Cascades uranium isotope separation

Figure 7. Parameters of an ideal separation cascade uranium isotope separation...

Fig. 4. Characteristics of an ideal separation cascade for uranium isotope separations. For this cascade a = 1.0043 Nj- = 3484 stages AU = 153.08mol/t ...

Figure 7 is a schematic representation of a section of a cascade. The feed stream to a stage consists of the depleted stream from the stage above and the enriched stream from the stage below. This mixture is first compressed and then cooled so that it enters the diffusion chamber at some predetermined optimum temperature and pressure. In the case of uranium isotope separation the process gas is uranium hexafluoride [7783-81-5] UF. Within the diffusion chamber the gas flows along a porous membrane or diffusion barrier. Approximately one-half of the gas passes through the barrier into a region... 

A uranium isotope separation plant has been operating as an ideal cascade to produce 200 kg of U/day in product containing 3.2 w/o while stripping tails to 0.2 w/o, from natural uranium feed containing 0.711 w/o U. 

The flrst U.K. uranium isotope separation plant, built in the early 1950 s, was based on gaseous difiusion. This phenomenon depends on the observation that the rate of passage of molecules through a membrane is inversely proportional to the square root of the molecular weight. The application of this principle in a cascade stage requires a compressor, membrane, control valve, and cooler. 

Calculate the values of the total light fraction flow rate (upflow) from stage 1 to stage N in the enriching section of an ideal cascade, as described in Example 9.1.2 for uranium isotope separation using countercurrent gas centrifuges. The overhead top product flow rate is 2 gmol/time = 1.18 Xiit = 0.9, xif = 0.0072. Employ the result provided in Problem 9.1.1. 

Cascade Design. The efficiency of a Zippe-type centrifuge, separating uranium isotopes when UF is the process gas, operating at a peripheral speed of 350 m/s and at a temperature of 320 K A = 2.85), would be expected to be... 

Separation of Uranium Isotopes by Cascade of Mass Diffusion Stages... 

O Equation (51.5) shows fVin increases as the overall separation is increased and as the separation factor a gets closer and closer to unity. For the latter reason, the minimum number of stages required for isotope separation can be very large. To cite a practical example, in a diffusion plant with a = 1.0043, producing 90% enriched product, and rejecting 0.3% tads, from natural uranium (0.7%) feedstock, w 1,870. Of course, under the conditions oftotal reflux no product is withdrawn, it is all held in the cascade as inventory. For finite product withdrawal, even more stages will be required. 

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