Oxygen Isotope and Fluorine Impurity Signatures during the Conversion of Uranium Ore Concentrates to Nuclear Fuel.

Within the front end of the nuclear fuel cycle, many processes impart forensic signatures. Oxygen-stable isotopes (δO values) of uranium-bearing materials have been theorized to provide the processing and geolocational signatures of interdicted materials. However, this signature has been minimally utilized due to a limited understanding of how oxygen isotopes are influenced during uranium processing.

In Situ Liquid Cell Transmission Electron Microscopy Study of Studtite Particle Formation and Growth via Electron Beam Radiolysis.

This study presents in situ observations of studtite (UOO(HO)·2HO) crystal growth utilizing liquid phase transmission electron microscopy (LP-TEM). Studtite was precipitated from a uranyl nitrate hexahydrate solution using hydrogen peroxide formed by the radiolysis of water in the TEM electron beam. The hydrogen peroxide (HO) concentration, directly controlled by the electron beam current, was varied to create local environments of low and high concentrations to compare the impact of the supersaturation ratio on the nucleation and growth mechanisms of studtite particles.

Identification and Elemental Impurity Analysis of Heterogeneous Morphologies in Uranium Oxides Synthesized from Uranyl Fluoride Precursors.

The surface morphology characteristics of postenrichment deconversion products in the nuclear fuel cycle are important for producing nuclear fuel pellets. They also provide the first opportunity for a microstructural signature after conversion to gaseous uranium hexafluoride (UF). This work synthesizes uranium oxides from uranyl fluoride (UOF) starting solutions by the wet ammonium diuranate route and a modification of the dry route.

Oxygen Isotope Fractionation in UO during Thermal Processing in Humid Atmospheres.

The incorporation of oxygen isotopes from water into uranium oxides during industrial processing presents a pathway for determining a material's geographical origin. This study is founded on the hypothesis that oxygen isotopes from atmospheric water vapor will exchange with isotopes of oxygen in solid uranium oxides during thermal processing or calcination. Using a commonly encountered oxide, UO, the exchange kinetics and equilibrium fractionation with water vapor (in a concentration range of 50-55% relative humidity) were investigated using processing temperatures of 400, 600, and 800 °C.

Oxygen Kinetic Isotope Effects in the Thermal Decomposition and Reduction of Ammonium Diuranate.

Oxygen stable isotopes in uranium oxides processed through the nuclear fuel cycle may have the potential to provide information about a material's origin and processing history. However, a more thorough understanding of the fractionating processes governing the formation of signatures in real-world samples is still needed. In this study, laboratory synthesis of uranium oxides modeled after industrial nuclear fuel fabrication was performed to follow the isotope fractionation during thermal decomposition and reduction of ammonium diuranate (ADU).

Effect of Diel Cycling Temperature, Relative Humidity, and Synthetic Route on the Surface Morphology and Hydrolysis of α-UO.

The speciation and morphological changes of α-UO following aging under diel cycling temperature and relative humidity (RH) have been examined. This work advances the knowledge of U-oxide hydration as a result of synthetic route and environmental conditions, ultimately giving novel insight into nuclear material provenance. α-UO was synthesized via the washed uranyl peroxide (UO) and ammonium uranyl carbonate (AUC) synthetic routes to produce unaged starting materials with different morphologies.

Impact of Controlled Storage Conditions on the Hydrolysis and Surface Morphology of Amorphous-UO.

The hydration and morphological effects of amorphous (A)-UO following storage under varying temperature and relative humidity have been investigated. This study provides valuable insight into U-oxide speciation following aging, the U-oxide quantitative morphological data set, and, overall, the characterization of nuclear material provenance. A-UO was synthesized via the washed uranyl peroxide synthetic route and aged based on a 3-factor circumscribed central composite design of experiment.

Quantifying Impurity Effects on the Surface Morphology of α-UO.

The morphological effect of impurities on α-UO has been investigated. This study provides the first evidence that the presence of impurities can alter nuclear material morphology, and these changes can be quantified to aid in revealing processing history. Four elements: Ca, Mg, V, and Zr were implemented in the uranyl peroxide synthesis route and studied individually within the α-UO.

Nuclear forensics investigation of morphological signatures in the thermal decomposition of uranyl peroxide.

The analytical techniques typically utilized in a nuclear forensic investigation often provide limited information regarding the process history and production conditions of interdicted nuclear material. In this study, scanning electron microscopy (SEM) analysis of the surface morphology of amorphous-UO samples calcined at 250, 300, 350, 400, and 450°C from uranyl peroxide was performed to determine if the morphology was indicative of the synthesis route and thermal history for the samples. Thermogravimetic analysis-mass spectrometry (TGA-MS) and differential scanning calorimetry (DSC) were used to correlate transitions in the calcined material to morphological transformations.

Quantifying Morphological Features of α-UO with Image Analysis for Nuclear Forensics.

Morphological changes in UO 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-UO, 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.

Characterization of Actinides Complexed to Nuclear Fuel Constituents Using ESI-MS.

Electrospray ionization-mass spectrometry (ESI-MS) was tested for its use in monitoring spent nuclear fuel (SNF) constituents including U, Pu, dibutyl phosphate (DBP), and tributyl phosphate (TBP). Both positive and negative ion modes were used to evaluate the speciation of U and Pu with TBP and DBP. Furthermore, apparent stability constants were determined for U complexed to TBP and DBP.

Failure of ESI spectra to represent metal-complex solution composition: a study of lanthanide-carboxylate complexes.

Electrospray ionization-mass spectrometry (ESI-MS) shows great promise as a rapid method to identify metal-ligand complexes in solution. However, its application for quantitative determination of the distribution of species present in complicated equilibria is still in its infancy, and a direct correlation between ions observed in the gas phase and species expected in solution must be made with caution. The present work focuses on a seemingly simple system; the complexation of lanthanide cations with the acetate ligand.