| Description |
The field of nuclear forensics requires measurable signatures to provide information on the composition, intended use, or origin of unknown, interdicted nuclear materials. New signature development, for process history identification, are of interest to the nuclear forensics community. This research focused on the investigation and development of quantitative morphological and crystallographic signatures created by changes in the processing and aging conditions of uranium oxide samples. This research first focused on the quantification of microstructural changes in α-U3O8 induced by varying the calcination temperature of α-U3O8. The resulting materials were characterized by powder X-ray diffractometry (p-XRD) to determine composition and scanning electron microscopy (SEM) for morphological analysis. Using the Morphological Analysis for Material Attribution (MAMA) software and the Kolmogorov−Smirnov two sample test (K−S test), distinct statistical differences were identified between the samples at 99.0% confidence. This was the first quantitative morphological study of α-U3O8 and the first to provide methods for identifying processing history for nuclear forensics. Next, research focused on both the morphological and crystallographic changes that take place during U-oxide aging at elevated temperatures. In these studies, a response surface design of experiment (DOE) was developed to model the changes occurring in the crystal structure using p-XRD and Rietveld refinement analysis of the p-XRD pattern. iv In addition, morphological changes in the aged samples were quantified using SEM imagery and the MAMA segmentation software. Both crystallographic and the morphological changes were modelled in the DOE. While the U3O8 samples showed little quantifiable evidence of either crystallographic or morphological changes, the UO2 readily oxidized changing both the morphology and crystallography. These results yield fundamental knowledge for the nuclear fuels community on the changing composition of nuclear fuels during reactor operation and to the nuclear forensics community to better identify nuclear material processing and storage conditions. Overall, this research provides novel signatures of U-oxide processing and storage based on crystallography and morphology. The results provide the first quantitative analysis of morphology features, first use of quantitative crystallography, and a detailed assessment of the longevity of these signatures following nuclear material use or storage under conditions relevant to the nuclear fuel cycle. |
