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Results for “uranium”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Isolation of a TMTAA-Based Radical in Uranium bis-TMTAA Complexes

Here, we report the synthesis, characterization, and electronic structure studies of a series of thorium(IV) and uranium(IV) bis-tetramethyltetraazaannulene complexes. These sandwich complexes demonstrate remarkable stability towards air and moisture, even at elevated temperatures. Electrochemical studies show the uranium complex to be stable in three different oxidation states; isolation of the oxidized species revealed a rare case of a non-innocent TMTAA ligand.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

An Allyl Uranium(IV) Sandwich Complex: Are ϕ Bonding Interactions Possible?

Abstract A method to explore head‐to‐head ϕ back‐bonding from uranium f‐orbitals into allyl π* orbitals has been pursued. Anionic allyl groups were coordinated to uranium with tethered anilide ligands, then the products were investigated by using NMR spectroscopy, single‐crystal XRD, and theoretical methods. The (allyl)silylanilide ligand, N ‐((dimethyl)prop‐2‐enylsilyl)‐2,6‐diisopropylaniline (LH), was used as either the fully protonated, singly deprotonated, or doubly deprotonated form, thereby highlighting the stability and versatility of the silylanilide motif. A free, neutral allyl group was observed in UI 2 (L1) 2 ( 1 ), which was synthesized by using the mono‐deprotonated ligand [K][ N ‐((dimethyl)prop‐2‐enyl)silyl)‐2,6‐diisopropylanilide] (L1). The desired homoleptic sandwich complex U[L2] 2 ( 2 ) was prepared from all three ligand precursors, but the most consistent results came from using the dipotassium salt of the doubly deprotonated ligand [K] 2 [ N ‐((dimethyl)propenidesilyl)‐2,6‐diisopropylanilide] (L2). This allyl‐based sandwich complex was studied by using theoretical techniques with supporting experimental spectroscopy to investigate the potential for phi (ϕ) back‐bonding. The bonding between U IV and the allyl fragments is best described as ligand‐to‐metal electron donation from a two carbon fragment‐localized electron density into empty f‐orbitals.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

Uranium Oxide Nanocrystals by Microwave-Assisted Thermal Decomposition: Electronic and Structural Properties

Uranium oxides have attracted much attention not only in the context of nuclear energy generation but also for their application as pristine catalysts or as supports for other (transition metal) oxides and (precious) metals. Their propensity to adopt high coordination numbers and manifest multiple oxidation states (from +II to +VI) makes them attractive candidates for catalyzed transformation reactions. In this paper, we report a new synthesis route to phase-pure, crystalline UO 2 nanoparticles via microwave-assisted decomposition of a molecular uranium(IV) precursor. Finally, the electronic structure and optical absorption properties of these nanocrystals were investigated using spectroscopic methods to evaluate their suitability for photo(electro)catalytic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

RBMK Uranium-Erbium Fuel

The history of the development and adoption of erbium fuel in RBMK is described. Research performed at the end of the 1980s – beginning of 1990s led to the conclusion that the optimal method of decreasing the steam coefficient of reactivity in RBMK is to add a consumable absorber – erbium. Computational and experimental work on the safety validation of the new fuel made it possible to adopt this fuel first in RBMK-1500 and then in RBMK-1000. The use of uranium-erbium fuel in RBMK made it possible to increase reactor safety, provide the requisite conditions for modernizing control rods, reduce the acuteness of the problem of storing spent fuel, and improve the economic indices of the fuel cycle. Considering the heightened interest in the use of erbium as a consumable absorber in VVER and some other reactors, the experience gained in developing and operating uranium-erbium fuel for RBMK could be helpful.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2015

Polyatomic interferences on high precision uranium isotope ratio measurements by MC-ICP-MS: Applications to environmental sampling for nuclear safeguards

Modern mass spectrometry and separation techniques have made measurement of major uranium isotope ratios a routine task; however accurate and precise measurement of the minor uranium isotopes remains a challenge as sample size decreases. One particular challenge is the presence of isobaric interferences and their impact on the accuracy of minor isotope 234 U and 236 U measurements. Furthermore, we present techniques used for routine U isotopic analysis of environmental nuclear safeguards samples and evaluate polyatomic interferences that negatively impact accuracy as well as methods to mitigate their impacts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Evaluating bis(2-ethylhexyl) methanediphosphonic acid (H 2 DEH[MDP]) based polymer ligand film (PLF) for plutonium and uranium extraction

This paper describes a new analyte extraction medium called polymer ligand film (PLF) that was developed to rapidly extract radionuclides. PLF is a polymer medium with ligands incorporated in its matrix that selectively and quickly extracts analytes. The main focus of the new technique is to shorten and simplify the procedure for chemically isolating radionuclides for determination through alpha spectroscopy. The PLF system was effective for plutonium and uranium extraction. The PLF was capable of co-extracting or selectively extracting plutonium over uranium depending on the PLF composition. As a result, the PLF and electrodeposited samples had similar alpha spectra resolutions.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Physical characterization of uranium oxide pellets and powder applied in the Nuclear Forensics International Technical Working Group Collaborative Materials Exercise 4

Physical characterization is one of the most broad and important categories of techniques to apply in a nuclear forensic examination. Physical characterization techniques vary from simple weighing and dimensional measurements to complex sample preparation and scanning electron microscopy-electron backscatter diffraction analysis. This paper reports on the physical characterization conducted by several international laboratories participating in the fourth Collaborative Materials Exercise, organized by the Nuclear Forensics International Technical Working Group. Methods include a range of physical measurements, microscopy-based observations, and profilometry. In conclusion, the value of these results for addressing key investigative questions concerning two uranium dioxide pellets and a uranium dioxide powder is discussed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Trace impurity analysis in uranium oxide via hybrid quantification techniques—gravimetric standard addition and isotope dilution mass spectrometry

Measurement methods for the analysis of trace impurities in uranium materials, essential in nuclear fuel production and nuclear forensics, are continuously improving. Analytical methods were developed with the goal of lowering uncertainties of next generation certified uranium oxide reference materials for trace impurity concentrations. Through addition of a traceable standard directly into the sample, gravimetric standard addition and isotope dilution followed by analysis on an inductively coupled plasma mass spectrometer can achieve lower uncertainties. In conclusion, results for 28 impurities in CRM 124-1 and 124-6 from NBL Program Office were used for validation of accuracy and comparisons of uncertainties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Separation of thorium from uranium ore

Thorium-230 has many research applications, but there is not a commercial source of this isotope. However, since 230 Th is part of the 238 U decay chain, it can be separated from naturally occurring uranium. In this work, a novel procedure was developed to separate thorium from uranium ore, consisting of leaching, liquid–liquid extraction, precipitations and ion exchange chromatography. Here, the final product was 91.32 ± 0.77 mg of thorium with a purity of 99.5 ± 1.2 wt%. Of that, 7.65 ± 0.10 mg was 230 Th and the remainder 232 Th. The total yield of 230 Th was 71.1 ± 5.4%. Ways to improve the yield by further processing the back-extraction solution are suggested.

230Th↗
DOE OSTI2020

An improved method for uranium separation from urine for rapid bioassay by inductively coupled plasma mass spectrometry

Bioassay monitoring is an important capability for any facility that works with significant amounts of radioactive material. The speed at which these analyses can be made is critical in the event of a potential exposure. Here, we present a new method that facilitates the rapid separation of uranium from a urine matrix for assay and isotopic determination by inductively coupled plasma mass spectrometry. This method is validated with archived urine samples that were previously analyzed using established, more time consuming methods. The sources of uncertainty for uranium assay and isotopic measurements are modelled using the Monte Carlo method to better understand the precision and accuracy of this method at the limit of quantification.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

International interlaboratory compilation of trace element concentrations in the CUP-2 uranium ore concentrate standard

Herein, a nuclear forensics investigation involving a uranium ore concentrate relies on accurate and precise analysis of impurities. Analytical data defensibility requires the use of reference materials as part of quality control. This study presents a compilation of trace element concentration results of the CUP-2 Uranium Ore Concentrate Standard measured by 11 different laboratories. The laboratories employed various dissolution methods, analytical preparation methods, and instrumental platforms. The data presented here contain concentrations of 66 impurities with up to 138 individual data points for each impurity. Consensus values have been assigned to each impurity following a statistical analysis of the data set.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Collaborative Study for Certification of Trace Elements in Uranium Ore Concentrate CRMs UCLO-1, UCHI-1, and UPER-1

Trace impurity patterns are important nuclear forensic signatures in uranium ore concentrates (UOCs) and Certified Reference Materials (CRMs) are used to validate the analysis methods employed by end users. Herein, we discuss the certification campaign for three new UOC CRMs from the National Research Council Canada: UCLO-1 (https://doi.org/10.4224/crm.2020.uclo-1), UCHI-1 (https://doi.org/10.4224/crm.2020.uchi-1), and UPER-1 (https://doi.org/10.4224/crm.2020.uper-1). This study involved 15 laboratories from 10 countries, using sector-field and (triple) quadrupole inductively-coupled plasma mass spectrometry to analyze 64 trace element impurities. We discuss the importance of the acids used for sample digestion, difficulties analyzing in a high uranium matrix, and data combination and uncertainty evaluation for this large dataset.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Qualitative assessment of uranium ore concentrates and related materials using scanning electron microscopy

Several studies have evaluated the morphology of uranium compounds produced under controlled conditions at the laboratory scale, but it is unclear whether the morphological characteristics of these materials persist in commercially produced uranium ore concentrates (UOCs). To assess the morphology in “real-world” UOCs, we qualitatively evaluated the morphological profile of secondary electron images from over 100 commercial UOCs using a previously published lexicon. We observe differences between samples with differing chemical composition and samples with similar chemical composition and differing provenance. Further, this work contextualizes morphology for commercially produced UOCs and will provide a basis for future machine learning efforts.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Preliminary investigation of an uncertainty budget for uranium isotope ratio analysis using a liquid sampling—atmospheric pressure glow discharge—orbitrap mass spectrometer system

The liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source has proven to be an effective analysis tool for making uranium isotope ratio measurements when coupled to high-resolution mass spectrometers, such as the Orbitrap. While previous studies have shown the capabilities of the LS-APGD for isotope ratio determination, a systematic evaluation of the measurement uncertainty of the technique has not been conducted. To this end, the International Standards Organizations (ISO) guidelines to the expression of uncertainty in measurement (GUM analysis) have been applied to generate an uncertainty budget. For this work, a preliminary assessment derived from the GUM analysis was performed. The uncertainty in the instrument blank determination has been identified as a primary factor contributing to measurement uncertainty for the LS-APGD-Orbitrap method. These findings for the specific test case of uranium isotopic analysis will be invaluable in applications across the breadth of isotope ratio mass spectrometry performed on this unique instrumental platform.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Model ages of three uranium metal CRMs and implications for radiochronometry data interpretation

In this study, we report 230 Th/ 234 U and 231 Pa/ 235 U model ages in three uranium metal certified reference materials with distinct production histories and isotopic compositions ranging from depleted to highly enriched (CRMs 112-A, 115, and 116-A). Here, our results provide the first model age values for these materials using multiple radiochronometers, which can be used as reference values for quality control of radiochronometry measurements performed during nuclear forensic investigations. Furthermore, we evaluate the model ages in the context of available production records for the materials, which provides insight into the processes that may impact radiochronometry systems during uranium metal production.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Sample screening of uranium ore concentrates using portable spectrophotometers: investigating the correlation between visible colors and chemical signatures

A research collaboration between the Japan Atomic Energy Agency and the Department of Energy’s National Nuclear Security Administration examined nuclear forensic signatures and analytical methods for tracing the origins of uranium ore concentrates (UOCs). Here, this study focuses on utilizing portable spectrophotometers capable of reflectance measurements in the visible light spectrum as a potential rapid screening tool for nuclear forensics analysis. Unlike laboratory-based near-infrared spectroscopy or digital image analysis, this research investigated the potential to correlate visible color measurements with key nuclear forensics signatures using seven types of UOC samples with known origins and three UOC certified reference materials. Results demonstrated that distinct color groups, quantified using CIELAB values, correlated with major uranium compounds. Furthermore, the findings indicated that trace elements can influence the UOC colors, providing additional insights into material characteristics. Although this approach requires further validation across a broader range of UOC species, this study demonstrated that simple colorimetric analysis using visible spectrophotometry, which does not require complex sample preparation or data processing, can serve as a practical and novel rapid tool for preliminary screening and attribution in nuclear forensics investigations.

and nuclear chemistry↗
DOE OSTI2017

Groundwater uranium stabilization by a metastable hydroxyapatite

In-situ remediation of groundwater uranium (U) contamination via the precipitation of uranyl phosphate (U-P) minerals is a promising, passive remedial approach for aquifers impacted by mobile hexavalent U (U(VI)). We demonstrate the efficacy of U stabilization in a contaminated aquifer using a metastable form of hydroxyapatite (mHAP) derived from fish bone. This material was reacted with depleted uranium (DU) contaminated groundwater both under ambient flow in-situ, and under pumped flow ex-situ. The U immobilized under both ambient and accelerated flow conditions was strongly bound in solid phases, with greater than 99% U removal from groundwater. Stable U uptake in excess of 50 g U/kg solid was achieved due to the precipitation of the crystalline U-P mineral chernikovite. Prior field trials yielded U immobilization by sorption alone, likely due to higher pH and alkalinity groundwater conditions, which increase the solubility of U-P phases via aqueous complexation. Our study is the first to demonstrate the feasibility of U immobilization by U-P precipitation from natural groundwater. Furthermore, these findings suggest that in groundwaters contaminated by U(VI) with circumneutral pH and low carbonate alkalinity, fish bone-derived hydroxyapatite is an effective material for in-situ U remediation that can be readily implemented, requiring no redox manipulation.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2021

Uptake of uranium by carbonate crystallization from reduced and oxidized hydrothermal fluids

This work evaluated the immobilization of uranium (U) through incorporation into calcite under reduced and oxidized conditions. We investigated how much U could be entrapped by calcite crystallizing in chloride solutions in autoclaves at temperatures from 162 to 300 °C. The oxidation state of U was set by controlling oxygen fugacity via redox buffers. Uranium was introduced into calcite growth media as a solid oxide compound or U aliquot. We found the uptake of tetravalent U by calcite is higher than that of hexavalent U by up to four orders of magnitude. Furthermore, we estimate that crystallization of a few mg of calcite immobilizes all dissolved U when 1 kg of solution is saturated with UO 2 under reduced hydrothermal conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗