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.     

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.     

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.     

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

A numerical method was developed to calculate the distribution of concentration of ²³⁵UF₆ in the rotating cylinder of a centrifuge. Satisfactory convergence was obtained by employing the formulation of convective terms devised for the computation of high Reynolds number flow. Moreover, the pressure diffusion term was linearized and approximated by a constant value, which significantly reduced the number of cases to be run on a computer. The results of numerical analysis for a centrifuge of counter-flow type are shown, and the effect brought upon the separative efficiency by changes in various parameters is discussed. The results of the present analysis are compared with those obtained from the existing theory, and the reasons for the discrepancy between the two results are explained. Finally, it is shown that the results of the numerical analysis agree well with the experimental data obtained previously by Beams et al.     

铀离心浓缩厂分离功率在线监测技术研究

利用研制的铀丰度在线监测装置对铀浓缩厂工艺管道中精料和贫料铀丰度进行在线监测,同时利用孔板流量计在线监测浓缩厂精料端工艺管线UF_6精料流量,然后利用分离功率方程计算得到分离功率。现场实验表明:在均不考虑物料损耗情况下,分离功率在线监测结果与铀浓缩厂分离功率申报值的相对偏差小于2.0%。     

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。     

Si同位素分离单机供料流量的优化

介绍了二元和多组分同位素混合物的分离功率表达式。以SiHCl3（硅氯仿）为工作气体,在分离装置上进行单机分离实验,得到了供料流量与各分离性能参数之间的关系。结果表明,当供料流量在20克每小时附近时,单机分离性能最佳。     

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).     

Comparison of Two Types of Ideal Cascades for Asymmetric Separation Processes

The energy spectra of γ-rays in water, concrete, iron and lead are calculated by PALLAS- PL, SP-Br code for the plane perpendicular incidence. The calculation takes into account both annihilation and bremsstrahlung photons as well as Compton scattered ones as the secondary source.

Comparisons of energy spectra calculated by PALLAS were made with those of the moments method in water, iron and lead. In the PALLAS calculation the bremsstrahlung is neglected for the source energy of 6 MeV in iron because the influence of the bremsstrahlung on the energy spectrum is considered to increase for high energy photons. While for the case of inclusion of the bremsstrahlung source, a comparison of PALLAS calculations with experiments is made in transmitted dose through lead for a plane perpendicular 8-MeV source, resulting in good agreement.

Several examples of the calculated energy spectra in each material are presented at penetration distances of 0.5-, 1.0-, 2.0-, 4.0-, 7.0-, 10.0-, 20.0- and 40.0-mfp in 43 mfp depth for source energies of 0.1-     

Optimum Cut of Separating Element as Function of Total Separation Factor and Mole Fraction of Component to be Separated

For a simplified model of separating elements where a total separation factor αβ is independent of values of cut ? (0≤?≤1), an optimum cut ?_opt in the sense that the cut makes a separative power δU maximum, was derived in terms of αβ, and a mole fraction x_F (0≤x _F≤1) of the component to be separated. When values of x^F is nearly equal to zero, the optimum cut ?^xF _opt?0 decreases and approaches to near 0, as the total separation factor becomes larger. On the contrary, when x_F is nearly equal to 1, the optimum cut ?^xF _opt?1 was found from calculation to be 1-?^xF _opt?0, and increases and approaches to near 1, as the total separation factor becomes larger. Moreover, in the case of x_F =0.5, the optimum cut is 0.5 regardless of αβ. Generally, the optimum cut ?_opt(x_F ) was solved to be in the form of a linear interpolation of the boundary values, ?x^F _opt?0 and ?x^F _opt?1.     

Separation Characteristics of Gas Centrifuges

An analytical method of solving the convection-diffusion equation is presented for the centrifugal separation of a binary isotopic gas mixture under the condition that the pure axial flow velocity field is attained. In the present method, it is assumed that the radial concentration profile can be expressed in the form of multi-term expansion, and the two-dimensional partial differential equation is transformed into a set of ordinary differential equations through the multiple integration in the radial direction.

Computations are made on UF₆ gas in various types of centrifuges which have the ports for feed, product, and waste on the end plates. The results of the present analysis are compared with the other results of existing theoretical analysis.

In spite of the approximate approach, the present method can provide a closer agreement with the two-dimensional finite difference method (FDM) proposed by Kai. Finally, it is shown that the results of the present analysis agree with the experimental data of Beams et al., using the internal flow pattern based on the boundary layer theory by Nakayama et al.     

Optimum Cut of Separating Element as a Function of Total Separation Factor

Calculation of one of the SIMBATH experiments was performed using the SIMMER-II code. The experiments were intended to simulate the fuel pin disintegration, the molten materials relocation and following materials redistribution that could occur during core disruptive accidents assumed in fast breeder reactors. The calculation by SIMMER-II showed that the incorporated step-wise fuel pin disintegration model and the modified particle jamming model were capable of reproducing the course of materials relocation within the identified ranges of the parameters which governed the blockages formation, i.e. the characteristic radius of solid particles jamming and/or sieving out in the flow and the effective particle viscosity. In particular the final materials redistribution calculated by SIMMER-II very well reproduced the experiment. This fact made it possible to interpret theoretically the mechanisms of flow blockages formation and related materials redistribution.     

Analysis of Power Supply Loss Accidents in UF6 Centrifuge Cascade with Side Flows

All-Interconnected Cascades is proposed as an example of production system to be designed to produce a number of side products of enriched uranium. To analyze the transient characteristics of the side product assays in the proposed cascades system, the code TWIN-SS is developed. If the rotor power supply loss for UF₆ centrifuges occurs for a short time in the finishing and/or the base cascades, an allowable power loss time permitting the side product assays to be maintained within the product assay specifications is revealed. Furthermore, even if a long time power supply loss occurs in one base cascade, it is shown that the side product assays can be controlled without the shut-down of the operation of All-Interconnected Cascades by operating an interstage reflux in the finishing cascade.     

以七氟丙烷为介质离心分离碳同位素

以七氟丙烷（C₃HF₇）为分离介质,通过气体离心法研究碳同位素的分离制备。利用国产气体离心机开展单机离心分离实验,通过气体质谱仪分析C₃HF₇样品,计算不同工况条件下的分离系数和单机分离功率,分离系数可达1.12。在单机实验结果的基础上,采用相对丰度匹配级联（MARC）模型,对富集¹³C的生产进行级联计算。选取分离功率最大的实验工况作为计算参数,通过三次级数分别为30、60、75的级联分离,可以将¹³C的丰度从天然丰度富集至30%以上。综合考虑单机实验和级联计算的结果,以C₃HF₇为介质离心分离碳同位素可行。     

Simple Formulae for Analyzing Matched Abundance Ratio Cascade with Constant Separation Factors for Multi-Component Isotope Separation

After the ratification of START-I the question of how to dispose safely and effectively of excess weapons plutonium, of which there is estimated to be about 501 in the USA and 501 in Russia, has become an important international issue. One of the most likely options is the proposal to use the excess weapons plutonium as MOX fuel in commercial LWRs. This paper evaluates fuel material flow and fuel cycle costs when weapons-grade plutonium is mixed with reactor-grade plutonium to fabricate the MOX fuel and to be recycled in Japanese commercial LWRs.

The results show the MOX fuel using weapons- and reactor-grade mixed plutonium facilitates multiple recycling, because the weapons-grade plutonium improves the isotopic composition of the MOX fuel working like a “purifier” of the degraded recycled plutonium. And they also indicate that it might be an economically realistic method in Japan to use the excess weapons plutonium in the commercial LWRs as MOX fuel if the fabrication cost and the reprocessing cost of MOX fuel are moderate compared to those of UO₂ fuel, assuming the MOX powder using weapons-grade plutonium would be provided free of charge.     

Numerical Calculation of H2-HT Separative Performances up to −0.3 MPa of Thermal Diffusion Column with Fairly Higher Hot-Wire Temperature

By using the two-dimensional rigorous numerical solution of flow and convection-diffusion equations, the H₂-HT separative performances of thermal diffusion column with 15 mm-radius and 288.15K cold-wall was analyzed up to ?0.3 MPa for higher hot-wire temperature (up to ?1,700K). Flow analysis has revealed: (1) The magnitude of the free convection is almost proportional to the pressure, and laminar solution of free convection could not be obtained at the pressure more than ?0.32 MPa. (2) The magnitude of the free convection increases gradually with ΔT (the temperature difference between hot and cold surfaces), when ΔT<–800 K. In the range of larger ΔT, the magnitude is almost constant or rather decreases gradually with ΔT. As a result, the laminar solution could always be obtained at the pressure less than ?0.32 MPa, no matter how large ΔT may be. Separative analysis for H₂-HT isotope separation has made clear that the thermal diffusion column with 288.15 K cold-wall should be operated at (1) 0.15–0.2 MPa, (2) ΔT that is as large as technically possible, and (3) the feed rate F of 50–100 cm³ (288.15 K, 0.1 MPa)/min.     

Uranium Isotope Separation by Cation Exchange Chromatography Using Uranous Sulfate Complexes

A nearly ideal displacement chromatography has been realized with an eluent of MgS0₄ and H₂SO₄ in the study of uranium isotope separation by means of cation exchange chromatography using uranous sulfate complexes. Uranium-235 was enriched at the end of the chromatogram and ²³⁸U was enriched at the front. Two long distance displacement experiments have been carried out, keeping an isotopic plateau region on the chromatogram. Consequently, good accumulation of the isotopic fractionation based on uranous-sulfate complex formation reactions obtained. The separation coefficient ε of this system was estimated to be about 5×10^?5.     

钯钇合金膜分离器的氕氘分离系数测定

文章设计钯钇合金膜氢同位素分离器，并系统研究分离系数与温度、分流比、气体流速等因素间的关系。研究结果表明：分离系数随温度的增加而下降，在573～723K范围内，对于66.2%H2-33.8%D₂气体，当进料流速为5L/min、分流比为0.1时，分离系数由2.09下降至1.85；而当分流比为0.2时，分离系数由1.74下降至1.52。随着分流比的增大，分离系数逐渐降低。在573K下，进料流量为5L/min时，对于15.0%H2-85.0%D₂，当分流比由0.050增大至0.534时，分离系数由2.43降低至1.35；对于66.2%H2-33.8%D₂，当分流比由0.050上升至0.688时，分离系数由2.87下降至1.30。对于一定的分离过程，原料气体流速存在最佳值，达到该值时，分离系数最大。