Uranium oxide synthetic pathway discernment through thermal decomposition and morphological analysis

Abstract

Many commercial processes exist for converting uranium from ore to the desired uranium compound for use in nuclear power or nuclear weapons. Accurately determining the processing history of the uranium ore concentrates (UOCs) and their calcination products, can greatly aid a nuclear forensics investigation of unknown or interdicted nuclear materials. In this study, two novel forensic signatures, based on nuclear materials synthesis, were pursued. Thermogravimetric analysis – mass spectrometry (TGA-MS) was utilized for its ability to discern UOCs based on mass changes and evolved gas species; while scanning electron microscopy (SEM), in conjunction with particle segmentation, was performed to identify microfeatures present in the calcination and reduction products (i.e. UO3, U3O8, and UO2) that are unique to the starting UOC. In total, five UOCs from common commercial processing routes including: ammonium diuranate (ADU), uranyl peroxide (UO4), sodium diuranate (SDU), uranyl hydroxide (UH), and ammonium uranyl carbonate (AUC), were synthesized from uranyl nitrate solutions. Samples of these materials were calcined in air at 400 °C and 800 °C. The 800 °C calcination product was subsequently reduced with hydrogen gas at 510 °C. The starting UOCs were investigated using TGA-MS; while SEM quantitative morphological analysis was used to identify signatures in the calcination products. Powder X-ray diffractometry (p-XRD) was used to identify the composition of each UOC and the subsequent calcination products. TGA-MS of the starting UOCs indicate temperature-dependent dehydration, volatilization, and reduction events that were unique to each material; thus making this a quantifiable signature of the initial material in the processing history. In addition, p-XRD, in conjunction with quantitative morphological analysis, was capable of discriminating calcination products of each processing history at the 99 % confidence level. Quantifying these nuclear material properties, enables nuclear forensics scientists to better identify the origin of unknown or interdicted nuclear materials.

Determining the Composition of a Mixed Material with Synthetic Data

“…The images of 100% ADU were acquired at a resolution of 1,024 × 884 with a HFW of 1.53 and 3.06 μm, whereas the images of 100% UH and 100% SDU were acquired at the same resolution but with a HFW of 3.06 and 6.13 μm, respectively. The images of mixtures of ADU-UH-SDU were acquired by first preparing the mixtures with U 3 O 8 samples that were previously described individually by Schwerdt et al (2019). The samples were stored under vacuum and at room temperature between their initial synthesis and mixing.…”

Overview of Algorithms for Using Particle Morphology in Pre-Detonation Nuclear Forensics

“…References [1][2][3][4][5][6][7] describe pre-detonation nuclear forensics goals. Pre-detonation nuclear forensics focuses on determining the source and route of nuclear materials and devices prior to their use in an improvised nuclear device or radiological dispersal device.…”

“…Pre-detonation nuclear forensics focuses on determining the source and route of nuclear materials and devices prior to their use in an improvised nuclear device or radiological dispersal device. Baseline morphology and discussion of the technical production details for four precipitation conditions (ADU, AUC, SDU, and MDU) are provided in [1,2]. Subsequent studies have investigated the quantitative morphological variations for a selection of these materials due to processing, aging, and/or storage conditions [3,4,7].…”

“…This review paper illustrates statistical issues using 22 quantitative morphological metrics (Appendix A describes these 22 metrics) derived from the analysis of scanning electron microscopy images (SEM) of each segmented particle [2,4,5]. Figure 1 highlights some example SEM images acquired from nuclear materials.…”

“…Figure 1 highlights some example SEM images acquired from nuclear materials. The left image is the raw unprocessed SEM image and the right image is the image following manual particle segmentation using the Morphological Analysis of Materials (MAMA) software [2,[8][9][10]. Morphological features are proving to be useful signatures to infer the chemical processing histories (which relate to forensics goals [1][2][3]) of uranium oxides.…”