Stefan Finsterle, Jeffrey R. McLachlan, Michael J. Hannon
et al.
The release of radionuclides initially encapsulated in a slowly degrading solid waste form and contained in an eventually corroding canister defines the source term for numerical simulations for the assessment of a geologic repository for high-level radioactive waste. While the details of waste degradation, canister corrosion, and dissolution and mobilization of the radionuclides in pore water include complex chemical reaction and transport processes that are coupled to the thermal, hydrological, microbiological, and mechanical conditions in the repository, the source-term model suitable for use in a numerical performance assessment model should be a defensible abstraction of these mechanisms. We developed a radiological source-term model and implemented it into a non-isothermal flow and transport simulator. While the proposed source-term model is applicable to various waste forms, canister systems, and disposal concepts, we specifically considered radionuclide releases from vitrified high-level waste placed in a cylindrical canister disposed in a deep vertical borehole repository. In this model, waste degradation is a function of temperature, and it can be adjusted to evaluate the influence of and propagate uncertainties in pH, passivation reactions, and chemical conditions as well as geometrical factors. The time-dependent, congruent release of safety-relevant radionuclides present in the decaying inventory is then calculated. Finally, the radionuclides are mobilized by diffusive and advective transport according to the thermo-hydraulic conditions prevailing in the near field of the repository, from where they migrate through the geosphere to the accessible environment. We examine the influence of the source-term model’s parameters on performance assessment calculations through sensitivity and uncertainty propagation analyses, identifying influential factors and confirming the upper bound of their impact. These considerations align with the overarching goal of repository design, which is to demonstrate that engineered and natural barriers can collectively delay radionuclide migration for timescales far exceeding human planning, thereby providing multiple, redundant barriers against environmental contamination.
M. P. Springstead, H. LeFevre, I. D. Huegel
et al.
In both astrophysics and the laboratory, sufficiently energetic ionizing radiation can create photoionized plasma that has complex opacity, emissivity, temperature, and density. Previous efforts have studied the steady state properties of photoionized plasmas, but little work has been done to look at the transient behavior at the leading edge of the photoionized regions. Here, we present a first-of-its-kind experiment to create a photoionization front in the laboratory and study its time-dependent evolution. In the experiments on the Z-Machine at Sandia National Laboratories, a Z-pinch dynamic hohlraum created a bright, 2 MJ x-ray source which drove a photoionization front into a gas cell with 1 atm of nitrogen. Using a combination of photon Doppler velocimetry and streaked visible spectroscopy, measurements of the front curvature and emission show the front had a supersonic velocity of 1580 ± 620 km/s, high ionization states of NIII and NIV, and curvature flattening consistent with non-diffusive radiation transport behavior. This new platform can be used to study transient photoionization physics similar to many radiation-driven systems, such as O-type stars emitting into molecular clouds, allowing detailed laboratory studies of this physics.
This study investigates the impact of local thermal non-equilibrium on the stability analysis of partially ionized plasma within a porous medium. The plasma, heated from below, is enclosed by various combinations of bounding surfaces. Both nonlinear (via the energy method) and linear (utilizing the normal mode analysis method) analyses are performed. Eigenvalue problems for both analyses are formulated and solved using the Galerkin method. The study also explores the effects of compressibility, medium permeability and magnetic fields on system stability. The collisional frequency among plasma components and the thermal diffusivity ratio significantly influence energy decay. The results reveal that the Rayleigh–Darcy number is identical for both nonlinear and linear analyses, thus eliminating the possibility of a subcritical region and confirming global stability. The principle of exchange of stabilities is validated, indicating the absence of oscillatory convection modes. Medium permeability, heat-transfer coefficient and compressibility delay the onset of convection, demonstrating stabilizing effects. Conversely, the porosity-modified conductivity ratio hastens the convection process, indicating destabilizing effects. Rigid–rigid bounding surfaces are found to be thermally more stable for confining the partially ionized plasma. Additionally, the magnetic field exerts a stabilizing influence.
In magnetically confined plasmas, gradients in density, temperature, and magnetic field generate low-frequency drift waves, which resonantly interact with plasma particles. In this investigation, we consider a nonlinear process due to which the energy of an accelerated particle may transfer to the O-mode present in the confined plasma system through a modulated field. This nonlinear process is based on a kinetic approach, analyzed using the Vlasov-Maxwell model system of equations. In this study, we derive the nonlinear dispersion relation for the O-mode incorporating gradient parameters and estimate its growth rate. Observational data from the Earth’s magnetosphere are used to analyze the influence of these gradient parameters and other plasma conditions. The results are relevant in predicting O-mode instabilities in inhomogeneous confined plasma systems, like Tokamaks, magnetospheric plasmas, etc.
Zachary Watson, Parker Adamson, Jorge Martinez-Ortiz
et al.
Complex plasma, consisting of ionized gas mixed with micron-sized dust particles, exhibit unique behaviors due to the mass disparity between dust grains and other plasma components. These disparities result in non-Hamiltonian dynamics that pose significant challenges for numerical modeling. Under specific conditions, the dust grains self-organize into crystal structures, driven by ion wakefields and subject to imperfections that induce dynamic phenomena like torsions—where dust grains couple and exhibit elliptical motion within the crystal lattice.To better understand these phenomena, we developed a near real-time interactive computer model grounded in laboratory conditions, specifically replicating the environment within a GEC RF reference cell. This model addresses the challenges of stiffness in differential equations by employing an innovative point charge approach, where each point charge is dynamically influenced by all dust grains, enhancing the model's accuracy and responsiveness. The system allows for user interaction, enabling the manipulation of parameters and near real-time observation of dust behavior. Our approach balances computational efficiency with the ability to simulate complex plasma dynamics, providing a powerful tool for the study of dusty plasma crystals.
The global acceptance of additive manufacturing has evolved with time and has proven to provide promising solutions to varied critical requirements of the nuclear industry. The components of a nuclear reactor, when built using additive manufacturing techniques, offer high microstructural control, making them versatile for a range of properties. These properties can be made easily achievable and tailorable by using functionally graded materials. The nuclear components with a wide range of properties are essential, as the environment inside and outside the reactor varies drastically. This study reviews the current progress in additive manufacturing techniques used for manufacturing functionally graded materials for nuclear applications, highlighting the gradient design methodologies and processing techniques. Additive Manufacturing techniques such as selective laser melting uses multiple powder feeders, and mechanical pre-mixing of powders along with controlled process parameters for effectively fabricating functionally graded materials. These materials possess superior mechanical properties (such as microhardness ranging up to 890 H00.5 and compressive strength up to 2040 MPa for FeCrCoNiMo0.5W0.75), thermal conductivity and thermal properties compared to monolithic counterparts. A comparative analysis of the manufacturing capabilities of the additive manufacturing techniques, along with the usage of advanced computational techniques such as AI in optimising process parameters for desirable strength and low defect generation, is also presented. The study emphasises on the need for strategies such as process parameters optimisation and data-driven design to fully utilise the potential of additively manufactured functionally graded materials in the nuclear sector.
The research presented in this article describes progress in applying stochastic methods, uncertainty quantification, parametric studies, and variance-based sensitivity analysis (also known as Sobol sensitivity analysis) to a full-core model of a nuclear thermal propulsion (NTP) system simulated via the radiation transport code Griffin to simulate neutronics. Our goal is to develop a reduced-order (surrogate) model that can be rapidly sampled with perturbations to multiple input parameters. In this NTP system, reactivity and power feedback affect the rotation of control drums (CDs), which is itself controlled by a hybrid proportional-integral-derivative (PID) controller actuated by the power demand and reactivity feedback from the numerical model. This model uses reactor kinetic feedback (mean generation time [Λ] and effective delayed neutron fraction [βeff] from a transient Griffin simulation executed via Griffin’s improved quasi-static solver to provide the kinetic parameters) as inputs to functions that control the CD rotation angle. By investigating numerous stochastic approaches, we developed a dual-purpose surrogate model of the NTP system, using polynomial regression in the Multiphysics Object-Oriented Simulation Environment (MOOSE) Stochastic Tools Module (STM). The trained model can be rapidly sampled while simultaneously perturbing various input parameters, such as coefficients on the PID control or temperature (directly affecting the neutron cross section). The surrogate model delivers accurate (within 5%) results at speeds orders of magnitude faster (minutes, not days of computational time) than the base model. Once the surrogate model has been trained, distributions of the uncertain parameters can be changed at will to investigate the effects of perturbing multiple inputs as well as the effects of these inputs on the model output. For example, coefficients used in the PID control system may vary due to some type of physical interference, or uncertainty may exist in the temperature of the neutron cross sections in various regions of the reactor. A distribution can be placed on these parameters, and operational boundaries can be determined. The goal of this work is to support development of an advanced control system for operating CDs in a functioning NTP system. This work is a scoping study of the MOOSE STM.
Sung-Young Yoon, Eun Jeong Hong, Junghyun Lim
et al.
We present an experimentally validated, engineering-oriented framework for the design and operation of pin-to-water (PTW) atmospheric discharges to produce hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) on demand. Motivated by industrial needs for safe, point-of-use oxidant supply, we combine time-resolved diagnostics (FTIR, OES), liquid-phase analysis (ion chromatography, pH, conductivity), and coupled plasma-chemistry/fluid simulations to link plasma state to aqueous H<sub>2</sub>O<sub>2</sub> yield. Under the tested conditions (14.3 kHz, 0.2 kW; electrode to quartz wall distance 12–14 mm; coolant setpoints 0–40 °C), H<sub>2</sub>O<sub>2</sub> concentration follows a reproducible non-monotonic trajectory: rapid accumulation during the early treatment (typical peak at ~15–25 min), followed by decline with continued operation. The decline coincides with a robust vibrational-temperature (T<sub>vib</sub>) threshold near ~4900 K measured from N<sub>2</sub> emission, and with concurrent NO<sub>X</sub> accumulation and bulk acidification. Global chemistry modeling and Fluent flow fields reproduce the observed trend and show that both vibrational excitation (kinetics) and convective transport (mass/heat transfer) determine the productive time window. Based on these results, we formulate practical design rules—electrode gap (power density), discharge current control, thermal/flow management, water quality, and OES-based T<sub>vib</sub> monitoring with an automated stop rule—that maximize H<sub>2</sub>O<sub>2</sub> yield while avoiding NO<sub>X</sub>-dominated suppression. The study provides a clear path for transforming mechanistic plasma insights into deployable, industrial H<sub>2</sub>O<sub>2</sub> generator designs.
Instabilities of Alfvén eigenmodes (AEs) are of significant concern because they can enhance the cross-field transport of fusion-born alpha particles beyond the neoclassical level in magnetic fusion plasmas. The threshold value of alpha-particle pressure for exciting AEs depends critically on the damping rate of AEs. The damping mechanisms include kinetic damping due to interactions with thermal particles, continuum damping due to AE frequency crossing Alfvén continuum, and radiative damping due to emitting kinetic Alfvén waves (KAWs). The radiative damping is substantial and can even prevail in high-temperature burning plasmas [1]. We revisit the radiative damping analytic theory for TAE in plasmas with low positive magnetic shear, considering TAE with an eigenfrequency near the bottom of TAE-gap and with poloidal harmonics of the same sign (even TAE). In contrast to earlier papers, we provide the damping calculations in real space rather than Fourier space. This approach is straightforward technically and more enlightening from a physics standpoint for benchmarking numerical calculations of radiative damping. The parametric dependence of the resulting damping rate agrees with that of Refs. [2-5], but it has a smaller numerical factor in front of it.
Terahertz (THz) waves, known as non-ionizing radiation owing to their low photon energies, can actually ionize atoms and molecules when a sufficiently large number of THz photons are concentrated in time and space. Here, we demonstrate the generation of ionizing, multicycle, 15-THz waves emitted from large-area lithium niobate crystals via phase-matched optical rectification of 150-terawatt laser pulses. A complete characterization of the generated THz waves in energy, pulse duration, and focal spot size shows that the field strength can reach up to 260 megavolts per centimeter. In particular, a single-shot THz interferometer is employed to measure the THz pulse duration and spectrum with complementary numerical simulations. Such intense THz pulses are irradiated onto various solid targets to demonstrate THz-induced tunneling ionization and plasma formation. This study also discusses the potential of nonperturbative THz-driven ionization in gases, which will open up new opportunities, including nonlinear and relativistic THz physics in plasma. Intense terahertz pulses, produced from a large-area lithium niobate wafer via phase-matched optical rectification of 150-terawatt laser pulses, ionize atoms and molecules and turn them into plasma.
The paper collects and discusses the results obtained in the theoretical investigation of cold plasmas by using a state-to-state self-consistent kinetic approach, coupling chemistry and free electron kinetics. Examples are selected, not only to review the most recent advancements made in updating and extending the chemical model, but also to highlight the role played in all these systems by excited states, either vibrational or electronic, in affecting the plasma evolution in the discharge and in the post-discharge phases in different discharge configurations. The response of the kinetic simulation to the accuracy of the dynamical data describing the collisional processes, to the theoretical scheme adopted for the vibrational levels of molecules, and to the inclusion of the relevant dissociation channels, is discussed also in the light of the comparison with experiments for model validation.
A detailed review of the scientific literature was undertaken to examine the most recent developments in plasma processing in the field of medicine. The first part of the review includes a detailed breakdown of the different types of coatings that can be applied onto medical devices using plasma, with a specific focus on antimicrobial surfaces. The developments in plasma-deposited biocompatibles, drug delivery and adhesive coatings in 2023 are described, and specific applications in additive manufacturing are highlighted. The use of plasma and plasma-activated liquids as standalone therapeutics continues to evolve, and pertinent advances in this field are described. In addition, the combination of plasma medicine with conventional pharmaceutical interventions is reviewed, and key emerging trends are highlighted, including the use of plasma to enhance drug delivery directly into tissue. The potential synergies between plasma medicine and chemotherapeutics for oncology and infection treatment are a growing area, and recent advancements are noted. Finally, the use of plasma to control excess antibiotics and to intentionally degrade such materials in waste streams is described.
In recent years, plasma medicine, as an innovative and rapidly growing field, has garnered increasing attention. Nonetheless, the fundamental mechanisms of the interaction processes of cold atmospheric plasma (CAP) and biomolecules remain under investigation. In this paper, a reactive molecular dynamic (MD) simulation with ReaxFF potential was performed to explore the interactions of reactive oxygen species (ROS) produced in CAP, exemplified by OH radicals, and four distinct oligonucleotides. The breakage of single-stranded oligonucleotides induced by OH is observed in the simulation, which could seriously influence the biological activity of cellular DNA. The base release induced by OH radicals means the loss of base sequence information, and the H-abstraction at nucleobases affects the gene strand complementarity, gene transcription, and replication. In addition, the dose effects of OH radicals on bond formation and breaking of oligonucleotides are also discussed by adjusting the number of ROS in the simulation box. This study can enhance the comprehension of interactions between CAP and DNA, thereby indicating possible improvements in plasma device optimization and operation for medical applications.
We investigate the effects of the magnetostatic (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>B</mi></mrow></semantics></math></inline-formula>) field topology on the plasma behavior in a 2D collisionless simulation setup that represents an axial–azimuthal cross-section of a Hall thruster. The influence of the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>B</mi></mrow></semantics></math></inline-formula>-field topology is assessed in terms of two principal design properties of the field in a typical Hall thruster, i.e., the field’s peak intensity along the axial direction, and the field’s axial distribution. The effects of the field’s intensity are investigated for three propellants—xenon, krypton, and argon. Whereas, the effects of the axial profile of the magnetic field are studied only for the xenon propellant as an example. We primarily aim to understand how the changes in the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>B</mi></mrow></semantics></math></inline-formula>-field topology affect the spectra of the resolved instabilities as well as the electrons’ transport characteristics and the contributions of various momentum terms to transport. The numerical observations on the instabilities’ characteristics are compared against the relevant existing theories to determine the extent to which the simulated and the theoretically predicted characteristics are consistent across the studied parameter space. It was, most notably, found that modes related to ion acoustic instability are dominantly present across the simulation cases. The ion transit time instability additionally develops at the highest <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>B</mi></mrow></semantics></math></inline-formula>-field intensities as a long-wavelength structure. The main influence of the axial profile of the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>B</mi></mrow></semantics></math></inline-formula> field on the plasma discharge was observed to be in terms of the electrons’ transport characteristics. Where possible, the insights from the simulations are discussed with respect to the relevant experimental observations available in the literature.
In this review, we detail the commonality of mathematical intuitions that underlie three numerical methods used for the quantitative description of electron swarms propagating in a gas under the effect of externally applied electric and/or magnetic fields. These methods can be linked to the integral transport equation, following a common thread much better known in the theory of neutron transport than in the theory of electron transport. First, we discuss the exact solution of the electron transport problem using Monte Carlo (MC) simulations. In reality we will go even further, showing the interpretative role that the diagrams used in quantum theory and quantum field theory can play in the development of MC. Then, we present two methods, the Monte Carlo Flux and the Propagator method, which have been developed at this moment. The first one is based on a modified MC method, while the second shows the advantage of explicitly applying the mathematical idea of propagator to the transport problem.
A Hamiltonian two-field gyrofluid model is used to investigate the dynamics of an electron-ion collisionless plasma subject to a strong ambient magnetic field, within a spectral range extending from the magnetohydrodynamic (MHD) scales to the electron skin depth. This model isolates Alfvén, Kinetic Alfvén and Inertial Kinetic Alfvén waves that play a central role in space plasmas, and extends standard reduced fluid models to broader ranges of the plasma parameters. Recent numerical results are reviewed, including (i) the reconnection-mediated MHD turbulence developing from the collision of counter-propagating Alfvén wave packets, (ii) the specific features of the cascade dynamics in strongly imbalanced turbulence, including a possible link between the existence of a spectral transition range and the presence of co-propagating wave interactions at sub-ion scales, for which new simulations are reported, (iii) the influence of the ion-to-electron temperature ratio in two-dimensional collisionless magnetic reconnection. The role of electron finite Larmor radius corrections is pointed out and the extension of the present model to a four-field gyrofluid model is discussed. Such an extended model accurately describes electron finite Larmor radius effects at small or moderate values of the electron beta parameter, and also retains the coupling to slow magnetosonic waves.
Multinational geological repositories (Multinational repositories: MNRs) will inevitably be features of the international radioactive waste management landscape in future decades. They will involve more complex requirements for long-term information management than national deep geological repositories (DGRs) but the considerations involved in managing these requirements also point to wider needs for transnational information management for any country with a national deep geological repository. This article looks at what information needs to be propagated into the future for both DGRs and MNRs, and for how long. It is argued that the critical requirements are quite limited and are readily achievable, with the most important period being the coming few hundred years. The transience of organisations and national boundaries, issues being addressed for MNRs, also affect any national programme, but are generally overlooked. It is concluded that there is a need to move towards international oversight of all geological disposal facilities, including a common system of regulations and information archiving, and that providing these is a potential role for the IAEA.
This paper explores the transition between Compton Scattering and Inverse Compton Scattering (ICS), which is characterized by an equal exchange of energy and momentum between the colliding particles (electrons and photons). This regime has been called Symmetric Compton Scattering (SCS) and has the unique property of eliminating the energy-angle correlation of scattered photons, and, when the electron recoil is large, transferring monochromaticity from one colliding beam to the other, resulting in back-scattered photon beams that are intrinsically monochromatic. The paper suggests that large-recoil SCS or quasi-SCS can be used to design compact intrinsic monochromatic γ-ray sources based on compact linacs, thus avoiding the use of GeV-class electron beams together with powerful laser/optical systems as those typically required for ICS sources. Furthermore, at low recoil and low energy collisions (in the 10 keV energy range), SCS can be exploited to heat the colliding electron beam, which is widely scattered with large transverse momenta over the entire solid angle, offering a technique to trap electrons into magnetic bottles for plasma heating.
SCWR (supercritical water cooled reactor) is one of the Generation IV reactors. This review summarizes the results of SCWR design concept development through numerical simulations carried out by the author-led team at the University of Tokyo and Waseda University from 1989 to 2014. They are core design, subchannel analysis, statistical thermal design, fuel rod design, development of fuel integrity criteria, plant system and heat balance, plant dynamics analysis, plant control, startup system, stability analysis, safety principle, safety criteria, safety analysis, transient subchannel analysis and fast reactor SCWR. A brief summary of experimental results on thermal hydraulics, materials and water chemistry follows. Discussion includes SCPR study by Japanese BWR manufacturers, comments on the 2005 INEEL SCWR report, misconceptions about SCWR and commercialization challenges. The SCWR is an innovation in light water reactors based on supercritical coal-fired power plant technology that has been in use worldwide for over half a century. This review covers most of the SCWR design and analysis. For researchers, it is a good subject to understand the design and analysis of light water reactors.