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2024 International Conference on physics of Reactors, PHYSOR 2024

作者： Sommer, Aaron Rahnema, Farzad Ougouag, Abderrafi M. Zhang, Dingkang DeHart, Mark Georgia Institute of Technology Nuclear & Radiological Engineering and Medical Physics Programs AtlantaGA United States

ISBN: (纸本)9780894487972

This paper uses a combined single-assembly and full-core benchmark problem based on a heat-pipe-cooled microreactor design to study the effect of core environment on homogenized multigroup macroscopic cross sections generated in a fifteen-group energy structure by the continuous-energy Monte Carlo code Serpent 2. These cross sections are evaluated in fuel pins, moderator rods, and heat pipes in selected locations within the single assembly and those corresponding locations in multiple such fuel assemblies at a set of locations within the full core. Effects of core environment on multigroup cross sections are determined using the obtained results. As expected, it is found that the effects of core environment on fifteen-group cross section data are much less marked than the same effects observed in published three-group cross sections. This finding applies across several reaction types in all selected materials. The maximum effect due to core environment found is 7.5% using fifteen-group cross section data versus 26.2% using three-group data. However, the effects remain significant even in the fifteen-group structure, which unequivocally demonstrates the imperative need for applying correction methods. Typical energy bins and reactions where this prominently occurs are intermediate and fast capture and fission in fuel, and intermediate scattering in heat pipes. This study confirms that many-group cross section libraries obtained from single assembly transport calculations produce full-core modeling results that are less sensitive to spectral effects arising from core environment than those generated using fewer group libraries. This study also demonstrates that on-the-fly correction of these libraries is still required for accurate modeling of an entire microreactor core. © 2024 AMERICAN nuclear SOCIETY. All rights reserved.

关键词： Serpentine

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Bis(tert-butoxydiphenylsilyl)amide Divalent Lanthanide Complexes

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Inorganic chemistry 2025年第22期64卷 2025 May 23页

作者： Grant R Wilkinson Sarah J Schultz Kaitlyn S Otte Maximilian G Bernbeck Henry S La Pierre School of Chemistry and Biochemistry Georgia Institute of Technology Atlanta Georgia 30332-0400 United States. Nuclear and Radiological Engineering and Medical Physics Program Georgia Institute of Technology Atlanta Georgia 30332-0400 United States.

The development of new ligand systems to stabilize "non-traditional/non-classical" divalent lanthanides is key to tuning the chemical and physical properties of their mixed principal quantum number 4f5d ground states. The design and study of novel ligand systems which stabilize occupation of differing orbitals within the 5d manifold for these ions constitutes an area ripe for exploration. Our efforts toward the development of redox-innocent bulky silylamide ligands to stabilize pseudo-octahedral coordination geometries for divalent lanthanides have resulted in the synthesis of the bis(-butoxydiphenylsilyl)amide ligand, whose coordination complexes with Sm, Eu, and Yb are reported herein. These systems have been fully characterized by single-crystal X-ray diffraction, elemental analysis, cyclic voltammetry, direct-current magnetometry, and infrared, nuclear magnetic resonance, and electronic absorption spectroscopies. Attempts to extend this system to the more reducing Tm ion resulted in an inseparable mixture of products from which crystals of the analogous Tm species and a reduced dinitrogen, bimetallic Tm-Tm complex bridged by a η-N radical could be identified. Though progress toward six-coordinate complexes of reducing "traditional/classical" divalent ions is noted for these systems, further work is needed to improve the synthetic utility of this ligand framework for the study of "non-traditional/non-classical" divalent lanthanides with a mixed-principal quantum number 4f5d ground state.

关键词： Cyclic voltammetry

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Computational Modeling of Radiation Effects in Carbon Fiber-Reinforced Polyethylene Composites 38

Computational Modeling of Radiation Effects in Carbon Fiber-...

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38th Technical Conference of the American Society for Composites, ASC 2023

作者： Li, Fuyue Woodrough, Mary Deo, Chaitanya School of Materials Science and Engineering Georgia Institute of Technology North Avenue AtlantaGA30332 United States Nuclear and Radiological Engineering Program GWW School of Mechanical Engineering Georgia Institute of Technology North Avenue AtlantaGA30332 United States

ISBN: (纸本)9781605956916

Radiation effect in carbon fiber-filled polyethylene composites are of importance in space and aircraft applications. A two-fold approach is employed to study radiation effects in carbon nanotube polyethylene as the exemplar. First, a radiation transport model is created with a single-wall carbon nanotube (SWCNT) as thin carbon slab superimposed on a slab of medium-density polyethylene matrix. Different weight fractions of SWCNT are examined and compared with an integrated model for the shielding abilities of galactic cosmic radiation. Second, molecular dynamics simulation with bond-order force field are conducted for 350 eV carbon recoil cascade simulation. Preliminary results discuss the effect of SWCNT on the radiation damage of crystalline polyethylene. Transport simulation demonstrate the efficacy of the slab model in predicting the shielding abilities and concluded that the dose increases with increasing SWCNT filler. Molecular dynamics simulations demonstrate that adding SWCNT enhances the radiation resistance with fewer free molecules produced. © 2023 by DEStech Publications, Inc. and American Society for Composites. All rights reserved.

关键词： Single-walled carbon nanotubes (SWCN)

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Risk-Informed Comparison of Atmospheric Plume Models for Dose-Based Advanced Reactor Licensing Siting 18

Risk-Informed Comparison of Atmospheric Plume Models for Dos...

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18th International Probabilistic Safety Assessment and Analysis, PSA 2023

作者： Wang, Jeffrey Clayton, Daniel Dewji, Shaheen Azim Nuclear and Radiological Engineering and Medical Physics Programs Georgia Institute of Technology AtlantaGA United States Sandia National Laboratories AlbuquerqueNM United States

ISBN: (纸本)9780894487927

This study conducts a comparison of atmospheric dispersion models for use in future advanced reactor licensing and Emergency Planning Zone (EPZ) siting. The comparison utilized the existing SOARCA Peach Bottom boiling water reactor (BWR) unmitigated long-term accident scenario source term and site location along with National Oceanic and Atmospheric Administration (NOAA) North American Mesoscale (NAM) 12 km weather data to simulate mean radial peak International Commission on Radiological Protection (ICRP) Publication 60 effective dose distributions. Two atmospheric transport and dispersion modeling techniques were compared using the Maccs code: (1) a conventional Gaussian straight-line plume segment model (GPM) built into Maccs, and (2) a newly released integration with HYSPLIT using Lagrangian particle in cell dispersion. The dose distributions were deconstructed into individual exposure pathways to investigate the significant differences caused by the dispersion models. Results demonstrated that in the far-field case, Maccs and HYSPLIT estimate similar mean peak dose quantities and, designating a 0.01 Sv threshold from the NRC approved NuScale risk-informed EPZ technical basis, Maccs and HYSPLIT both place the EPZ limit far beyond current regulatory requirements. However, in the near-field case within a few kilometers of the facility boundary, HYSPLIT predicts a dose distribution several orders of magnitude larger than Maccs does. While HYSPLIT may be based in more realistic assumptions and physical phenomena compared to Gaussian Maccs, the utilization of coarse underlying weather grid sizes and lack of specific near-field dispersal modeling results in overly conservative estimation of consequences near to site boundaries. For advanced reactors such as small and micro reactors, whose source terms generate plumes not expected to reach beyond the near-field, HYSPLIT modeling could result in prohibitively high dose distributions. © 2023 Proceedings of 18th Internati

关键词： Dispersion Gaussian Lagrangian Maccs Near-field

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In-Vivo Detector Arrays for Time-Dependent Inhalation Radiation Contamination Assessment

In-Vivo Detector Arrays for Time-Dependent Inhalation Radiat...

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IEEE Symposium on nuclear Science (NSS/MIC)

作者： Y. Wei S. A. Dewji Nuclear and Radiological Engineering and Medical Physics Programs Georgia Institute of Technology Atlanta Georgia United States of America

ISBN: (数字)9798350388152

ISBN: (纸本)9798350388169

In response to radiological or nuclear emergencies, prompt assessment of internal radiation contamination is critical for triage assessment and medical countermeasures administrations. The NAIS-2’2 NaI(Tl) scintillation detectors were selected to construct a scanning system to measure internalized gamma-ray emitting radionuclide contamination in warfighters. A mesh-type adult female anthropomorphic phantom of 165 cm height and 65 kg weight was used, and an eight-point detector grid was implemented covering critical body areas (head, neck, chest, abdomen, and hip) implemented in the Monte-Carlo simulation tool, PHITS. The gamma depositions from critical radionuclides were simulated across all organs of interests. Biokinetic modeling data of each radionuclide were incorporated to determine the time-dependent retention in these organs and the gamma depositions in the detectors. To optimize the number and position of detectors for contamination characterization, a scoring algorithm was developed by analyzing the pseudo planes across the anterior and posterior of the phantom. These planes were subdivided into fine meshes to simulate the gamma flux, which were then integrated with biokinetics to compute the detector counting efficiencies at various times post-inhalation. This integration will enable the identification of the optimal detector array configuration, achieving the best counting statistics for various combinations of radionuclide sources, times post-exposure, and phantom morphologies, and the reconstruction of total contamination patterns.

关键词： Semiconductor device measurement Monte Carlo methods Semiconductor detectors Phantoms Morphology Detectors Biological systems

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A hybrid few-group homogenization approach for coupled nodal diffusion-thermal hydraulic analysis of nuclear thermal propulsion reactors

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Annals of nuclear Energy 2025年 222卷

作者： Smith, Jacob D. Kotlyar, Dan Nuclear and Radiological Engineering and Medical Physics Program George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology AtlantaGA30332-0405 United States

Multiphysics coupled analysis for nuclear Thermal Propulsion (NTP) systems are important for producing accurate core safety margins as the operation dependent thermal–hydraulic (T/H) parameters vary drastically across the core. Through the range of coupled physics model's fidelities, neutronics solutions for NTP reactors are primarily found using Monte Carlo (MC) transport solvers, which produce accurate results at the cost of high computational expense. The motivation for this research is to avoid the computational bottleneck of obtaining high-fidelity, neutronics solutions at every iteration by replacing the MC code with a reduced-order nodal diffusion code. Nodal diffusion analysis is widely used for Light Water Reactors (LWRs) with a standard method that involves pre-generated group constants for unique fuel types homogenized on the assembly level. A series of publications from the authors has detailed the efforts devoted to conducting steady-state, isothermal neutronics modeling of a NERVA-derived NTP reactor core using the nodal diffusion code, DYN3D, with homogenized two-group constant generated with the MC code Serpent and uniform discontinuity factors (UDFs) found using a Jacobian-Free Newton Krylov method (JFNK). The work presented in this paper is the culmination of these efforts, featuring the first demonstration of the finalized hybrid cross section generation approach and the subsequent use in full core simulations. The hybrid approach uses both full core and infinite lattice MC models to efficiently generate two-group homogenized parameters with unique T/H fields representative of a power ramp-up, interpolating on both cross sections and discontinuity factors as a function of control drum angle, fuel temperature, moderator temperature, and moderator coolant density. The results show that the hybrid approach to pre-generating group constants and correction parameters produces a set of data that can be used to obtain accurate – in comparison to the refe

关键词： Importance sampling

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Efficiency Comparison of Radiation Transport Variance Reduction Methods for Wide-Area Environmental Contamination Assay Applications 14

Efficiency Comparison of Radiation Transport Variance Reduct...

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14th International Conference on Radiation Shielding, ICRS 2022 and 21st Topical Meeting of the Radiation Protection and Shielding Division, RPSD 2022

作者： Asano, E. Dewji, S. Nuclear and Radiological Engineering and Medical Physics Programs George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology AtlantaGA30313 United States

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Insights into Calculating Reference Discontinuity Factors with Serpent Monte Carlo Code

SSRN

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SSRN 2024年

作者： Fridman, Emil Smith, Jacob D. Kotlyar, Dan Dresden Germany Nuclear and Radiological Engineering and Medical Physics Program George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology AtlantaGA30332-0405 United States

This study explores the calculation of Reference Discontinuity Factors (RDFs) using Serpent, focusing on the methodology and potential pitfalls. In two-step reactor analyses, consistently generated RDFs are crucial for aligning homogeneous nodal diffusion results with the reference heterogeneous transport solution. However, the Serpent internal diffusion solver, based on the Analytic Function Expansion Nodal (AFEN) method, may not be compatible with other nodal methods such as NEM. Additionally, the solver can suffer from instabilities, particularly in multi-group calculations, leading to erroneous RDFs. Despite these challenges, Serpent can generate the necessary raw data for RDF calculation, which can be accurately processed using external diffusion solvers. Two numerical examples - a 1D fuel-reflector model and a 2D SMR core model - illustrate the effects of consistent and inconsistent RDFs on simulation accuracy. The study underscores the importance of using compatible diffusion solvers and thoroughly assessing RDFs to avoid errors in reactor simulations. © 2024, The Authors. All rights reserved.

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Single-Phase Ternary Compounds with a Disordered Lattice and Liquid Metal Phase for High-Performance Li-Ion Battery Anodes

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Nano-Micro Letters 2023年第5期15卷 36-50页

作者： Yanhong Li Lei Zhang Hung-Yu Yen Yucun Zhou Gun Jang Songliu Yuan Jeng-Han Wang Peixun Xiong Meilin Liu Ho Seok Park Wenwu Li School of Chemical Engineering Sungkyunkwan University2066Seobu-roJangan-guSuwon-SiGyeonggi-Do 440-746Korea School of Physics Huazhong University of Science and TechnologyWuhan 430074People’s Republic of China School of Materials Science and Engineering Georgia Institute of TechnologyAtlantaGA 30332USA Department of Chemistry National Taiwan Normal UniversityTaipei 11677TaiwanPeople’s Republic of China Samsung Advanced Institute for Health Sciences and Technology(SAIHST) Sungkyunkwan University2066 SeoburoJangan-guSuwon 440-746Korea SKKU Advanced Institute of Nano Technology(SAINT) Sungkyunkwan University2066 SeoburoJangan-guSuwon 440-746Korea SKKU Institute of Energy Science and Technology(SIEST) Sungkyunkwan University2066 SeoburoJangan-guSuwon 440-746Korea

Si is considered as the promising anode materials for lithium-ion batteries(LIBs)owing to their high capacities of 4200 mAh g-1and natural ***,severe electrode pulverization and poor electronic and Li-ionic conductivities hinder their practical *** resolve the afore-mentioned problems,we first demonstrate a cation-mixed disordered lattice and unique Li storage mechanism of single-phase ternary GaSiP_(2)compound,where the liquid metallic Ga and highly reactive P are incorporated into Si through a ball milling *** confirmed by experimental and theoretical analyses,the introduced Ga and P enables to achieve the stronger resistance against volume variation and metallic conductivity,respectively,while the cation-mixed lattice provides the faster Li-ionic diffusion capability than those of the parent GaP and Si *** resulting GaSiP_(2)electrodes delivered the high specific capacity of 1615 mAh g-1and high initial Coulombic efficiency of 91%,while the graphite-modified GaSiP_(2)(GaSiP_(2)@C)achieved 83%of capacity retention after 900 cycles and high-rate capacity of 800 at 10,000 mA ***,the LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)//Ga SiP_(2)@C full cells achieved the high specific capacity of 1049 mAh g-1after 100 cycles,paving a way for the rational design of high-performance LIB anode materials.

关键词： Multinary compounds Liquid metal GaSiP_(2) Disordered lattice Li-ion batteries

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Collective excitations in the tetravalent lanthanide honeycomb antiferromagnet Na2PrO3

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Physical Review B 2021年第12期103卷 L121109-L121109页

作者： M. J. Daum A. Ramanathan A. I. Kolesnikov S. Calder M. Mourigal H. S. La Pierre School of Physics Georgia Institute of Technology Atlanta Georgia 30332 USA School of Chemistry and Biochemistry Georgia Institute of Technology Atlanta Georgia 30332 USA Neutron Scattering Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Nuclear and Radiological Engineering and Medical Physics Program School of Mechanical Engineering Georgia Institute of Technology Atlanta Georgia 30332 USA

Thermomagnetic and inelastic neutron-scattering measurements on Na2PrO3 are reported. This material is an antiferromagnetic honeycomb magnet based on the tetravalent lanthanide Pr4+ and has been proposed to host dominant antiferromagnetic Kitaev interactions. These measurements reveal magnetic fluctuations in Na2PrO3 below an energy of 2 meV as well as crystal-field excitations around 230 meV. The latter energy is comparable to the scale of the spin-orbit interaction and explains both the very small effective moment of around 1.0μB per Pr4+ and the difficulty to uncover any static magnetic scattering below the ordering transition at TN= 4.6 K. By comparing the low-energy magnetic excitations in Na2PrO3 to those of the isostructural spin-only compound, Na2TbO3, a microscopic model of exchange interactions is developed that implicates dominant and surprisingly large Heisenberg exchange interactions J≈1.1(1) meV. Although antiferromagnetic Kitaev interactions with K≤0.2J cannot be excluded, the inelastic neutron-scattering data of Na2PrO3 is best explained with a Δ=1.22 easy-axis XXZ exchange anisotropy.

关键词： Spin dynamics Lanthanides Crystal-field theory Kitaev-Heisenberg model

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