Hasil untuk "Plasma physics. Ionized gases"

Biwei Zhu, Zhiguang Deng, Xuemei Wang et al.

IntroductionShallow machine learning algorithms exhibit low efficiency in fault diagnosis under the conditions of small-sample and unlabeled data. To address this critical problem, this paper focuses on developing an effective fault diagnosis method suitable for cross-reactor-type scenarios, which is of great significance for improving the safety and operational level of nuclear power plants.MethodsA cross-reactor-type fault diagnosis method based on adversarial transfer learning is proposed. By integrating deep learning and transfer learning techniques, a hybrid domain-adversarial learning model is constructed. The overall loss function of the model is designed to effectively extract transferable features between related reactor types, and corresponding validation experiments are carried out to verify the model's feasibility and effectiveness.ResultsThe experimental validation shows that the proposed hybrid domain-adversarial learning model can effectively extract transferable features across different reactor types, which solves the problem of low efficiency of shallow machine learning algorithms in fault diagnosis under small-sample and unlabeled data conditions. The model achieves reliable fault diagnosis performance in cross-reactor-type scenarios.DiscussionWhen applied to cross-reactor-type nuclear power plant fault diagnosis, the research findings can significantly enhance the safety of nuclear power plants, improve their economic performance and operational efficiency. Furthermore, this research effectively promotes the intelligence level and autonomous decision-making capabilities of nuclear power plants, providing a valuable technical reference for the intelligent development of the nuclear power industry.

Edward Martin, Thomas B. Scott, Mahmoud Bakr et al.

Inertial Electrostatic Confinement Fusion (IECF) devices have garnered increased recognition for their potential as compact, portable neutron sources for use in the generation of medical isotopes and various neutron-based interrogation techniques. This study investigates the shielding requirements for a laboratory enclosure that houses a deuterium-deuterium (DD) fueled IECF device. The simulation framework was first validated by reproducing the ambient dose equivalent, H*(10), conversion coefficient reference values, confirming the suitability of Geant4 for dose deposition measurements. Simulations were then used to evaluate neutron moderation and removal in various shielding materials, investigating five different concrete constituents and water, with the performance assessed relative to UK Ionising Radiations Regulations 2017 (IRR17) dose-rate limits. Neutron and gamma fluences were tallied in defined volumes of 40cm3, H*(10) measurements were then calculated using ICRP 74 conversion coefficients. The simulation results show that an IECF device can be operated safely at a neutron rate of 1×105ns−1 within public dose limits, recording <500nSvh−1 at a distance of 1.6m, with 10cm of all concretes tested other than Barite (Heavy) concrete, which measured 501nSvh−1. The results also show that a safe environment for radiation workers can be constructed, allowing the device to be operated at 1×107ns−1 if 30cm of water or ordinary concrete (OC1) is employed. The findings contribute to the understanding of optimal shielding configurations required to mitigate neutron radiation from IECF devices. Ensuring adherence to regulatory safety standards is paramount in the deployment of these fusion devices within populated areas. This research underscores the importance of selecting appropriate materials and thicknesses to achieve effective radiation protection, thereby facilitating the safe operation of IECF devices and contributing to advancements in medical isotope production and neutron-based interrogation technologies.

Asif Mahmud, Subhashish Meher, Peter Renner et al.

The nuclear industry is increasingly acknowledging the advantages of additive manufacturing (AM) due to its improved design flexibility and reduced manufacturing steps for producing complex engineering components. This study demonstrates the successful fabrication of nearly fully dense, nuclear-grade Grade-91 and, for the first time, Grade-92 Ferritic/Martensitic (F/M) steels via laser powder directed energy deposition (DED). Through rigorous process optimization, specifically tailoring laser power and scan speed, relative densities exceeding 99.8% were achieved in deposited 10 ×10×12 mm3 blocks, yielding exceptional build quality. The resulting microstructures exhibited a characteristic lath martensite morphology, indicative of the rapid solidification inherent to the DED process. While both alloys showed this general microstructure, the addition of tungsten (W), slightly higher carbon content, and higher geometrically necessary dislocation (GND) density in Grade-92 significantly influences mechanical properties, evidenced by a substantial increase in Vickers hardness (425 ± 12 HV) compared to Grade-91 (386 ± 14 HV). Estimated yield strengths, derived from hardness measurements, were 1063 MPa and 1195 MPa for Grade-91 and Grade-92, respectively. These findings suggest DED as a viable and promising route for manufacturing high-performance F/M steel components tailored for demanding nuclear applications, paving the way for improved reactor designs and enhanced operational efficiency.

Thi-Mai-Dung Do, Yang Yaru, Takashi Kikuchi et al.

Potassium-based geopolymers were synthesized with varying initial water content (7–10 mol %). Samples were initially cured under tight-lidded conditions at different temperatures (room temperature, 40 °C, and 60 °C) for the initial 24 h and then transitioned to ambient curing without lid. Analysis of the pore size distribution revealed that higher initial water content generally led to larger pores, while higher curing temperatures resulted in smaller pores. Vickers hardness measurements showed a dependence on both initial water content and curing temperature. The electron beam irradiation was processed up to 16 kGy by pulsed linear electron accelerator at Nagaoka University of Technology and up to 992 kGy by electron beam irradiation at the Takasaki Institute of Advanced Quantum Science. The Vickers hardness of a selected sample remained largely unchanged even after electron beam irradiation up to a high dose.

Terttaliisa Lind, Fredrik Espegren, Detlef Suckow

During severe accidents in nuclear power plants, filtered containment venting system is foreseen to be employed once the containment pressure increases above a pre-set value called venting pressure. Ag-zeolite filters are applied in filtered containment venting systems to retain iodine and organic iodides in the gas phase. In this work, the applicability of Ag-zeolites to not only retain gas phase iodine species, but to also catalyze hydrogen recombination has been experimentally investigated under challenging high humidity conditions. Tests were performed in the medium-scale facility using two Ag-zeolites, one of them designed to both retain gas phase iodine species and recombine hydrogen, the other one designed to only retain gas phase iodine species. Experiments studied the effect of residence time and the carrier gas mixture (steam, N2 or air) on the retention of organic iodine, represented in the tests by CH3I, and hydrogen recombination rate with the two Ag-zeolites. The experiments were carried out under the conditions expected in the containment during severe accidents, however, considering practical limitations. The effects of pressure and the presence of contaminant gases (CO, N2O) were investigated in additional tests not included in this study. The steam fraction in the tests varied between 32% and 90%, air fraction was 0%, 5% or 19%, and hydrogen content either 2.5% or 5%. Nitrogen made up the balance for the gas atmosphere. Gas residence time in the zeolite bed was either 100 m or 200 m. Both zeolites showed high retention of CH3I under all the gas atmospheres as long as the residence time in the reaction chamber was 200 m. CH3I retention was lower when the residence time was reduced to 100 m. Hydrogen recombination was more dependent on the gas atmosphere, as expected. The effect of the gas atmosphere on the hydrogen recombination and retention is discussed.

Guido Deissmann, Erika Neeft, Diederik Jacques

Long time frames are to be considered in the safety and performance assessment of deep geological disposal of intermediate and high level radioactive waste. Geochemical conditions will change in the waste, conditioning matrix, waste package, engineered barriers and the host rock–all components present at the disposal cell scale. This aspect of geological disposal was the focus of the work package ACED (Assessment of chemical evolution of intermediate level (ILW) and high level (HLW) waste at disposal cell scale) in the EURAD project (the European Joint Programme on Radioactive Waste Management). The first part of this review provided a narrative of the geochemical evolution of the disposal cell. In this second part, an overview is given about methods and approaches that can be used to gain further insights into the processes driving the geochemical evolution, more in particular (i) laboratory and in-situ experiments, (ii) archaeological and natural analogues, and (iii) modelling tools. The review concludes with a short discussion on the consequences on material properties, waste forms and radionuclide mobility.

Ruoyu Han, Jie Bai, Jiaqi Yan et al.

Underwater pulsed discharge, where intense reactions between ionized gas and condensed-state water exist, can be a joint problem of both physics and chemistry. The study tries to build a comprehensive visualization of nanosecond-risetime discharge initiated by a conductive coating and its successive multi-physical effects. The scenario is established via a pair of thin-plate electrodes positioned on both sides of the coating, and diagnosed using high-speed backlight photography synchronized with electrical and optical measurements. For the sprayed Cu/Ag composite coating, the current density can achieve 20 A mm−2 which is high enough to induce the surface ‘electrical explosion’ and breakup the conductive matrix within 500 ns. By increasing the discharge energy from 0.5 to 10 J, the explosion of coating can exhibit different discharge types as exploding wires. Adopting a thicker carbon foil or cermet sheet can reduce the current density and energy deposition rate, which converts the global explosion to partial ones, significantly increasing the lifetime. With the aid of the conductive coating, the breakdown delay diminishes, and hot plasma spots form in 100 ns due to non-uniform Joule heating of the pulsed current, which gradually evolve to a plasma bubble cluster above the lower-conductive coating (bypassing branch). Once the high-conductive plasma channel bridges two electrodes, it will be intensively heated (MW-level energy deposition rate) and rapidly expand, accompanied by underwater shock wave (102 kPa @30 cm) and bubble/cavity generation (20 mm maximum). Finally, microscopic characterization has been made, and the erosion morphology suggests typical arc erosion features (pits, cracks, etc) and nanoparticles condensation from evaporated materials.

C. Gaillard, H. Lotz, L. Sarrasin et al.

We present new insights into the study of the UO2+x/U4O9 equilibrium in UO2 as a function of the hyper-stoichiometry (x) by coupling HERFD-XANES at the uranium M4-edge with micro-Raman spectroscopy mapping. XANES allowed the measurement of uranium speciation in the samples, while Raman spectroscopy was used to individually characterize the composition and localization of the different oxide phases. UO2 pellets were oxidized under dry conditions at temperatures above the UO2+x/U4O9 phase transition to reach hyper-stoichiometries in the range of 0.01 ≤ x ≤ 0.1. Combining both techniques, we could determine the proportions of U4O9 and UO2+x. We show that at a low O/U ratio, U4O9 is present as small clusters inside UO2 grains. As the O/U increases, we found evidence of the formation of a network of U4O9 crystallized inside the UO2+x grains. The variation of the UO2+x phase hyper-stoichiometry (x) was evaluated as a function of the sample oxidation.

Fergus Gibb, John Beswick, Karl Travis

Driven by major advances in deep drilling technology and the geological understanding of the deep continental crust over the past 70 years, disposal in deep boreholes has moved from being technically unachievable to the point that it now offers a viable solution for the most hazardous nuclear wastes that could effectively be implemented “tomorrow”—i.e., within a few years. Moreover, disposal in deep boreholes is arguably superior in almost every respect to the mined and engineered repositories being pursued for high level waste by most countries. During the first 50 years of their evolution, almost all deep borehole disposal concepts shared five key aspects: (i) the hole was as deep as possible, (ii) it was vertical, (iii) it was fully cased, and (iv) it was in “hard” basement rock (v) saturated with aqueous fluid (groundwater). Technical advances in drilling over the last 20 years have encouraged proposed versions of the concept which depart from one or more of these aspects, but it is our contention that all five fundamental aspects should be retained. This paper summarises the more important arguments supporting this view. In order to meet the necessary post-closure (radiological) safety requirements, engineer out possible operational problems during construction and waste-package deployment, and capitalise on the main benefits of borehole disposal, the hole itself must be over 3 km deep, vertical, fully cased, and in suitably hard (ideally granitic) host rock saturated with aqueous fluid.

Margarita Baeva, Yann Cressault, Petr Kloc

The radiative heat transfer in arc plasma models is considered from the point of view of its description in terms of a net emission coefficient, the method of spherical harmonics in its lowest order, and the discrete ordinate method. Net emission coefficients are computed, applying approximate analytical and numerical approaches and a multi-band representation of the spectral absorption coefficient with three kinds of its averaging and two datasets. Self-consistent access to the radiative heat transfer is applied to a two-dimensional axisymmetric model of a free-burning arc in argon at atmospheric pressure. The results obtained from the models employing the net emission coefficient, the method of spherical harmonics, and the discrete ordinate method are compared.

D.R. Shklyar, N.S. Artekha

Despite the undoubted importance of having fairly simple analytical expressions for the refractive indices of wave modes in a magnetoactive plasma, such expressions are known only in some particular cases. For electron waves with frequencies much higher than the lower hybrid resonance frequency, such an expression is known only for whistler waves in a dense plasma when the electron plasma frequency significantly exceeds the electron cyclotron frequency. In this Letter, we propose simple operational expressions for the refractive indices of all four electron modes in a magnetoactive plasma, namely, the fast magnetosonic, also called whistler mode, the slow extraordinary mode, the ordinary mode, and the fast extraordinary mode. The form of these expressions does not depend on the value of the ratio of plasma frequency to cyclotron frequency.

Rose Montgomery, Bruce Bevard, Paul Cantonwine et al.

At present, spent nuclear fuel (SNF) assemblies discharged from US commercial power plants are placed into dry storage following a short cooling time (<10 years) in the plant’s spent fuel pool. The process of packaging the spent fuel into dry-storage canisters includes a drying step to remove residual water from the canister. During the drying process, the fuel rod cladding may reach temperatures as high as 400°C. Oak Ridge National Laboratory (ORNL) is performing destructive examinations of high burnup (HBU) (>45 GWd/MTU) SNF rods to address knowledge and data gaps related to extended interim storage and eventual transportation for disposal. The rods examined include four different kinds of fuel rod cladding: standard Zircaloy-4 (Zirc-4), low-tin (LT) Zirc-4, ZIRLO, and M5. Three rods were subjected to a thermal transient to assess the effects of decay-heat-driven high temperatures expected during vacuum drying of the fuel as it is prepared for interim dry storage. The examinations focus on the composite fuel rod performance, as compared with the performance of defueled rod cladding, and establish the baseline mechanical properties of a fuel rod before interim dry storage. The key results of these examinations are presented, including the measured mechanical and fatigue properties, observations of cladding hydrogen pickup and hydride reorientation effects on rod performance, effects of the simulated drying temperatures on rod performance, and general conclusions of SNF performance in extended interim dry storage and transport. The rods were found to be strong and durable in the expected loading conditions, even considering the formation of radial hydrides associated with vacuum drying. The combined testing provides a broad body of data supporting extended interim storage and transportation performance of HBU spent fuel.

Weihua Jiang

The space-charge effects of pulsed high-current electron beams are very important to high-power particle beam accelerators and high-power microwave devices. The related physical phenomena have been studied for decades, and a large number of informative publications can be found in numerous scientific journals over many years. This review article is aimed at systematically summarizing most of the previous findings in a logical manner. Using a normalized one-dimensional mathematical model, analytical solutions have been obtained for the space-charge-limited current of both planar diode and drifting space. In addition, in the case of a beam current higher than the space-charge-limited current, the virtual cathode behavior and beam current reflection are quantitively studied. Furthermore, the criteria of steady-state virtual cathode formation are investigated, which leads to the physical understanding of the unstable nature of the virtual cathode. This review article is expected to serve as an integrated source of related information for young researchers and students working on high-power microwaves and pulsed particle beams.

Ryota Nishimura, Tomohiro Seino, Keigo Yoshimura et al.

To realize the development of a long plasma source with a uniform electron density distribution in the axial direction, the spatial distribution of plasma under a multi-cusp magnetic field was analyzed using a KEIO-MARC code. Considering a cylindrical plasma source with an axial length of 3000 mm and a cross-sectional diameter of 100 mm, in which the filament electrode was the electron source, the electron density distribution was calculated using the residual magnetic flux density, <i>B</i>_res, and the number of permanent magnets installed at different locations surrounding the device, <i>N</i>_mag, as design parameters. The results show that both <i>B</i>_res and <i>N</i>_mag improved the uniformity of the electron density distribution in the axial direction. The maximum axial electron density decreased with increasing <i>N</i>_mag and increased with increasing <i>B</i>_res. These trends can be explained by considering the nature of the multi-cusp field, where particles are mainly confined to the field-free region (FFR) near the center of the plasma column, and the loss of particles due to radial particle transport. The use of multiple filaments at intervals shorter than the plasma decay length dramatically improved axial uniformity. To further improve axial uniformity, the filament length and FFR must be properly set so that electrons are emitted inside the FFR.

Tomiris Ismagambetova, Mukhit Muratov, Maratbek Gabdullin

In this paper, a new ion–ion screened potential was numerically calculated, which takes into account the ion core effect, i.e., the influence of strongly bound electrons. The pseudopotential model describing the shielding of ion cores and the screening using the density response function in the long wavelength approximation were used. To study the influence of this ion core effect on dense plasma’s structural and thermodynamic properties, the integral Ornstein–Zernike equation was solved in the hypernetted chain approximation. Our results show that the ion core has a significant impact on ionic radial distribution functions and thermodynamic properties when compared to the results obtained for the Yukawa potential, which does not take the ion core into account. Increasing the steepness of the core edge or decreasing the depth of the minimum leads to more pronounced screening due to bound electrons.

Sergio Thadeu Tavares da Silva Junior, Rodrigo Andres Miranda Cerda, Sarah Gomes da Silva Paes da Costa et al.

Plasma propulsion, or electric propulsion, arises from the need to explore deep space in a more economical and efficient manner. The cylindrical Hall Thruster (CHT) is an electric propulsion device that offers high propellant utilization and performance at smaller dimensions and lower power levels than traditional plasma propulsion devices. The reduced dimensions of the CHT operating at lower power levels make it an interesting option to provide propulsion of CubeSats and small satellites. The CHT consists of a channel with an annular anode through which neutral gas is injected. The neutral gas is then ionized by magnetized electrons injected from an external hollow cathode. The resulting plasma ions are ejected from the device due to the positive electrostatic potential at the anode, giving thrust. The aim of this work is to understand and study the plasma in the discharge channel of a CHT through numerical simulations. The numerical code describes the plasma with a hybrid model in which the electrons are treated as a fluid and the ions and neutral atoms as pseudo particles. The simulations were conducted for two different potential values at the anode, namely, 150 V and 300 V, representing different modes of operation. The results obtained with this simplified model allow to obtain an optimal configuration for a future prototype to be implemented at the Plasma Physics Laboratory at the University of Brasilia.

Zhanbin Chen

An accurate and computationally efficient determination of the cross sections for electron collision ionization of molecules has various applications, such as plasma physics and atmospheric science. In the case of large molecules, ab initio calculations are often difficult and time‐consuming. Here, we develop a feed forward neural network to predict the electron impact ionization cross sections of complex molecules. The training (predicting) set in the method consists of a series of theoretical ionization cross sections for small (large) molecules obtained from the combined model, which integrates the Binary‐Encounter‐Bethe and Deutsch‐Märk models. Several complex systems or targets involving electron collision ionization are evaluated, including molecules such as CH, CH, CH, CH, C, CHO, and CHO. The root mean square errors of the trained and predicted cross sections by the neural network (compared to the values from the combined model) are found to be approximately .0086 and .0930 (in 10 cm), respectively, (using the CHO molecule as an example), indicating our results are very high accuracy. The excellent agreement between the predicted values and the actual values indicates that the neural network is a practical and powerful tool for determining the electron collision ionization cross sections of complex molecules and can provide valuable insights into the dynamics process. Apart from its fundamental importance, this study has far‐reaching implications for gas discharge, low‐temperature plasmas, and fusion edge plasmas and so forth.

N. Gnedin, P. Madau

The transformation of cold neutral intergalactic hydrogen into a highly ionized warm plasma marks the end of the cosmic dark ages and the beginning of the age of galaxies. The details of this process reflect the nature of the early sources of radiation and heat, the statistical characteristics of the large-scale structure of the Universe, the thermodynamics and chemistry of cosmic baryons, and the histories of star formation and black hole accretion. A number of massive data sets from new ground- and space-based instruments and facilities over the next decade are poised to revolutionize our understanding of primeval galaxies, the reionization photon budget, the physics of the intergalactic medium (IGM), and the fine-grained properties of hydrogen gas in the “cosmic web”. In this review, we survey the physics and key aspects of reionization-era modeling and describe the diverse range of computational techniques and tools currently available in this field.

Susan Ortner

A nuclear power plant is a highly complex installation. Its design is a response to many drivers, including neutronic efficiency, thermal efficiency, economic efficiency, radiation safety, structural integrity, ease of monitoring and maintenance. The correct selection of structural materials has been key in achieving long term structural integrity, as different plant designs and operating conditions impose different combinations of requirements on the materials. This paper describes the reasoning behind structural materials choices and the changing perspectives on the interplay with other design imperatives in historic, current and future plant designs. It also describes the campaigns of materials development put in place to meet novel materials challenges specific to nuclear plant.

Yu-ki Tanaka, Taiki Osawa, Yoshikazu Yamagishi et al.

Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) often causes serious infections in hospitals. Vancomycin is widely accepted as the standard therapy for MRSA infection, but its widespread use has resulted in the generation of vancomycin-resistant <i>S. aureus</i> (VRSA). To reduce the potential risk of MRSA and VRSA emergence in aquatic environments, we investigated the degradation of methicillin and vancomycin by cold atmospheric pressure plasma jet (APPJ) irradiation using N₂, O₂, and CO₂ gases. The concentrations of methicillin and vancomycin in distilled water were decreased in a time-dependent manner by the plasma jet irradiation; that is, compared with the pre-treatment levels, the concentrations of methicillin and vancomycin were reduced by 20 to 50% after plasma jet irradiation for 10 s. No methicillin and vancomycin signals were detected after 300 s irradiation. Reactive species generated from the plasma jet electrophilically attacked and fragmented the antibiotic molecules. The present method realizes direct plasma ignition in a solution, and therefore, the reactive species can easily react with antibiotic molecules. In addition, plasma can be generated from various gas species that are abundant in the atmosphere. Therefore, cold APPJ irradiation can be a powerful, cost-effective, and environmentally friendly means for the treatment of antibiotics in aqueous samples.