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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

UV Shielding of Bacillus pumilus SAFR-032 Endospores by Martian Regolith Simulants

As exploration of the solar system advances with life detection missions on the horizon, the concern for planetary protection has grown considerably. When attempting to detect extraterrestrial life, the likelihood of false positives from terrestrial contamination must be minimized. The Exposing Microorganisms in the Stratosphere (E-MIST) balloon project aims to evaluate whether resilient terrestrial bacteria can survive stressors in a Mars-like environment. This is accomplished by sending Bacillus pumilus SAFR-032, an endospore-forming bacterial isolate from a spacecraft assembly facility, to the Earth's middle stratosphere (30-38 kilometers), where low temperature and pressure and high radiation and dryness conditions are similar to the surface of Mars. Previous ground and flight tests showed that the vast majority of SAFR-032 spores (99.99 percent) were inactivated by direct sunlight due to ultraviolet (UV) radiation. This observation led us to explore the role of dust shielding in changing microbial survivorship outcomes. To determine the dust particle distributions and density for potentially shielding microbes from UV radiation, samples of a Martian dust simulant were mixed with SAFR-032 spores. The dry heat sterilized simulant used was JSC MARS-1, weathered volcanic ash from Hawaii that displays many chemical and physical properties similar to the Martian soil as characterized by the Viking Lander 1, including reflectance spectrum, chemical composition, mineralogy, grain size, specific gravity, and magnetic properties. First, scanning electron microscopy was undertaken to visualize the aggregation of the spores with dust particles (i.e., shading effects), and samples of varying dust concentrations were subsequently irradiated with UVC light to test survivorship outcomes. After a relationship between dust concentration and spore survivorship was determined, a solar simulator capable of irradiating samples with a fuller UV spectrum (less than 280-400 nanometers) was used to perform a more robust middle stratosphere simulation. Taken together, we will use results from the ground-based irradiation studies to feed into experimental designs for the next E-MIST ultra-long duration polar balloon flight launched by NASA.

Stratosphere↗
NASA NTRSDate not supplied

Refractory Carbides for Hydrogen Erosion Resistance in Carbon Tubes for Nuclear Thermal Propulsion

As crewed travel becomes more common to the Moon and beyond, space nuclear propulsion-based craft offer reduced travel times and double the specific impulse compared to conventional chemical rockets. The nuclear core and its integral hydrogen propellant channels will require advanced refractory carbide coatings over a carbon/carbon substrate for hydrogen resistance. Using ab initio and other computational techniques, we studied select (Zr/Ta/Nb)C mixed carbide systems for erosion resistance and hydrogen diffusion using realistic levels of carbon vacancies and experimentally obtainable stoichiometries. Various contributions to the formation and hydrogen erosion free energies were calculated, including configurational, electronic, and vibrational terms. Our calculations indicate that ZrC is less likely to lose carbon than NbC or TaC, providing an explanation for heritage NERVA data on ZrC and NbC mass loss performance. Additionally, binary mixtures show compositions that are more stable than their end-member counterparts. Hydrogen diffusion in stoichiometric ZrC was found to be slightly higher than previously theorized, with the caveat that hydrogen saturation of carbon vacancies will hinder further hydrogen diffusion through the bulk, while hydrogen diffusion in ZrNbC is slightly enhanced over ZrC. And finally, we show that as carbon is depleted, the deformation mechanism of ZrC changes from brittle to ductile. Though many questions still remain as to the bulk performance of these materials, these trends and results are important in terms of materials selection efforts for hydrogen-resistant coatings on carbon/carbon substrates.

William C Tucker↗
NASA NTRSDate not supplied

Refractory Carbides for Hydrogen Erosion Resistance in Carbon Tubes for Nuclear Thermal Propulsion

As crewed travel becomes more common to the Moon and beyond, space nuclear propulsion-based craft offer reduced travel times and double the specific impulse compared to conventional chemical rockets. The nuclear core and its integral hydrogen propellant channels will require advanced refractory carbide coatings over a carbon/carbon substrate for hydrogen resistance. Using \textit{ab initio} and other computational techniques, we studied select (Zr/Ta/Nb)C mixed carbide systems for erosion resistance and hydrogen diffusion using realistic levels of carbon vacancies and experimentally obtainable stoichiometries. Various contributions to the formation and hydrogen erosion free energies were calculated, including configurational, electronic, and vibrational terms. Our calculations indicate that ZrC is less likely to lose carbon than NbC or TaC, providing an explanation for heritage NERVA data on ZrC and NbC mass loss performance. Additionally, binary mixtures show compositions that are more stable than their end-member counterparts. Hydrogen diffusion in stoichiometric ZrC was found to be slightly higher than previously theorized, with the caveat that hydrogen saturation of carbon vacancies will hinder further hydrogen diffusion through the bulk, while hydrogen diffusion in ZrNbC is slightly enhanced over ZrC. And finally, we show that as carbon is depleted, the deformation mechanism of ZrC changes from brittle to ductile. Though many questions still remain as to the bulk performance of these materials, these trends and results are important in terms of materials selection efforts for hydrogen-resistant coatings on carbon/carbon substrates.

William C. Tucker↗
NASA NTRSDate not supplied

Refractory Carbides for Hydrogen Erosion Resistance in Carbon Tubes for Nuclear Thermal Propulsion

As crewed travel becomes more common to the Moon and beyond, space nuclear propulsion-based craft offer reduced travel times and double the specific impulse compared to conventional chemical rockets. The nuclear core and its integral hydrogen propellant channels will require advanced refractory carbide coatings over a carbon/carbon substrate for hydrogen resistance. Using ab initio and other computational techniques, we studied select (Zr/Ta/Nb)C mixed carbide systems for erosion resistance and hydrogen diffusion using realistic levels of carbon vacancies and experimentally obtainable stoichiometries. Various contributions to the formation and hydrogen erosion free energies were calculated, including configurational, electronic, and vibrational terms. Our calculations indicate that ZrC is less likely to lose carbon than NbC or TaC, providing an explanation for heritage NERVA data on ZrC and NbC mass loss performance. Additionally, binary mixtures show compositions that are more stable than their end-member counterparts. Hydrogen diffusion in stoichiometric ZrC was found to be slightly higher than previously theorized, with the caveat that hydrogen saturation of carbon vacancies will hinder further hydrogen diffusion through the bulk, while hydrogen diffusion in ZrNbC is slightly enhanced over ZrC. And finally, we show that as carbon is depleted, the deformation mechanism of ZrC changes from brittle to ductile. Though many questions still remain as to the bulk performance of these materials, these trends and results are important in terms of materials selection efforts for hydrogen-resistant coatings on carbon/carbon substrates.

William C Tucker↗
DOE OSTI2023

Bounding Pressure and Flammability Evaluations for a Department of Energy Standard Canister Loaded with Aluminum-Clad Spent Fuel

This report presents bounding pressurization and flammability evaluations from the radiolytic gas generation expected during extended (>50 years) dry storage of aluminum-clad spent nuclear fuel (ASNF) elements in a sealed Department of Energy (DOE) Standard Canister. The primary questions involving extended ASNF dry storage center around the adequacy of dry storage conditioning processes (i.e., drying) and the behavior of residual hydrated aluminum oxides on the cladding—specifically, the radiolytic breakdown of chemically bound water in these corrosion products. The objectives of the presented work include providing a bounding assessment of the pressure with respect to the DOE Standard Canister’s structural integrity limits and identifying the potential for forming flammable or explosive gas mixtures (i.e., exceedance of the lower flammability limit of the molecular hydrogen [H2] and oxygen [O2] concentrations). The evaluation results confirm the findings of previous, more complex M&S work. That is, the structural integrity of the canister remains unchallenged by a wide margin. Nevertheless, it is important to recognize that the presented pressure calculations consider a full breakdown of the chemisorbed water, including a consequent release of all available H2. In reality, the breakdown of water in these systems will likely remain incomplete, due to competing chemical and radiolytic reactions, thereby attaining an equilibrium in the storage environment.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Start-up of Silo 130 Waste Retrieval at La Hague: first Step Towards Reducing Legacy Inventory - 20020

On June 25, 2019, the first grapple of waste and debris was lifted from Silo 130, one of the most challenging legacy waste storage silos at La Hague. This was the achievement of more than ten years of studies and efforts focused on solving some very unique technical and safety challenges, and on designing an innovative, efficient solution. The waste is from de-cladding materials from past Gas-Cooled Reactor fuel reprocessing operations. It is an unsorted mixture of magnesium cladding pieces, graphite debris, and various other metallic waste types. These materials can be chemically reactive and therefore need specific dispositions for handling and storing. The building is more than 40 years old and does not meet modern standards. French safety authorities have required the silo to be emptied. After about three years of operation, the bulk of this waste will be removed and placed in safe storage, pending the selection of a final conditioning solution. Removal of bottom debris will then be possible. When finished, this operation will bring a conclusion to a significant legacy-related hazard on the site. The silo will then be available for final cleaning and de-activation. This paper will describe the technical, safety, and economical challenges, and the various decisions and optimizations that led to the definition of the process and technology to be implemented. Several innovative features were developed and implemented, in all sections of the project: project organization, progressive approach for the waste disposition strategy, light building design, customized and robust retrieval technology, processing technologies involving the most modern robotic and sorting techniques, storage method... Several of these first-of-a-kind innovative features have been developed and qualified specifically for this application, using the detailed qualification procedure specified for all La Hague projects. The facility was built in less than five years, overcoming various difficulties along the line. Commissioning is now finished with the combined efforts of the project, engineering, start-up, and operating teams assisted by dedicated suppliers. The facility is now ramping-up. The paper will also report on the commissioning and start-up of the facility and describe the first operational results. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

A Step toward Process Electrification: Microwave-Assisted Co-Gasification of Waste Plastics and Biomass to Produce Clean Energy

Barely 9% of the 353 million metric tons of plastic waste produced worldwide over the last two decades has been recycled, with the majority of it being either landfilled or incinerated. Recycling and upcycling plastic waste is thus essential in mitigating environmental pollution. Gasification is the thermochemical conversion of solid carbon feedstock at high temperatures using a gasifying agent to produce hydrogen-rich syngas. Existing gasification technologies are energy-intensive and require high operating temperatures (>1000 °C), leaving them uncommercial. Microwave heating has sparked attention in a variety of chemical processes due to its specific advantages over traditional heating technologies, such as rapid and selective heating to improve process efficiency. NETL’s research team recently investigated the synergistic advantages of corn stover and mixed plastics in producing hydrogen-rich syngas via microwave heating. As a continuation of the research, this study provides an outlook over the non-catalytic versus catalytic effects of plastic-corn stover gasification via process electrification to enhance H2 production, minimize undesired tar, and improve process efficiency. Our aim is to provide complete electrification of the existing gasification process by using waste plastics as a starting block to produce valuable fuel and support the nation’s net zero goals.

Abedin, Ashraf↗
NASA NTRS1992

Micro Electric Propulsion Feasibility

Miniature, 50 kg class, strategic satellites intended for extended deployment in space require an on-board propulsion capability to perform needed attitude control adjustments and drag compensation maneuvers. Even on such very small spacecraft, these orbit maintenance functions can be significant and result in a substantial propellant mass requirement. Development of advanced propulsion technology could reduce this propellant mass significantly, and thereby maximize the payload capability of these spacecraft. In addition, spacecraft maneuverability could be enhanced and/or multi-year mission lifetimes realized. These benefits cut spacecraft replacement costs, and reduce services needed to maintain the launch vehicles. For SDIO brilliant pebble spacecraft, a miniaturized hydrazine propulsion system provides both boost and divert thrust control. This type of propulsion system is highly integrated and is capable of delivering large thrust levels for short time periods. However, orbit maintenance functions such as drag make-up require only very small velocity corrections. Using the boost and/or divert thrusters for these small corrections exposes this highly integrated propulsion system to continuous on/off cycling and thereby increases the risk of system failure. Furthermore, since drag compensation velocity corrections would be orders of magnitude less than these thrusters were designed to deliver, their effective specific impulse would be expected to be lower when operated at very short pulse lengths. The net result of these effects would be a significant depletion of the on-board hydrazine propellant supply throughout the mission, and a reduced propulsion system reliability, both of which would degrade the interceptors usefulness. In addition to SDIO brilliant pebble spacecraft, comparably small spacecraft can be anticipated for other future strategic defense applications such as surveillance and communication. For such spacecraft, high capability and reliability, minimal detectability and low cost are requirements. All these miniature spacecraft share a common characteristic: because of their on-board electronic equipment they have, by design, solar order 50-100 W. In a relative sense, such spacecraft are power rich when compared to other larger spacecraft. This power rich situation is offset by very tight mass budgets, which make reductions in propellant mass requirements a key issue in meeting overall spacecraft minimum mass goals. In principle, power rich and propellant poor brilliant pebbles class spacecraft can benefit from using high specific impulse electric propulsion to reduce chemical propellant mass requirements. However, at power levels of order 50 W, arcjets cannot be made to function, ion thrusters are too complex and heavy and resistojets have too low a specific impulse. Recognizing these capability limitations in existing electric propulsion technology, the SDIO/IST sponsored the Phase I SBIR Micro Electric Propulsion (MEP) thruster study described in this report. The objective of this study was to examine the feasibility of developing a very simple, low mass and small volume, electric thruster for operation on hydrazine at less than 100 W of input power. The feasibility of developing such a MEP thruster was successfully demonstrated by EPL by the discovery of a novel plasma acceleration process. The sections in this report summarize the approach, test results and major accomplishments of this proof-of-concept program.

Aston, Graeme↗
DOE OSTI2020

Structure–activity relationship-based chemical classification of highly imbalanced Tox21 datasets

Abstract The specificity of toxicant-target biomolecule interactions lends to the very imbalanced nature of many toxicity datasets, causing poor performance in Structure–Activity Relationship (SAR)-based chemical classification. Undersampling and oversampling are representative techniques for handling such an imbalance challenge. However, removing inactive chemical compound instances from the majority class using an undersampling technique can result in information loss, whereas increasing active toxicant instances in the minority class by interpolation tends to introduce artificial minority instances that often cross into the majority class space, giving rise to class overlapping and a higher false prediction rate. In this study, in order to improve the prediction accuracy of imbalanced learning, we employed SMOTEENN, a combination of Synthetic Minority Over-sampling Technique (SMOTE) and Edited Nearest Neighbor (ENN) algorithms, to oversample the minority class by creating synthetic samples, followed by cleaning the mislabeled instances. We chose the highly imbalanced Tox21 dataset, which consisted of 12 in vitro bioassays for > 10,000 chemicals that were distributed unevenly between binary classes. With Random Forest (RF) as the base classifier and bagging as the ensemble strategy, we applied four hybrid learning methods, i.e., RF without imbalance handling (RF), RF with Random Undersampling (RUS), RF with SMOTE (SMO), and RF with SMOTEENN (SMN). The performance of the four learning methods was compared using nine evaluation metrics, among which F 1 score, Matthews correlation coefficient and Brier score provided a more consistent assessment of the overall performance across the 12 datasets. The Friedman’s aligned ranks test and the subsequent Bergmann-Hommel post hoc test showed that SMN significantly outperformed the other three methods. We also found that a strong negative correlation existed between the prediction accuracy and the imbalance ratio (IR), which is defined as the number of inactive compounds divided by the number of active compounds. SMN became less effective when IR exceeded a certain threshold (e.g., > 28). The ability to separate the few active compounds from the vast amounts of inactive ones is of great importance in computational toxicology. This work demonstrates that the performance of SAR-based, imbalanced chemical toxicity classification can be significantly improved through the use of data rebalancing.

Idakwo, Gabriel↗
DOE OSTI2025

Multiscale Mechanical Characterization of Mineral-Reinforced Wood Cell Walls

Studying the multiscale mechanics of bio-based composites offers unique perspectives on underlying structure–property relations. Cellular materials, such as wood, are highly organized, hierarchical assemblies of load-bearing structural elements that respond to mechanical stimuli at the microscopic, mesoscopic and macroscopic scale. In this study, we modified oak wood with nanocrystalline ferrihydrite, a widespread ferric oxyhydroxide mineral, and characterized the resulting mechanical properties of the composite at various levels of organization. Ferrihydrite nanoparticles were deposited inside the wood cell wall by an in situ chemical reaction, resulting in increased stiffness and hardness of the functionalized secondary cell wall, as evidenced by region-specific nanoindentation tests under an electron microscope. Chemically modified and pristine wood samples were characterized by using atomic force microscopy in the bimodal frequency modulation mode, which produced topographical images from the cellular ultrastructure with high lateral resolution and localized nanomechanical information across distinct cell wall layers. In conclusion, despite mineral reinforcement at the cell wall level, the macroscopic fracture behavior examined through three-point flexural testing remained unchanged upon modification, as cell–cell adhesion could be impaired by harsh chemical conditions.

Cells↗
NASA NTRS1990

Space vehicle propulsion systems - Environmental space hazards

An evaluation of hazards which exist in geo-lunar space and have the potential to negatively affect a long-term mission-oriented spacecraft systems is presented based on published data. The hazards are categorized as pervasive (radiation), incident specific (meteoroids and thermal shock), and chemically corrosive (monatomic oxygen). It appears that the number one priority should be the development of new materials; and the secondary concern should be the development of fabrication techniques for the exterior hull, so that incident specific hazards can be minimized in an active fashion. The pervasive hazard can be dealt with by exploring on-board circuit technology with ancillary monitoring systems. Effects of thermal shock on the exterior nozzle, directional gimbals, and internal combustion chamber geometry seem to need more investigation.

Bahr, G. K.↗
DOE OSTI2022

Chemical Thermodynamic Modeling of Molten Salts to Support Off-Gas Abatement Systems

The reprocessing of used nuclear fuel by any means will liberate gaseous fission products, such as hydrogen ( 3 H), carbon ( 14 C), noble gases ( 85 Kr), and halogens ( 129 I), from the irradiated fuel. These elements will distribute through chemical processing operations and partition into process off-gas streams, and the specific volatile release fractions will be dictated by the chemical and physical properties of the system. A recent assessment found that there were significant knowledge gaps regarding the release quantities of volatile radionuclides from individual unit operations. These knowledge gaps limited the ability to determine what dedicated off-gas treatment technologies could be required for electrochemical-based reprocessing facilities. Unfortunately, experimental efforts to quantify release fractions are limited by the challenges associated with performing experiments using irradiated fuel. This report documents preliminary thermodynamic predictions of iodine and tritium release from chloride-based molten salts as part of an effort to better direct resources toward those experiments (both simulant and irradiated) that will be of the greatest impact. It was predicted that less than 0.5% of tritium was expected to be released and that nearly all of that amount would be released as H 2 . Thermochemical data for hydrogen (H 2 ) are of high fidelity, and no additional validation is recommended. Less than 0.05% of iodine was predicted to be released, with the primary volatile species being Cs 2 I 2 . Unlike the tritium predictions, the data underpinning the iodine release predictions are of low quality. It is recommended that a limited experimental program be dedicated to expanding the current physical property and thermodynamic property data for iodine in electrochemical processing and molten salt conditions, including vapor pressure measurements for the dimerized species predicted to comprise the majority of iodine release. Validating and improving the thermodynamic properties used in predictive modeling can reduce the need for expensive testing with irradiated fuel.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1988

High speed inlet calculations with real gas effects

A 2-D steady-state Navier-Stokes solver has been upgraded to include the effects of frozen and equilibrium air chemistry for applications to high speed flight vehicles. To provide a computationally economical first order approximation to the high temperature physics, variable thermodynamic data is used for the chemically frozen mode to allow for a variation with temperature of the air specific heats and enthalpy. For calculations involving air in chemical equilibrium, a specially modified version of the NASA Lewis Chemical Equilibrium Code, CEC, is used to compute the chemical composition and resultant thermochemical properties. The upgraded solver is demonstrated by comparing results from calorically perfect (C sub p=constant), thermally perfect (frozen) and equilibrium air calculations for a variety of geometries, and flight Mach numbers.

Coirier, William J.↗
NASA NTRS1988

High speed inlet calculations with real gas effects

A 2-D steady-state Navier-Stokes solver has been upgraded to include the effects of frozen and equilibrium air chemistry for applications to high speed flight vehicles. To provide a computationally economical first order approximation to the high temperature physics, variable thermodynamic data is used for the chemically frozen mode to allow for a variation with temperature of the air specific heats and enthalpy. For calculations involving air in chemical equilibrium, a specially modified version of the NASA Lewis Chemical Equilibrium Code, CEC, is used to compute the chemical composition and resultant thermochemical properties. The upgraded solver is demonstrated by comparing results from calorically perfect (C sub p=constant), thermally perfect (frozen) and equilibrium air calculations for a variety of geometries, and flight Mach numbers.

Coirier, William J.↗
NASA NTRS2017

Biosignatures in the Context of Low Energy Flux

Many of the features that are thought of as biosignatures - including the mediation of chemical and physical processes with speed, specificity, and selectivity - result directly or indirectly from life's unique capability to mediate and direct energy flux. As such, it is important to consider the impact that differences in energy flux may have on the quantity and quality of evidence for life. Earth differs from every other body in our solar system in the magnitude of biologically-usable energy flux into a liquid water environment. On a global basis, the capture of light energy into photosynthesis and the flux of chemical energy represented in the products of that photosynthesis (organic material + O2) are about six and four orders of magnitude larger, respectively, than the flux of energy represented in geochemical sources. Our conception of what an inhabited world "looks like" and our intuition about how to search for life are based in this high-energy context. Energy fluxes on worlds beyond Earth may be better approximated by the million-fold smaller flux provided to Earth's biosphere by geochemical sources. As a result, the nature, abundance, and quality of evidence for life that could be expected on an inhabited extraterrestrial world within our solar system may differ profoundly from that found on Earth. Understanding this potential difference in quantitative terms provides important context for the formulation of life detection strategies. The influence of energy flux on biosignatures can be evaluated through reference to the two basic purposes into which life partitions energy flux: (1) Life expends energy to sustain existing biomass in a metabolic steady state (metabolically functional but non-growing). The formal representation of this relationship in the traditional microbiology literature equates biomass directly with energy flux. The direct implication is that worlds having lower energy flux will have correspondingly lower potential to support biomass. Life detection strategies that directly target extant organisms should therefore be prepared to encounter average biomass densities that may be many orders of magnitude smaller than those found in most of Earth's surface environments (2) Life expends energy to synthesize new biomass. An end-member case in which new biomass is created at the energy-limited rate and the corresponding cells are immediately destroyed (so that the energy partitioned to cell maintenance is minimized) establishes an upper bound on the rate at which biological material can enter a bulk global pool. For a specified bulk concentration [i] of any particular biological compound, i, or for biologically produced matter overall, this synthesis rate, R (sub i), defines a characteristic time scale tau (sub i) equals [i] divided by R (sub i). tau (sub i) can be thought of as (a) the minimum time required for biosynthesis to yield a specific bulk concentration (e.g., a detection threshold) of i, and (b) the average residence time of i within a bulk pool when [i] is held in steady state through a balance between biosynthesis and attrition by physical, chemical, or biological consumption. tau (sub i) becomes an important quantity in considering the potential utility of enantiomeric excess (as a product of homochiral biosynthesis) as a biosignature. Spontaneous racemization of amino acids acts to "erase" the signature of homochiral synthesis over time scales that may range from hundreds to hundreds of thousands of years, depending on temperature. For environments in which low energy flux translates to low rates of biosynthesis, including the synthesis of homochiral amino acids, amino acid residence times in pools having detectable concentrations may compare to or significantly exceed the time scale for racemization. This and similar consequences of long residence times should be considered in the formulation of life detection strategies based on detection of biologically-produced species. Fluxes of biologically-useful energy on potentially habitable worlds within our solar system are, at present, not well constrained. Improving such constraint has the potential to inform priorities in the formulation and targeting of search-for-life strategies, based on the implications of energy flux for the abundance and quality of biosignatures overall, and in specific categories.

ENERGY FLUX↗
DOE OSTI2024

Modeling Approach for the Aluminum-clad Dry Storage Pilot using HFIR Fuel

To confirm that the dry storage of aluminum-clad research reactor spent nuclear fuel (ASNF) will remain within the safety envelope after applied drying schemes and that the resulting evolution of the gas space composition, temperature, and pressure conditions are understood, a dry storage pilot project is being established. The pilot will incorporate an instrumented lid for discrete interval or for on-demand gas composition and temperature monitoring of two DOE Standard Canisters (DSCs) loaded with three High Flux Isotope Reactor (HFIR) inner cores per DSC. Each DSC would be subjected to a separate alternative candidate drying scheme. Canisters will undergo 1 to 5 years of monitoring, including internal temperature and gas sampling to track pressure and composition changes. This report outlines the approach for modeling the ASNF-in-canister behavior in terms of evolving gas space conditions for the ASNF dry storage pilot using HFIR fuel. The ASNF has an adherent surface oxyhydroxide layer comprised of boehmite/bayerite that generates hydrogen when subjected to irradiation. Three-dimensional multi-physics computational fluid dynamics simulations will be executed to compute the thermal field within the DSC and provide inputs to a chemical model employed to compute pressure buildup as hydrogen is generated in the system. Implemented in Cantera, the chemical model solves gas phase and aluminum oxyhydroxide surface-mediated radiolysis reactions. Gas phase reactions are sourced from Wittman and Hanson (2015), whereas surface-mediated reactions are incorporated by fitting experimental data using an optimization algorithm (Abboud, 2023). Water radiolysis reactions from Wren and Ball (2001) are adopted with modifications as described in Abboud (2023c). Understanding the effect of the hydrogen buildup over time is important for long-term storage safety considerations. Modeling results will include the canister pressure, temperature, and composition evolution from the initial helium backfill with the addition of radiolytically-evolved chemical species (e.g., hydrogen and oxygen). The specific HFIR cores for the pilot program have not yet been selected, and the overall design is still in development. The CFD-chemical model used for this work will be based on prior models with necessary updates to allow for improved accuracy and efficiency. The experimental data obtained from the HFIR demonstration will be used to improve and validate the computational models to predict the ASNF-in-canister behavior.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

CSGL: chemical synthesis graph learning for molecule representation

Abstract Motivation Molecule representation learning (MRL) translates molecules into a real vector space, serving as input to downstream tasks in biology, chemistry, and computer science. This article introduces a chemical synthesis graph learning (CSGL) framework, which enhances MRL by considering both the atomic structures of molecules and their roles in chemical reactions through a hierarchical graph representation. Specifically, molecules are first modeled based on their molecular graphs, which capture atomic-level structural information. They are then further refined using a chemical synthesis graph, where nodes represent reactant and product molecule sets, and edges encode chemical transformations between reactants and products (e.g. changes in molecular structures). CSGL optimizes molecular embeddings of reactant and product nodes in a fashion that ensures the embeddings conform to a chemical balance constraint. Results Experimental results show that our method CSGL achieves strong performance on a variety of tasks, including product prediction, reaction classification, and molecular property prediction. Availability and implementation https://github.com/li-2023/CSGL.

Biochemistry & Molecular Biology↗
DOE OSTI2024

Assessment of Fluoropolymer Production and Use With Analysis of Alternative Replacement Materials

This report focuses on fluoropolymers, which are a subgroup of the much larger class of fluorinated chemicals known as per- and polyfluoroalkyl substances (PFAS). Clearly distinguishing fluoropolymers is important to understanding their distinctive chemical properties, associated risks and benefits, and roles in commerce. In this report, the factors that are considered in a lifecycle assessment (LCA) of fluoropolymers will be discussed. These include the manufacturing of fluoropolymers, their use in industry, and available replacement technologies. Emphasis is placed on fluoropolymer plastics because of their extensive use in the commerce sectors considered here, specifically aerospace, automotive, battery, building construction, chemical processing, electronics, infrastructure, semiconductor, solar panel, and wind energy industries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗