the SMART.     

Chemical absorbent for catching halogen-containing gases discharged from isotope separation plants

The results of industrial tests of a cascade of chemical absorbents for catching spent halogen-containing processes gases during discharge into the atmosphere are discussed. It is noted that the volume of the discharged gases decreases as a result of CO₂ absorption. The HF and Cl₂ content in passing gas can serve as a criterion for the completion of each catching step; Cl₂ detection after the last step is a service life criterion for all chemical absorbents of a facility without exception. The average catching efficiency is 99.7 and 98.5% with respect to fluorine- and chlorine-containing components, respectively. An approximate calculation of the near-ground concentration of HF and Cl₂ is performed. The gases discharged by the isotope separation plant at the Siberian Chemical Combine were purified at the level of the maximum admissible concentration for the working zone and not at the level of the technical norm established individually for each industrial enterprise. Equipping nuclear fuel cycle enterprises with such systems will make it possible to decrease environmental contamination considerably.     

离心萃取级联分离锂同位素的数学模型

萃取法分离锂同位素有望替代汞齐法消除汞害,但需多级萃取才能获得高丰度同位素,采用离心萃取机替代萃取澄清槽形成萃取级联系统可提升分离效率。基于萃取法分离锂同位素、离心萃取分离原理和级联理论,借鉴气体离心级联分离同位素的方法,引入分流比概念,建立了离心萃取级联分离锂同位素单级、多级的数学模型和级联的平衡时间模型,对离心萃取级联分离锂同位素进行计算分析。离心萃取级联是一种类似全回流矩形级联形式,取料量对级联级数有着很大的影响,级联存在最大取料丰度限制,级联平衡时间受到目标丰度和离心萃取机级停留时间(处理能力)影响,采用多步法级联可有效减少平衡时间。该数学模型可指导工艺的设计,为下一步的产业化应用提供理论依据。     

Crossflow-induced vibrations of heat exchanger tube banks

This paper presents a mathematical model for crossflow-induced vibration of tube banks. Motion-dependent fluid forces and various types of flow noises are incorporated in the model. An analytical solution for the fluid inertia force, hydrodynamic damping force, and fluid elastic force is given for tube banks arranged in an arbitrary pattern. Based on the model, a better understanding of the vibrations of heat exchanger tube banks subjected to various flow excitations can be developed.     

离心长级联水力学动态数值模拟

针对已有的调节方法无法进行离心长级联水力学动态模拟的问题,提出了一种新的调节方法。该方法从中间供料级出发,根据机器滞留量和管道额定流量向两端逐级调节阀门,从而得到离心长级联稳定运行时的水力学状态。50级和100级的数值模拟结果表明,该方法不受离心机水力学特性参数的限制,大幅缩短了调节时间,可以较快得到满足水力学要求的级联设计参数。在级联稳定运行的基础上,通过改变供料量,分别研究了在有无阀门自动调节作用时水力学扰动在长级联中的传播情况。     

Calculation of the Optimal Parameters of a Cascade for Separating a Multicomponent Mixture of Isotopes

A method is developed for determining the optimal parameters of a cascade for separating multicomponent isotopic mixtures with a prescribed output concentration for the target isotope. The method is flexible with respect to cascade efficiency criteria. It is based on a systematic calculation of the parameters of a counterflow symmetric cascade with prescribed structural parameters and waste concentration of steps with respect to the valuable (as a rule, the light) isotope. The computational procedure developed includes iterative refinement of the initial approximations of the concentration of nontarget isotopes in the steps. The waste concentration of the steps with respect to the target isotope is varied in order to find the best cascade variant in accordance with the optimization criterion chosen. The properties of cascades optimized with respect to the criterion of minimum total flux are investigated. It is shown that they differ from the nonmixing criteria with respect to the separated isotopes that are conventionally used in the theory of multicomponent separation.     

Collision cascade temperature

Interaction of a projectile with a solid has been considered in detail. It has been found that any collision cascade generated by a projectile can be characterized by the average kinetic energy of cascade atoms that represents an “instantaneous temperature” of the cascade during its very short lifetime (10⁻¹² s). We refer to this value as the “dynamic temperature” in order to emphasize the fact that cascade atoms are in a dynamic equilibrium and have a definite energy distribution. The dynamic temperature defines the electron distribution in the cascade area and, hence, the ionization probability of sputtered atoms. The energy distribution of cascade atoms and, as a consequence, the dynamic temperature can be found experimentally by measuring the energy distribution of sputtered atoms. The calculated dynamic temperature has been found to be in good agreement with the experimental data on ion formation in the case of cesium and oxygen ion sputtering of silicon. Based on the developed model we suggest an experimental technique for a radical improvement of the existing cascade sputtering models.     

Contaminative Behavior of Plutonium Chloride on Protein Film

This paper deals with the contaminative behavior of plutonium chloride on a protein film, which was studied in order to contribute to the knowledge of actual skin contamination. The experiments were carried out by changing such factors as soiling time, radioactive concentration, the concentration of coexisting electrolyte, acidity of the soiling solution and washing time.

It was found that the contamination of plutonium varied with soiling time and with the acidity of the soiling solution. Maximum contamination was observed at pH 0.9.

The mechanism of contamination is discussed, and it is concluded that contamination would appear be promoted by the formation of aggregated plutonium produced by the interaction with the surface of the protein film.