Isotope separation by gaseous diffusion

Martensson, M., K. E. Holmberg, C. Lofman and E. I. Eriksson. 1958. Some types of membranes for isotope separation by gaseous diffusion. Proc. 2nd United Nations Inti Conf. Pencil Uses of Atomic Energy. 4 395-404., Geneva. 

Fain. D.E., and W.K. Brown, 1974, U.S. Atomic Energy Commission Report "Neon isotope separation by gaseous diffusion transport in the transition flow regime with regular geometries."... 

Martensson, M., et al. Some Types of Membranes for Isotope Separation by Gaseous Diffusion, PICG(2) 4 395 (1958). 

Massignon, D. Characteristics of Barriers That Can Be Used for Isotope Separation by Gaseous Diffusion, PICG (2) 4 388 (1964). 

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. 

Examples of separations of isotopes are in Table 20.3(b). The concentration of U-235 listed there was accomplished in a cascade of 2100 columns, each with an effective height of 14.6m, inner tube 5 cm dia, gap 0.25 mm, hot surface 87-143°C, and cold surface 63°C, just above the condensation temperature at the operating pressure of 6.7 MPa. Although the process was a technical success, it was abandoned in favor of separation by gaseous diffusion which had only 0.7% of the energy consumption. 

Scheme 4.3 Synthesis ofthe volatile uranium compound UFj, which is used for the separation of 0.6% from the major isotope u by gaseous diffusion. Only can be used for nuclear weapons because - in contrast with U - it is fissible in a fast neutron-initiated chain reaction [4].

Figure 4.2 The l<-25 facility in Oak Ridge (left) where uranium isotopes were separated by gaseous diffusion of UFg. The atomic bomb which destroyed Hiroshima on August 6, 1945 (right), was based on from this facility (courtesy of the Manhattan Project Heritage Preservation Association) [5].

Bilous, O., and G. Counas Determination of the Separation Factor of the Uranium Isotopes Produced by Gaseous Diffusion, PlCG(2j 4 405 (1958). 

One way of separating oxygen isotopes is by gaseous diffusion of carbon monoxide. The gaseous diffusion process behaves like an effusion process. Calculate the relative rates of effusion of... 

It was proved that isotopes other than uranium, such as those of Ar, Ne, O, and H, could also be separated by gaseous diffusion (Fain and Brown 1974). The membranes developed for this purpose are made from alumina, gold, or glass (Konishi et al. 1983 Evans et al. 1983). Attanpts were made to use polymeric membranes for separating the isotopes. The manbranes from polyethylene terephthalate (PET),... 

Uranium oxide [1344-57-6] from mills is converted into uranium hexafluoride [7783-81-5] FJF, for use in gaseous diffusion isotope separation plants (see Diffusion separation methods). The wastes from these operations are only slightly radioactive. Both uranium-235 and uranium-238 have long half-Hves, 7.08 x 10 and 4.46 x 10 yr, respectively. Uranium enriched to around 3 wt % is shipped to a reactor fuel fabrication plant (see Nuclear REACTORS, NUCLEAR FUEL reserves). There conversion to uranium dioxide is foUowed by peUet formation, sintering, and placement in tubes to form fuel rods. The rods are put in bundles to form fuel assembHes. Despite active recycling (qv), some low activity wastes are produced. 

UFe is important in the separation of uranium isotopes by gaseous diffusion (p. 1259). 

The next stage of development went to polymer chemists and development engineers, as the expertise of Roy Plunkett was really in fluorine chemistry. The first great application was in the separation of the isotope U-235 from U-238 by gaseous diffusion of UFe to make atomic bombs, as the gas uranium hexafluoride was exceedingly corrosive and destroyed conventional gaskets and seals. PTFE was just what was needed to form the diffusion membrane, as it was not attacked by fluorine. When peace returned, PTFE registered the trademark of Teflon in 1944. 

Fluorine is used in the separation of uranium, neptunium and plutonium isotopes by converting them into hexafluorides followed by gaseous diffusion then recovering these elements from nuclear reactors. It is used also as an oxidizer in rocket-fuel mixtures. Other applications are production of many fluo-ro compounds of commercial importance, such as sulfur hexafluoride, chlorine trifluoride and various fluorocarbons. 

After the outbreak of World War II in 1939, leading nuclear scientists realized that a new type of weapon was possible, based on atomic fission. A key requirement was the separation of the isotope of mass 235 (only 0.7%) present in natural uranium. By 1941, it was clear that the only practicable process was by gaseous diffusion of uranium(VI) fluoride, the sole compound of sufficient volatility. However, this attacked normal organic materials rapidly, being almost as reactive as elemental fluorine. 

VOIDS. Empty spaces of molecular dimensions occurring between closely packed solid particles, as in powder metallurgy. Their presence permits barriers made by powder metallurgy techniques to act as diffusion membranes for separation of uranium isotopes in the gaseous diffusion process. 

Fiejacques, C., O. Bilous, J. Dizmier, D. Massignon and P. Plurien, 1958, Principal results obtained in France in studies of the separation of the uranium isotopes by gaseous diffusion, in Proc. 2nd U14. Int. Conf. on Peaceful Uses of Atomic Energy 4 (Production of Nuclear Materials and Isotopes), 418. 

Fuel enrichment. All practicable enrichment processes require the uranium to be in the form of a gas. UFg, which readily sublimes (p. 1269), is universally used and, because fluorine occurs in nature only as a single isotope, the compound has the advantage that separation depends solely on the isotopes of uranium. The first, and until recently the only, large-scale enrichment process was by gaseous diffusion which was originally developed in the Manhattan Project to produce nearly pure U for the first atomic bomb (exploded at Alamogordo, New Mexico,... 

Theoretically, diffusion should effect the difficult separation of isotopic gases from one another because of the difference in rates of diffusion of the constituent gaseous isotopes. However, the problem faced in such a separation by fractional diffusion is the one that arises from the fact that difference in respective densities of isotopes is generally very slight, so that die method in practice is a very laborious one. It is obvious that if diffusion were allowed to proceed for a long time, the composition of the gas mixture would become identical at both sides of the partition. If, however, only half of the gaseous mixture is allowed to diffuse... 

When a — 1 < 1, as in separating uranium isotopes by gaseous diffusion, this equation reduces to... 

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