供料条件对气体离心机分离性能影响的数值研究

采用有限差分方法离散线性化的Navier-Stokes方程组,研究不同供料条件对离心机内部流场和分离性能的影响,得到了不同供料条件下的流场,采用改进的径向平均法求解丰度方程得到单机的分离功率,绘制了分离功率随供料条件各参数的变化曲线。计算结果表明:不同供料条件下,离心机内部流场和分离性能差别明显,供料位置、轴向速度扰动量和角向速度扰动量是供料气流影响流场和分离性能的主要参数;对给定离心机模型存在最佳的供料位置和角度。     

离心法分离锗同位素实验研究

采用气体离心法,以GeF4作为分离介质,通过国产离心机的单机实验成功分离了锗同位素,初步掌握了不同供料流量、分流比下GeF4离心分离的基本全分离系数,得到的基本全分离系数大于1.40,并且通过1-2-1级联实验及相关计算,对高丰度76GeF4产品的生产进行了模拟。实验证明,以GeF4为工作介质,采用国产离心机分离锗同位素可以获得高丰度的76GeF4产品。     

以正辛烷为介质离心分离碳同位素

以正辛烷(C₈H₁₈)为分离介质,利用离心机进行了一系列单机分离实验,研究了其单机分离性能。通过质谱分析,得到了不同供料压强、滞留量下的基本全分离系数、分流比等单机参数：基本全分离系数接近或大于1.10,最高可达1.13。在单机实验数据的基础上,采用相对丰度匹配级联（MARC）的计算模型,对正辛烷离心分离级联的参数进行了初步估算,估算结果显示,采用联级分离可将¹³C浓缩至约11%。     

以三氯化硼为介质离心分离硼同位素

为了实现硼同位素的分离制备,采用气体离心法,以三氯化硼为工作介质进行离心分离研究。通过单机分离实验,对三氯化硼样品进行质谱分析,得到不同供料流量、分流比条件下的基本全分离系数,并在此基础上进行富集硼-10的离心分离级联计算。结果表明,以三氯化硼为工作介质离心分离硼同位素可行;三氯化硼的基本全分离系数可达1.08;使用30级矩形级联或60级相对丰度匹配级联一次分离可以获得丰度大于60%的硼-10同位素产品,二次分离可以获得丰度大于90%的硼-10同位素产品。该研究的开展可为离心法生产高丰度硼同位素产品提供参考。     

离心机分离功率的影响因素

目前，稳定同位素的大量需求和广泛应用极大地推动了离心分离技术的快速发展。本文通过价值函数和分离功率的统一表达式，推导出用全分离系数、供料量、分流比和供料丰度表示的分离功率的表达式。在推导的过程中，对全分离系数、供料量、分流比和供料丰度各个因素没有任何的限制条件，其适用的范围更广泛。同时，应用分离功率的一般表达式，分析了各个因素对分离功率的影响。     

多供取料的Q模型级联的数学描述

同位素分离中可能需要具有多个供料和取料的级联,以满足复杂的分离需求,取得更好的分离效果.对多供取料级联的分析,比传统三股流级联的分析复杂得多.获得多供取料下的级联数学描述,能够减少分析中的困难.本文针对多分段的连续流量的Q模型级联,在多供取料情况下,给出了描述级联的流量和同位素组分丰度在级联中分布的解析表达式,讨论了方...     

用于多组分分离的中间取料矩形级联的优化设计

多组分同位素混合物的某一中间组分通常在分离级联的中间某级达到峰值,但一般的级联均采用从级联组两端取出产品和废料的工艺。为得到丰度较高的中间组分产品,最好在级联中间取料。本工作研究矩形级联中使用中间取料方式以提高级联分离的中间组分丰度。通过数值模拟计算和数值优化,研究了级联两端取料量和级联供取料位置等参数对中间取料中目标组分丰度的影响。采用单参数分析,估计了级联各参数的取值范围以及它们对目标组分丰度的影响。通过优化计算,在供料丰度和流量不变、产品流量不变的情况下,得到了可以生产更高丰度中间组分产品的级联。     

以二氧化碳为介质扩散分离碳同位素的可行性研究

为进一步提高气体扩散法分离¹³C同位素的效率,在前期初步实验的基础上,开展单级扩散分离参数优化实验研究,并进行高丰度¹³C同位素制备的级联方案初步设计。在相对优化的实验参数条件下,气体扩散分离二氧化碳的基本全分离系数可以达到1.01以上。对单级分离实验数据进行计算,初步拟合出供料流量与膜前后压强的函数关系。采用多元分离理论对扩散分离二氧化碳进行级联分析计算,以天然二氧化碳为原料,可通过两次级联分离获得高丰度¹³C同位素。第一次阶梯级联分离的重馏分¹³C同位素丰度大于42%,并将其作为第二次阶梯级联分离的供料,第二次阶梯级联分离的轻馏分¹³C同位素丰度大于90%。     

以三氯化硼为介质离心分离硼同位素

为了实现硼同位素的分离制备,采用气体离心法,以三氯化硼为工作介质进行离心分离研究。通过单机分离实验,对三氯化硼样品进行质谱分析,得到不同供料流量、分流比条件下的基本全分离系数,并在此基础上进行富集硼-10的离心分离级联计算。结果表明,以三氯化硼为工作介质离心分离硼同位素可行;三氯化硼的基本全分离系数可达1.08;使用30级矩形级联或60级相对丰度匹配级联一次分离可以获得丰度大于60%的硼-10同位素产品,二次分离可以获得丰度大于90%的硼-10同位素产品。该研究的开展可为离心法生产高丰度硼同位素产品提供参考。     

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。     

Value Function and Separative Power for Asymmetric Separation Process

The separative power of a separating process is represented by the increase of the value of an isotope mixture which passes through the process. The separative power must be independent of the feed concentration, and is expressed by an arbitrary function of the heads and tails separation factors α and β, the functional form being chosen to suit practical convenience. This functional form is used to determine a value function, which is used for calculating the total separative power of an isotope separating cascade. When the constituent elements are asymmetric, different values are obtained for this separative power even if the cascade is operated under the same input and output conditions (i.e. flow rates and concentrations of feed, product and waste). In the present analysis, the functional form of the separative power is so determined as to minimize this dependence on asymmetry. When the feed concentration is very small compared with unity, as in the cases of heavy water production and uranium enrichment, the functional form to be adopted is σU = L{(α-l)β In β-(β-1) In α}/{ αβ-1), with which the dependence on asymmetry becomes almost negligible. On the other hand, when the feed concentration is nearly unity, the functional form agrees with that obtained by Bulang et al.: σU_B = L{(β-1)α In α—(α—1) In β}/(α β—1).     

Effects of Partition Wall within Packings on Separative Performances of Water Distillation for H2O-HTO Isotope Separation

For the performance assessment of H₂O-HTO isotope separation by distillation, three-dimensional internal vapor flow and concentration profiles were obtained numerically for two types of packing of 6 mm of inner diameter and 6 mm of height: One is a simple cylindrical tube (packing I) and the other diametrically partitioned with an internal wall (packing II). The results of the concentration profiles were used to estimate separative performances of the packings. The total mass transfer rate of HTO from vapor to liquid per unit area of vapor-liquid interface per unit vapor flow rate decreased with an increase in the vapor flow rate, and the value for the packing II is smaller than that for the packing I in the range of relatively small vapor flow rate. Each separative power for the packing I and II has a maximum value of 1.4×10^–7 g/s at the Reynolds number of the vapor Re_v of 54 and 3.7×10^–7 g/s at Re_v =160, respectively.     

Multivariate analysis with covariance matrix applied to separative power modeling of a gas centrifuge

In this work, the least-squares methodology with covariance matrix is applied to determine a data curve fitting to obtain a performance function for the separative power δU of an ultracentrifuge as a function of variables that are experimentally controlled. The experimental data refer to 460 experiments on the ultracentrifugation process for uranium isotope separation. The experimental uncertainties related to these independent variables are considered in the calculation of the experimental separative power values, determining an experimental data input covariance matrix. The process variables, which significantly influence the δU values, are chosen to give information on the ultracentrifuge behaviour when submitted to several levels of feed flow rate F, cut θ and pressure in the product line, P_p. After the model goodness-of-fit validation, a residual analysis is carried out to verify the assumed basis concerning its randomness and independence and mainly the existence of residual heteroscedasticity with any explained regression model variable.     

Oxygen Potential of Cs2U4O12/Cs2U4O13 Equilibrium

A batch distillation of tritiated water (～10 nCi/cm³) has been performed in a packed column 1.6cm inner diameter x 100 cm high. Packings were Dixon rings made of SUS. Time variations of tritium activity were measured by changing vapor flow rate within the column, and then the separative performances, such as the separation factors and the separative power per unit charge, were obtained. The maximum values of the total separation factor and the separative power per unit charge were 1.45 and 2.0x10^?2, respectively. The vapor flow rate from the reboiler decreases as the batch operation proceeds, so that a simulation with a fixed stage-number, the usual case, could not sufficiently predict the experimental values. We have therefore developed a simulation procedure where the number of hypothetical stages can be changed during the batch operation in order to predict the dynamic column behavior obtained from the experiments. The simulation result with the variable stage-number agreed with the experimental one.     

Separative Power of 2-Up 1-Down Ideal Cascades

Interstage flows are analyzed for ideal cascades composed of asymmetric separation elements. It is shown that, in such a cascade, the separative power is additive, that is, the summation of the separative powers of all stages equals the total separative power of the ideal cascade composed of asymmetric separators. This is proved by calculation establishing that the total sum of interstage flows is equal to that obtained by dividing the total separative power of the cascade by the separative power per unit flow of the elements. A similar additive property is also evidenced for separative powers relevant to the desired and undesired materials. As a concrete example, a 2-up 1-down cascade is discussed.     

Flow Induced Vibrations in Gas Tube Assembly of Centrifuge

A centrifuge essentially consists of a rotor rotating at very high speed. Gas tube assembly, located at the center of the rotor, is used to introduce feed gas into the rotor and remove product and waste streams from it. The gas tube assembly is thus a static component, the product and waste scoops of which are lying in the high pressure region of a fluid rotating at very high speed. This can cause flow induced vibrations in the gas tube assembly. Such vibrations affect not only the mechanical stability of the gas tube assembly but may also reduce the separative power of the centrifuge. In a cascade, if some of the centrifuges have gas tube vibration, then cascade performance will be affected.

A theoretical analysis of the effect of waste tube vibrations on product and waste flow rates and pressures in the centrifuge is presented. A simple stage consisting of two centrifuges, in which one has tube vibration, is considered for this purpose. The results are compared with experiment. It is shown that waste tube vibration generates oscillations in waste and product flow rates that are observable outside the centrifuge.     

基于Q级联理论估算同位素生产的成本

在决定某种同位素的生产之前,有必要进行生产的经济性分析,以了解和确保生产的经济可行性。本文给出一种用离心法生产非铀同位素的成本分析方法。利用Q模型级联(简称Q级联)理论得到同位素分离的原料利用率与级联相对总流量的关系。通过利用公开的离心法铀同位素分离的单位分离功价格数据,避免生产成本分析中涉及分离单元成本和人员成本等多个复杂因素,在假定分离部分成本正比于分离工厂规模情况下,导出了成本分析的简单公式,可根据原料成本、铀单位分离功价格、原料利用率等对产品成本进行评估和优化。并以铅同位素²⁰⁸Pb的生产为例,对成本分析的过程进行了阐述。结果表明：利用本文的方法,成本分析简单易行。     

Numerical Analysis of Separative Power of Isotope Centrifuges, (II)

It is found from numerical analysis that a strong influence is exerted on the separative efficiency of centrifuges by the thermal convection arising from the temperature difference prevailing between the end plates of a centrifuge drum—known as “Ekman suction”. The numerical method previously developed by Nakayama & Torii is used to compute the distributions of concentration resulting from considerations of both thermal convection and forced flow.

The effect of Ekman suction is represented by the parameter λ_E(≡(a²√E _ρpsV?T)/(16 lρDT₀)), different values of which were adopted in the calculations, as were other parameters such as λ(≡G_F/(?ηlρpD), G_F: feed rate) for the forced flow and θ representing the cut. The separative efficiency of an exemplified counter-flow type centrifuge is found to reach 58% when λ_e≒0.7, λ≒1.0 and θ≒O.3, with a product port radius r _p= 0.5.

It is also shown that the thermal convection in the Stewartson layer near the side wall of a centrifuge drum affects the separative, efficiency to relatively small but not negligible extent.