Simulation Code Research Articles

Design and Development of a Portable Neutron Detection System Based on a 6Li-Doped ZnS(Ag) Scintillator

In this study, the design and development of a portable neutron detection system based on a 6LiF + ZnS(Ag) scintillator was carried out. The detector system was first modeled using the Monte Carlo simulation code MCNP. As a result of the detector simulation, the materials and photomultiplier tubes (PMTs) were supplied for the system, and the material properties and thicknesses were optimized for the best scintillator, with the EJ-420 (Eljen Technology), consisting of 95% 6Li dispersed in ZnS(Ag), chosen because it has a distinctive feature with regard to high thermal neutron detection efficiency. Since this material has been shown to offer a significant advantage in favor of neutron detection in mixed radiation fields with gammas and neutrons, the pulse shape discrimination method was employed. To achieve this, a proper electronic circuit was developed to discriminate the pulses from neutrons and gammas. In the experimental step, the EJ-420 scintillator with a 50-mm diameter was optically coupled with a special fast PMT (Hamamatsu H1949-51 model). In conclusion, this study, which underlines the performed simulations for a neutron detector configuration, gives the obtained experimental results showing discrimination capability in neutron/gamma detection using a 241Am-Be neutron source. The results show that the EJ-420 is a good scintillator due to its highly enriched 6Li transmator, which results in more effective neutron measurements when a portable neutron detector design is chosen.

Observational signatures of the dust size evolution in isolated galaxy simulations

We aim to provide observational signatures of the dust size evolution in the interstellar medium (ISM). In particular, we explore indicators of the polycyclic aromatic hydrocarbon (PAH) mass fraction ($q_ PAH $), defined as the mass fraction of PAHs relative to the total dust grains. In addition, we validate our dust evolution model by comparing the observational signatures from our simulations to observations. We used the hydrodynamic simulation code, GADGET4-OSAKA to model the dust properties of Milky Way-like and NGC 628-like galaxies representing star-forming galaxies. This code incorporates the evolution of grain size distributions driven by dust production and interstellar processing. Furthermore, we performed post-processing dust radiative transfer calculations with SKIRT based on the hydrodynamic simulations to predict the observational properties of the simulations. We find that the intensity ratio between 8 um and 24 um ($I_ nu um )/I_ nu um )$) is correlated with $q_ PAH $ and can be used as an indicator of the PAH mass fraction. However, this ratio is influenced by the local radiation field. We suggest the 8 um -to-total infrared intensity ratio ($ I_ nu um )/ I_ TIR $) as another indicator of the PAH mass fraction, since it is tightly correlated with the PAH mass fraction. Furthermore, we explored the spatially resolved evolutionary properties of the PAH mass fraction in the simulated Milky Way-like galaxy using $ I_ nu um )/ I_ TIR $. We find that the spatially resolved PAH mass fraction increases with metallicity at $Z due to the interplay between accretion and shattering, whereas it decreases at $Z because of coagulation. Also, coagulation decreases the PAH mass fraction in regions with a high hydrogen surface density. Finally, we compared the above indicators in the NGC 628-like simulation with those observed in NGC 628 by Herschel Spitzer and JWST . Consequently, we find that our simulation underestimates the PAH mass fraction throughout the entire galaxy by a factor of $ 8$ on average. This could be due to the efficient loss of PAHs by coagulation in our model, suggesting that our treatment of PAHs in dense regions needs to be improved.

3D code for MAgneto-Thermal evolution in Isolated Neutron Stars, MATINS: thermal evolution and light curves

ABSTRACT The thermal evolution of isolated neutron stars is a key element in unravelling their internal structure and composition and establishing evolutionary connections among different observational subclasses. Previous studies have predominantly focused on one-dimensional or axisymmetric two-dimensional models. In this study, we present the thermal evolution component of the novel three-dimensional magnetothermal code MATINS (MAgneto-Thermal evolution of Isolated Neutron Star). MATINS employs a finite volume scheme and integrates a realistic background structure, along with state-of-the-art microphysical calculations for the conductivities, neutrino emissivities, heat capacity, and superfluid gap models. This paper outlines the methodology employed to solve the thermal evolution equations in MATINS, along with the microphysical implementation that is essential for the thermal component. We test the accuracy of the code and present simulations with non-evolving magnetic fields of different configurations (all with electrical currents confined to the crust and a magnetic field that does not thread the core), to produce temperature maps of the neutron star surface. Additionally, for a specific magnetic field configuration, we show one fully coupled evolution of magnetic field and temperature. Subsequently, we use a ray-tracing code to link the neutron star surface temperature maps obtained by MATINS with the phase-resolved spectra and pulsed profiles that would be detected by distant observers. This study, together with our previous article focused on the magnetic formalism, presents in detail the most advanced evolutionary code for isolated neutron stars, with the aim of comparison with their timing properties, thermal luminosities and the associated X-ray light curves.

Finite element analysis of a rubber bearing base isolator under vertical and horizontal loads using a nonlinear hyper-viscoelastic material model

This research is devoted to developing a finite element model using Abaqus code for the computer simulation of an in-house developed and manufactured rubber bearing subjected to static vertical and cyclic horizontal loads. A high-damping rubber compound was designed. The material behavior of the rubber was assumed to be described by the hyper-viscoelastic model. Both linear (Prony series) and nonlinear (strain hardening power law) viscoelastic relationships were used in conjunction with the Ogden-Roxburgh equation to take the addition of the stress softening phenomenon or Mullins effect into consideration. The parameters of the material model were determined using MCalibration code in which an optimization technique was used, and data obtained in experiments carried out on test specimens were fitted into the selected model. The results of the simulations were compared with their corresponding experimental data carried out on the rubber bearing. The force-displacement behavior, stress and strain fields, and computed energy were presented and discussed. It is shown that the nonlinear viscoelastic model accompanied by the Mullins effect gives the best results. Moreover, the model could accurately predict the energy variations during the earthquake loading.

Electric field driven focusing and transport of plasma ion beams by micro-glass capillaries beyond the self-focusing limit

Micro-glass capillaries emerge as an important tool for the lossless guiding and focusing of ion beams (Kojima 2018 J. Phys. B: At. Mol. Opt. Phys. 51 042001). The self-focusing mechanism of the capillaries is primarily governed by charged patches induced on their inner walls by the incident beam (Stolterfoht et al 2002 Phys. Rev. Lett. 88 133201). However, the dominance of space charge forces over self-focusing forces in intense (J ≈ 1 A m−2) ion beams establishes a self-focusing limit (Maurya et al 2019 J. Phys. D: Appl. Phys. 52 055205), posing challenges to beam focusing beyond this limit. In this work, a novel method is introduced, demonstrating electrical control over the charge patch dynamics through an externally applied bias voltage, thereby enabling the focusing of Ar ion beams beyond the self-focusing limit. Experimental results reveal that adjusting the biasing voltage allows overcoming the self-focusing limit, resulting in the generation of a high-intensity ( Jout≈3.05×105 A m−2) nano-beam (∼160 nm). Furthermore, electrical control is shown to enhance the performance of both straight and tapered capillaries (SC/TC), with the TC being more effective for nano-beam generation. A Particle-In-Cell (PIC) simulation code has been developed to explain the experimental results. The implications of high-intensity nano ion beams in advancing nanopatterning, nanoscale material analysis, and matter wave interferometry, underscore significant contributions to research and innovation within electronics, materials science, nanotechnology, and emerging quantum technologies.

A Generic Implementation of the D1S Methodology for Dose Rate Assessment by Monte Carlo Codes in Fusion Applications

Dose rate assessment is of utmost importance in fusion reactors because of the maintenance operations that these facilities will require. The standard way to perform this assessment in ITER is use of the Direct 1-Step (D1S) methodology, which consists of performing neutron transport simulation, material activation, and decay photon transport simulation in one step and thus in one simulation only. Usually, implementation of the D1S methodology requires changing the source files in a reference Monte Carlo code. The purpose of the present work is to develop an easy-to-implement method for Monte Carlo codes to help calculate the dose rate in fusion reactors. To do so, the proposal is to act on nuclear data only and not on source files of the simulation codes. This is done by replacing prompt photon production in evaluation files by suitable decay photon production, taking into account radioactive decays of radionuclides and irradiation history. This study was to be applied first on the TRIPOLI-4® Monte Carlo code for the sake of simplicity. TRIPOLI-4 is the reference code for particle transport at CEA. The verification and validation process relies first on a comparison to the reference Rigorous 2-Step (R2S) methodology and then on an experiment, the so-called Frascati Neutron Generator (FNG) dose experiment. The nuclear database to be changed is of the ENDF-6 format, a recurrent format in neutronics studies. The analysis studied both neutron and photon responses to check if the simulation was performing normally in a physical way and to compare the results with references provided by simulations based on the R2S methodology or by the FNG dose experiment. The simulations have proven to be in good agreement with the experimental results.

Groundwater contamination modelling in Ayad River Basin, Udaipur

Groundwater, a vital freshwater resource catering to agricultural, domestic, and industrial needs, faces a pressing challenge of contamination due to escalating human activities. This study focuses on the Ayad River Basin in the Udaipur district of Rajasthan, employing the FEFLOW simulation code for the first time. A steady-state numerical model and a groundwater contaminant prediction model for total dissolved solids (TDS), nitrate, and fluoride were developed, simulating trends over the next five years with an accuracy exceeding 95%. The results reveal an eastward increase in TDS, nitrate, and fluoride concentrations, attributed to contamination from two waste disposal sites-Titadi and Baleecha. Titadi, operational for four decades until closure in 2010, retains residual waste over 32 thousand m2. The initiation of a new dumping ground at Baleecha by the Udaipur Municipal Corporation post-2010 exacerbates regional contamination. Nitrate contamination is particularly high in agricultural zones with excessive chemical fertilizer usage. Of the 27 scenarios tested, 23 support using the water for irrigation but would require treatment before using it for drinking. Recommendations include deploying a chemical sensor network for real-time data input into the web enabled FEFLOW model, real-time monitoring and alerts, and a mobile application providing personalized guidance on water usage and health risks in case of contamination. This study can be beneficial to decision-makers, who work on the policy and groundwater management strategies.

Performance of NB-CTMFD Detector Versus Ludlum 42-49B, and Fuji NSN3 Detectors for Hard (Am-Be) and Soft (Cf-252 Fission) Energy Spectra Neutron Sources Within Lead/Concrete Shielded Configurations

Abstract This paper presents the results of neutron detection efficiency and dosimetry between a nonborated centrifugally tensioned metastable fluid detector (NB-CTMFD) configured to detect fast (>0.1 MeV) versus two widely used combined thermal and fast neutron detection devices of similar form factors: moderated He-3 based Ludlum-42-49BTM neutron detector, and, the Fuji NSN3TM pressurized nitrogen-methane filled neutron detector. The one-on-one performance comparisons were conducted using hard (Am-Be) and soft (Cf-252 fission) neutron spectra isotope neutron sources positioned behind various levels of lead and concrete shielding ranging in thickness from 0 cm (unshielded) to up to 30 cm. The comparisons were conducted together with Monte Carlo N-Particle (MCNP) code simulations to account for 3-D effects and to relate the detection sensitivity with the dose rate. The MCNP model results for the neutron energy spectrum were validated versus experimental measurements using the H*TMFD. While the Ludlum and NSN3 detectors operate at a fixed sensitivity setting, the NB-CTMFD detector could be operated at various sensitivity levels by varying the tensioned metastable negative pressure (Pneg) from 0.3 MPa to 0.7 MPa. The NB-CTMFD (configured for fast: >0.1 MeV neutron detection at Pneg = 0.7 MPa) offered relative sensitivity enhancements of up to 15x greater than the Ludlum and ∼5x greater than the NSN3 detector for low shielding thicknesses. For larger thicknesses, the advantage factor for NB-CTMFD unit reduces with increased fast neutron removal via down-scattering, which benefits the Ludlum and NSN3 detectors. Our companion paper compares performance with a Cf-252 spectrum using a borated CTMFD (covering dual energy bins: thermal-epithermal and fast energy ranges) wherein, it is demonstrated that the advantage factor for the CTMFD (if borated) remains elevated at the 5–10x higher level for low and large shielding thicknesses and soft and hard neutron spectra.

Performance of Borated Centrifugally Tensioned Metastable Fluid Detector Detector Versus Ludlum 42-49B, Fuji NSN3 Detectors for Fission Energy Spectrum Neutron Detection With the Source Within Lead/Concrete Shielded Configurations

Abstract This paper presents the results of neutron detection efficiency and dosimetry between a borated centrifugally tensioned metastable fluid detector (B-CTMFD) configured to detect thermal to fast neutrons versus two widely used neutron detection devices of similar form factors: moderated He-3 based Ludlum-42-49B neutron detector, and, the Fuji Electric's NSN3TM (NNSN3) pressurized nitrogen-methane filled neutron detector. The one-on-one performance comparisons were conducted using soft (Cf-252 fission) neutron spectrum isotope neutron sources positioned behind various levels of lead and concrete shielding ranging in thickness from 0 cm (unshielded) to up to 30 cm. The comparisons were conducted with Monte Carlo N-Particle transport code (MCNP) code simulations to account for three-dimensional effects and to relate the absolute detection rate with the dose rate—to derive the sensitivity factor (cpm/μSv/h). While the Ludlum 42-49B and NSN3 detectors operate at a fixed sensitivity setting, the centrifugally tensioned metastable fluid detector (CTMFD) can be (and was) operated to detect and separate the contributions from epithermal (0.02 eV–0.2 MeV) and from fast (>0.2 MeV) neutrons at various sensitivity levels by varying the tensioned metastable negative pressure (Pneg) from 0.3 MPa to 0.7 MPa. The B-CTMFD (configured for detecting the full 0.02 eV to 12 MeV neutrons >0.1 MeV neutron detection at Pneg = 0.7 MPa) offered relative sensitivity enhancements of up to ∼22× greater than Ludlum and over 5× greater than NSN3, over the 0-15 cm range of Pb shielding, and the 0–30 cm concrete shield thickness. The contribution from detecting down scattered neutrons increases with increased thickness, especially for concrete shielding. The B-CTMFD design overcomes the detection penalty (up to 60% depending on shielding type and thickness) inherent in the nonborated centrifugally tensioned metastable fluid detector (NB-CTMFD), designed only to detect fast-energy neutrons—as described in the companion (Part-1) paper. However, unlike the NB-CTMFD, which used 100% decafluorapentane (DFP) (C5H2F10), the B-CTMFD requires the use of an azeotropic mixture of DFP, methanol, and tri-methyl borate (TMB—C3H9BO3, using natural boron) in 80:4:16 proportion. The B-CTMFD was about 6 times more sensitive than NB-CTMFD under the most heavily shielded condition and, taken together, also offered 2-energy bin neutron spectroscopic enablement, together with 22-5× higher absolute efficiency and relative sensitivity compared with the nonspectroscopic Ludlum (He-3) and NSN3 (methane-nitrogen) based detectors. From an intrinsic efficiency standpoint, the B-CTMFD operating at Pneg = 0.7 MPa state demonstrated ∼103× higher intrinsic efficiency over Ludlum 42-49B and NSN3 detectors, respectively.

Nanoparticle shape factor impact on double diffusive convection of Cu-water nanofluid in trapezoidal porous enclosures: A numerical study

Enclosures that contain both fluid and porous regions are utilized in various industries and geophysical processes to enhance heat and mass transfer. These enclosures find applications in fields such as geothermal engineering, drying of porous solids, cooling of electronics, metal solidification, and many others. In line with the motivation behind these applications, the present study explores double diffusion in the naturally convective flow of water-based nano fluid saturated in the trapezoidal porous enclosure and containing Copper (Cu) nano particles. The impact of uniformly applied radiative heat flux and nano particle shape factor is also accounted. A numerical investigation was carried out using a finite difference methodology integrated into a computational MATLAB code for numerical simulation. The simulation aimed to study the effect of nanoparticle shape factor on the effectiveness of a porous medium, which is exposed to two distinct objectives: enhancing heat transfer and optimizing mass transfer within a fluid-saturated porous medium. This research conducts a meticulous parametric exploration, underscoring the pivotal roles played by Darcy number (Da), nanofluid shape factor (m), Rayleigh number (Ra), thermal radiation (Rd), buoyancy ratio (Nr), and Lewis number (Le) in shaping the dynamics of flow, heat, and concentration transfer. The analysis of Nusselt and Sherwood numbers reveals that changing the shape of nano-particles from spheres to bricks increases the heat flux and mass flux coefficients by approximately 0.33% and 1.37% respectively. The results show a significant increase in Nusselt and Sherwood numbers, with blade-shaped nanoparticles demonstrating approximately a 2.97% and 10.82% improvement, respectively, compared to sphere-shaped nanoparticles. The outcome of this analysis yields an exhaustive dataset encompassing Nusselt and Sherwood numbers can be written as mathematical functions based on the parameters we talked about earlier.

The difficult path to coalescence: massive black hole dynamics in merging low-mass dark matter haloes and galaxies

ABSTRACT We present a high-resolution numerical study of the sinking and merging of massive black holes (MBHs) with masses in the range of $10^3 - 10^7 \, \mathrm{M}_\odot$ in multiple minor mergers of low-mass dark matter haloes without and with galaxies ($4\times 10^8 \, \mathrm{M}_\odot \lesssim {M}_{\mathrm{halo}} \lesssim 2\times 10^{10} \, \mathrm{M}_\odot)$. The ketju simulation code, a combination of the gadget tree solver with accurate regularized integration, uses unsoftened forces between the star/dark matter components and the MBHs for an accurate treatment of dynamical friction and scattering of dark matter/stars by MBH binaries or multiples. Post-Newtonian corrections up to order 3.5 for MBH interactions allow for coalescence by gravitational wave emission and gravitational recoil kicks. Low-mass MBHs ($\lesssim 10^5 \, \mathrm{M}_\odot$) hardly sink to the centre or merge. Sinking MBHs have various complex evolution paths – binaries, triplets, free-floating MBHs, and dynamically or recoil ejected MBHs. Collisional interactions with dark matter alone can drive MBHs to coalescence. The highest mass MBHs of $\gtrsim 10^6 \, \rm M_\odot$ mostly sink to the centre and trigger the scouring of dark matter and stellar cores. The scouring can transform a centrally baryon-dominated system into a dark-matter-dominated system. Our idealized high-resolution study highlights the difficulty to bring in and keep low-mass MBHs in the centres of low-mass haloes/galaxies – a remaining challenge for merger assisted MBH seed growth mechanisms.

Al–B4C-(Gd, Gd2O3) composite materials: Synthesis and characterization for neutron shielding applications

In this study, Al–20%B4C-x%Gd and Al–20%B4C-x%Gd2O3 (x = 1, 3, 5) composite powders were prepared using a high-energy planetary ball milling method to enhance the physical properties of Al–B4C neutron shielding composites. The prepared powders were subjected to uniaxial cold compaction at 500 MPa, resulting in cylindrical specimens. Subsequently, the specimens were sintered in a tube furnace at 600 °C for 1 h under an Ar atmosphere to prevent oxidation. The microstructure of the resulting composites was characterized using X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX). Archimedes density, hardness, and corrosion tests were performed on the compacted samples. Moreover, the composite's thermal and fast neutron absorption rates were calculated using the MCNP6.2 simulation code. The neutron equivalent dose rate was experimentally determined using the Am–Be neutron source. The simulation results demonstrated that the composite materials containing Gd exhibited the highest thermal neutron absorption rate, while those containing Gd2O3 demonstrated the highest fast neutron absorption rate. This research contributes valuable insights into the design and utilization of neutron-absorbing materials with suitable mechanical properties.

Synergistic effects of Gd2O3 and SiO2 in enhancing the acoustic, mechanical, and shielding qualities of borate glasses

This study comprehensively analyzes the gamma radiation shielding, mechanical, and acoustic properties of novel glass composites formulated from B2O3, SiO2, and Gd2O3. Utilizing the MCNPX simulation code and Phy-X: PSD software, key parameters such as Linear Attenuation Coefficient, Half Value Layer (HVL), Mean Free Path (MFP), and Effective Atomic Number (Zeff) were meticulously evaluated for three distinct glass compositions, denoted as GL-1, GL-2, and GL-3. The investigation revealed that incorporating Gd2O3 and SiO2 notably enhances the radiation shielding efficiency of these glasses, which is evident from the decreasing trends in HVL and MFP values across the series. Employing the Makishima and Mackenzie (MM) model, this study further delved into the mechanical and acoustic characteristics of the glass samples. An increase in Gd2O3 and SiO2 content, substituting B2O3, was observed to augment the bond dissociation energy and adjust the packing density, consequently improving the elastic moduli. These mechanical enhancements were quantified through measurements of Young's modulus, bulk modulus, shear modulus, and longitudinal modulus. Acoustic properties were also calculated, including Longitudinal and Transverse velocities, mean velocity, and acoustic impedance. These parameters demonstrated a consistent improvement correlating with the increasing rigidity and mechanical strength of the glass samples, particularly for the GL-3 composition. The study concludes that the GL-3 glass sample exhibits superior performance regarding gamma photon attenuation, mechanical robustness, and acoustic properties. This underscores its potential as an effective material for radiation shielding in various industrial applications, benefiting from its enhanced mechanical and acoustic features.

Stochastic computer experiments of the thermodynamic irreversibility of bulk nanobubbles in supersaturated and weak gas-liquid solutions.

Spontaneous gas-bubble nucleation in weak gas-liquid solutions has been a challenging topic in theory, experimentation, and computer simulations. In analogy with recent advances in crystallization and droplet formation studies, the diffusive-shielding stabilization and thermodynamic irreversibility of bulk nanobubble (bNB) mechanisms are revisited and deployed to characterize nucleation processes in a stochastic framework of computer experiments using the large-scale atomic/molecular massively parallel simulator code. Theoretical bases, assumptions, and limitations underlying the irreversibility hypothesis of bNBs, and their computational counterparts, are extensively described and illustrated. In essence, it is established that the irreversibility hypothesis can be numerically investigated by converging the system volume (due to the finiteness of interatomic forces) and the initial dissolved-gas concentration in the solution (due to the single-bNB limitation). Helium nucleation in liquid Pb17Li alloy is selected as a representative case study, where it exhibits typical characteristics of noble-gas/liquid-metal systems. The proposed framework lays down the bases on which the stability of gas-bNBs in weak and supersaturated gas-liquid solutions can be inferred and explained from a novel perspective. In essence, it stochastically marches toward a unique irreversible state along out-of-equilibrium nucleation/growth trajectories. Moreover, it does not attempt to characterize the interface or any interface-related properties, neither theoretically nor computationally. It was concluded that bNBs of a few tens of He-atoms are irreversible when dissolved-He concentrations in the weak gas-liquid solution are at least ∼50 and ∼105 molm-3 at 600 and 1000K (and ∼80 MPa), respectively, whereas classical molecular dynamics -estimated solubilities are at least two orders of magnitude smaller.

Monte Carlo Source Convergence Diagnosis Method and Thermal-Physics Coupling Method Based on Functional Expansion Tallies

In iterative Monte Carlo calculations for nuclear reactors, the inactive cycles should be calculated first to ensure that the source distribution is converged, and then the tallies of various parameters in the active cycles can begin. In order to acquire the mesh-free distribution of the fission source, this research proposes the functional expansion tallies (FET) source convergence diagnosis method in the Reactor Monte Carlo code, which is a self-developed stochastic simulation code maintained by the Reactor Engineering Analysis Laboratory of Tsinghua University. Due to the randomness in Monte Carlo calculations and the difficulty in determining the precise source convergence, this paper proposes a diagnostic tool based on function curve similarity and moving average, and proposes an online real-time source convergence diagnosis method. The FET online source convergence method can terminate the calculation of the inactive cycle in real time according to the convergence diagnostic tool; thus it can greatly decrease the calculation time. The precise and effective transfer of data between different meshes is a difficult issue of thermal and physical coupling. Converting two separate meshes and transferring the data are exceptionally difficult and complex tasks within the conventional nuclear thermal-physics coupling approach. By applying the FET method to nuclear thermal-physics coupling, the mesh-free continuous-space fission source distribution can be obtained, which is suitable for more complex meshes. Additionally, computational memory can be minimized by replacing (transforming) the data from numerous mesh power distribution data points with the coefficients of the function.

Lead Fast Reactor Thermal-Hydraulic Testing Facilities in Support of the UK Advanced Modular Reactor Program

The Westinghouse lead-cooled fast reactor (LFR) is a next-generation nuclear power plant whose primary mission is to reduce front-end capital costs and generate flexible and cost-competitive electricity for global markets, while offering mission versatility and satisfying the highest safety and sustainability standards. The LFR is an economical choice for carbon-free power generation to meet the ambitious goals of reducing carbon emissions. The plant utilizes passive safety systems for high reliability and public safety. The LFR testing program aims to fill the technology gaps in the key materials, components, and systems of the LFR plant. It provides demonstrations of LFR engineering that reduce the uncertainty of the LFR design and experimental data for the verification and validation of the modeling and simulation computer codes. With the support of the LFR phenomena identification and ranking table, the phenomena important to plant safety with insufficient states of knowledge have been identified and a Westinghouse testing plan developed to address them. The United Kingdom Advanced Modular Reactor Program Phase 2 was purposed to advance the level of design maturity toward eventual regulatory approval and deployment. Westinghouse and its partners have developed eight state-of-the-art test facilities within the program. Among them, the Passive Heat Removal Facility, Versatile Lead Facility, Lead Water Interaction Facility, and the Lead Freezing Facility are thermal-hydraulic testing facilities, with the other four facilities dedicated to testing lead corrosion and material mechanical behavior in lead. The design, development, and testing of the four thermal-hydraulic facilities are presented in this paper. A variety of computer codes ranging from system-level analysis, component-level analysis, and high-resolution computational fluid dynamics analysis, are utilized to support the development of the facilities. The analyses provide operational and accidental conditions in the LFR to identify major testing conditions and inform the facility design and testing matrix. With a significant amount of experimental data being generated with these highly instrumented test facilities, the computer codes and models will be benchmarked against the experimental results to improve their validation and verification status.

Parameterization of H2SO4 and organic contributions to volatile PM in aircraft plumes at ground idle

ABSTRACT Volatile Particulate Matter (vPM) emissions are challenging to measure and quantify, since they are not present in the condensed form at the engine exit plane and they evolve to first form in the aircraft plume and then continue to grow and change as they mix and dilute in the ambient atmosphere. To better understand the issues associated with the initial formation and growth of vPM, a modeling study has been undertaken to examine several key parameters that affect the formation and properties of the vPM that is created in the initial cooling and dilution of the aircraft exhaust. A modeling tool (Aerosol Dynamic Simulation Code, ADSC) that was developed and enhanced over a series of past research projects supported by NASA, DoD’s SERDP/ESTCP, and FAA was used to perform a parametric analysis of vPM. The parameters of fuel sulfur content (FSC), emitted condensable hydrocarbon (HC) concentrations, and the species profile of the HCs were used to construct a computational matrix that framed a wide range of expected parameter values. This computational matrix was executed for two representative commercial aircraft engines at ground idle and results were obtained for distances of 250 m and 1000 m downstream. From prior results, the most significant vPM emissions occur at the lowest power settings, so an engine power condition of 7% rated thrust was used. A primary goal of the parametric study is to develop an updated vPM modeling methodology and also to help interpret data collected in experimental campaigns. The parameterization proposed here allows the vPM emission composition and particle numbers to be estimated in greater detail than current methods. The aim is to provide additional understanding on how the vPM properties vary with fuel and engine parameters to increase the utility of vPM predictions. Implications: Volatile Particulate Matter (vPM) is an important contribution to the total PM emitted by aviation engines. While vPM is not currently a part of engine emissions certification regulations, vPM is used in aviation environmental impact assessments and for air quality modeling in and around airports. Current methods in use, such as FOA, were developed before many recent advances in experimental data acquisition and in understanding of vPM processes. The parameterization proposed here allows the vPM emission composition and particle numbers to be estimated in greater detail than current methods. These estimates can be used to develop inventories and provide a better estimate of total emission for most aviation engines. Its use in international regulatory tools can inform possible future regulatory actions regarding vPM.

The Stagger Code for Accurate and Efficient, Radiation-coupled Magnetohydrodynamic Simulations

We describe the Stagger code for simulations of magnetohydrodynamic (MHD) systems. This is a modular code with a variety of physics modules that will let the user run simulations of deep stellar atmospheres, sunspot formation, stellar chromospheres and coronae, proto-stellar disks, star formation from giant molecular clouds, and even galaxy formation. The Stagger code is efficiently and highly parallelizable, enabling such simulations with large ranges of both spatial and temporal scales. We describe the methodology of the code and present the most important of the physics modules, as well as its input and output variables. We show results of a number of standard MHD tests to enable comparison with other, similar codes. In addition, we provide an overview of tests that have been carried out against solar observations, ranging from spectral line shapes, spectral flux distribution, limb darkening, intensity and velocity distributions of granulation, to seismic power spectra and the excitation of p-modes. The Stagger code has proven to be a high-fidelity code with a large range of uses.

Galaxies with grains: unraveling dust evolution and extinction curves with hydrodynamical simulations

Dust in galaxies is an important tracer of galaxy properties and their evolution over time. The physical origin of the grain size distribution, the dust chemical composition, and, hence, the associated ultraviolet-to-optical extinctions in diverse galaxies remains elusive. To address this issue, we introduce a model for dust evolution in the RAMSES code for simulations of galaxies with a resolved multiphase interstellar medium. Dust is modelled as a fluid transported with the gas component, and is decomposed into two sizes, 5 nm and 0.1 μm, and two chemical compositions for carbonaceous and silicate grains. This dust model includes the growth of dust by accretion of elements from the gas phase and by the release of dust in stellar ejecta, the destruction by thermal sputtering, supernovae, and astration, and the exchange of dust mass between the two main populations of grain sizes by coagulation and shattering. Using a suite of isolated disc simulations with different masses and metallicities, the simulations can explore the role of these processes in shaping the key properties of dust in galaxies. The simulated Milky Way analogue reproduces the dust-to-metal mass ratio, depletion factors, size distribution and extinction curves of the Milky Way. Galaxies with lower metallicities reproduce the observed decrease in the dust-to-metal mass ratio with metallicity at around a few 0.1 Z⊙. This break in the dust-to-metal ratio corresponds to a galactic gas metallicity threshold that marks the transition from an ejecta-dominated to an accretion-dominated grain growth, and that is different for silicate and carbonaceous grains, with ≃0.1 Z⊙ and ≃0.5 Z⊙ respectively. This leads to more Magellanic Cloud-like extinction curves, i.e. with steeper slopes in the ultraviolet and a weaker bump feature at 2175 Å, in galaxies with lower masses and lower metallicities. Steeper slopes in these galaxies are caused by the combination of the higher efficiency of gas accretion by silicate relative to carbonaceous grains and by the low rates of coagulation that preserves the amount of small silicate grains. Weak bumps are due to the overall inefficient accretion growth of carbonaceous dust at low metallicity, whose growth is mostly supported by the release of large grains in SN ejecta. We also show that the formation of CO molecules is a key component to limit the ability of carbonaceous dust to grow, in particular in low-metallicity gas-rich galaxies.

Inner Radiation Belt Simulations During the Successive Geomagnetic Storm Event of February 2022

AbstractStarting from 29 January 2022, a series of solar eruptions triggered a moderate geomagnetic storm on 3 February 2022, followed subsequently by another. Despite the typically minimal impact of unintense storms on space technology, 38 out of the 49 Starlink satellites underwent orbital decay, re‐entering Earth's atmosphere. These satellite losses were attributed to enhanced atmospheric drag conditions. This study employs numerical simulations, utilizing our test particle simulation code, to investigate the dynamics of the inner radiation belt during the two magnetic storms. Our analysis reveals an increase in proton density and fluxes during the transition from the recovery phase of the first storm to the initial phase of the second, primarily driven by intense solar wind dynamic pressure. Additionally, we assess Single Event Upset (SEU) rates, which exhibit a 50% increase in comparison to initial quiet conditions.