Year
2015
Abstract
In Nuclear Safeguards it is important for control purposes to know the enrichment of uranium nuclear materials under safeguards. The IAEA and the South African SSAC mostly use the MGAU code to determine the enrichment. It is known that the MGAU code provides accurate results when both 235U and 238U isotopes are in secular equilibrium with their immediate short-lived daughter products. In this study, Ammonium Diuranate (ADU) samples were collected from uranium plants in mines and other ADU and uranium ore concentrates samples were collected from a uranium processing plant. These samples were counted using a High Purity Gamma Spectroscopy (HPGS) system and the collected spectra analysed using the MGAU code. We show that for freshly separated uranium samples, the MGAU code computes an “apparent” enrichment which might be mistaken for the “true” enrichment when the separation time is short but not known. Without prior knowledge of the separation time, for example, for Illicit trafficking samples, it is possible that freshly separated natural uranium samples can be regarded as enriched uranium samples, conversely, illicit trafficking samples whose MGAU enrichment results exhibit natural enrichment should suggest that the material has been removed from the source for a period long enough to achieve secular equilibrium.