Isotope separation practical

A practical isotope separation plant can operate at neither minimum reflux (where the separation is zero, but the rate of production is high), nor at minimum number of stages (where the rate of production is zero, but the separation is high). A compromise is required. Since optimum reflux varies with stage number it is customary to employ tapered cascades for isotope separation. This results in marked savings in material hold-up, and in plant size and investment. 

Selective excitation of wavepackets with ultrashort broadband laser pulses is of fundamental importance for a variety of processes, such as the coherent control of photochemical reactions [36-39] or isotope separation [40--42]. It can also be used to actively control the molecular dynamics in a dissipative environment if the excitation process is much faster than relaxation. For practical applications it is desirable to establish an efficient method that allows one to increase the target product yield by using short laser pulses of moderate intensity before relaxation occurs [38]. 

The interest of using fine-pore thin-film ceramic or metal membranes for isotope separation (e.g. uranium) is still apparent even after years of production practice [Miszenti and Nannetti, 1975 Sumitomo Electric Industry, 1981]. Isotopes other than uranium, such as those of Ar or Ne [Isomura, et al., 1969 Fain and Brown, 1974], can also be separated by gaseous diffusion. The membrane materials having been successfully tested for these specific applications include alumina, glass and gold. 

In Table 12 the distribution of sodium ions between water and chloroform (referred to g HjO/g CHCI3) is presented in dependence on the different polyethers. All results were obtained under analogous conditions with 0.1 mmol Na and 0.1 mmol polyether in the system where the pH-value was established to be 8 by adding 10 mmol of tetraethylammonium chloride. The establishment of the equilibrium requires less than 60 min in all systems and was followed by the y-activity of the sodium isotopes and the P-activity of C-labeled polyethers. The enrichment of one of the sodium isotopes in a practical scale from a Na/ Na-mixture can only be achieved in a system where the distribution ratio (Na ),/(Na ) g is not too high. However, in contrast to the enrichment of stable isotopes from a sample with natural isotope abundance, the enrichment of Na or of Na from an isotopic mixture is not of great importance because these two isotopes can be produced by nuclear reactions. On the other hand, the investigations on sodium isotopic separations are of common interest in respect to further knowledge about isotopic effects. 

The investigated extraction systems with lithium and calcium have shown that the lighter isotopes are always enriched in the organic phase where the cyclic polyether is present. This is advantageous for the production of Li but not for the production of the heavy calcium isotopes. The different distribution of the element between the two phases, which one needs for as high as possible isotopic fractionations in one phase, causes a practical isotopic separation only in the organic phase (see Chap. 2.4). In most of the chromatographic experiments with cyclic polyethers, the heavier isotopes were enriched in the first fractions of the elution band. Here, it is of minor... 

The present result indicates the practical isotope separation for - Si wfll be realized. 

This chapter gives a brief account of the nuclear fission reaction and the most important fissile fuels. It continues with a short description of a typical nuclear power plant and outlines the characteristics of the principal reactor types proposed for nuclear power generation. It sketches the principal fuel cycles for nuclear power plants and points out the chemical engineering processes needed to make these fuel cycles feasible and economical. The chapter concludes with an outline of another process that may some day become of practical importance for the production of power the controlled fusion of light elements. The fusion process makes use of rare isotopes of hydrogen and lithium, which may be produced by isotop>e separation methods analogous to those used for materials for fission reactors. As isotope separation processes are of such importance in nuclear chemical engineering, they are discussed briefly in this chapter and in some detail in the last three chapters of this book. 

As the oceans of the world contain about 10 kg of deuterium and resources of lithium minerals are of comparable magnitude, it is clear that if this fusion reaction could be utilized in a practical nuclear reactor, the world s energy resources would be enormously increased. Although intensive research is being conducted on confinement of thermonuclear plasmas, it is not yet clear whether a practical and economic fusion reactor can be developed. If fusion does become practical, isotope separation processes for extracting deuterium from natural water and for concentrating from natural lithium will become of importance comparable to the separation of U from natural uranium. 

Table 12.1 lists separated isotopes that are being produced on a significant industrial scale. In addition to these, separated isotopes of practically all natural elements are being produced in research quantities by the U.S. Department of Energy (DOE) and by the atomic energy agencies of England, France, the Soviet Union, and other nations. 

Np and Ny/ are the minimum number of enrichment and stripping stages, respectively. In isotope separations a is often very close to one In a can then be replaced by (a — 1). In practice some product flow is desired, the fraction withdrawn at the enrichment stage being known as "the cut" PIF. The number of stages required to produce the composition Xp then increases. The most economic, and thus also the most common, type of cascade for processes with near unity a is the so-called ideal cascade. In this there is no mixing of streams of unequal conc trations, thus j in Fig. 2.8. Alfliougfa the number of... 

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