Applying nuclear forensic signatures in response to a nuclear security event from a South African nuclear facility

Abstract

Uranium ore concentrates, also known as yellowcake, are a critical component of the nuclear fuel cycle and the result of uranium mining and processing. Uranium ore concentrate s refers to a group of uranium chemical compounds that include U3O8, UO3, UO2, and UO4xH2O (where x = 2 or 4). The distributions of trace elements in uranium ore concentrates may be linked to the geologic conditions under which the parent uranium ore developed, and so are unique to each deposit type. These chemical signatures might subsequently be employed as a crucial tool in nuclear forensic examination. In this study, several samples of uranium ore concentrate and uranium ore samples have been analyzed for their trace elements, rare earth elements, morphology, and isotopic ratios. This project aimed to apply nuclear forensic signatures in responding to nuclear security events from a nuclear facility in SA. Uranium ore concentrates and uranium ore samples were analyzed using gamma detector, SEM/EDS, and inductively coupled plasma mass spectrometry. It was found that the activity ratio of 235U/238U for uranium ore concentrates samples ranged between 0.0271 ± 0.0016 and 0.0393 ± 0.0082 respectively, while the activity ratio of 235U/238U for uranium ore samples ranged from 0.0326 ± 0.0021 and 0.0391 ± 0.00037. The sample images of uranium ore concentrates showed similar characteristics, as both have pores between their grains. They both have a grape-like shape stacked together. Uranium ore concentrates consisted of agglomerates particles. These results showed a difference in particle shape and texture. The aggregates of fine particles are reasonably common in all the uranium ore concentrates samples and may have been produced during vapor condensation, nucleation and coagulation of particulates in the mine furnace. SEM/EDS results in uranium ore concentrate samples contained 60 ð€‚± 70 % of uranium. The uranium ore samples studied displayed a fine texture. SEM/EDS in uranium ore samples showed the oxygen (O), aluminum (Al), sulfur (S), potassium (K), iron (Fe) impurities and uranium was not detected. Uranium ore concentrate and uranium ore samples could be differentiated by elemental and rare earth elements concentrations. The results showed that the elemental concentrations of the uranium ore concentrates samples might be used to differentiate them from one another. Impurity elements, Ca, K, Mg and Na were the most dominant elements in both uranium ore samples. The mean concentrations in U ore1 were in the order K > Mg > Na > Ca respectively, while the mean concentrations in U ore2 were in the order K > Mg > Ca > Na respectively. Therefore, the differences displayed by impurity elements were not only different in the concentrations of these elements but the shapes of the spectrum formed were also significantly

different. The C1-chondrite rare earth elements patterns of UOCblack showed fractionation of light rare earth elements and flat enriched heavy rare earth elements and a significant negative Eu anomaly. UOC CUP-2 showed depleted light rare earth elements and flat heavy rare earth elements. ADU rare earth elements pattern showed fractionation for all the elements. The uranium ore concentrates analyzed showed large variability in rare earth element patterns as well as Eu anomalies. Rare earth element patterns for both uranium ore samples showed enriched light rare earth elements and depletion of heavy rare earth elements. During early ore processing of the uranium ore studied in this work, rare earth element abundances and U isotopes did not fractionate. The CN-REE patterns difference for all samples demonstrate that the rare earth element signatures remain effective forensic indications despite in-situ leaching processes. The (234U)/ (238U) isotope ratios of uranium ore concentrate samples ranged between 0.169 ± 0.00936 and 4.810 ± 4.540, where the (235U)/ (238U) is between 0.00615 ± 0.00005309 and 0.348 ± 0.326. The (234U)/ (238U) as isotope ratios of the U ore1 and U ore2 samples ranged between (21.90 ± 4.08) x 10-5and (5.65 ± 1.17) x 10-5, where the (235U)/ (238U) is between 0.0289 ± 0.00496 and 0.00760 ± 0.00167 respectively. It was found that the results for the (235U)/ (238U) ratios showed large differences between the uranium ore concentrate and uranium ore samples. Similar to the (235U)/ (238U) ratios, there are a significant difference for the (234U)/ (238U) ratios of the uranium ore concentrate and uranium ore samples. The activity ratio of 234U/238U and 235U/238U of uranium ore concentrate and uranium ore samples was 10.144 and 0.047 respectively. Due to the natural abundance of 235U being used to derive its isotopic concentration from the observed isotopic concentration of 238U, the activity ratio for 235U/238U was equal to the continental average of 0.047 for all samples. The uranium ore concentrate and uranium ore samples showed that they could be differentiated from one another based on the study's findings. These results reported here demonstrate that they can be applied during nuclear forensic events.