Other Isotope Separation Processes

Many other methods for separating isotopes have been described. A partial list includes membrane and membrane pervaporation, thermal diffusion of liquids, mass diffusion, electrolysis and electro-migration, differential precipitation, solvent extraction, biological microbial enrichment, and more. Although not discussed in 

Davies, E., 1973 Uranium Enrichment by Gas Centrifuge (London, Mills Boon, Ltd.) 

Benedict, M., Pigford, M., Levi, H. W., 1981 Nuclear Chemical Engineering, 2ndEd. (New York, McGraw-Hill) 

1951 The Theory of Isotope Separation (New York, McGraw-Hill) 

Ishida, T., Lujii, Y. 2006 Enrichment of Isotopes in Kohen, A., Limbach, H. H. Isotope effects in Chemistry and Biology (Boca Raton, FL, CRC Press, Taylor Francis) 

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We have observed that countercurrent separation devices achieve considerable separation under driving forces such as chemical potential gradient and the external force of a centrifugal force field. As illustrated in equations (3.1.44) and (3.1.50), there is another type of force, the thermal diffusion force. The separation achieved thereby in a closed two-bulb cell has been illustrated in Section 4.2.5.I. We have already illustrated conceptually how thermal diffusion can achieve separation in a countercurrent column via Figures 8.1.1(a)-(h). For UF isotope separation, however, the radial separation factor in a two-bulb cell is much smaller than for other isotope separation processes. In a countercurrent column, this value is reduced by about 50%. As a result, thermal diffusion columns are not used at all for any practical/large-scale separation. More details on thermal diffusion columns are available in Pratt (1967, chap, viii) and Benedict et al. (1981, pp. 906-915), where one can find information on the primary references. 

Enrichment, Isotopic—An isotopic separation process by which the relative abundances of the isotopes of a given element are altered, thus producing a form of the element that has been enriched in one or more isotopes and depleted in others. In uranium enrichment, the percentage of uranium-235 in natural uranium can be increased from 0.7% to >90% in a gaseous diffusion process based on the different thermal velocities of the constituents of natural uranium (234U, 235U, 238U) in the molecular form UF6. 

Although the selected isotope separation process was deemed superior to any other separation method then known, it had certain deficien-... 

Several papers in this volume deal with transport in various kinds of liquids others examine critically the fundamental statistical-mechanical theory determining isotope effects for both equilibrium and kinetic processes in condensed as well as gaseous systems. These studies are of interest not only because they serve as a framework for comparing the merits of different isotope separation processes, but they provide powerful tools for using isotope effect data to obtain an understanding of inter-molecular forces in condensed and adsorbed phases and changes in intramolecular forces in isolated molecules. The title of this volume has accordingly been broadened from that of the symposium to reflect the wider scope of its contents. 

Our examination of the photochemical literature of uranium clearly shows that extensive attention has been given to UFg, while other compounds, until recently, have been almost ignored. The attention given to UFg, of course, relates back to the great interest in achieving a low cost laser induced isotope separation process for uranium isotopes. The economics of isotope separation, which have been briefly discussed by Letokhov and Moore (61), have consequently dictated the direction of much of the applied photochemical research on uranium compounds. Nonetheless, from the existing spectroscopic and photochemical data outlined here it would be expected that coordination and... 

The separation factor defined in this way is useful because in many isotope separation processes, it is independent of composition. The ratio y/x, on the other hand, may vary strongly with composition. 

In some isotope separation processes it is impractical to operate a stage at a cut of for mechanical or hydraulic reasons, and in others the separative capacity of the stage is higher at a cut substantially different from In the Becker separation nozzle process described in Chap. 14, the separative capacity of a stage producing a heads stream at a given rate is substantially hi er at a cut of than at a cut of j. 

A. Liquid Mixtures.— Aliphatic and alicyclic perfluorocarbons first became available in commercial quantities just over three decades ago. The impetus towards their large-scale production came from the war-time Manhattan Project when it was realized that the chemical stability and inertness of these materials, combined with their unexpectedly low solubility in most other common organic solvents, might prove useful in uranium isotopic separation processes based on... 

The electromagnetic separation plant built during World War 11 at Oak Ridge, involved two types of calutrons, alpha and beta. The larger alpha calutrons were used for the enrichment of natural uranium, and the beta calutrons were used for the final separation of U from the pre-enriched alpha product. For the electromagnetic separation process, UO was converted into UCl [10026-10-5] with CCl. The UCl was fed into the calutron for separation. The calutron technique has been used to separate pure samples of and stable isotopes of many other elements. The Y-12 calutron... 

Other reasons for investigating plutonium photochemistry in the mid-seventies included the widely known uranyl photochemistry and the similarities of the actinyl species, the exciting possibilities of isotope separation or enrichment, the potential for chemical separation or interference in separation processes for nuclear fuel reprocessing, the possible photoredox effects on plutonium in the environment, and the desire to expand the fundamental knowledge of plutonium chemistry. 

Until the advent of modem physical methods for surface studies and computer control of experiments, our knowledge of electrode processes was derived mostly from electrochemical measurements (Chapter 12). By clever use of these measurements, together with electrocapillary studies, it was possible to derive considerable information on processes in the inner Helmholtz plane. Other important tools were the use of radioactive isotopes to study adsorption processes and the derivation of mechanisms for hydrogen evolution from isotope separation factors. Early on, extensive use was made of optical microscopy and X-ray diffraction (XRD) in the study of electrocrystallization of metals. In the past 30 years enormous progress has been made in the development and application of new physical methods for study of electrode processes at the molecular and atomic level. 

The interest in ceramic membranes grew, together with the interest in membrane separation processes, due to their specific properties. They are chemically stable, can withstand high temperatures and are noncompressible. These characteristics made them the only materials available, which could withstand the harsh environment in the isotope separation. On the other hand, the brittleness of most materials is a problem and so is the selectivity. 

In a process such as liquid-liquid extraction the enthalpy balance is usually unimportant, and the temperature can be assumed constant through the column of stages. Here the question is simply how do the components of the input feed streams distribute. Any other process, such as washing, isotope separation, etc. for which the enthalpy balance is unimportant, requires only the answer to the same simple question. 

Bulk techniques still have a place in the search for presolar components. Although they cannot identify the presolar grain directly, they can measure anomalous isotopic compositions, which can then be used as a tracer for separation procedures to identify the carrier. There are several isotopically anomalous components whose carriers have not been identified. For example, an anomalous chromium component enriched in 54Cr appears in acid residues of the most primitive chondrites. The carrier is soluble in hydrochloric acid and goes with the colloidal fraction of the residue, which means it is likely to be submicron in size (Podosck el al., 1997). Measurements of molybdenum and ruthenium in bulk primitive meteorites and leachates from primitive chondrites show isotopic anomalies that can be attributed to the -process on the one hand and to the r- and /7-processes on the other. The s-process anomalies in molybdenum and ruthenium correlate with one another, while the r- and /7-process anomalies do not. The amounts of -process molybdenum and ruthenium are consistent with their being carried in presolar silicon carbide, but they are released from bulk samples with treatments that should not dissolve that mineral. Thus, additional carriers of s-, r-, and/ -process elements are suggested (Dauphas et al., 2002). 

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