Tails optimum composition

In the future, it is probable that the supplier of emichment services will permit a customer to specify the assay ( U content) of the tails to which feed is to be stripped so as to minimize the combined cost to the customer of natural UF feed and separative work. F re 12.20 shows qualitatively the effect of tails composition on the contributions to product cost arising from costs for feed and for separative work in stripping and enriching sections. The amount of separative work required in the enriching section is independent of tails composition. But the cost of separative work required in the stripping sections varies from zero when = zp (no stripping) to infinity when xw = 0. Conversely, the cost of feed varies from infinity when Xftf = zp to a minimum at rcn =0, as may be seen from Eq. (12.152). There is therefore an optimum tails assay Xo between Xu = 0 and Xfy = zp, at which the sum of the cost of separative work and the cost of natural uranium feed is a minimum. 

An equation for evaluating the optimum tails composition is derived by substituting explicitly into Eq. (12.152) for the unit cost of product cp the separation potentials < p, w, and expressed in terms of the conesponding weight fractions xp, xw> nd xp by Eq. (12.144) ... 

When cp from Eq. (12.158) is substituted into Eq. (12.159) and optimum tails composition Xq is substituted for the result is... 

Figure 12.21 shows the dependence of optimum tails composition on the feed-to-separative work cost ratio. 

An interesting interpretation may be pven Eq. (12.161). The optimum tails composition is... 

The optimum interstage UF flow rate is that of an ideal cascade. For example, in the enriching section of a close-separation ideal cascade making product of composition yp at rate P, the UFj flow rate in stage tails is given by Eq. (12.132). In the notation of fliis section,... 

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