Uranium isotopes SUBJECT

Discussion of processes for industrial separation of uranium isotopes cannot be as complete as the discussion of deuterium separation in Chap. 13. The detailed technology of the most economical and most promising processes is subject to security classification and to proprietary restrictions. Nevertheless, processes for enriching uranium can be described in sufficient detail to make their principles clear and to illustrate the similarities and differences between them and processes for separating isotopes of light elements. 

If a gas mixture is subjected to a very rapid centrifugation, the components will be separated because of the slightly different forces acting on the various molecules owing to their different masses. The heavier molecules thus lend to accumulate at the periphery of the centrifuge. This method is also used for separation of uranium isotopes. 

During its lifetime, a fusion reactor presents little radiation hazard. The internal structure, particularly the vacuum containment vessel and the heat exchanger, will be subject to intense neutron bombardment. The neutrons will convert some of the elements of the structure into long-lived radioactive isotopes. Selecting construction materials that do not easily become activated can minimize radioisotope production. No material is entirely resistant to neutron activation, thus the decommissioning of a fusion reactor will require the handling and disposal of potentially hazardous radioactive isotopes. Because of the lack of uranium, plutonium, and fission products, the total radiation exposure hazard from the decommissioned fusion reactor is 10,000 to 1,000,000 less than from a decommissioned fission reactor. 

Confirmation of this explanation is unequivocally provided by the presence in the reactor zones of at least half of the more than 30 fission products of uranium. Although soluble salts, such as tho.se of the alkali and alkaline earth metals, have been leached out, lanthanide and platinum metals remain along with traces of trapped krypton and xenon. Most decisively, the observed distribution of the various isotopes of these elements is that of fission products as opposed to the distribution normally found terrestrially. The reasons for the retention of these elements on this particular site is clearly germane to the problem of the long-term storage of nuclear wastes, and is therefore the subject of continuing study. 

Bismuth is the most diamagnetic of all metals and has low thermal conductivity. Since bismuth expands upon solidification, it is used to make castings for objects subjected to high temperatures. It is used as a replacement for lead in solders, shot for hunting, fishing sinkers, ceramic glazes, and brasses for plumbing applications. It is also used as a carrier for (an isotope of uranium) fuel in atomic reactors. Ionic compounds of bismuth are used in cosmetics and medicine. 

The isotope undergoes fission when bombarded with neutrons. However, its natural abundance is only 0.72 percent. To separate it from the more abundant isotope, uranium is first converted to UEg, which is easily vaporized above room temperature. The mixture of the and UFg gases is then subjected to... 

In this chapter, we tried to present an overview of the properties of uranium (the element, isotopes, and main compounds) that are relevant to the subject matter of this book. An understanding of the industrial aspects of uranium processing, and especially its role in the NFC, is essential in order to appreciate the ways uranium affects our lives. We also tried to briefly discuss the main analytical techniques that are used in the characterization of uranium, whether as a major component, a minor component, or a trace in environmental and biological samples. A detailed description of the analytical techniques will be given in the following chapters. 

Up to now, reprocessed uranium has only been used for the fabrication of a limited number of test fuel assemblies. For this type of fuel, the uranium fraction from the spent fuel reprocessing process is again subjected to an isotope enrichment procedure to obtain a content which is sufficiently high for reactor operation (3.8% in the example shown in Tables 3.1 and 3.2.). Besides the naturally occurring isotopes and this material contains mainly gener-... 

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