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In the present study, surface morphological differences of mixtures of triuranium octoxide (U3O8), synthesized from uranyl peroxide (UO4) and ammonium diuranate (ADU), were investigated. The purity of each sample was verified using powder X-ray diffractometry (p-XRD), and scanning electron microscopy (SEM) images were collected to identify unique morphological features. The U3O8 from ADU and UO4 was found to be unique. Qualitatively, both particles have similar features being primarily circular in shape. Using the morphological analysis of materials (MAMA) software, particle shape and size were quantified. UO4 was found to produce U3O8 particles three times the area of those produced from ADU. With the starting morphologies quantified, U3O8 samples from ADU and UO4 were physically mixed in known quantities. SEM images were collected of the mixed samples, and the MAMA software was used to quantify particle attributes. As U3O8 particles from ADU were unique from UO4, the composition of the mixtures could be quantified using SEM imaging coupled with particle analysis. This provides a novel means of quantifying processing histories of mixtures of uranium oxides. Machine learning was also used to help further quantify characteristics in the image database through direct classification and particle segmentation using deep learning techniques based on Convolutional Neural Networks (CNN). It demonstrates that these techniques can distinguish the mixtures with high accuracy as well as showing significant differences in morphology between the mixtures. Results from this study demonstrate the power of quantitative morphological analysis for determining the processing history of nuclear materials. [ABSTRACT FROM AUTHOR]

This study aims to determine forensic signatures for processing history of UO2 based on modifications in intermediate materials within the uranyl peroxide route. Uranyl peroxide was calcined to multiple intermediate U-oxides including Am-UO3, α-UO3, and α-U3O8 during the production of UO2. The intermediate U-oxides were then reduced to α-UO2 via hydrogen reduction under identical conditions. Powder X-ray diffractometry (p-XRD) and X-ray photoelectron spectroscopy (XPS) were used to analyze powders of the intermediate U-oxides and resulting UO2 to evaluate the phase and purity of the freshly synthesized materials. All U-oxides were also analyzed via scanning electron microscopy (SEM) to determine the morphology of the freshly prepared powders. The microscopy images were subsequently analyzed using the Morphological Analysis for Materials (MAMA) version 2.1 software to quantitatively compare differences in the morphology of UO2 from each intermediate U-oxide. In addition, the microscopy images were analyzed using a machine learning model which was trained based on a VGG 16 architecture. Results show no differences in the XRD or XPS spectra of the UO2 produced from each intermediate. However, results from both the segmentation and machine learning proved that the morphology was quantifiably different. In addition, the morphology of UO2 was very similar, if not identical, to the intermediate material from which it was prepared, thus making quantitative morphological analysis a reliable forensic signature of processing history. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To identify the role of waste composition and sediment interactions in controlling Pu and Am mobility in contaminated sediments at Hanford, a legacy nuclear site, Pu and Am concentrations in solutions equilibrated with contaminated sediments from beneath the 216-Z-9 (Z-9) Trench were compared to the solubilities of PuO 2 materials, synthesized by methods representative of the disposed wastes, in the absence of sediments. This work shows that the solubilities of PuO 2 materials synthesized by different methods, and with varying particle sizes, agree with PuO 2 (am,hyd), although dissolution kinetics differed between materials. According to saturation index (SI) calculations, PuO 2 (am,hyd) is likely also controlling Pu release from sediments under conditions where phosphate concentrations are low. However, both Pu-phosphate and Am-phosphate phases, identified in SI calculations and by high resolution transmission electron microscopy, play roles in controlling release in low pH, high phosphate, shallow sediments just below the Z-9 Trench. The elevated phosphate is likely due to decomposition of tributyl phosphate from waste solutions over time. Sediments from deeper in the subsurface beneath the Z-9 Trench are less acidic and contain less phosphate, with Pu solubility likely controlled by PuO 2 (am,hyd) that precipitated following neutralization of the acidic waste stream. Controls on Am concentrations in deeper sediments are more complex and potentially involve sediment adsorption and/or release from Pu (1- x) Am x O 2 following Am in-growth. The concentrations of both Pu and Am were elevated in the colloidal fraction associated with shallow sediments, but not in PuO 2 experiments, suggesting the presence of Pu/Am pseudocolloids (e.g., Pu/Am associated with mineral colloids). However, Pu and Am association with the colloidal size fraction was not observed in deeper sediments, suggesting transport of Pu and Am to these depths beneath the Z-9 Trench was not due to colloidal transport. [Display omitted] • Pu solubility in contaminated Hanford sediments compared with PuO 2 without sediments. • Solubility controlling phases revealed by thermodynamically derived saturation indices. • PuO 2 solubility matches PuO 2 (am,hyd) regardless of synthesis or particle size. • PuO 2 (am,hyd), Am/Pu-phosphate and adsorbed Am control solubility as a function of depth. • Trace Pu/Am concentrations in deeper sediments are not due to colloidal transport. [ABSTRACT FROM AUTHOR]

Morphological changes in U 3 O 8 based on calcination temperature have been quantified enabling a morphological feature to serve as a signature of processing history in nuclear forensics. Five separate calcination temperatures were used to synthesize α-U 3 O 8 , and each sample was characterized using powder X-ray diffraction (p-XRD) and scanning electron microscopy (SEM). The p-XRD spectra were used to evaluate the purity of the synthesized U-oxide; the morphological analysis for materials (MAMA) software was utilized to quantitatively characterize the particle shape and size as indicated by the SEM images. Analysis comparing the particle attributes, such as particle area at each of the temperatures, was completed using the Kolmogorov-Smirnov two sample test (K-S test). These results illustrate a distinct statistical difference between each calcination temperature. To provide a framework for forensic analysis of an unknown sample, the sample distributions at each temperature were compared to randomly selected distributions (100, 250, 500, and 750 particles) from each synthesized temperature to determine if they were statistically different. It was found that 750 particles were required to differentiate between all of the synthesized temperatures with a confidence interval of 99.0%. Results from this study provide the first quantitative morphological study of U-oxides, and reveals the potential strength of morphological particle analysis in nuclear forensics by providing a framework for a more rapid characterization of interdicted uranium oxide samples.