Advanced Code Research Articles

Optimization method for the design of hexagonal fuel assemblies

The duct wall and inter-assembly gap make up ∼5–15% of the volume of a typical fast reactor core and these components have a profound impact on the system neutron economy. In this paper, a methodology for the design of optimum hexagonal fuel assembly geometries was developed. For each nuclear reactor core made up of ducted assemblies there exists a unique optimum solution of duct wall thickness and inter-assembly gap, where these components have the minimum impact on the core neutron balance while adhering to applicable structural constraints. The assembly duct wall must maintain its structural integrity and intended function while being exposed to a harsh environment of pressure, temperature and neutron fluence causing elastic and inelastic deflections and swelling. Analytical expressions, applicable to any internally pressurized hexagonal structure, were defined for the peak stress and elastic wall deflection. Detailed analysis of fuel assembly duct designs requires finite element code analysis, radial bowing analysis codes and the full temperature, flux and stress distribution over the lifetime of the assembly in the core to accurately estimate creep deformation. The simple analytical methodology presented in this paper can provide a good initial guess for an optimal geometry to be iteratively improved and refined using more advanced codes and methods.

A STATCOM with Supercapacitors for Low-Voltage Ride-Through in Fixed-Speed Wind Turbines

Fixed-speed wind generator (FSWG) technology has an important presence in countries where wind energy started to be developed more than a decade ago. This type of technology cannot be directly adapted to the grid codes, for example those requirements related to the immunity level under voltage dips. That behavior is typically referred as low-voltage ride through (LVRT), and it usually implies certain reactive and active power injection requirements, both during a voltage dip and during the voltage recovery. In this context, a review is presented of the LVRT exigencies present in some of the countries with the most advanced grid codes (Denmark, Germany, Spain and the United Kingdom). In this paper, the capabilities of STATCOM-based devices for fulfilling the LVRT requirements in FSWGs are analyzed. For this purpose, two technologies are considered: a STATCOM with a supercapacitor, which improves its energy storage features; and a STATCOM with a supercapacitor and a DC-DC converter, to achieve higher discharge levels.

A Preliminary study on the seismic conceptual design

The seismic conceptual design is an essential part of seismic design codes. It points out that the term “seismic conceptual design” should imply three aspects, i.e., the given concept itself, the specific provisions related to the given concept and the designing following the provisions. Seismic conceptual design can be classified into two categories: the strict or traditional seismic conceptual design and the generalized seismic conceptual design. The authors are trying to define for both conceptual designs their connotations and study their characteristics, in particular, the differences between them. Authors emphasize that both conceptual designs sound very close, however, their differences are apparent. The strict conceptual designs are usually worked out directly from engineering practice and/or lessons learnt from earthquake damage, while the generalized conceptual designs are resulted in a series of visions aiming to realize the general objectives of the seismic codes. The strict conceptual designs, (traditional conceptual designs) are indispensable elements of seismic codes in assuring designed structures safer and the generalized conceptual designs are playing key roles in directing to a more advanced and effective seismic codes.

Optimized parallel decoding of difference set codes for high speed memories

The interest in using advanced Error Correction Codes (ECCs) to protect memories and caches is growing. This is because as process technology downscales, errors are more frequent and also tend to affect multiple bits. For SRAM memories and caches, latency is a limiting factor and ECCs have to provide low decoding times that can in most cases be only achieved with the use of a parallel decoder. One important issue with parallel decoders is that they typically require large circuit area to be implemented. One type of ECCs that has been explored for memory protection is Difference Set (DS) codes. In this research note, an optimized parallel decoding scheme for DS codes is presented and evaluated. The results show that the circuit area and the decoding delay are reduced compared to a traditional implementation. In addition, the new scheme enables a reduction in the number of parity check bits thus reducing the memory size.

Prediction of the pull-out strength of chemical anchors in natural stone

The applicability of some numerical models for the prediction of the failure mechanism and of the bearing capacity of post-installed threaded rods chemically anchored in basalt, sandstone and limestone is investigated, as well as the reliability of theoretical formulations conceived for concrete. The numerical predictions, performed by means of engineering structural analysis software and advanced numerical codes, are compared with the results of an experimental research related to chemical anchors in natural stone. The minimum embedment depth for such fastening system is identified.

Wind turbine rotor blade monitoring using digital image correlation: a comparison to aeroelastic simulations of a multi-megawatt wind turbine

Optical full-field measurement methods such as Digital Image Correlation (DIC) provide a new opportunity for measuring deformations and vibrations with high spatial and temporal resolution. However, application to full-scale wind turbines is not trivial. Elaborate preparation of the experiment is vital and sophisticated post processing of the DIC results essential. In the present study, a rotor blade of a 3.2 MW wind turbine is equipped with a random black-and-white dot pattern at four different radial positions. Two cameras are located in front of the wind turbine and the response of the rotor blade is monitored using DIC for different turbine operations. In addition, a Light Detection and Ranging (LiDAR) system is used in order to measure the wind conditions. Wind fields are created based on the LiDAR measurements and used to perform aeroelastic simulations of the wind turbine by means of advanced multibody codes. The results from the optical DIC system appear plausible when checked against common and expected results. In addition, the comparison of relative out-ofplane blade deflections shows good agreement between DIC results and aeroelastic simulations.

An experimental study on local fuel–coolant interactions by delivering water into a simulated molten fuel pool

Analyses of severe accidents for sodium-cooled fast reactors have indicated that there is the possibility that the accident could proceed into a transition phase where a large whole-core-scale pool containing sufficient fuel to exceed prompt criticality by fuel compaction might be formed. Local fuel–coolant interaction (FCI) in the pool is regarded as one of the probable initiators that could lead to such compactive fluid motions. To clarify the mechanisms underlying this interaction, in this study a series of experiments was conducted by delivering a given quantity of water into a simulated molten fuel pool (formed with a low-melting-point alloy). Based on the experimental data obtained from a variety of conditions, interaction characteristics including the pressure-buildup as well as resultant mechanical energy release and its conversion efficiency, is checked and compared. From the analyses, it is confirmed that under our experimental conditions the water volume, melt temperature and water release position are observable to have remarkable impact on the interaction, while the role of water subcooling seems to be less prominent. The analyses also suggest that the pressurization and resultant mechanical energy release during local FCIs should be intrinsically limited, due to an observed suppressing role caused by the increasing of coolant volume entrapped within the pool as well as the transition of boiling mode. The evidence and fundamental data from this work will be utilized for future analyses and improved verifications of computer models developed in advanced fast reactor safety analysis codes.

Terahertz Vibrations and Hydrogen-Bonded Networks in Crystals

The development of terahertz technology in the last few decades has made it possible to obtain a clear terahertz (THz) spectrum. THz vibrations clearly show the formation of weak bonds in crystals. The simultaneous progress in the code of first-principles calculations treating noncovalent interactions has established the position of THz spectroscopy as a powerful tool for detecting the weak bonding in crystals. In this review, we are going to introduce, briefly, the contribution of weak bonds in the construction of molecular crystals first, and then, we will review THz spectroscopy as a powerful tool for detecting the formation of weak bonds and will show the significant contribution of advanced computational codes in treating noncovalent interactions. From the second section, following the Introduction, to the seventh section, before the conclusions, we describe: (1) the crystal packing forces, the hydrogen-bonded networks and their contribution to the construction of organic crystals; (2) the THz vibrations observed in hydrogen-bonded molecules; (3) the computational methods for analyzing the THz vibrations of hydrogen-bonded molecules; (4) the dispersion correction and anharmonicity incorporated into the first-principles calculations and their effect on the peak assignment of the THz spectrum (5) the temperature dependence; and (6) the polarization dependence of the THz spectrum.

ADAMANT: A surface and volume integral-equation solver for the analysis and design of helicon plasma sources

We present a full-wave numerical tool, dubbed ADAMANT (Advanced coDe for Anisotropic Media and ANTennas), devised for the analysis and design of radiofrequency antennas which drive the discharge in helicon plasma sources. ADAMANT relies on a set of coupled surface and volume integral equations in which the unknowns are the surface electric current density on the antenna conductors and the volume polarization current within the plasma. The latter can be inhomogeneous and anisotropic whereas the antenna can have arbitrary shape. The set of integral equations is solved numerically through the Method of Moments with sub-sectional surface and volume vector basis functions. This approach allows the accurate evaluation of the current distribution on the antenna and in the plasma as well as the antenna input impedance, a parameter crucial for the design of the feeding and matching network. We report several numerical examples which serve to validate ADAMANT against other well-established numerical approaches as well as experimental data. The numerical accuracy of the computed solution versus the number of basis functions in the plasma is also assessed. Finally, we employ ADAMANT to characterize the antenna of a real-life helicon plasma source.

Fully Coupled Three-Dimensional Dynamic Response of a Tension-Leg Platform Floating Wind Turbine in Waves and Wind

A dynamic model for a tension-leg platform (TLP) floating offshore wind turbine is proposed. The model includes three-dimensional wind and wave loads and the associated structural response. The total system is formulated using 17 degrees of freedom (DOF), 6 for the platform motions and 11 for the wind turbine. Three-dimensional hydrodynamic loads have been formulated using a frequency- and direction-dependent spectrum. While wave loads are computed from the wave kinematics using Morison's equation, the aerodynamic loads are modeled by means of unsteady blade-element-momentum (BEM) theory, including Glauert correction for high values of the axial induction factor, dynamic stall, dynamic wake, and dynamic yaw. The aerodynamic model takes into account the wind shear and turbulence effects. For a representative geographical location, platform responses are obtained for a set of wind and wave climatic conditions. The platform responses show an influence from the aerodynamic loads, most clearly through quasi-steady mean surge and pitch responses associated with the mean wind. Further, the aerodynamic loads show an influence from the platform motion through a fluctuating rotor load contribution, which is a consequence of the wave-induced rotor dynamics. Loads and coupled responses are predicted for a set of load cases with different wave headings. Further, an advanced aero-elastic code, Flex5, is extended for the TLP wind turbine configuration and the response comparison with the simpler model shows a generally good agreement, except for the yaw motion. This deviation is found to be a result of the missing lateral tower flexibility in the simpler model.

A system-level FPGA design methodology for video applications with weakly-programmable hardware components

High-performance video applications with real-time requirements play an important role in diverse application fields and are often executed by advanced parallel processors or GPUs. For embedded scenarios with strict energy constraints such as automotive image processing, FPGAs represent a feasible power-efficient computer platform. Unfortunately, their hardware-driven design concept results in long development cycles and impedes their acceptance in industrial practice. Additionally, the verification of the FPGA's correctness and its performance figures are unavailable until a very late development stage, which is critical during design space exploration and the integration in complex embedded systems. Weakly-programmable architectures, supporting design and run-time reuse via flexible hardware components, represent a promising and efficient FPGA development approach. However, they currently lack suitable design and verification methodologies for real-time scenarios. Therefore, this paper proposes a system-level FPGA development concept for video applications with weakly-programmable hardware components. It combines rapid software prototyping with component-based FPGA design and advanced formal real-time analysis and code generation techniques. The presented approach enables an early verification of the application's correctness, including exact performance figures. It provides a software-level verification of weakly-programmable hardware components and an automated assembly of the final hardware design. The developed tools and their usability are demonstrated by a binarization and a dense block matching application, which represents a basic preprocessing step in automotive image processing for driver assistance systems. When compared to a hand-optimized variant, the generated hardware design achieves comparable performance and chip area figures without requiring significant hardware integration effort.

Investigation of the Aerodynamic Analysis of Super Long–Span Bridges by Using ERA-Based Reduced-Order Models

AbstractReduced-order models (ROM) are computationally efficient techniques, which have been used widely for predicting unsteady aerodynamic response of airfoils and wings. However, they have not been applied extensively to perform unsteady fluid dynamic analysis of super long–span bridges. This paper discusses the application of a reduced-order computational fluid dynamics (CFD) model based on the eigensystem realization algorithm (ERA) in the aerodynamic analysis of three well-studied long-span bridges. The aerodynamic impulse responses of the Great Belt Bridge (GBB) and Stonecutters and Messina Strait Bridges were used to construct the aerodynamic ROM, and then the aerodynamic forces due to arbitrary inputs and their corresponding flutter derivatives were evaluated and compared to those of the model coupled with an advanced CFD code. Results demonstrate reasonable prediction power and high computational efficiency of the technique that can serve for preliminary design, optimization, and control purpose...

The Interface Region Imaging Spectrograph (IRIS)

The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s temporal resolution and 1 km/s velocity resolution over a field-of-view of up to 175 arcsec x 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332-1358, 1389-1407 and 2783-2834 Angstrom including bright spectral lines formed in the chromosphere (Mg II h 2803 Angstrom and Mg II k 2796 Angstrom) and transition region (C II 1334/1335 Angstrom and Si IV 1394/1403 Angstrom). Slit-jaw images in four different passbands (C II 1330, Si IV 1400, Mg II k 2796 and Mg II wing 2830 Angstrom) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec x 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation.

Phenomena identification and ranking table for thermal-hydraulic phenomena during a small-break LOCA with loss of high pressure injection

Currently Appendix K of 10 CFR 50 is used in the United States to evaluate models for the emergency cooling systems of light-water reactors. To assure that these models are accurate enough to ensure that the cooling systems are satisfactory, code scalability, applicability and uncertainty methodologies are used to evaluate the uncertainty in system analysis code predictions due to the various models. One cornerstone of this methodology is the development of the Phenomenon Identification and Ranking Table (PIRT), which summarizes the thermal-hydraulic phenomenon associate with a particular accident scenario and ranks their importance in determining the effectiveness of core cooling and the parts of the accident for which the phenomenon may be important. In this paper the PIRT developed by the Institute for Nuclear Safety Systems for a small-break LOCA with loss of high-pressure emergency coolant injection is analyzed in detail and several modifications are proposed based on a mechanistic understanding of the phenomenon involved. The resulting PIRT should provide a more accurate guide for model evaluation and development in advanced thermal-hydraulic system analysis codes.

Theoretical Approaches to Structure and Spectroscopy of Earth Materials

The characterization of complex materials in terms of their structure, electronic, magnetic, vibrational, thermodynamic or other physical and chemical properties is often a challenging task that requires the combination of a number of complementary techniques. Experimental approaches such as diffraction or spectroscopic methods usually provide fingerprint information about the material under investigation. The interpretation of measured data is either done by reference to analogue materials or by constructing a theoretical (e.g., structural) model that fits the experimental data. For the latter, computational methods have become very powerful in recent years. For example, Rietveld refinement of powder diffraction data or curve fitting of various spectra is now done on a routine basis. The continuous improvement in hardware performance resulting in a huge and progressive increase of computing power by a factor of ~1000 per decade, as well as advanced algorithms and codes provide the basis for predictive modeling of material properties ab initio , i.e., from first principles using quantum chemical methods such as density functional theory (DFT). DFT enthalpy predictions for the major lower mantle minerals, MgSiO3 perovskite and post-perovskite, periclase (MgO) and CaSiO3 perovskite at zero temperature, over the relevant pressure range from the transition zone to the core-mantle boundary can be made in a few hours on an office PC. Free energy calculations for these phases at finite temperatures using lattice vibrational modes in the (quasi-)harmonic approximation require at most a couple of days. More realistic compositions of these mantle minerals with Fe substituting some of the Mg atoms in a solid solution are computationally more demanding but have also become accessible. The same is true for structural investigations of disordered phases, such as glasses, melts and fluids. Both first-principles and classical molecular dynamics simulations are useful methods for a statistically significant sampling of disordered structures. …

Medical application of innovative nuclear-physical technologies

Heart and cancer-related diseases are considered to be one of the biggest problems of today’s health world. Therefore, it is important to perform fundamental research of human tissues and external biological influence on these tissues, as well as develop and implement new innovative instruments of applied physics for diagnosis and treatment of heart and cancer diseases. This paper presents overview of modern technical methods based on using ionizing radiation for medical purposes. In particular, new effective instruments of nuclear and high energy physics are considered in context of their implementation for the diagnosis and cancer treatment. Physical principles and main characteristics of PET imagining are discussed, as well as examples of successful implementation of protons (heavy ions) for the treatment are presented. A detailed overview of new advanced detector technologies and codes for modeling the processes of penetration of radiation with the matter is given. Perspective ideas of new nuclear instrumental technologies and methods are discussed. The problem of interconnection of fundamental research and bio-medical field is discusses, considering this as one of the obligatory conditions for successful implementation of new research instruments for advanced medical diagnosis technologies and treatment.

CORONIUM IN THE LABORATORY: MEASURING THE Fe XIV GREEN CORONAL LINE BY LASER SPECTROSCOPY

The green coronal line at 530.3 nm was first observed during the total solar eclipse of 1869. Once identified as emitted by Fe XIV, it became clear that this highly charged ion was typical for the range of temperatures found in coronal plasmas, stellar winds, outflows, and accretion disks. Under these conditions of high ionization, the strongest transitions are in the X-ray, extreme ultraviolet, and ultraviolet wavelength range, with only few optical lines. For these so-called forbidden coronal lines, only scarce laboratory data is available, and even advanced atomic theory codes cannot yet predict their wavelengths with the accuracy required for precise absolute velocity determinations of such plasmas. Here we report on a study of the Fe XIV line, a key coronal transition of a highly charged ion, using laser spectroscopy in an electron beam ion trap, obtaining the first laboratory measurement of 530.2801(4) nm for its rest wavelength. The result enables the determination of absolute line shifts and line broadenings in hot turbulent plasmas and astrophysical environments, with an error bar of only 0.24 km s–1. In addition, our measurement provides a much-needed benchmark for advanced atomic structure calculations, which are fundamental for astronomy.

Adaptive Rate Control for Multi-Antenna Multicast in OFDM Systems

We propose two rate control schemes for multi-antenna multicast in OFDM systems, which aim to maximize the minimum average rate over all users in a multicast group. In our system, we do not require all multicast users to successfully recover the signals received on each subcarrier. In contrast, we allow certain loss for multicast users, such that the multicast transmission rate can be increased. We assume that the loss-repairing can be completed at upper protocol layers via advanced fountain codes. Following this principle, we formulate the rate control problem via beamforming in multi-antenna multicast to optimize the minimum achievable rate for all multicast users. While the computation complexity to solve for the optimal beamformer is prohibitively high, we propose a suboptimal iterative rate control scheme. Moreover, we modify the above optimization problem by selecting a ?xed proportion of users on each subcarrier. The beamformer searching process will then be performed only based on the selected users on each subcarrier, such that the complexity can be further reduced. We also solve this new problem with a low complexity approach. Theoretical analyses and simulation results show that our proposed two rate control schemes can have higher minimum average rate than the baseline scheme without rate control, while achieving low complexity.

Factors Influencing Physician Determination of Code Status in the Emergency Department

Emergency physicians frequently manage critically ill patients and are expected to determine code status, advanced directives and the level of care expected by patients and families accurately and efficiently. Research has shown that advanced directives and code status do alter treatment decisions in the emergency department (ED), but many emergency physicians do not feel comfortable having this discussion despite research showing no resistance from patients or their families. This may indicate that systemic and educational factors influence an emergency physicians comfort level and ability to determine code status in the ED. This study aims to identify specific barriers to this process. All 82 emergency physicians employed by a 2-hospital urban academic ED were recruited to complete a survey via email. Eighty-nine percent of physicians surveyed participated, including 36 (86%) attendings and 37 (93%) residents. The survey asked emergency physicians to identify their level of training, sources they routinely check and consider valid in determining a patient's code status, barriers to the process, comfort with the paperwork, and level of formal education about the topic. Responses to each question were computed as a percentage of the total number of participants. Subgroups of attendings and residents were also compared. Results indicate that there are significant barriers to efficiently determining code status in the ED. The majority of participants review nursing home notes (99%), contact the health care proxy (93%) or contact the next of kin (78%), but five other sources were also routinely utilized by at least a quarter of participants. Only a legal “Do Not Resuscitate” (DNR) document and speaking with an official health care proxy were considered valid by more than 75% of participants. Twenty-nine percent of participants did not feel comfortable accessing the proper paperwork to make a patient DNR, and only 47% were familiar with the name of the official document for placing these orders in the state where they practice (“MOLST”). Tellingly, only 39% of emergency physicians have received formal didactics on this subject, and 69% have mistakenly intubated and resuscitated a patient they later found to be DNR. Despite no significant difference between residents and attendings who reported receiving formal training about advanced directives (p=0.8092), residents were significantly more likely than attendings to report not being comfortable with proper documentation of code status (p=0.0002) and to cite lack of training as a problem with both in person (p=0.0281) and phone assessment (p =0.0095) of code status. Determining a patient's advanced directives or code status in the ED is a critical task for emergency physicians. The results of this study revealed that emergency physicians are routinely checking multiple sources to determine a patient's code status; however, there is a lack of agreement as to which of these sources is considered valid. Despite consulting multiple sources, many emergency physicians still report resuscitating a patient who had been previously declared DNR. Resident emergency physicians reported lower comfort levels and were more likely to identify lack of formal education as a barrier as compared to attending emergency physicians despite no significant difference between the groups in reported training. Although experience may compensate for lack of training, the results of this study suggest that there could be a role for residency education on this topic.

Evaluation of debris bed self-leveling behavior: A simple empirical approach and its validations

During a hypothetical core-disruptive accident (CDA) in a sodium-cooled fast reactor (SFR), degraded core materials can form roughly conically-shaped debris beds over the core-support structure and/or in the lower inlet plenum of the reactor vessel from rapid quenching and fragmentation of core material pool. However, coolant boiling may lead ultimately to leveling of the debris bed that is crucial to the relocation of molten core and heat-removal capability of debris bed. To clarify the mechanisms underlying this self-leveling behavior, several series of experiments were elaborately designed and conducted in recent years under the collaboration between Japan Atomic Energy Agency (JAEA) and Kyushu University (Japan). Based on the experimental observations and quantitative data obtained (mainly the time variation of bed inclination angle), a simple empirical approach to predict the self-leveling development depending on particle size, particle density and gas velocity was proposed. To confirm the rationality and wide applicability of this approach, over the past few years extensive efforts have been made by performing modeling investigations against a large number of experimental data covering various conditions, including difference in bubbling mode, bed geometry and range of experimental parameters. The present contribution synthesizes these efforts and gives detailed comparative analyses of the performed validations, thus, providing some insight for a better understanding of CDAs and improved verifications of computer models developed in advanced fast reactor safety analysis codes.