Effects of Separation Processes on Minor Uranium Isotopes in Enrichment Cascades

Abstract

In natural uranium, there are trace amounts of the “minor isotope” 234U in addition to the more abundant 235U and 238U. Uranium irradiated in a reactor and separated from the spent reactor fuel by reprocessing will contain additional minor isotopes. In uranium enrichment, cascades of separating units are tuned to produce the desired level of the isotope 235U, but the levels of other isotopes will also change. Measurement of the assays of the 235U in the feed, product and withdrawal streams of each stage allow the calculation of the stage separation factor for the 235U. The separation factors for the other isotopes may be calculated. In this aritcle, two methods of modeling the separation factors in a way that represents the physics of two enrichment processes, gas centrifuge and gaseous diffusion, are explored. This technique could be a valuable tool in nuclear forensics. For example, it could be important to know the origin of a sample of highly enriched uranium, found either in intercepted material or in explosive debris. Analysis that could point to the enrichment plant where the uranium was produced could immediately identify weaknesses in safeguards and physical security systems.