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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Incipient class II mixed valency in a plutonium solid-state compound

Electron transfer in mixed-valent transition-metal complexes, clusters and materials is ubiquitous in both natural and synthetic systems. The degree to which intervalence charge transfer (IVCT) occurs, dependent on the degree of delocalization, places these within class II or III of the Robin–Day system. In contrast to the d-block, compounds of f-block elements typically exhibit class I behaviour (no IVCT) because of localization of the valence electrons and poor spatial overlap between metal and ligand orbitals. Here, in this paper, we report experimental and computational evidence for delocalization of 5f electrons in the mixed-valent Pu III /Pu IV solid-state compound, Pu 3 (DPA) 5 (H 2 O) 2 (DPA = 2,6-pyridinedicarboxylate). The properties of this compound are benchmarked by the pure Pu III and Pu IV dipicolinate complexes, [Pu III (DPA)(H 2 O) 4 ]Br and Pu IV (DPA) 2 (H 2 O) 3 ·3H 2 O, as well as by a second mixed-valent compound, Pu III [Pu IV (DPA) 3 H 0.5 ] 2 , that falls into class I instead. Metal-to-ligand charge transfer is involved in both the formation of Pu 3 (DPA) 5 (H 2 O) 2 and in the IVCT.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The CIELO collaboration: Progress in international evaluations of neutron reactions on Oxygen, Iron, Uranium and Plutonium

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies - 16O, 56Fe, 235;8U and 239Pu - with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2016

Sandia Review of High Bridge Associates Report: Comparison of Plutonium Disposition Alternatives: WIPP Diluted Plutonium Storage and MOX Fuel Irradiation

The subject report from High Bridge Associates (HBA) was issued on March 2, 2016, in reaction to a U.S. Department of Energy (DOE) program decision to pursue down-blending of surplus Pu and geologic disposal at the Waste Isolation Pilot Plant (WIPP). Sandia National Laboratories was requested by the DOE to review the technical arguments presented in the HBA report. Specifically, this review is organized around three technical topics: criticality safety, radiological release limits, and thermal impacts. Questions raised by the report pertaining to legal and regulatory requirements, safeguards and security, international agreements, and costing of alternatives, are beyond the scope of this review.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Chemical Disposition of Plutonium in Hanford Site Tank Wastes

This report examines the chemical disposition of plutonium (Pu) in Hanford Site tank wastes, by itself and in its observed and potential interactions with the neutron absorbers aluminum (Al), cadmium (Cd), chromium (Cr), iron (Fe), manganese (Mn), nickel (Ni), and sodium (Na). Consideration also is given to the interactions of plutonium with uranium (U). No consideration of the disposition of uranium itself as an element with fissile isotopes is considered except tangentially with respect to its interaction as an absorber for plutonium. The report begins with a brief review of Hanford Site plutonium processes, examining the various means used to recover plutonium from irradiated fuel and from scrap, and also examines the intermediate processing of plutonium to prepare useful chemical forms. The paper provides an overview of Hanford tank defined-waste–type compositions and some calculations of the ratios of plutonium to absorber elements in these waste types and in individual waste analyses. These assessments are based on Hanford tank waste inventory data derived from separately published, expert assessments of tank disposal records, process flowsheets, and chemical/radiochemical analyses. This work also investigates the distribution and expected speciation of plutonium in tank waste solution and solid phases. For the solid phases, both pure plutonium compounds and plutonium interactions with absorber elements are considered. These assessments of plutonium chemistry are based largely on analyses of idealized or simulated tank waste or strongly alkaline systems. The very limited information available on plutonium behavior, disposition, and speciation in genuine tank waste also is discussed. The assessments show that plutonium coprecipitates strongly with chromium, iron, manganese and uranium absorbers. Plutonium’s chemical interactions with aluminum, nickel, and sodium are minimal to non-existent. Credit for neutronic interaction of plutonium with these absorbers occurs only if they are physically proximal in solution or the plutonium present in the solid phase is intimately mixed with compounds or solutions of these absorbers. No information on the potential chemical interaction of plutonium with cadmium was found in the technical literature. Definitive evidence of sorption or adsorption of plutonium onto various solid phases from strongly alkaline media is less clear-cut, perhaps owing to fewer studies and to some well-attributed tests run under conditions exceeding the very low solubility of plutonium. The several studies that are well-founded show that only about half of the plutonium is adsorbed from waste solutions onto sludge solid phases. The organic complexants found in many Hanford tank waste solutions seem to decrease plutonium uptake onto solids. A number of studies show plutonium sorbs effectively onto sodium titanate. Finally, this report presents findings describing the behavior of plutonium vis-à-vis other elements during sludge dissolution in nitric acid based on Hanford tank waste experience gained by lab-scale tests, chemical and radiochemical sample characterization, and full-scale processing in preparation for strontium-90 recovery from PUREX sludges.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Transformation of Ferrihydrite to Goethite and the Fate of Plutonium

Understanding the interactions between plutonium and iron (oxy)hydroxide minerals is necessary to gain a predictive understanding of plutonium environmental mobility and to evaluate long-term performance of nuclear waste repositories. We investigated the fate of plutonium during the formation of ferrihydrite and its subsequent transformation into goethite. Ferrihydrite was synthesized with varying quantities of Pu(IV) following either a sorption or coprecipitation process; the ferrihydrite was then aged hydrothermally to yield goethite. Additionally, the synthesized materials were characterized via extended X-ray absorption fine structure spectroscopy, transmission electron microscopy, and acid leaching to elucidate the nature of plutonium association with ferrihydrite and goethite. In samples prepared following the sorption method, plutonium was identified in two different forms: a PuO 2 precipitate and a surface-sorbed plutonium complex. For the samples prepared via coprecipitation, no PuO 2 formation occurs in the ferrihydrite precursor and in the goethite experiments where plutonium concentration is ≤1000 ppm (mg kg –1 ). In these coprecipitation products, plutonium is strongly bound to the minerals either via formation of an inner sphere complex, or via an incorporation process. In the coprecipitation experiments, PuO 2 formation only occurs at the highest plutonium concentration (3000 ppm), suggesting that during ferrihydrite transformation into goethite, part of the plutonium can be remobilized to form PuO 2 nanoparticles. Collectively, our results demonstrate that the nature of plutonium associated with the precursor ferrihydrite (adsorbed vs coprecipitated) will have a direct impact on the association of plutonium with its alteration product (goethite). Furthermore, the data illustrate that some properties of plutonium association with the precursor ferrihydrite are retained through the transformation into goethite. These findings show that plutonium strongly associates with iron (oxy)hydroxides formed through coprecipitation processes and in these materials, plutonium can be strongly retained by the iron minerals.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Water Solubility of Plutonium and Uranium Compounds and Residues at TA-55

Understanding the water solubility of plutonium and uranium compounds and residues at TA-55 is necessary to provide a technical basis for appropriate criticality safety, safety basis and accountability controls. Individual compound solubility was determined using published solubility data and solution thermodynamic modeling. Residue solubility was estimated using a combination of published technical reports and process knowledge of constituent compounds. The scope of materials considered includes all compounds and residues at TA-55 as of March 2016 that contain Pu-239 or U-235 where any single item in the facility has more than 500 g of nuclear material. This analysis indicates that the following materials are not appreciably soluble in water: plutonium dioxide (IDC=C21), plutonium phosphate (IDC=C66), plutonium tetrafluoride (IDC=C80), plutonium filter residue (IDC=R26), plutonium hydroxide precipitate (IDC=R41), plutonium DOR salt (IDC=R42), plutonium incinerator ash (IDC=R47), uranium carbide (IDC=C13), uranium dioxide (IDC=C21), U 3 O 8 (IDC=C88), and uranium filter residue (IDC=R26). This analysis also indicates that the following materials are soluble in water: plutonium chloride (IDC=C19) and uranium nitrate (IDC=C52). Equilibrium calculations suggest that PuOCl is water soluble under certain conditions, but some plutonium processing reports indicate that it is insoluble when present in electrorefining residues (R65). Plutonium molten salt extraction residues (IDC=R83) contain significant quantities of PuCl 3 , and are expected to be soluble in water. The solubility of the following plutonium residues is indeterminate due to conflicting reports, insufficient process knowledge or process-dependent composition: calcium salt (IDC=R09), electrorefining salt (IDC=R65), salt (IDC=R71), silica (IDC=R73) and sweepings/screenings (IDC=R78). Solution thermodynamic modeling also indicates that fire suppression water buffered with a commercially-available phosphate buffer would significantly reduce the solubility of PuCl 3 by the precipitation of PuPO 4 .

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

The effects of chronic diseases on plutonium urinary excretion in former workers of the Mayak Production Association

The radiochemical analysis of plutonium activity in urine is the main method for indirect estimation of doses of internal exposure from plutonium incorporation in professional workers. It was previously shown that late-in-life acute diseases, particularly those that affect the liver, can promote accelerated rates of release of plutonium from the liver with enhanced excretion rates. This initial study examines the relationships of some chronic diseases on plutonium excretion as well as the terminal relative distribution of plutonium between the liver and skeleton. Fourteen cases from former workers at the Mayak Production Association (Mayak PA) who provided from 4–9 urine plutonium bioassays for plutonium, had an autopsy conducted after death, and had sufficient clinical records to document their health status were used in this study. Enhanced plutonium excretion was associated with more serious chronic diseases, including cardiovascular diseases and other diseases that involved the liver. These chronic diseases were also associated with relatively less plutonium found in the liver relative to the skeleton determined by analyses conducted after autopsy. These data further document health conditions that affect plutonium biokinetics and organ deposition and retention patterns and suggest that health status should be considered when conducting plutonium bioassays as these may alter subsequent dosimetry and risk models.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Sources, seasonal cycling, and fate of plutonium in a seasonally stratified and radiologically contaminated pond

Unlike short-term laboratory experiments, studies at sites historically contaminated with radionuclides can provide insight into contaminant migration behavior at environmentally-relevant decadal timescales. One such site is Pond B, a seasonally stratified reservoir within Savannah River Site (SC, USA) has low levels (μBq L –1 ) of plutonium in the water column. Here, we evaluate the origin of plutonium using high-precision isotope measurements, investigate the impact of water column geochemistry on plutonium cycling during different stratification periods, and re-evaluate long-term mass balance of plutonium in the pond. New isotopic data confirm that reactor-derived plutonium overwhelms input from Northern Hemisphere fallout at this site. Two suggested mechanisms for observed plutonium cycling in the water column include: (1) reductive dissolution of sediment-derived Fe(III)-(oxyhydr)oxides during seasonal stratification and (2) plutonium stabilization complexed strongly to Fe(III)-particulate organic matter (POM) complexes. While plutonium may be mobilized to a limited extent by stratification and reductive dissolution, peak plutonium concentrations are in shallow waters and associated with Fe(III)-POM at the inception of stratification. This suggests that plutonium release from sediments during stratification is not the dominant mechanism driving plutonium cycling in the pond. Importantly, our analysis suggests that the majority is retained in shallow sediments and may become increasingly recalcitrant.

54 ENVIRONMENTAL SCIENCES↗