Studies on Isotope Separation of Lithium by Electromigration in Fused Lithium Bromide and Potassium Bromide Mixture, (III)

Enrichment of ⁶Li by means of electromigration was carried out in fused LiBr-KBr mixture of a composition of 1.54 (Li/K in chemical equivalent ratio).

The electromigration brought about by 847,000 C of charge transported at 520°C, produced in the cathode compartment 38.4 meq. of Li salt with an abundance ratio of the isotopes (⁷Li/⁶Li) of 7.03, as compared with the initial value of 12.58. The distribution of the total amount of salt and of the salt composition in the migration tube agreed well with the results previously obtained on the enrichment of ⁷Li. It is suggested that, in veiw of the similarity in phase diagrams between UCl₄-CaCl₂ and LiBr-KBr systems, there are logical possibilities of ²³⁵U enrichment by analogous procedure.     

Studies on Isotope Separation of Lithium by Electromigration in Fused Lithium Bromide and Potassium Bromide Mixture, (I) Enrichment of Lithium-7

Lithium-7 was enriched by electromigration at 500° C in fused LiBr-KBr mixture.

The migration cell was made of Pyrex glass; zircon sand (100–200 mesh) was used for packing material, and graphite rods as electrodes.

The electromigration was carried out for 13.4 days at a constant electric current of 165 mA.

The distribution of the abundance ratio of the Li isotopes and of the composition of the salt in the migration cell were investigated. The abundance ratio of the Li isotopes (⁷Li/⁶Li) in the anode compartment was found to change from the original value of 12.20 to 46.9. The composition (Li/K in chemical equivalent ratio) of the salt reached roughly constant at 1.41 throughout the migration cell except in the vicinity of the cathode, and the value was not affected by the composition of the feed salt. It is the selective transport of salt of this composition toward the anode compartment by capillary action in the migration cell that is considered the mechanism that makes sustained electromigration possible. The mechanism of the accumulation of the isotope effect is also discussed.     

Isotope Separation by Multiple Contact, (II)

An analytical procedure for the frontal process has been developed for the case in which (1) the mobile fluid phase proceeds stepwise from one contacting unit to the next, (2) isotopic exchange equilibrium is attained between the mobile and stationary phases in all the units, and (3) chemical refluxing occurs always at the frontal edge of the region containing the fluid phase.

Equations were derived for the isotopic abundance ratio of a chemical substance at any refluxing unit and for the early part of a breakthrough curve. It was possible to obtain an approximate estimate for the separation factor and for the number of contacting units when a breakthrough curve was drawn from experiment. Finally, a comparison of the frontal process with the reverse frontal process was made with some numerical examples.     

The Isotope Effect in the Electromigration of Sodium-Ion in Fused Sodium Nitrate

The isotope effect of sodium-ion in countercurrent electromigration (Klemm's method) has been investigated for a system of fused sodium nitrate labelled with the radioactive nuclide ²²Na. Two runs were made (Experiments A and B, respectively). In Experiment A, the fused salt chain, Al(cathode)-NaNO₃-Pt(anode) was electrolyzed for 20 hr at 340°C with a current density of 1.3 A/cm² in the separating tube. In Experiment B, electrolysis was carried out for 67 hr at 380°C with a current density of 1.5 A/cm² in the separating tube. After electromigration, a change was observed in the specific activity of sodium in the separating tube. The elementary process separation factor, defined as the ratio of the mobilities of the isotopic ions, i.e., V _Na-22/V _Na-23, was calculated to be 1.0023 for Experiment A and 1.0017 for B. The mass effect for sodium ion in fused sodium nitrate was calculated to be ?0.045±0.006 (standard deviation).     

基于光化学锂同位素分离条件的同位素比率测量

从光化学锂同位素分离实验研究的需求出发,基于其分离条件,提出了一种测量锂同位素比率的方法。该方法利用锂原子蒸气对探测光吸收峰的峰值来计算锂的同位素比率,避开了测量原子密度时所需的吸收信号频率定标与光强随频率变化积分中积分限的选择问题。该方法还根据锂同位素吸收谱的特殊性采用具有较强吸收效应的⁶Li的D₂线对应的吸收峰峰值,可在原子蒸气中⁶Li含量较低时提高对比率的测量精度。设计并搭建了实验装置,对该方法进行了测试。同一条件下所测得的同位素比率相对标准偏差小于1%,表明该方法对光化学分离方法中锂同位素比率相对变化是敏感的。这意味着该方法可作为以原子蒸气为分离介质的激光锂同位素分离研究的诊断手段。     

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。     

Separation of Isotope Mixture in a Two-Dimensional Supersonic Jet

A numerical analysis is presented on the separation of UF₆ isotope mixture in a supersonic jet from a two-dimensional sonic nozzle, based on the kinetic theory of gas in the continuum region.

The results of calculation for the diffusion flux are found to be in fairly good agreement at low Knudson numbers with the results of experiment given by Becker et al.     

Separation of Isotope Mixture in a Free Molecular Jet

With the aim of finding the most desirable set of conditions for powder metallurgical preparation of graphite matrix fuels containing thorium carbide, the properties and structure of fuel samples prepared by compacting various mixtures of powdered material followed by heating were investigated.

It was found that of the resulting compacts those consisting of (1) purified and milled natural graphite powder, (2) metallic thorium powder and (3) furfuryl alcohol as binder showed the best properties after heating to 600°C. These compacts possessed 1.90–2.40 g/cc density, 3.5–10.0 kg/mm² Vickers hardness, a thermal expansion coefficient at 900°C of about 14×10^?6/°C in the direction parallel to, and 2.5times;10^?6/°C normal to pressing direction, and a thermal conductivity, in the same temperature range, of 0.02 (parallel) and 0.07cal/cm-sec°C (normal).

Since these favorable properties and structural features are not impaired by heating to about 2,000°C subsequent to treatment at 600°C, it can be said that a new, simple and effective set of conditions for fuel preparation has been found.     

Enrichment of Stable Isotopes, (IV) Theoretical Treatment of Ion-Exchange Systems Used for Lithium Isotope Separation

In order to gain an insight into exchange systems used for Li-isotope separation, experiments have been made from the point of rate theory. From the resulting data were derived equations related to the plate height due either to particle or to film diffusion. Using these equations, the plate height values based on particle and on film diffusion were determined by curve fitting. Further, ion-exchange reactions at the front and tail boundaries of the Li adsorption band were investigated in detail. Finally, the validity of the equations derived was proved by good agreement found with the experimental data obtained on an Li-elution system under steady state.     

Isotope Separation of Argon by Axial Flow Turbo-Machine, (I)

The strong dependence on molecular weight shown by the compression ratio of a turbo-molecular pump for high vacuum suggests its possible utility for isotope separation. The separation factor obtainable with a multistage turbo-machine was estimated by means of a simplified calculation assuming molecular flow, and zero net throughput. The separation factor depends on the rotating speed of the pump, and attains maximum value when the speed of the blades is close to the most probable speed of the molecules.

To study this effect experimentally, the separation factors were measured on Ar isotopes as a function of pressure and speed of rotation, using a turbo-molecular pump for high vacuum. The Ar gas was fed into the higher pressure side of the pump, to flow against the impeller action through the pump stages, and emerge on the lower- pressure side with its light component enriched. The abundance ratio between ³⁶Ar and ⁴⁰Ar was measured to determine the separation factor. The measured values of separation factor were 1.40, 1.65, 1.80 and 1.95 at 4,500, 6,000, 9,000 and 12,000 r.p.m., respectively, which were fairly close to the calculated data at low working pressures, but fell appreciably short of prediction as the pressure increased.     

Isotope Separation with Drift Tube, (I)

A new method of isotope detection and separation based on transport phenomena of ions in gases, which consist of a drift tube, is proposed and the analytical expression of resolution power of the method has been derived from a diffusion equation. The expression shows that the resolution power increases with the square root of the voltage supplied to the tube. A simple drift tube was constructed and natural Li was isotopically separated in Ne 100 Torr with the maximum resolution power, about 2. The variations of the resolution power with the applied voltage were measured by using the ion source of ⁶Li and ⁷Li separately and compared with calculations.     

Separation of Argon Isotope Mixture in an Axisymmetric Supersonic Jet

The diffusive separation of ³⁶A/⁴⁰A isotope mixture in an axisymmetric supersonic jet was analyzed numerically with account taken of the pressure diffusion in the jet.

An approximate equation is proposed which gives the diffusion flux of the lighter component into the peripheral stream as a function of cut and Mach number.

The experimental results presented by Becker, et al. are found to be in fairly good agreement with the results of calculation by the proposed equation.     

硼同位素分离工艺与生产技术

在苯甲醚—三氟化硼体系中采用化学交换法,进行硼同位素分离生产性实验,可使~(10)B在液相富集,~(11)B在气相中富集。在此基础上,进行硼同位素分离试生产。获得交换塔和络合塔正常运行参数,开发在分解塔内将络合物成功分解的工艺技术,验证在交换塔内采用聚四氟乙烯丝网填料富集硼同位素可行性,探讨操作压力、流量等工艺参数对~(10)B富集的影响,为实现硼同位素分离工业化的正式投建提供依据。     

光化学法锂同位素分离中化学反应速率常数测量

氢气与锂蒸气的化学反应速率常数是激光化学法锂同位素分离过程的一个重要参数。本文以可调谐半导体激光器为工具,通过监测锂原子蒸气对光的吸收测量原子蒸气密度的相对变化,建立了一种测量该速率常数的方法。在光化学锂同位素分离的典型条件下测得化学反应速率常数为9.0×10^-22 m³/s。该数值对于未来锂同位素分离装置中激光照射时间和氢气密度等参数的选择具有重要指导意义。     

Rapid Separation of Fission-Product Rare Earths and Yttrium by Electromigration

The separation of fission-product La, Ce, Pr, Nd and Y was performed in 4 min by electro-migration. As complexing agent, nitrilotriacetic acid was used at two concentrations of the NTA ion selected so as to optimize mutual separation of the elements. Rapid location of the zone on the paper strip reached after migration was obtained by color reaction of the carrier added to the irradiated sample. The purity of the elements thus separated was checked by γ-ray spectrometry. At the higher concentration of NTA ([[NTA]=1.0×10^?2M, pH=4.1) under which all of rare earths and Y migrate toward the anode, the elements were well separated from each other, although appreciable amounts of other F.P. were also found in each fraction. On the other hand, at the lower NTA concentration ([NTA]=4.0 × 10^?3M, pH=2.0) where the F.P. all migrate toward the cathode, each zone contained the isotopes of the respective element almost exclusively, except for a few small photo-peaks attributable to other elements. In each fraction, the 92.5 min ¹⁴²La and 14 min ¹⁴³La, the 14 min ¹⁴⁶Ce (24 min ¹⁴⁶Pr), the 24 min ¹⁴⁶Pr and 12 min ¹⁴⁷Pr, the 1.8 hr ¹⁴⁹Nd, the 20.3 min ⁹⁴Y and 10.9 min ⁹⁵Y were identified from the energies of photo-peaks and their decay rates.     

Theory of Chromatographic Separation of Isotopes, (II)

A mathematical model for chromatographic isotope separation systems is derived starting from a simple theoretical equation for concentration profiles in an ideal displacement chromatogram. The theoretical equation is combined with appropriate material balances to develop a set of equations which relate the size, production rate and start-up time of chromatographic separation equipment to the degree of isotope enrichment. These equations are easy to use, and require a minimum of empirical data.

The model incorporates a series of simplifying assumptions which are valid for displacement chromatographies where the isotopic separation coefficient is small and the degree of enrichment accomplished in a single column is not very high. Thus the model is applicable to most isotope separation systems of practical interest (including uranium enrichment), although it may be inadequate for certain special cases.     

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.