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McGuffin DL, Lucas DD, Balboni E, Nasstrom JS, Lundquist KA, Knight KB. Predictive modeling of atmospheric nuclear fallout microphysics. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 951:175536. [PMID: 39155003 DOI: 10.1016/j.scitotenv.2024.175536] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2024] [Revised: 07/23/2024] [Accepted: 08/13/2024] [Indexed: 08/20/2024]
Abstract
The capability to predict size, composition, and transport of nuclear fallout enables public officials to determine immediate and prolonged guidance in the event of a nuclear incident. Predictive computer models of fallout can also provide useful insight for nuclear forensic response when detailed radiochemical processes can be reliably included. Current post-detonation nuclear fallout models prescribe particle size distributions empirically or semi-empirically, based on measurements across limited conditions pertaining to tests conducted primarily in Nevada and the Pacific. These empirical fallout relationships may be subject to large uncertainties in particle size and radionuclide activity distribution if used to extrapolate to other regions with different environmental conditions (e.g., urbanized areas). Replacing empirical relationships with physics-based microphysical process modeling can enable significant advances in the fidelity of predictive models simulating distributions of fallout across diverse environments. Particle microphysics describes the formation and evolution of fallout particles, as well as the interaction of radioactive material with entrained particles, which requires accounting for fundamental processes such as nucleation, condensation, and coagulation. The objective of this perspective article is to summarize computational techniques to simulate particle microphysical processes advancing the fidelity of predicting nuclear fallout. We review current empirical models for simulating post-detonation fallout and assess promising research directions moving towards physics-based predictive systems.
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Affiliation(s)
- D L McGuffin
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
| | - D D Lucas
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
| | - E Balboni
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
| | - J S Nasstrom
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
| | - K A Lundquist
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
| | - K B Knight
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
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2
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Weerakkody EN, Dubowsky SE, Glumac NG. Emission Spectra of Uranium Particulates at High Temperature. APPLIED SPECTROSCOPY 2024; 78:692-701. [PMID: 38715421 DOI: 10.1177/00037028241247574] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/04/2024]
Abstract
The emission spectrum of micron-scale uranium particulates at high temperatures in the ultraviolet, visible, and near-infrared spectral regions is investigated using a heterogeneous shock tube. Temperatures from 3000 to 9000 K are characterized in an inert argon environment and with incremental amounts of added oxygen. Atomic line spectra do not emerge above the continuum emission spectrum until between 4500 and 5000 K in pure argon, and 6100 and 6600 K in 1% oxygen. For 5% oxygen, however, the threshold for atomic emission drops below 3800 K. Uranium monoxide molecular emission in the strongest visible band at 595.4 nm is not observed at any condition. Uncertainties in particle temperature determination in high-temperature shock tube environments are discussed, and limitations to such measurements are presented, such as those from experimental factors such as the powder loading method and expected detection limits of uranium species in relevant conditions.
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Affiliation(s)
- Emily N Weerakkody
- Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
- Physical and Life Sciences Division, Lawrence Livermore National Laboratory, Livermore, California, USA
| | - Scott E Dubowsky
- Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
| | - Nick G Glumac
- Mechanical Science and Engineering Department, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
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3
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Kwapis EH, Borrero J, Latty KS, Andrews HB, Phongikaroon SS, Hartig KC. Laser Ablation Plasmas and Spectroscopy for Nuclear Applications. APPLIED SPECTROSCOPY 2024; 78:9-55. [PMID: 38116788 DOI: 10.1177/00037028231211559] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
The development of measurement methodologies to detect and monitor nuclear-relevant materials remains a consistent and significant interest across the nuclear energy, nonproliferation, safeguards, and forensics communities. Optical spectroscopy of laser-produced plasmas is becoming an increasingly popular diagnostic technique to measure radiological and nuclear materials in the field without sample preparation, where current capabilities encompass the standoff, isotopically resolved and phase-identifiable (e.g., UO and UO2 ) detection of elements across the periodic table. These methods rely on the process of laser ablation (LA), where a high-powered pulsed laser is used to excite a sample (solid, liquid, or gas) into a luminous microplasma that rapidly undergoes de-excitation through the emission of electromagnetic radiation, which serves as a spectroscopic fingerprint for that sample. This review focuses on LA plasmas and spectroscopy for nuclear applications, covering topics from the wide-area environmental sampling and atmospheric sensing of radionuclides to recent implementations of multivariate machine learning methods that work to enable the real-time analysis of spectrochemical measurements with an emphasis on fundamental research and development activities over the past two decades. Background on the physical breakdown mechanisms and interactions of matter with nanosecond and ultrafast laser pulses that lead to the generation of laser-produced microplasmas is provided, followed by a description of the transient spatiotemporal plasma conditions that control the behavior of spectroscopic signatures recorded by analytical methods in atomic and molecular spectroscopy. High-temperature chemical and thermodynamic processes governing reactive LA plasmas are also examined alongside investigations into the condensation pathways of the plasma, which are believed to serve as chemical surrogates for fallout particles formed in nuclear fireballs. Laser-supported absorption waves and laser-induced shockwaves that accompany LA plasmas are also discussed, which could provide insights into atmospheric ionization phenomena from strong shocks following nuclear detonations. Furthermore, the standoff detection of trace radioactive aerosols and fission gases is reviewed in the context of monitoring atmospheric radiation plumes and off-gas streams of molten salt reactors. Finally, concluding remarks will present future outlooks on the role of LA plasma spectroscopy in the nuclear community.
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Affiliation(s)
- Emily H Kwapis
- Nuclear Engineering Program, Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, USA
| | - Justin Borrero
- Nuclear Engineering Program, Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, USA
| | - Kyle S Latty
- Nuclear Engineering Program, Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, USA
| | - Hunter B Andrews
- Radioisotope Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | | | - Kyle C Hartig
- Nuclear Engineering Program, Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, USA
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Finko M, Koroglu B, Rodriguez KE, Rose TP, Crowhurst JC, Curreli D, Radousky HB, Knight KB. Stochastic optimization of a uranium oxide reaction mechanism using plasma flow reactor measurements. Sci Rep 2023; 13:9293. [PMID: 37286551 DOI: 10.1038/s41598-023-35355-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Accepted: 05/16/2023] [Indexed: 06/09/2023] Open
Abstract
In this work, a coupled Monte Carlo Genetic Algorithm (MCGA) approach is used to optimize a gas phase uranium oxide reaction mechanism based on plasma flow reactor (PFR) measurements. The PFR produces a steady Ar plasma containing U, O, H, and N species with high temperature regions (3000-5000 K) relevant to observing UO formation via optical emission spectroscopy. A global kinetic treatment is used to model the chemical evolution in the PFR and to produce synthetic emission signals for direct comparison with experiments. The parameter space of a uranium oxide reaction mechanism is then explored via Monte Carlo sampling using objective functions to quantify the model-experiment agreement. The Monte Carlo results are subsequently refined using a genetic algorithm to obtain an experimentally corroborated set of reaction pathways and rate coefficients. Out of 12 reaction channels targeted for optimization, four channels are found to be well constrained across all optimization runs while another three channels are constrained in select cases. The optimized channels highlight the importance of the OH radical in oxidizing uranium in the PFR. This study comprises a first step toward producing a comprehensive experimentally validated reaction mechanism for gas phase uranium molecular species formation.
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Affiliation(s)
- Mikhail Finko
- Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA.
| | - Batikan Koroglu
- Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA
| | - Kate E Rodriguez
- Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA
| | - Timothy P Rose
- Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA
| | | | - Davide Curreli
- Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois Urbana-Champaign, Champaign, IL, 61820, USA
| | - Harry B Radousky
- Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA
| | - Kim B Knight
- Lawrence Livermore National Laboratory, Livermore, CA, 94550, USA
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Uranium Dust Cloud Combustion: Burning Characteristics and Absorption Spectroscopy Measurements. JOURNAL OF COMBUSTION 2022. [DOI: 10.1155/2022/3570238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
This study characterized uranium metal dust cloud combustion using absorption spectroscopy, imaging, and broadband emission measurements. Other metals were similarly combusted to establish correlations between results from this study and those found in the literature. It was determined that the burn temperature of uranium was limited to the volatilization temperature of uranium dioxide. Combustion behavior was similar to that of other refractory metals in terms of burn time and the observation of exploding particle behavior.
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Loukhovitski BI, Pelevkin AV, Sharipov AS. Toward size-dependent thermodynamics of nanoparticles from quantum chemical calculations of small atomic clusters: a case study of (B 2O 3) n. Phys Chem Chem Phys 2022; 24:13130-13148. [PMID: 35587125 DOI: 10.1039/d2cp01672a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present a method for obtaining canonical partition functions and, accordingly, temperature-dependent thermodynamics of arbitrary-sized (nano) particles from electronic structure calculations of the corresponding small size atomic clusters. The guiding idea here is to extrapolate the basic properties underlying the thermochemistry of clusters (electronic energies, rotational constants, and vibrational frequencies) rather than the thermodynamic functions themselves. The thus obtained scaling dependences for these basic properties expressed in a simple analytical form provide an efficient tool for fast evaluation of the size-selected thermochemical data for particles of any nuclearity. To exemplify the performance of the methodology, neutral stoichiometric boron oxide clusters are considered. To this end, the geometry and various physical properties of the energetically lowest-lying (B2O3)n (n = 1,…,8) structures are found using density functional theory and the authors' multistage hierarchical procedure customized for global optimization of quite large cluster structures. With these data and based on the physically consistent scaling regularities for the principal cluster properties, the size-selected thermodynamic functions of boron oxide particles in the gas phase, such as enthalpy, entropy, and specific heat capacity, are derived. The variation of these characteristics with increasing cluster size is discussed in detail as well. To facilitate handling of the temperature and size dependences we have found here in further chemical kinetic and equilibrium modeling, the tabulated thermodynamic functions of interest are fitted for n = 1,…,1000 to the standard seven-parameter Chemkin polynomials.
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Affiliation(s)
- Boris I Loukhovitski
- Central Institute of Aviation Motors, Aviamotornaya 2, Moscow 111116, Russia. .,Joint Institute for High Temperatures of the Russian Academy of Sciences, Izhorskaya 13 Bldg. 2, Moscow 125412, Russia
| | - Alexey V Pelevkin
- Central Institute of Aviation Motors, Aviamotornaya 2, Moscow 111116, Russia. .,Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilova 38, Moscow 119991, Russia
| | - Alexander S Sharipov
- Central Institute of Aviation Motors, Aviamotornaya 2, Moscow 111116, Russia. .,Joint Institute for High Temperatures of the Russian Academy of Sciences, Izhorskaya 13 Bldg. 2, Moscow 125412, Russia
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The effect of oxygen concentration on the speciation of laser ablated uranium. Sci Rep 2022; 12:4030. [PMID: 35256710 PMCID: PMC8901731 DOI: 10.1038/s41598-022-07834-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Accepted: 02/24/2022] [Indexed: 11/09/2022] Open
Abstract
In order to model the fate and transport of particles following a nuclear explosion, there must first be an understanding of individual physical and chemical processes that affect particle formation. One interaction pertinent to fireball chemistry and resultant debris formation is that between uranium and oxygen. In this study, we use laser ablation of uranium metal in different concentrations of oxygen gas, either 16O2 or 18O2, to determine the influence of oxygen on rapidly cooling uranium. Analysis of recovered particulates using infrared absorption and Raman spectroscopies indicate that the micrometer-sized particulates are predominantly amorphous UOx (am-UOx, where 3 ≤ x ≤ 4) and UO2 after ablation in 1 atm of pure O2 and a 1% O2/Ar mixture, respectively. Energy dispersive X-ray spectroscopy (EDS) of particulates formed in pure O2 suggest an O/U ratio of ~ 3.7, consistent with the vibrational spectroscopy analysis. Both am-UOx and UO2 particulates convert to α-U3O8 when heated. Lastly, experiments performed in 18O2 environments show the formation of 18O-substituted uranium oxides; vibrational frequencies for am-U18Ox are reported for the first time. When compared to literature, this work shows that cooling timescales can affect the structural composition of uranium oxides (i.e., crystalline vs. amorphous). This indicator can be used in current models of nuclear explosions to improve our predicative capabilities of chemical speciation.
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Wimpenny J, Eppich GR, Marks N, Ryerson F, Knight KB. Characterizing major and trace element compositions in fallout melt glass from a near-surface nuclear test. JOURNAL OF ENVIRONMENTAL RADIOACTIVITY 2022; 243:106796. [PMID: 34933215 DOI: 10.1016/j.jenvrad.2021.106796] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Revised: 12/02/2021] [Accepted: 12/08/2021] [Indexed: 06/14/2023]
Abstract
The chemical and isotopic compositions of fallout melt glasses from nuclear tests contain a range of information constraining the physical conditions within the fireball and the mechanisms of fallout formation but historic studies tended to exclude the behavior of stable major and trace elements. Here, we present a large study specifically focused on major and trace element relationships within a population of macroscale fallout samples from a single event. We interpret these data to better constrain how fallout melt glass formation in near surface environments is influenced by that environment and demonstrate how major and trace element abundances can provide useful insights into chemical processes within the fireball. Data confirm that the uranium in the fallout glass population derives from two isotopically distinct endmembers: isotopically enriched uranium (presumably from the weapon), and natural composition uranium that may be a combination of anthropogenic and environmental materials from within the blast zone. The similarity between major and trace element concentrations in fallout and corresponding local soils from the event site confirm the local soils as the most probable source of entrained material into the fireball and the source of carrier material into which the bomb vapor was incorporated. The lack of correlation between major and trace element abundances with size indicates that volatility driven processes, such as condensation from the fireball, do not control the composition of macroscale fallout melt glass. Although the fallout has major and trace element chemical characteristics broadly similar to those of the local, associated soils, some systematic differences are observed between the two populations. Fallout melt glass is depleted in volatile elements such as K, Na, Tl and Pb, consistent with heating to temperatures above ∼1000 °C for 3-10 s. This is supported by the results of laser heating experiments performed on rhyolitic soil at temperatures (1600-2200 °C) and timescales (1-120 s) that are broadly relevant to fallout formation conditions. Relative enrichments of metals such as Cu and Co do not correlate with the abundance of uranium, suggesting that fallout also records input of near field anthropogenic materials. Our observations suggest that major chemical features can be related to processing in the fireball and used to inform the thermal-chemical evolution of the system. Ultimately, these data are consistent with a fallout formation mechanism that involves rapid melting of surface materials to form carrier material melts with minor incorporation of bomb vapor and a degree of volumetric volatile loss due to heating.
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Affiliation(s)
- Josh Wimpenny
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA, 94550, USA.
| | - Gary R Eppich
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA, 94550, USA
| | - Naomi Marks
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA, 94550, USA
| | - Frederick Ryerson
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA, 94550, USA; Institut de physique du globe de Paris, Paris, France
| | - Kim B Knight
- Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA, 94550, USA
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Koroglu B, Dai Z, Finko M, Armstrong MR, Crowhurst JC, Curreli D, Weisz DG, Radousky HB, Knight KB, Rose TP. Experimental Investigation of Uranium Volatility during Vapor Condensation. Anal Chem 2020; 92:6437-6445. [PMID: 32233449 DOI: 10.1021/acs.analchem.9b05562] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The predictive models that describe the fate and transport of radioactive materials in the atmosphere following a nuclear incident (explosion or reactor accident) assume that uranium-bearing particulates would attain chemical equilibrium during vapor condensation. In this study, we show that kinetically driven processes in a system of rapidly decreasing temperature can result in substantial deviations from chemical equilibrium. This can cause uranium to condense out in oxidation states (e.g., UO3 vs UO2) that have different vapor pressures, significantly affecting uranium transport. To demonstrate this, we synthesized uranium oxide nanoparticles using a flow reactor under controlled conditions of temperature, pressure, and oxygen concentration. The atomized chemical reactants passing through an inductively coupled plasma cool from ∼5000 to 1000 K within milliseconds and form nanoparticles inside a flow reactor. The ex situ analysis of particulates by transmission electron microscopy revealed 2-10 nm crystallites of fcc-UO2 or α-UO3 depending on the amount of oxygen in the system. α-UO3 is the least thermodynamically preferred polymorph of UO3. The absence of stable uranium oxides with intermediate stoichiometries (e.g., U3O8) and sensitivity of the uranium oxidation states to local redox conditions highlight the importance of in situ measurements at high temperatures. Therefore, we developed a laser-based diagnostic to detect uranium oxide particles as they are formed inside the flow reactor. Our in situ measurements allowed us to quantify the changes in the number densities of the uranium oxide nanoparticles (e.g., UO3) as a function of oxygen gas concentration. Our results indicate that uranium can prefer to be in metastable crystal forms (i.e., α-UO3) that have higher vapor pressures than the refractory form (i.e., UO2) depending on the oxygen abundance in the surrounding environment. This demonstrates that the equilibrium processes may not dominate during rapid condensation processes, and thus kinetic models are required to fully describe uranium transport subsequent to nuclear incidents.
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Affiliation(s)
- Batikan Koroglu
- Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Zurong Dai
- Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Mikhail Finko
- Nuclear Plasma and Radiological Engineering, College of Engineering, University of Illinois at Urbana-Champagne, Urbana, Illinois 61801, United States
| | - Michael R Armstrong
- Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Jonathan C Crowhurst
- Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Davide Curreli
- Nuclear Plasma and Radiological Engineering, College of Engineering, University of Illinois at Urbana-Champagne, Urbana, Illinois 61801, United States
| | - David G Weisz
- Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Harry B Radousky
- Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Kim B Knight
- Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
| | - Timothy P Rose
- Physical and Life Sciences, Lawrence Livermore National Laboratory, Livermore, California 94550, United States
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Harilal SS, Kautz EJ, Bernacki BE, Phillips MC, Skrodzki PJ, Burger M, Jovanovic I. Physical conditions for UO formation in laser-produced uranium plumes. Phys Chem Chem Phys 2019; 21:16161-16169. [PMID: 31294428 DOI: 10.1039/c9cp02250c] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
We investigate the oxidation of uranium (U) species, the physical conditions leading to uranium monoxide (UO) formation and the interplay between plume hydrodynamics and plasma chemistry in a laser-produced U plasma. Plasmas are produced by ablation of metallic U using nanosecond laser pulses. An ambient gas environment with varying oxygen partial pressures in 100 Torr inert Ar gas is used for controlling the plasma oxidation chemistry. Optical emission spectroscopic analysis of U atomic and monoxide species shows a reduction in the emission intensity and persistence with increasing oxygen partial pressure. Spectral modelling is used for identifying the physical conditions in the plasma that favor UO formation. The optimal temperature for UO formation is found to be in the temperature range of ∼1500-5000 K. The spectrally integrated and spectrally filtered (monochromatic) imaging of U atomic and molecular species reveals the evolutionary paths of various species in the plasma. Our results also highlight that oxidation in U plasmas predominantly occurs at the cooler periphery and is delayed with respect to plasma formation, and the dissipation of molecular species strongly depends on oxygen partial pressure.
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Affiliation(s)
- S S Harilal
- Pacific Northwest National Laboratory, Richland, WA 99352, USA.
| | - E J Kautz
- Pacific Northwest National Laboratory, Richland, WA 99352, USA.
| | - B E Bernacki
- Pacific Northwest National Laboratory, Richland, WA 99352, USA.
| | - M C Phillips
- Pacific Northwest National Laboratory, Richland, WA 99352, USA. and Optics Science Center, University of Arizona, Tucson, AZ 85721, USA and Opticslah, LLC, 2350 Alamo Ave. SE, Albuquerque, NM 87106, USA
| | - P J Skrodzki
- Department of Nuclear Engineering and Radiological Sciences, University of Michigan, MI 48109, USA and Center for Ultrafast Optical Science, University of Michigan, MI 48109, USA
| | - M Burger
- Department of Nuclear Engineering and Radiological Sciences, University of Michigan, MI 48109, USA and Center for Ultrafast Optical Science, University of Michigan, MI 48109, USA
| | - I Jovanovic
- Department of Nuclear Engineering and Radiological Sciences, University of Michigan, MI 48109, USA and Center for Ultrafast Optical Science, University of Michigan, MI 48109, USA
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