Search

Plutonium research has been stifled by the significant number of administrative controls and safety procedures, space and instrumentation limitations in radiological gloveboxes, and the potential for personnel and equipment contamination. To address the limited number of spectroscopic studies in Pu-bearing compounds in the current scientific literature, this work presents the use of double-walled cells (DWCs) in "clean" buildings/laboratories as an alternative to research in radiological gloveboxes. This study reports the first laser-induced breakdown spectroscopy (LIBS) experiments of a PuO2 pellet contained within a DWC, where the formation of elemental (atomic and ionic) species as well as the evolution from elemental to molecular products (Pu x O y) was measured. Raman spectroscopy was also used to characterize the surface of the ablated pellet and the particulates deposited on the window of the inner cell. The full width half-maximum of the T2g band enabled us to obtain an estimate of the temperature at the pellet surface after the ablation pulse and the particulates based on the crystal lattice disorder. Particulates deposited on the window of the DWC during laser ablation were characterized using scanning electron microscopy, where molten irregular particulates and spheroids were observed. This exciting research conducted in a DWC describes our initial attempts to incorporate LIBS in the arsenal of spectroscopic tools for nuclear forensics applications. [ABSTRACT FROM AUTHOR]

The dissolution step of uranium and mixed oxide uranium-plutonium spent nuclear fuel is a key initial step of a new alternative hydrometallurgical method—the CARBEX process. The study considers carbonate oxidizing systems NaHCO3/Na2CO3–H2O2/2Na2CO3·3H2O2/М2S2O8, where M = Na, K, or NH4+, for dissolving actinide oxide powders. The chemical and physical factors that determine the rate of oxidative dissolution of powdered individual oxides UO2, U3O8, PuO2 and NpO2 in carbonate media were found. The results obtained are important for the development of the oxidative and sonochemical options of dissolution of highly calcined crystalline samples of uranium, plutonium and neptunium oxides, as well of spent nuclear fuel in carbonate media. [ABSTRACT FROM AUTHOR]

Diffuse reflectance spectroscopy measurements in the shortwave infrared (930–1600 nm) spectral region were acquired for Pu2(C2O4)3•9H2O and its thermal decomposition product, PuO2. We analyzed a total of eight PuO2 samples that were produced at different calcination temperatures (300, 350, 450, 525, 600, 675, 750, and 900 °C). Our goal was to identify spectroscopic fingerprints that could be used to gain retrospective information regarding the production parameters of these important nuclear compounds. The diffuse reflectance spectrum of Pu2(C2O4)3•9H2O features several broad bands that currently preclude detailed analysis. However, all PuO2 samples produced relatively sharp spectral features that got sharper and more intense for samples that were produced at higher calcination temperatures. The electronic band observed at 1433 nm in the diffuse reflectance spectra of PuO2 was found to be a sensitive indicator of crystallinity; a result that is corroborated by ancillary Raman spectroscopy measurements. Principal component analysis of diffuse reflectance spectra was able to clearly rank and categorize PuO2 samples based on the calcination temperature that was employed during their production. Thus, we show herein that important retrospective information pertaining to the process history of PuO2 can be gained through the relatively simplistic combination of diffuse reflectance spectroscopy and principal component analysis. This discovery presents a new method for determining the provenance and process history of PuO2 and should have an impact in the fields of nuclear forensics and nuclear nonproliferation. Graphical Abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]

The Raman spectrum of PuO2 was measured up to 13,000 cm−1 with three different laser excitation wavelengths spanning the resonance (405 nm), near‐resonance (457 nm), and preresonance (514 nm) energy range. Approximately 26 never‐before‐seen bands were observed between 3500 and 13,000 cm−1. Given the very high energy of the Raman shifts of these bands and the relative insensitivity of their spectral position to the interrogating laser wavelength, they are believed to arise from an electronic origin. These bands are present in both freshly calcined and radiolytically aged PuO2, although a broad luminescence is observed in the aged material, which obscures many of the high frequency features. In situ laser annealing of the material attenuated this luminescence and allowed for clear observation of these never‐before‐seen spectral features. Discovery of these high‐energy bands presents a new way of identifying PuO2 for nuclear nonproliferation and forensics purposes. [ABSTRACT FROM AUTHOR]

The Raman spectrum of PuO2 was measured up to 13,000 cm−1 with three different laser excitation wavelengths spanning the resonance (405 nm), near‐resonance (457 nm), and preresonance (514 nm) energy range. Approximately 26 never‐before‐seen bands were observed between 3500 and 13,000 cm−1. Given the very high energy of the Raman shifts of these bands and the relative insensitivity of their spectral position to the interrogating laser wavelength, they are believed to arise from an electronic origin. These bands are present in both freshly calcined and radiolytically aged PuO2, although a broad luminescence is observed in the aged material, which obscures many of the high frequency features. In situ laser annealing of the material attenuated this luminescence and allowed for clear observation of these never‐before‐seen spectral features. Discovery of these high‐energy bands presents a new way of identifying PuO2 for nuclear nonproliferation and forensics purposes. [ABSTRACT FROM AUTHOR]

[Display omitted] • ab initio modelling predicts morphology and surface speciation of PuO 2 nanoparticles. • Nanoparticle shapes as a function of temperature and partial pressure of gasses. • H 2 O and CO 2 co-adsorption has a significant impact on the surface composition. • Step toward more realistic models for adsorbates and actinide oxides. Among the most pressing challenges faced by the UK nuclear industry is how to safely handle its large stockpile of plutonium dioxide. In particular, understanding how the exposed surfaces interact with the environment is critical to establishing the chemical reactivity and determining suitable processing and storage conditions. In this work, we apply an ab initio modelling approach to predict the morphology and surface speciation of stoichiometric and oxygen deficient PuO 2 nanoparticles as a function of temperature and in the presence of individually- and co-adsorbed H 2 O and CO 2. We find that co-adsorption of the two species has a significant impact on the surface composition, resulting in the equilibrium particle morphology being strongly dependent on the storage conditions. This work provides valuable insight into the behaviour of nanoparticulate PuO 2 in the presence of ubiquitous small molecules and marks an important step toward more realistic models extendable to other adsorbates and actinide oxides. [ABSTRACT FROM AUTHOR]

In recent years, the hydrothermal conversion of actinide (IV) oxalates into nanometric actinide dioxides (AnO2) has begun to be investigated as an alternative to the widely implemented thermal decomposition method. We present here a comparison between the hydrothermal and the conventional thermal decomposition of Pu(IV) oxalate in terms of particle size, morphology and residual carbon content. A parametric study was carried out in order to define the temperature and time applied in the hydrothermal conversion of tetravalent Pu-oxalate into PuO2 and to optimize the reaction conditions. [ABSTRACT FROM AUTHOR]

• DFT calculations were performed on the adsorption and reaction behaviors of room environment gases (i.e., O 2 , H 2 , H 2 O) on the PuO 2 (111) surface. • The stoichiometric PuO 2 (111) slab is inert under O 2 atmosphere within a large temperature and pressure range. • H 2 O prefers to stay as molecular state when adsorbing on PuO 2 (111) and dissociative adsorption of H 2 remains thermodynamically stable at H 2 -pressure as low as ∼10−35 bar under room temperature. • Kinetic analysis reveals the dynamical properties of PuO 2 surface under H 2 -rich atmosphere with increased temperature. Adsorption and reaction properties of environmental gases including O 2 , H 2 , and H 2 O on the PuO 2 (111) surface were studied via density functional theory simulations along with thermodynamic and kinetic analysis. Simulation results show that the stoichiometric PuO 2 (111) remains intact under O 2 atmosphere and extremely low or high O 2 pressure is required to form oxygen vacancy or adsorbed-O on the surface. The H 2 O prefers to stay as molecular state when adsorbing on PuO 2 (111) and a relatively high humidity is required for H 2 O to be stably binding on the surface. For H 2 interaction with PuO 2 , the dissociative adsorption of H 2 molecule induces reduction of Pu(IV) ions to Pu(III), and remains thermodynamically stable at H 2 pressure as low as ∼10−35 bar under room temperature. Kinetic modeling shows that at temperature below 350 K, the PuO 2 (111) surface is mainly covered by OH species when exposing to H 2 environment while bare metal sites appear with increased temperature and reaction time. [Display omitted] [ABSTRACT FROM AUTHOR]

The interaction of collision cascades initialized by alpha decays in PuO 2 crystals with xenon, helium and mixed Xe-He bubbles of linear dimensions of 1–2 nm was studied by a molecular dynamics technique. The bubbles were not destroyed by the cascades studied, however individual fast Xe and He atoms could be released. These fast atoms received high energies up to 90% of the collision cascade energy (80 keV). Also, the diffusion migration of helium atoms to the region of the crystal lattice damaged by the collision cascade was detected. Xenon atoms did not diffuse to the damage area on the simulated time scale. However, the xenon clusters changed their shape in the disordered surroundings. [ABSTRACT FROM AUTHOR]

The release of clusters from the surface of PuO 2 nanocrystals caused by the alpha decay collision cascades was simulated using the molecular dynamics. The clusters containing up to several hundred particles were recorded. The obtained size distributions of the clusters were characterized by relatively high probabilities of the formation of large clusters. The total kinetic energy of the released material reached tens of percent of the total energy of the collision cascade. Single ions, both plutonium and oxygen, could have kinetic energies of up to several thousand electron-volts. The electric charge of the clusters in most cases was close to zero, although clusters with significant negative charges were also observed. [ABSTRACT FROM AUTHOR]

In the framework of the radioactive waste drum characterization using neutron coincidence counting, the Nuclear Measurement Laboratory of French Alternative Energies and Atomic Energy Commission (CEA) Cadarache is studying plastic scintillators as an alternative to ideal but costly 3He gas proportional counters. Plastic scintillators are at least five times cheaper for the same detection efficiency, and in addition, they detect fast neutrons three orders of magnitude more quickly than 3He detectors. However, they are sensitive to gamma rays with no pulse shape discrimination abilities for large detection volumes, which implies the necessity to identify precisely gamma background sources that may affect the useful signal. This article presents a detailed analysis of the gamma-ray spectrum of a radioactive waste drum containing glove box filters contaminated by plutonium dioxide. Classical gamma emissions following alpha and beta disintegrations are identified, and also those accompanying inelastic scattering (n, n') or radiative capture (n, γ) reactions in the whole waste drum, and (α, n) or (α, p) reactions in the filtration media, which can lead to neutron-gamma coincidences parasitizing useful coincidences from plutonium spontaneous fissions. [ABSTRACT FROM AUTHOR]

Introduction: Radiochemical production is one of the richest in terms of data for analytical control, high-quality implementation of which is impossible without using type approved reference materials (RMs). Industry-specific institutes used to satisfy the demand for RMs, many of which nowadays have ceased this type of activities due to various reasons. The paper in question covers problems of metrological support in radiochemical production caused by the lack of type approved RMs.Materials and methods: Technologies used for obtaining homogeneous reference material for radiochemical production are described. Methods and measuring instruments used for certifying RMs are listed.Results: Results of developing certified reference materials at Mayak Production Association are given. Examples of codeveloping RMs of triuranium octoxide and plutonium dioxide are provided.Discussion and conclusions: Assessment of the current situation in terms of provision of type approved RMs is given. The paper provides data on availability of raw material, quality of instrument and methodological base in order to create a reference material production site at Mayak Production Association. Results of step-by-step solutions to problems of metrological assurance in radiochemical production are presented. Research prospects of developing RMs for inductively coupled plasma mass spectrometry are outlined. An outlook is given and practical proposals are formulated in the paper. The proposals in question are related to the interaction between institutes and enterprises of the field in terms of developing type approved RMs.