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All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

FY19 Report for Instrumentation Development for the Transient Testing Program

This report details the technical activities and accomplishment carried out under funding from the Department of Energy (DOE) Nuclear Technology Research and Development (NTRD) program for in-pile instrumentation supporting the transient testing program in FY19. These activities were performed in support of cross-cutting transient testing experiment objectives. The purpose of this report is to provide a summary of key technical work, of particular interest to nuclear irradiation test experimenters and in-pile instrumentation engineers. During FY19, development activities are focused on deployment of devices to perform online measurement of neutron flux, temperature, and mechanical behaviors in nuclear fuels experiments. Specifically, these R&D activities include in-pile investigations at the Transient Reactor Test (TREAT) facility throughout the year. Other in-pile instrumentation R&D activities are being carried out under other DOE programs, which may be recognized but not the focus of this document. A brief summary of activities and accomplishments is first provided for each major activity. More detailed summaries are presented in appendices.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

A decam search for an optical counterpart to the LIGO gravitational-wave event GW151226

We report the results of a Dark Energy Camera optical follow-up of the gravitational-wave (GW) event GW151226, discovered by the Advanced Laser Interferometer Gravitational-wave Observatory detectors. Our observations cover 28.8 deg{sup 2} of the localization region in the i and z bands (containing 3% of the BAYESTAR localization probability), starting 10 hr after the event was announced and spanning four epochs at 2–24 days after the GW detection. We achieve 5σ point-source limiting magnitudes of i≈21.7 and z≈21.5, with a scatter of 0.4 mag, in our difference images. Given the two-day delay, we search this area for a rapidly declining optical counterpart with ≳3σ significance steady decline between the first and final observations. We recover four sources that pass our selection criteria, of which three are cataloged active galactic nuclei. The fourth source is offset by 5.8 arcsec from the center of a galaxy at a distance of 187 Mpc, exhibits a rapid decline by 0.5 mag over 4 days, and has a red color of i−z≈0.3 mag. These properties could satisfy a set of cuts designed to identify kilonovae. However, this source was detected several times, starting 94 days prior to GW151226, in the Pan-STARRS Survey for Transients (dubbed as PS15cdi) and is therefore unrelated to the GW event. Given its long-term behavior, PS15cdi is likely a Type IIP supernova that transitioned out of its plateau phase during our observations, mimicking a kilonova-like behavior. We comment on the implications of this detection for contamination in future optical follow-up observations.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Solution algorithms for nonlinear transient heat conduction analysis employing element-by-element iterative strategies

The particular problems investigated in the present study arise from nonlinear transient heat conduction. One of two types of nonlinearities considered is related to a material temperature dependence which is frequently needed to accurately model behavior over the range of temperature of engineering interest. The second nonlinearity is introduced by radiation boundary conditions. The finite element equations arising from the solution of nonlinear transient heat conduction problems are formulated. The finite element matrix equations are temporally discretized, and a nonlinear iterative solution algorithm is proposed. Algorithms for solving the linear problem are discussed, taking into account the form of the matrix equations, Gaussian elimination, cost, and iterative techniques. Attention is also given to approximate factorization, implementational aspects, and numerical results.

Winget, J. M.↗
DOE OSTI2019

A novel liquid-mediated nucleation mechanism for explosive crystallization in amorphous germanium

We report a novel mechanism for explosive crystallization in amorphous germanium (a-Ge), which operates through liquid-mediated nucleation occurring under extreme thermal gradient conditions. The crystallization kinetics of sputter-deposited films with thicknesses ranging from 30 to 150 nm were characterized using in situ movie-mode dynamic transmission electron microscopy (MM-DTEM). After localized heating from a short laser pulse, explosive liquid phase nucleation (LPN) was observed to occur during the early stage (<2 μs) of crystallization in the thicker (>50 nm) films deposited on silicon nitride substrates. The crystallization front propagated at ~12–15 m/s and produced nanocrystalline microstructure with ~50 nm grains. A mechanism involving the existence of a relatively thick (>100 nm) transient liquid layer and a high nucleation rate is proposed to explain the behavior. In conclusion, the key thermodynamic and kinetic features as well as the feasibility of the mechanism are further explored by employing parametric and systematic phase-field modeling and simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Transient nature of fast relaxation in metallic glass

Metallic glasses exhibit fast mechanical relaxations at temperatures well below the glass transition, one of which shows little variation with temperature known as nearly constant loss (NCL). Despite the important implications of this phenomenon to deformation, the origin of the relaxation is unclear. Through molecular dynamics simulations of a model metallic glass, Cu 64.5 Zr 35.5 , we implement molecular dynamics dynamical mechanical spectroscopy (MD-DMS) with system stress decomposed into atomic-level stresses to identify the group of atoms responsible for NCL. This work demonstrates that NCL relaxation is due to transient groups of atoms that revert to the typical atomic-level viscoelastic behavior over picosecond timescales. They are homogenously distributed throughout the glass and have no outstanding features, rather than having defect-like local structure as previously reported.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Kilovoltage Intrafraction Monitoring for Prostate Intensity Modulated Arc Therapy: First Clinical Results

Purpose: Most linear accelerators purchased today are equipped with a gantry-mounted kilovoltage X-ray imager which is typically used for patient imaging prior to therapy. A novel application of the X-ray system is kilovoltage intrafraction monitoring (KIM), in which the 3-dimensional (3D) tumor position is determined during treatment. In this paper, we report on the first use of KIM in a prospective clinical study of prostate cancer patients undergoing intensity modulated arc therapy (IMAT). Methods and Materials: Ten prostate cancer patients with implanted fiducial markers undergoing conventionally fractionated IMAT (RapidArc) were enrolled in an ethics-approved study of KIM. KIM involves acquiring kV images as the gantry rotates around the patient during treatment. Post-treatment, markers in these images were segmented to obtain 2D positions. From the 2D positions, a maximum likelihood estimation of a probability density function was used to obtain 3D prostate trajectories. The trajectories were analyzed to determine the motion type and the percentage of time the prostate was displaced {>=}3, 5, 7, and 10 mm. Independent verification of KIM positional accuracy was performed using kV/MV triangulation. Results: KIM was performed for 268 fractions. Various prostate trajectories were observed (ie, continuous target drift, transient excursion, stable target position, persistent excursion, high-frequency excursions, and erratic behavior). For all patients, 3D displacements of {>=}3, 5, 7, and 10 mm were observed 5.6%, 2.2%, 0.7% and 0.4% of the time, respectively. The average systematic accuracy of KIM was measured at 0.46 mm. Conclusions: KIM for prostate IMAT was successfully implemented clinically for the first time. Key advantages of this method are (1) submillimeter accuracy, (2) widespread applicability, and (3) a low barrier to clinical implementation. A disadvantage is that KIM delivers additional imaging dose to the patient.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Proton-Coupled Electron Transfer in a Ruthenium(II) Bipyrimidine Complex in Its Ground and Excited Electronic States

In this work, proton-coupled electron transfer (PCET) was studied for the ground and excited electronic states of a [Ru(terpy)(bpm)(OH 2 )(PF 6 ) 2 ] complex, Ru-bpm. Cyclic voltammetry measurements show that the Ru(II)-aqua moiety undergoes PCET to form a Ru(IV)-oxo moiety in the anodic region, while the bpm ligand undergoes PCET to form bpmH 2 in the cathodic region. The photophysical behavior of Ru-bpm was studied using steady-state and femtosecond transient UV–vis absorption spectroscopy, coupled with density functional theory (DFT) calculations. The lowest-lying excited state of Ru-bpm is described as a (Ru → bpm) metal-to-ligand charge-transfer (MLCT) state, while the metal-centered (MC) excited state was found computationally to be close in energy to the lowest-energy bright MLCT state (MC state was 0.16 eV above the MLCT state). The excited-state kinetics of Ru-bpm were found via transient absorption spectroscopy to be short-lived and were fit well to a biexponential function with lifetimes $τ_1$ = 4 ps and $τ_2$ = 65 ps in aqueous solution. Kinetic isotope effects of 1.75 ($τ_1$) and 1.61 ($τ_2$) were observed for both decay components, indicating that the solvent plays an important role in the excited-state dynamics of Ru-bpm. Based on the pH-dependent studies and the results from prior studies of similar Ru-complexes, we hypothesize that the 3 MLCT state forms an excited-state hydrogen-bond adduct with the solvent molecules and that this process occurs with a 4 ps lifetime. The formation of such a hydrogen-bond complex is consistent with the electronic density accumulation at the peripheral N atoms of the bpm moiety in the 3 MLCT state. The hydrogen-bonded state 3 MLCT decays to the ground state with a 65 ps lifetime. Such a short lifetime is likely associated with the efficient vibrational energy transfer from the 3 MLCT state to the solvent.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

The Role of the Solvent in the Condensed-Phase Dynamics and Identity of Chemical Bonds: The Case of the Sodium Dimer Cation in THF

When a solute molecule is placed in solution, is it acceptable to presume that its electronic structure is essentially the same as in the gas phase? In this paper, we address this question from a simulation perspective for the case of the sodium dimer cation (Na 2 + ) molecule in both liquid Ar and liquid tetrahydrofuran (THF). In previous work, we showed that when local specific interactions between a solute and solvent are energetically on the order of a hydrogen bond, the solvent can become part of the chemical identity of the solute. Here, using mixed quantum/classical molecular dynamics simulations, we see that for the Na 2 + molecule, solute--solvent interactions lead to two stable, chemically-distinct coordination states (Na(THF) 4 -Na(THF) 5 + and Na(THF) 5 -Na(THF) 5 + ) that are not only stable themselves as gas-phase molecules but that also have a completely new electronic structure with important implications for the excited-state photodissociation of this molecule in the condensed phase. Furthermore, we show through a set of comparative classical simulations that treating the solute's bonding electron explicitly quantum mechanically is necessary to understand both the ground-state dynamics and chemical identity of this simple diatomic molecule; even use of the quantum-derived potential of mean force is insufficient to describe the behavior of the molecule classically. Lastly, we calculate the results of a proposed transient hole-burning experiment that could be used to spectroscopically disentangle the presence of the different coordination states.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Differential Microscopic Mobility of Components within a Deep Eutectic Solvent

From macroscopic measurements of deep eutectic solvents such as glyceline (1:2 molar ratio of choline chloride to glycerol), the long-range translational diffusion of the larger cation (choline) is known to be slower compared to that of the smaller hydrogen bond donor (glycerol). However, when the diffusion dynamics are analyzed on the subnanometer length scale, we discover that the displacements associated with the localized diffusive motions are actually larger for choline. This counterintuitive diffusive behavior can be understood as follows. The localized diffusive motions confined in the transient cage of neighbor particles, which precede the cage-breaking long-range diffusion jumps, are more spatially constrained for glycerol than for choline because of the stronger hydrogen bonds the former makes with chloride anions. The implications of differential localized mobility of the constituents should be especially important for applications where deep eutectic solvents are confined on the nanometer length scale and their long-range translational diffusion is strongly inhibited (e.g., within microporous media).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ultrafast Electron Transfer in Au-Cyanobacteria Hybrid for Solar to Chemical Production

The rise of inorganic-biohybrid organisms for solar-to-chemical production has spurred mechanistic investigations into the dynamics of the biotic-abiotic interface to drive the development of next-generation hybrid systems. The model system, cyanobacteria-gold nanoparticle hybrids, combines a light harvester with a photosynthetic bacterium to drive the reduction of CO2 to glycerol with improved efficiency and increased glycerol production by 14.6%, in comparison to cyanobacteria only. In this work, we report insights into this unique photochemical behavior and propose a charge-transfer pathway from Au nanoparticle to cyanobacteria. Transient absorption (TA) spectroscopy revealed that photoexcited electron transfer rates are on the order of a few ps to the potential electron acceptor in photosystem II. This work represents a promising platform to utilize a conventional spectroscopic methodology to extract insights from more complex biotic-abiotic hybrid systems.

charge transfer↗
DOE OSTI2022

Sensitivity of Global Ocean Deoxygenation to Vertical and Isopycnal Mixing in an Ocean Biogeochemistry Model

Large-scale loss of oxygen under global warming is termed “ocean deoxygenation” and is caused by the imbalance between physical supply and biological consumption of oxygen in the ocean interior. Significant progress has been made in the theoretical understanding of ocean deoxygenation; however, many questions remain unresolved. The oxygen change in the tropical thermocline is poorly understood, with diverging projections among different models. Physical oxygen supply is controlled by a suite of processes that transport oxygen-rich surface waters into the interior ocean, which is expected to weaken due to increasing stratification under global warming. Using a numerical model and a series of sensitivity experiments, the role of ocean mixing is examined in terms of effects on the mean state and the response to a transient warming. Both vertical and horizontal (isopycnal) mixing coefficients are systematically varied over a wide range, and the resulting oxygen distributions in equilibrated and transient simulations are examined. The spatial patterns of oxygen loss are sensitive to both vertical and isopycnal mixing, and the sign of tropical oxygen trend under climate warming can reverse depending on the choice of mixing parameters. An elevated level of isopycnal mixing disrupts the vertical advective-diffusive balance of the tropical thermocline, increasing the mean state oxygen as well as the magnitude of the transient oxygen decline. These results provide first-order explanations for the diverging behaviors of simulated tropical oxygen with respect to ocean mixing parameters.

58 GEOSCIENCES↗
DOE OSTI2016

Spectroscopic elucidation of energy transfer in hybrid inorganic–biological organisms for solar-to-chemical production

We present that the rise of inorganic–biological hybrid organisms for solar-to-chemical production has spurred mechanistic investigations into the dynamics of the biotic–abiotic interface to drive the development of next-generation systems. The model system, Moorella thermoacetica–cadmium sulfide (CdS), combines an inorganic semiconductor nanoparticle light harvester with an acetogenic bacterium to drive the photosynthetic reduction of CO 2 to acetic acid with high efficiency. In this work, we report insights into this unique electrotrophic behavior and propose a charge-transfer mechanism from CdS to M. thermoacetica. Transient absorption (TA) spectroscopy revealed that photoexcited electron transfer rates increase with increasing hydrogenase (H 2 ase) enzyme activity. On the same time scale as the TA spectroscopy, time-resolved infrared (TRIR) spectroscopy showed spectral changes in the 1,700–1,900-cm -1 spectral region. The quantum efficiency of this system for photosynthetic acetic acid generation also increased with increasing H 2 ase activity and shorter carrier lifetimes when averaged over the first 24 h of photosynthesis. However, within the initial 3 h of photosynthesis, the rate followed an opposite trend: The bacteria with the lowest H 2 ase activity photosynthesized acetic acid the fastest. These results suggest a two-pathway mechanism: a high quantum efficiency charge-transfer pathway to H 2 ase generating H 2 as a molecular intermediate that dominates at long time scales (24 h), and a direct energy-transducing enzymatic pathway responsible for acetic acid production at short time scales (3 h). Lastly, this work represents a promising platform to utilize conventional spectroscopic methodology to extract insights from more complex biotic–abiotic hybrid systems.

14 SOLAR ENERGY↗
DOE OSTI2024

Development of Whole System Digital Twins for Advanced Reactors: Leveraging Graph Neural Networks and SAM Simulations

Here, in this work, we introduce a novel method to develop whole system digital twins (DTs) for advanced nuclear reactors. This method treats a complex reactor system as a heterogeneous graph: with the system components as different types of graph nodes and their physical interconnections as edges. Based on the heterogeneous graph, a graph neural network combining graph convolution and temporal node attention is developed as the DT, facilitating a comprehensive understanding of the system's dynamic behavior. By utilizing the System Analysis Module (SAM) code for simulating various operational transients, we develop a graph-based database that trains the DT. This DT is characterized by two primary functions: It can infer the entire system's status using sparse node information, and it can predict the progress of transients based on current and historical system information. Our approach is validated through case studies on the Experimental Breeder Reactor II (EBR-II) system and a generic Fluoride-salt-cooled High-temperature Reactor (gFHR), demonstrating the DT's accuracy in forecasting operational transients. The DT's rapid computation capabilities enhance its potential for supporting advanced reactor operations, offering benefits in intelligent simulation, autonomous control, and anomaly detection, paving the way for improved safety analysis and intelligent component health management for advanced reactor systems and reducing their operations and maintenance cost.

EBR-II↗
DOE OSTI2015

Environmental, Transient, Three-Dimensional, Hydrothermal, Mass Transport Code - FLESCOT

The purpose of the project was to modify and apply the transient, three-dimensional FLESCOT code to be able to effectively simulate cesium behavior in Fukushima lakes/dam reservoirs, river mouths, and coastal areas. The ultimate objective of the FLESCOT simulation is to predict future changes of cesium accumulation in Fukushima area reservoirs and costal water. These evaluation results will assist ongoing and future environmental remediation activities and policies in a systematic and comprehensive manner.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Kinematics of Parsec-scale Jets of Gamma-Ray Blazars at 43 GHz within the VLBA-BU-BLAZAR Program

We analyze the parsec-scale jet kinematics from 2007 June to 2013 January of a sample of γ-ray bright blazars monitored roughly monthly with the Very Long Baseline Array at 43 GHz. In a total of 1929 images, we measure apparent speeds of 252 emission knots in 21 quasars, 12 BL Lacertae objects (BLLacs), and 3 radio galaxies, ranging from 0.02c to 78c; 21% of the knots are quasi-stationary. Approximately one-third of the moving knots execute non-ballistic motions, with the quasars exhibiting acceleration along the jet within 5 pc (projected) of the core, and knots in BLLacs tending to decelerate near the core. Using the apparent speeds of the components and the timescales of variability from their light curves, we derive the physical parameters of 120 superluminal knots, including variability Doppler factors, Lorentz factors, and viewing angles. We estimate the half-opening angle of each jet based on the projected opening angle and scatter of intrinsic viewing angles of knots. We determine characteristic values of the physical parameters for each jet and active galactic nucleus class based on the range of values obtained for individual features. We calculate the intrinsic brightness temperatures of the cores, T{sub b,int}{sup core}, at all epochs, finding that the radio galaxies usually maintain equipartition conditions in the cores, while ∼30% of T{sub b,int}{sup core} measurements in the quasars and BLLacs deviate from equipartition values by a factor >10. This probably occurs during transient events connected with active states. In the Appendix, we briefly describe the behavior of each blazar during the period analyzed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

Report on the ASCR Workshop on Modeling and Simulation of Exascale Systems and Applications

In the last few years, numerous studies commissioned by the Department of Energy (DOE), the Defense Advanced Research Projects Agency (DARPA), and others have examined the challenges that will have to be overcome for computational science to achieve exascale, a two order-of-magnitude increase in capability beyond what is possible today. Exponential growth in the number of devices (Moore’s Law) is expected to continue unabated, but the end of Dennard scaling, and hence the growth in performance of individual processors, has led to exponential growth in concurrency. Power consumption has also grown to the point where the cost of the electrical power for systems threatens to exceed the cost of acquiring them. Ever-shrinking devices, and the growth in their number, are expected to increase the rate of soft, or transient, errors such that applications will no longer be able to assume correct behavior of the underlying machine. Adapting to such systems will require new mathematical algorithms that minimize synchronization and data movement, and a new generation of scientific software. Rather than addressing these issues in isolation, a new process of “Co-Design” is being pursued in which application and computer scientists work toward the common goal of an exascale ecosystem of systems and applications. Modeling and simulation (ModSim) is a critical part of this process. It enables scientists and engineers to analyze future algorithms, applications, and computing systems, long before they are realized, and make the necessary design decisions such that exascale science is broadly achieved. Later, when exascale applications and systems are realized, ModSim technology will enable us to understand their behavior, debugging and optimizing them. Given the increasing importance of modeling and simulation, a workshop was organized by DOE/ASCR to assess the current state of the art and to identify research challenges that must be overcome in this field. Fifty experts, representing academia, industry, and government, participated in the workshop, and others contributed both beforehand and afterwards. This report summarizes their findings.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2017

Internal Nozzle Flow Simulations of Gasoline-Like Fuels under Diesel Operating Conditions

Spray formation in internal combustion engines with direct injection is strictly correlated with internal nozzle flow characteristics, which are in turn influenced by fuel physical properties and injector needle motion. This paper pre-sents a series of 3D simulations that model the in-nozzle flow in a 5-hole mini-sac diesel injector. Two gasoline-like naphtha fuels, namely full-range and light naphtha, were tested under operating conditions typical of diesel applica-tions and were compared with n-dodecane, selected from a palette used as diesel surrogates. Validated methodolo-gies from our previous work were employed to account for realistic needle motion. The multi-phase nature of the problem was described by the mixture model assumption with the Volume of Fluid method. Cavitation effects were included by means of the Homogeneous Relaxation Model and turbulence closure was achieved with the Standard k-ε model in an Unsteady Reynolds-Averaged Navier-Stokes formulation. The results revealed that injector perfor-mance and propensity to cavitation are influenced by the fuel properties. Analyses of several physical quantities were carried out to highlight the fuel-to-fuel differences in terms of mass flow rate, discharge coefficients, and fuel vapor volume fraction inside the orifices. A series of parametric investigations was also performed to assess the fuel response to varied fuel injection temperature, injection pressure, and cross-sectional orifice area. For all cases, the strict correlation between cavitation magnitude and saturation pressure was confirmed. Owing to their higher volatil-ity, the two gasoline-like fuels were characterized by higher cavitation across all the simulated conditions. Occur-rence of cavitation was mostly found at the needle seat and at the orifice inlets during the injection event’s transient, when very small gaps exist between the needle and its seat. This behavior tended to disappear at maximum needle lift, where cavitation was absent for all fuels. Differences in mass flow rate between the naphtha fuels and n-dodecane were measured and ascribed to the different densities of the three fuels. Nevertheless, they were found to be smaller than expected, owing to the lower viscosity of the gasoline-like fuels. This beneficial influence of the lower viscosity was shown to be less effective at higher temperature, where the relative viscosity differences de-creased.

Torelli, R.↗
DOE OSTI2012

Report on the ASCR Workshop on Modeling and Simulation of Exascale Systems and Applications

In the last few years, numerous studies commissioned by the Department of Energy (DOE), the Defense Advanced Research Projects Agency (DARPA), and others have examined the challenges that will have to be overcome for computational science to achieve exascale, a two order-of-magnitude increase in capability beyond what is possible today. Exponential growth in the number of devices (Moore's Law) is expected to continue unabated, but the end of Dennard scaling, and hence the growth in performance of individual processors, has led to exponential growth in concurrency. Power consumption has also grown to the point where the cost of the electrical power for systems threatens to exceed the cost of acquiring them. Ever-shrinking devices, and the growth in their number, are expected to increase the rate of soft, or transient, errors such that applications will no longer be able to assume correct behavior of the underlying machine. Adapting to such systems will require new mathematical algorithms that minimize synchronization and data movement, and a new generation of scientific software. Rather than addressing these issues in isolation, a new process of "Co-Design" is being pursued in which application and computer scientists work toward the common goal of an exascale ecosystem of systems and applications. Modeling and simulation (ModSim) is a critical part of this process. It enables scientists and engineers to analyze future algorithms, applications, and computing systems, long before they are realized, and make the necessary design decisions such that exascale science is broadly achieved. Later, when exascale applications and systems are realized, ModSim technology will enable us to understand their behavior, debugging and optimizing them. Given the increasing importance of modeling and simulation, a workshop was organized by DOE/ASCR to assess the current state of the art and to identify research challenges that must be overcome in this field. Fifty experts, representing academia, industry, and government, participated in the workshop, and others contributed both beforehand and afterwards. This report summarizes their findings.

97 MATHEMATICS AND COMPUTING↗