Separation Process Hydrogen Isotopes

Table 8.4 Possible processes for heavy water production (Rae, H. K., Ed., Separation of hydrogen isotopes, ACS Symp. Ser. 68, 134 (1978)) ...

Rae, H.K. "Selecting Heavy Water Processes" ACS Symposium Series No. 68, Separation of Hydrogen Isotopes, H.K. Rae (Editor). American Chemical Society, Washington, 1978... 

Since 1952, most of the tritium measured in the atmosphere originates from thermonuclear explosions. Like hydrogen, deuterium and tritium also exhibit molecular isomerism. Because of the important differences between the relative atomic masses of the three isotopes, their physical properties (e.g., density, enthalpy of vaporization) differ greatly. This allows an easier isotopic separation than for any other element. Several separation processes are used for the enrichment and separation of hydrogen isotopes. Most of these processes use isotopic exchange reactions (e.g., H D-H O or NH3-HD) and to a lesser extent fractional distillation and water electrolysis (e.g., Norway, Canada). 

G-S [Girdler sulphide] A process for separating hydrogen isotopes, using the equilibrium between water and hydrogen sulfide ... 

The nozzle separation process utilizes the centrifugal forces which occur upon diversion of a gas stream. A gas stream of uranium(VI) fluoride, helium and hydrogen is directed along a curved wall and then split by a peeling off plate into two gas streams with enrichment of the heavier and lighter isotopes respectively. 

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. 

Once the radioactive fission products are isolated by one of the separation processes, the major problem in the nuclear chemical industry must be faced since radioactivity cannot be immediately destroyed (see Fig. 10-7c for curie level of fission-product isotopes versus elapsed time after removal from the neutron source). This source of radiation energy can be employed in the food-processing industries for sterilization and in the chemical industries for such processes as hydrogenation, chlorination, isomerization, and polymerization. Design of radiation facilities to economically employ spent reactor fuel elements, composite or individually isolated fission products such as cesium 137, is one of the problems facing the design engineer in the nuclear field. 

The non-equilibrium effect is much stronger than the equilibrium effect. Numerical values of the coefficient of selectivity for different plasma-chemical processes of isotope separation stimulated by vibrational excitation are presented in Fig. 3-13. A detailed consideration of the Treanor-effect isotope separation can be found in Akulintsev, Gorshunov, and Neschi-menko (1977,1983) for nitrogen and carbon monoxide isotopes and in Eletsky and Zaretsky (1981) and Margolin, Mishchenko, and Shmelev (1980) for hydrogen isotopes. 

Finally, the possibility of an integrated Pd-based membrane system is also related to the possibility of separating hydrogen isotopes in nuclear reactors and in the ability to process fuel impurities such as tritiated water and methane. 

A potential application of the WGS reaction carried out in an MR is represented by the tritium recovery process from tritiated water from breeder blanket fluids in fusion reactor systems. The hydrogen isotopes separation at low concentration in gaseous mixtures is a typical problem of the fusion reactor fuel cycle. In fact, the tritium produced in the breeder needs a proper extraction process to reach the required purity level. Yoshida et al. (1984) carried out experimental and theoretical studies of a catalytic reduction method which allows tritium recovery from tritiated water with a high conversion value (> 99.99%) at a relatively low temperature, while Hsu and Buxbaum (1986) studied a palladium-catalysed oxidative diffusion... 

The rates of processes involving different hydrogen isotopes are generally different. This difference, called the kinetic isotope effect, can be easily characterized by the isotope separation factor S. For example, for a discharge reaction of proton and deuteron donors, this quantity is defined as the ratio of specific reaction rates ... 

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