Reprocessed Uranium Hexafluoride Purification from 232,234,236 U in Pentaflow Gas-Centrifuge Cascades
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REPROCESSED URANIUM HEXAFLUORIDE PURIFICATION FROM 232,234,236U IN PENTAFLOW GAS-CENTRIFUGE CASCADES
V. A. Palkin
UDC 621.039.31;621.039.516.22
A computational experiment was performed to purify reprocessed uranium hexafluoride from 232,234,236U in an additional product flow of cascades with a specified number of gas centrifuges in stages. The method used in the calculations takes into account the dependence of the separation coefficients of gas centrifuges on their feed flow and flow division factor. A cascade scheme for purification with simultaneous production of low-enrichment uranium from natural uranium in the main product is investigated. The cascade has to feed flows with regenerated natural-uranium hexafluoride, two product flows, and one waste flow. The cascade parameters that increase the purification efficiency are determined. It is shown that uranium hexafluoride in the products of the cascade satisfies the ASTM C996–15 international specifications established for low-enrichment commercial grading.
Reprocessed uranium separated from spent nuclear fuel is best used as a nuclear material because of its continuous accumulation and the depletion of natural-uranium reserves. The concentration of the primary fissile isotope 235U in reprocessed uranium is ordinarily higher than in the natural raw material; but, it contains 232,234,236U, which impedes its use. The methods developed for isotopic restoration of reprocessed uranium using cascade methods and dilution operations make it possible to lower its concentration to an acceptable level, but there are definite drawbacks [1–7]. The main ones lead to loss of valuable natural raw material and enriched product as well as to additional expenditures on separative work. An effective method of decreasing the concentration calls for a pentaflow cascade with two feed flows, two product flows, and one waste flow [2]. Natural uranium hexafluoride is supplied to the main feed flow and reprocessed uranium is supplied to the additional feed flow. Low-enrichment uranium, whose characteristics are determined by the natural uranium, is produced in the main product flow. In addition the ASTM C996–15 international specifications established for commercial grading of uranium hexafluoride are satisfied. The flow and concentration of 235U and the additional product flow coincide with the analogous parameters of reprocessed uranium in the feed. The 232,234,236U concentration in this product, corresponding to purified reprocessed uranium, decreases significantly. The purification effect is due to mixing of reprocessed and natural uranium inside the cascade as well as mass transfer of the indicated isotopes into the cascade waste flow. The method of [2] is characterized by small additional expenditures on purification. It showed its efficacy in practice in similar purification of contaminated waste uranium hexafluoride in gas centrifuge cascades with additional product flow. A drawback of using reprocessed uranium, which impedes its use, is low productivity due to the small flow
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