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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
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 OSTI2023

Pertechnetate/perrhenate–capped Zr/Hf–Dihydroxide Dimers: Elucidating Zr–TcO 4 Co–Mobility in the Nuclear Fuel Cycle

Spent nuclear fuel contains heavy element fission products that must be separated for effective reprocessing for a safe and sustainable nuclear fuel cycle. 93 Zr and 99 Tc are high-yield fission products that co-transport in liquid-liquid extraction processes. Here we seek atomic-level information of this co-extraction process, as well as fundamental knowledge about Zr IV (and Hf IV ) aqueous speciation in the presence of topology-directing ligands such as pertechnetate (TcO 4 – ) and non-radioactive surrogate perrhenate (ReO 4 – ). In this context, we show that the flat tetrameric oxyhydroxyl-cluster [M IV 4 (OH) 8 (H 2 O) 16 ] 8+ (and related polymers) is dissociated by perrhenate/pertechnetate to yield isostructural dimers, M 2 (OH) 2 (XO 4 – ) 6 (H 2 O) 6 • 3H 2 O (M=Zr/Hf IV ; X=Re/Tc VII ), elucidated by single-crystal X-ray diffraction. We used these model compounds to understand the pervasive 93 Zr- 99 Tc coextraction with further speciation studies in water, nitric acid, and tetrabutylphosphate (TBP) -kerosene; where the latter two media are relevant to nuclear fuel reprocessing. SAXS (small angle X-ray scattering), compositional evaluation, and where experimentally feasible, ESI-MS (electrospray ionization mass spectrometry) showed that perrhenate/pertechnetate influence Zr/Hf IV -speciation in water. Here, in Zr-XO 4 solvent extraction studies to simulate fuel reprocessing, we provide evidence that TcO 4 – enhances extraction of Zr IV , and compositional analysis of the extracted metal-complexes (Zr-ReO 4 study) is consistent with the crystallized Zr IV 2 (OH) 2 (Re VII O 4 – ) 6 (H 2 O) 6 •dimer.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2023

Kinetics of the Temperature-Dependent e aq - and ·OH Radical Reactions with Cr(III) Ions in Aqueous Solutions

The reactivity of chromium(III) species with the major oxidizing and reducing radiolysis products of water was investigated in aqueous solutions at temperatures up to 150 °C. The reaction between the hydrated electron (e aq - ) and Cr(III) species showed a positive temperature dependence over this temperature range. The reaction was also studied in pH 2.5 and 3.5 solutions for the first time. This work also studied the reaction between acidic Cr(III) species and the hydroxyl radical (·OH). It was found that Cr 3+ did not react significantly with the ·OH radical, but the first hydrolysis species, Cr(OH) 2+ , did with a rate coefficient of k= (7.2±0.3)×10 8 M -1 s -1 at 25 °C. The oxidation of Cr(OH) 2+ by the ·OH radical formed an absorbing product species that ultimately oxidized to give Cr(VI). In conclusion, these newly measured reaction rates allow for the development of improved models of aqueous chromium speciation for the effective remediation of liquid high-level nuclear waste via vitrification processes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

The electronic Raman scattering spectrum of PuO 2

Here the Raman spectrum of PuO 2 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 PuO 2 , 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 PuO 2 for nuclear nonproliferation and forensics purposes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2026

Identification of a key water molecule involved in the macrophage migration inhibitory factor‐catalyzed tautomerization of para ‐hydroxyphenylpyruvate using neutron crystallography

Abstract Neutron crystallography was used to determine a 2.5‐Å resolution all‐atom structure of macrophage migration inhibitory factor (MIF) interacting with 3‐(4‐hydroxyphenyl)‐pyruvate (HPP). MIF is a pro‐inflammatory, pro‐tumorigenic protein that may be an attractive therapeutic target. MIF catalyzes the interconversion of the keto and enol forms of HPP by a tautomerase reaction. Although HPP is evidently not a physiological substrate of MIF, many compounds that inhibit this activity in enzymatic assays have been found also to inhibit physiological activities of MIF. Therefore, the MIF‐catalyzed HPP tautomerization reaction is used in initial screening of compounds in the search for inhibitors of MIF physiological activity. The neutron diffraction‐derived crystal structure reveals the position of a water molecule involved in the tautomerization reaction, and also confirms the charged state of lysine‐32 in the active site. The structure confirms the previously proposed catalytic mechanism of MIF, with the N‐terminal Pro‐1 abstracting a proton to generate an HPP enolate intermediate which is subsequently protonated. The structure reported herein reveals that this proton is supplied by a neighboring water molecule. Along with the neutron structure, a room‐temperature synchrotron x‐ray crystal structure reveals a covalent adduct between HPP and MIF. While this adduct is a result of radiation‐induced chemistry, its formation confirms the catalytic role of the active site residue because a covalent complex could only form if the reactive carbon of the substrate is correctly positioned by the enzyme.

Schröder, Gabriela C. [Department of Molecular and↗
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 interlaboratory collaboration to determine consensus 231 Pa/ 235 U model ages of a uranium certified reference material for nuclear forensics

Application of the 231 Pa/ 235 U radiochronometer for nuclear forensic investigations is challenged by a lack of certified reference materials with 231 Pa/ 235 U model purification dates. The Japan Atomic Energy Agency, Los Alamos National Laboratory, and Lawrence Livermore National Laboratory completed an interlaboratory study measuring 231 Pa/ 235 U model ages of New Brunswick Laboratory CRM U100. Results from independent laboratories were combined to calculate a consensus 231 Pa/ 235 U model purification date for CRM U100 of March 26, 1959 ± 237 days. This 231 Pa/ 235 U consensus date for CRM U100 may be used by the nuclear forensic community for quality control of 231 Pa/ 235 U radiochronometry measurements of unknown materials.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Determining P, S, Br, and I content in uranium by triple quadrupole inductively coupled plasma mass spectrometry

The trace impurities of a uranium ore concentrate (UOC) can be examined to determine mine source, methods of production, and quality. This study presents a method to determine the concentration of halides and main group elements, specifically P, S, Br and I, utilizing triple quadrupole inductively coupled plasma–mass spectrometry. These analytes were measured in a uranium matrix to simulate a UOC sample. The concentrations determined with this method showed agreement with known values. Solutions with and without uranium were compared. A UOC certified reference material, CUP-2, was analyzed to further demonstrate the effectiveness of the method.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

A highly-enriched 244 Pu reference material for nuclear safeguards and nuclear forensics measurements

A highly-enriched 244 Pu isotope dilution reference material has been prepared and characterized for metrologically traceable measurements of very small quantities of plutonium. The amount of plutonium in samples associated with nuclear safeguards and nuclear forensic measurements can be significantly less than 1 ng. Accordingly, the ability to quantify the amount and isotopic composition of plutonium from a single mass-spectrometric analysis is particularly desirable. The highly-enriched 244 Pu reference material, described here, will minimize the magnitude of spike corrections necessary to obtain accurate information on plutonium isotopic composition from isotope dilution measurements.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2020

Inline gamma-spectrometry of fission product elements after rapid high-pressure ion chromatographic separation

Analysis of irradiated material shortly after irradiation can be non-trivial due to highly radioactive activation and fission isotopes increasing dead time in gamma-ray detection systems, often requiring a “cooling-period” between receipt of a sample and the subsequent analysis. A direct separation–detection method has been developed combining ion chromatography and inductively coupled mass spectrometry for rapid, low-level analysis of fission products; it cannot, however, detect certain short-lived species below the detection limit of the system. In this paper we report the implementation of an inline gamma-ray detector, which was added post-separation, pre-analysis, to test the quality and utility of elementally-isolated gamma-ray spectroscopy.

Inline gamma-ray detection↗
DOE OSTI2020

New measurements of gamma-ray energies and their absolute intensities from the decay of 231 Pa

Accurate nuclear data for the decay of 231 Pa is highly important for non-destructive analysis in the areas of radiochronometry and nuclear forensics. However, the evaluated nuclear data for this isotope is lacking; many previous measurements have large uncertainties and only two measurements are used to determine the absolute intensities. In this work, we present modern measurements of the major gamma-ray emissions from the decay of 231 Pa to 227 Ac including the energies and absolute intensities. For many of these measurements, the error envelopes have been significantly decreased compared to previous measurements, while remaining in good agreement. The absolute intensity of the 283 keV reference line was measured as 0.0163(2).

231Pa↗
DOE OSTI2020

Side-reaction products identified for photo-nuclear production of 99 Mo

Production of 99 Mo by the 100 Mo (γ, n) 99 Mo reaction through the bremsstrahlung process using an electron accelerator is one of the feasible options currently pursued by several countries. In this work, we report experimental results on identification of side-reaction products after the irradiation of natural and enriched 100 Mo targets. Side-reaction products identified include various Mo, Nb and Zr isotopes. Comparison of experimentally determined reaction production rates with those determined based on theoretical cross-sections will be presented. Moreover, activation products formed due to presence of impurities introduced during the manufacturing of the Mo targets will also be discussed.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Transactinide studies with sulfur macrocyclic extractant using mercury

Mercury extraction has been studied in nitric and hydrochloric acids with hexathia-18-crown-6 dissolved in carbon tetrachloride. Batch study experiments have been performed to determine the best conditions for maximum extraction. In both acids, Hg(II) was best extracted at low molarity while almost no extraction was observed above 2 M. Furthermore, speciation studies were carried out in an attempt to describe the extraction mechanism, but the exact composition of the extracted species was not determined. The extraction kinetics were studied to assess the feasibility of this crown ether for extracting Cn and/or Fl in a future online experiment.

197mHg↗
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 OSTI2020

Enhanced detection limits for radiokrypton analysis

In this paper, we present a method for improving detection limits of Atom Trap Trace Analysis for the krypton radioisotopes 85 Kr and 81 Kr. For the case of 85 Kr this work demonstrates that systematic use of isotopically depleted gas for calibration and extended conditioning of the instrument results in a detection limit of 900 85 Kr atoms per 11 μl of Kr gas, equivalent to a 85 Kr/Kr isotopic abundance of 3 x 10 -15 . This improvement of roughly two orders of magnitude over previously reported limits will help to expand the reach of radiokrypton dating towards longer age ranges where most of the radioisotopes have decayed. Additionally, the method offers an opportunity to investigate radiokrypton production via spontaneous fission within naturally occurring minerals to understand potential underground production of these isotopes.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Effect and measurement of residual water in CaCl 2 intended for use as electrolyte in molten salt electrochemical processing

We report CaCl 2 has applications for electrochemical processing of nuclear materials. Thermal dehydration leads to formation of oxide ions, which are shown to react and cause precipitation of dissolved CeCl 3 that was selected as a surrogate for actinide chlorides. Thus, measurement of residual water in CaCl 2 is an essential capability. Thermogravimetric analysis (TGA) was shown to underestimate starting water concentration. Subsequent analysis of solid samples via acid–base titration and cyclic voltammetry (CV) of the molten salt yielded consistent values within 5% for residual water. Hydroxides were shown to be unstable, thus oxygen is retained as oxide ions. Thus, total water in a sample of CaCl 2 can be quantified by combining TGA with with either CV of molten salt or titration of salt samples. The importance of quantifying residual water in the salt was demonstrated by showing that cerium chloride (surrogate for actinide chlorides) will react with oxide ions in CaCl 2 to form insoluble oxides and oxychlorides.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Uncovering Uranium Isotopic Heterogeneity of Fuel Pellets from the Fifth Collaborative Materials Exercise of the Nuclear Forensics International Technical Working Group

In 2017, the Nuclear Forensics International Technical Working Group (ITWG) organized their fifth 37 Collaborative Materials Exercise (CMX-5). The exercise samples were two uranium dioxide fuel pellets 38 manufactured from the same starting materials by different processes to have similar bulk isotopic 39 composition, but different spatial uranium isotopic distributions. Sets of identical materials were sent to 40 all participating laboratories, who then utilized their existing nuclear forensic capabilities to 41 independently analyse fuel pellets and identify similarities and differences of the materials’ 42 characteristics. The analytical methods used to probe the fuel pellets included ex situ, such as sectioning 43 or breaking up the pellets and analyzing dissolved pieces using inductively coupled plasma mass 44 spectrometry (ICP-MS), analyzing particles collected from intact or fragmented pellets by secondary ion 45 mass spectrometry (SIMS), as well as in situ methods, such as laser ablation coupled with ICP-MS, 46 autoradiography and nanoSIMS. In this paper we present the results of these independent analyses and 47 compare the capabilities of those nuclear forensic analytical methods to uncover details of the isotopic 48 heterogeneity of uranium fuel pellets.

Nuclear Forensic Analysis of Uranium Fuel Pellets,↗
DOE OSTI2021

Chemical processes for recovery and purification of high-purity uranium-234 from aged plutonium-238

This work describes a streamlined approach to the recovery and purification of 234 U from aged 238 Pu. Key modifications to conventional techniques are described that result in an efficient uranium and plutonium separation process that successfully produced tens of grams of ultrahigh purity 234 U at Oak Ridge National Laboratory. A new processing scheme was developed using an anion exchange column run in a cycling mode with HNO 3 media as the primary uranium purification process. This was followed with a uranyl peroxide precipitation step to purify and solidify the uranium before conversion to U 3 O 8 . Both the traditional uranyl peroxide precipitation method and a new cascade uranyl peroxide precipitation process were used for final purification of the 234 U.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗