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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Alloying effect of Nb and Sn on the Zirconium alloy fuel claddings behavior at high temperature oxidation in steam - 6.1 STP-2016-0072

As the material of fuel claddings for water cooled reactors most commonly used binary and multicomponent zirconium alloys Zr-Nb (E110,M5), Zr-Sn-Fe (Zircaloy-2,-4) and Zr-Nb-Sn-Fe (E635, Zirlo) are used, which improvement extends, in particular, by varying their composition by Nb, Sn and Fe. At the same time, the importance is given to ensuring the safe operation of the fuel rods not only in normal conditions but also in emergency situations such as LOCA. In this paper the researches results of the studies of influence of alloying elements Nb, Sn (and Fe) on corrosion resistance and embrittlement at high temperature steam oxidation of fuel claddings based on alloys types Zr-xNb (x=1.0/2.5) and Zr-xNb-ySn-zFe (x=0.6/2.4; y=0.24/1.1; z=0.18/0.34) made with using zirconium sponge are presented. High temperature steam oxidation tests were carried out at temperatures of 1000, 1100 and 1200 deg. C with continuous measurement of the weight gain during the experiment and subsequent cooling in steam with rate ∼ 20 deg. C/s. The studies of kinetics of high-temperature oxidation in steam, structural-phase state changes, alloying elements distribution, absorbed hydrogen content and residual ductility after rapid cooling of the oxidized specimens were made. The difference in the oxidation kinetics of the materials studied was revealed, it decreases with the oxidation temperature increase. At the same time, an increase of the Sn content in the alloy influences on specimens 'breakaway' oxidation intensification at 1000 deg. C. It is shown that the mechanical properties of fuel claddings oxidized under the same conditions depend on their alloying composition, the hydrogen fraction absorbed by the specimen and formed by the oxidation ZrO2, a-Zr(O) and 'ex-β' layers structure, which in turn varies depending on the alloy composition. The increase of Nb, Sn and Fe content in the zirconium alloy leads to decrease in residual ductility of fuel claddings after high temperature steam oxidation. According to obtained results the most resistant to high-temperature steam oxidation and embrittlement at temperatures of 1000-1200 deg. C among the materials studied is Zr-1Nb alloy. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2018

Effects of Chemical Wastes on Concrete through Spectroscopic and Computational Models - 18405

Liquid mercury was used as a coolant for early fast reactors, as catalyst in the dissolution of uranium alloy fuels, lithium isotope separation and other processes. Cesium is produced during nuclear fission reactions within the reactor. The interaction between chemical contaminants and solid structures can cause structural damages (e.g. dislocations) and consequently modify the material's mechanical properties. Another problem associated with the interaction of chemical contaminants and metal structures is corrosion pitting. Mercury intrusion porosimetry (MIP) has been utilized to investigate the pore structure of the cement material. The overall goal of this project is to determine the physiochemical interactions of Hg and Cs to steel and concrete using spectroscopic analysis: - Evaluate the physicochemical interactions of Hg and Cs to steel and concrete using spectroscopic techniques under standard conditions; - Evaluate the impact of environmental conditions (temp., salt content, pH, and time) on the physicochemical interactions of Hg and Cs to steel and concrete using spectroscopic techniques. Conclusion and Future Work: Adsorption process depends on the surface morphology. Surface morphology analysis demonstrated that concrete samples had a heterogenous surface. Adsorption of Mercury and Cesium are more favorable onto heterogeneous regions such as edges, grooves, and wrinkles. The mechanism for cation removal by concrete includes surface complexation and ion exchange. Overall adsorption of Mercury was more favorable than Cesium onto concrete. Continuing investigations will be focusing on application considerations such as multicomponent interactions and desorption studies.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Phase Equilibria in Systems Relevant to Pyroprocessing

Pyroprocessing has many advantages for the recovery and recycle of actinides, especially the transuranic elements, in used nuclear fuel. It has several unique features that distinguish it from other used fuel treatment technologies such as the ability to handle short-cooled fuel, a small process footprint, and production of metallic uranium and uranium - transuranic (U/TRU) products that can be directly fabricated into metallic fuel for advanced reactors. Recovery of the uranium and U/TRU products from the used fuel occurs in an electrorefining step. Uranium and transuranics in the used fuel (metal or reduced oxide) are dissolved at the anode in a molten chloride electrolyte, and electrodeposited at two different cathodes - one for uranium and another for the uranium - transuranic product. During this process, fission products less noble than uranium and transuranics (i.e., lanthanides, alkali and alkaline earth) anodically dissolve into the electrolyte, while only uranium and U/TRU are electrodeposited at the respective cathodes. Thus, there is a buildup of active metal and lanthanide fission products in the molten salt electrolyte. The goal of this work is to improve the fundamental understanding of the chemistry of actinides and transuranics in this complex, multicomponent solution. The fundamental thermodynamic properties of the multi-component molten salt electrolytes are complicated due to the formation of ternary and more complex compounds. As the actinides anodically dissolve at the anode and deposited at the cathode, a gradient in the concentration develops at the anode/electrolyte and the cathode/electrolyte interfaces. Ternary phase formation could impact the performance of the electrorefining system by influencing the chemical activity and thus the redox potentials of the actinide chlorides in the molten salt solution. Literature data on the LiCl-KCl-UCl{sub 3} system is limited, sometimes conflicting, and may reflect the use of older analytical instrumentation, which was less accurate than that currently available. In addition, there has not been any investigation of the low UCl{sub 3} concentration region of the system, which is the region relevant to electrorefining. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

String-Like Transport in Superionic Conductors

Superionic or fast-ion conductors are multicomponent solid-state systems in which one sublattice becomes mobile and exhibits extraordinarily high ionic conductivity before the melting within the solid state. Uranium dioxide (UO{sub 2}) - the fuel material of choice in most nuclear reactors - shows superionic behavior, although the mechanism of fast ion transport of the mobile oxygen ions, and its implication, is not well-understood. UO{sub 2} belongs to the category of Type II superionics wherein the conductivity rises gradually with increasing temperature, without an attendant phase change. In a recent work, using atomistic simulations and available neutron and x-ray scattering data, we have shown that all Type II superionic conductors exhibit a well-defined onset of dynamic disorder at a characteristic temperature T{sub α} = (∼2000 K for UO{sub 2}). Unlike the familiar superionic or Bredig transition temperature T{sub α} (∼2650 K for UO{sub 2}) that is associated with a second-order thermodynamic phase transition, T{sub α} represents an order-disorder (O-D) transition that marks a structural and kinetic crossover from a crystalline state to a semi-ordered state. In the temperature range between T{sub α} and T{sub λ}, the oxygen ions in UO{sub 2} exhibit jammed dynamics even though the mobile oxygen ions favor collective hopping from one native crystalline site to another. This cooperative dynamics manifests as dynamical heterogeneity (DH) - the tendency of highly mobile oxygen ions to form dynamic clusters, and dynamical facilitation (DF) - the mode of system relaxation facilitated solely through the kinetic ions transferring their mobility to neighboring ions. The jammed dynamics portrayed by the oxygen ions is similar to that observed in supercooled liquids and glassy materials, and other disordered systems such as granular media and polymers. In the current work, we probe the ionic dynamics in UO{sub 2} for the presence of another ubiquitous signature of glassy and jammed systems, namely, the one-dimensional string-like motion of the mobile species. Unlike the uncorrelated vacancy exchanges and interstitial migration in defected crystalline states, the string motion is a collective mechanism among the mobile species wherein each member of the string induces the next member to move in a correlated, sequential fashion. Using atomistic simulations, we demonstrate that oxygen ions in UO{sub 2} are transported through a string-like mechanism in the temperature range between T{sub α} and T{sub λ}, and the probability distribution of occurrence of the strings varies exponentially with string length. The discovery of string-like motion of the oxygen ions is somewhat surprising given the crystalline underpinning of the mobile species and the dynamic tendency of the oxygen ions to hop between lattice sites. In addition to dynamical heterogeneity and dynamical facilitation, our work has added one more entry, namely the occurrence of string-like transport, to the list of phenomenological similarities between superionic conductors and jammed systems. Using atomistic simulations, we have established the occurrence of string-like ionic motion among the oxygen ions in UO{sub 2} between temperatures T{sub α} - the order-disorder (O-D) transition temperature, and T{sub λ} - the Bredig transition temperature. As observed in other jammed systems, the length of the strings is observed to have an exponential distribution implying that the probability of occurrence of a smaller string is much higher than that of a longer string. Interestingly, using Temperature-Accelerated Dynamics (TAD) we have also established that string-like hopping takes place at temperatures lower than T{sub α}; these results will be published elsewhere. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Initial Assessment of Cover Degradation Features at the Mexican Hat, Utah, UMTRCA Disposal Site - 19556

The Mexican Hat, Utah, Uranium Mill Tailings Radiation Control Act (UMTRCA) Title I Disposal Site is located on the Navajo Reservation in southeast Utah. The US Nuclear Regulatory Commission licensed the site to the US Department of Energy Office of Legacy Management (LM) for custody and long-term care. LM manages long-term surveillance and maintenance activities at the site with the principal goal of protecting human health and the environment. The disposal cell was designed to encapsulate low-level radioactive mill tailings and other residual radioactive materials (RRM) in a way that minimizes the need for active maintenance and limits radon gas emanation and precipitation infiltration. The disposal cell has a multicomponent cover, consisting of a 60 cm thick (24 inch), low-permeability, bentonite-amended radon barrier, overlain by a 15 cm thick (6 inch) sandy gravel bedding/filter layer and a 30 cm thick (12 inch) riprap erosion-protection layer. Under UMTRCA, designs intended to control and contain RRM shall be effective for up to 1000 years, to the extent reasonably achievable and, in any case, for at least 200 years. In 2016, multiple subtle depressions were identified on the rock cover along the toe and lower portions of the northeast side slope of the disposal cell. Due to concerns regarding potential impacts to disposal cell performance and erosion resistance, evaluations of the depressions and cell cover design and construction were initiated. The evaluations included reviews of the disposal cell as-built drawings and supporting design calculations for the rock cover components. Also, in 2017, a weather monitoring station was installed at the site to collect continuous site-specific meteorological data, and repeatable ground-based light imaging, detection, and ranging (lidar) topographical and aerial photogrammetry surveys were implemented to monitor for potential changes in the surface depression features. The evaluations also included visual inspections of the depressions, and in 2018, small-area manual excavations of the rock cover components (test pits) were performed to observe the conditions of the cover components, scan for radioactivity, and observe evidence of erosion on the surface of the radon barrier material. Voids and incisions were discovered within the radon barrier on the north and northeast side slopes of the disposal cell. Visual observations at test pits indicate that the bedding/filter material is highly segregated and may not be in conformance with the disposal cell engineering and construction design specifications. Post-construction development of a weak to strongly cemented material has also been observed immediately below the base of the bedding layer in test pits with observed radon barrier degradation. A series of radiological surveys have been performed at the site, and radiological readings have not exceeded natural background conditions in the vicinity of the site. Thus, the site remains protective of human health and the environment. Implementation of continuous radiological monitoring at the site will be initiated in fall 2018 through the deployment of radon cups and thermoluminescent dosimeters to obtain data that provides supporting evidence that the disposal cell remains protective of human health and the environment. Evaluations to determine the cause(s) of the depression features and associated radon barrier erosion are ongoing. Possible mechanisms of cover degradation identified thus far include segregated bedding material that would allow for higher precipitation runoff velocities, resulting in erosion of the radon barrier; post-construction cementation of radon barrier or aeolian material that could negatively affect the performance of the radon barrier; cation exchange leading to the development of cementation; and aeolian deposition affecting precipitation runoff. Moreover, geotechnical sampling and testing is planned to verify spatial cover conditions relative to design specifications. The resulting information will be used to identify possible causes for the surface depressions and associated radon barrier degradation, gain insight on potential long-term performance implications along the side slopes of the disposal cell, and identify potential corrective actions. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Water and Ammonia Desorption from 5A Zeolite

The objective of this project is to demonstrate the adsorption and desorption characteristics of water and ammonia on 5A zeolite during regeneration conditions. As discussed in literature, zeolite material is a crystalline hydrated aluminosilicate material. Zeolites have high cation exchange ability and are commonly used as adsorbents in separation and purification processes. The property of uniformly sized pores allows zeolites to selectively separate gases. Because they have varying ion selectivity, there is competitive adsorption in a multicomponent mixture. 5A zeolite has a uniform pore diameter of 5 Angstroms. Water and ammonia are miscible components with similar molecular weights and size. This makes distinguishing the two compounds difficult using mass spectrometry. In a previous study, it was shown that water tends to desorb from 5A zeolite from 40 deg. C to 353 deg. C with peaks at 177 deg. C and 244 deg. C, while ammonia tends to desorb from 300 deg. C to 580 deg. C with a peak at 436 deg. C as determined using a Micromeritics AutoChem 2920 Instrument. The one drawback of using a Micromeritics Instrument is that only a few milligrams of sample material can be used. Bench scale tests can better demonstrate desorption characteristics of water and ammonia during regeneration from 5A zeolite material. Water in argon carrier gas and ammonia in hydrogen carrier gas will be tested separately, then a mixture of the two will be tested. Initial bake-out conditions: hydrogen carrier gas, slowly raise temp to approximately 450 deg. C until desired moisture content <100 ppm is achieved. Water loading: argon carrier gas through bubbler until breach is observed using the residual gas analyzer (RGA). Ammonia loading: hydrogen carrier gas through system until breach is observed using RGA. Regeneration conditions: hydrogen carrier gas, raise temp to approximately 300 deg. C, then slowly to 450 deg. C. Observe signals on RGA. Weigh samples between tests and integrate RGA signals. Accomplishments: Developed work control documentation and completed safety related requirements; Flow sheet and test system development; Initial bake-out of first sample. Testing will determine if regenerating zeolite material can be safely accomplished by high-temperature bake-out to remove ammonia. If unsuccessful, ammonia would only be removed at the end of life.

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

Advances in PFAS Monitoring and Remediation Using a Functionalized Material Approach - 20080

The growing global concerns about the effects to public health from human exposure to per- and polyfluoroalkyl substances (PFAS) motivates the development of strategies for reliable monitoring of PFAS in environmental streams, as well as for their rapid, effective removal if detected. For the continuous PFAS monitoring, an inexpensive, field-deployable, in situ sensor is urgently needed; yet the prevalent in situ techniques often struggle to strike a balance between the practical sensitivity and selectivity demands of the real world. Similarly, for effective PFAS removal, strategies for their fast, selective, and quantitative capture are desired, yet the present commercially available sorbents are unable to meet the requirements of rapid, quantitative capture of all PFAS components, and are notably inefficient in removing the more toxic smaller chains. To address these twin challenges, Pacific Northwest National Laboratory is developing strategies for improved detection and remediation of PFAS. For the rapid, selective, quantitative removal of PFAS from environmental streams, the strategy relies on designing capture probes with exclusively tailored electronic and spatial affinities for the PFAS that are able to selectively capture them from environmental streams. For the in situ detection and quantification of PFAS in complex, multicomponent matrices such as groundwater, the approach relies on the targeted capture of specific PFAS by these PFAS-specific capture probes immobilized on a platform. The platform acts as an electrode to directly measure PFAS concentration through a proportional change in electrical response upon their capture. A combination of optimization of platform design and incorporation of additional, sensitive detection modalities have allowed us to achieve detection limits as low as 0.5 ng/L for detection of PFAS compounds (compared to the 70 ng/L Health Advisory Limit of the U.S. Environmental Protection Agency). (authors)

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Tracking Radioactive Isotopes in HVAC and Application for Hot Cell Analyses - 20155

In recent years, the surge in the number of isotope production facilities under design has increased the need to analyze isotope migration in facility Heating, Ventilation, and Air Conditioning (HVAC) during normal operations and accident scenarios. These facilities are used to produce isotopes for medical, security, and industrial applications and as such are subject to license and regulatory requirements 10CFR20, 10CFR30, 10CFR50, and 10CFR70. GOTHIC, a general-purpose thermal-hydraulics software package, includes the ability to model isotopic tracers, radioactive decay and isotope migration as well as HEPA and charcoal filters for isotope retention. A GOTHIC model was developed by Zachry Nuclear Engineering (ZNE) to examine the effect of negative room pressure, HEPA filtration, and HVAC fluctuations on radiation areas, hot cells and gloveboxes. Radioactive tracers were used to simulate the concentration of spills within contaminated areas, track the migration of isotopes of interest, and determine the isotopic retention and buildup on facility HEPA filters. A variety of isotopes with concern to dose (e.g., Kr-85, Sr-90, I-131, etc.), including their decay and progeny, are included in the analysis. Negative pressures are maintained in the regions of interest by a representative central HVAC system equipped with a volumetric fan that exhausts to the environment after a series of isolation valves and HEPA filters. GOTHIC is an industry trusted tool for providing engineering solutions for a variety of applications, including fission product tracking, aerosol and particulate transport and ventilation assessments. The software provides an integrated analysis environment that includes a graphical user interface (GUI) for constructing analysis models, a numerical solver that includes parallel processing capabilities and a post-processor for evaluating simulation results. It solves the conservation equations for mass, momentum and energy for multicomponent, multi-phase flow in lumped parameter and multi-dimensional geometries (1, 2, or full 3D), including the effects of turbulence, diffusion and buoyancy. It has been developed and maintained under a Quality Assurance program in compliance with the requirements of 10CFR50 Appendix B and applicable portions of ASME NQA-1 since 1995. GOTHIC has been used for assessing both forced and natural convection conditions for a wide range of applications, including: - Tracking concentration of hazardous gases and chemicals for habitability and safety assessments - Determining ventilation and filtration requirements and optimizing location and arrangement of these systems - Room heat-up, including diverse and Flexible coping strategies for Extended Loss of AC Power (FLEX/ELAP) - Equipment Qualification (EQ) A distinctive feature of GOTHIC is the ability to track many different fields/substances in a simulation, including user defined tracer elements, in the liquid, vapor and droplet fields as well as surfaces and filters. This capability allows GOTHIC to model fission product transport and release or the removal of particulates or harmful toxins from exhaust gases using a spray scrubber or other types of filtration systems. GOTHIC also includes models for engineered equipment, such as fans, filters, charcoal filters, dryers/demisters, dampers, etc. The aerosols and other filtered material are removed or accumulated in these components. The range of aerosol and radiological applications that GOTHIC has been used for includes: - Source Term: Primary Coolant (Equilibrium) Activity; Non-Water Coolant Source/Leakage. - Conditions for Iodine Re-evolution: Sump/Suppression Pool Conditions and pH; - RWST Conditions and pH. - Isotope Removal Mechanisms: Containment Sprayed and Unsprayed Region Mixing; Charcoal Filter Heating due to Iodine decay. - Radionuclide Transport and Decay: Post-LOCA Release in containment; Transport between connected Compartments and vent systems; Groundwater transport of radionuclides. - Non-Newtonian Fluid modeling for sludge, waste tanks, etc. ADAMS ML071581053 (titled 'Best Practice Guidelines for the use of CFD in Nuclear Reactor Safety Applications') poses guidelines for applying single phase CFD codes in nuclear reactor safety problems and GOTHIC is listed as a 'tool for 3D flows' and 'dispersal and deposition of radionuclides.' The Nuclear Quality Assurance (NQA) pedigree of GOTHIC is an important aspect for applications in the nuclear industry. The fundamental tracer models (convective transport, molecular and turbulent diffusion, removal mechanisms, etc.) have been verified using analytical solutions and validated against applicable separate effects tests. Also, GOTHIC has been benchmarked to many integrated effects tests, including Phebus FP (Fission Product). GOTHIC gives good agreement for the buildup and decay of fission products in Phebus Test 3. The model developed by ZNE demonstrates GOTHIC's applicability and acceptability for use in analyzing the migration and retention of radioactive isotopes and their progeny in normal operation and accident scenario analyses for isotope production facilities, hot cells, and gloveboxes. The tracer activities calculated by GOTHIC can then be used in downstream radiation transport and shielding codes like RADTRAD-NAI{sup C}, MCNP{sup R}, and MicroShield{sup R} to determine on-site and of-site doses. (authors)

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

Efficient Mesofluidic Separation of Large Particles in nuclear slurries - 20408

Efficient and effective particle separation is essential to cleanup of many nuclear wastes. For example, particle separation may be used to accelerate settle-decant bottlenecks that limit the throughput necessary to achieve the U.S. Department of Energy waste cleanup mission in a timely manner. Particle separation may be used to protect downstream processing equipment from pulses of solids that may be encountered near (within a few feet of) liquid-solid interfaces during waste transfer operations, thereby preventing work stoppages. Effective particle separation may permit efficient sludge washing. These are only a few of the ways in which particle separation is important. Yet, efficient and effective particle separation in nuclear processing environments remains challenging. For example, settle-decant operations permit larger and heavier particles to settle, leaving smaller, lighter particles suspended. However, settle-decant operations are slow, convection currents may resuspend solids, hindered settling of multicomponent slurries remains incompletely understood, and predictive models for settling in graduated cylinders fail to match limited observations of settling in large waste tanks. Additionally, pumping operations can cause turbulent resuspension of particles when the pump intake is close to the settled solids layer. Filtration techniques that use membranes or partially permeable barriers retain larger particles, permitting smaller particles to permeate. However, filters, including dead-end filtration, are prone to clogging and caking, operate at elevated pressures due to minimal void volume, and increase in pressure during operations, which require more control systems. Therefore, the need for high throughput particle separation techniques that operate with modest pressure drops persists. A novel mesofluidic separator presents the opportunity to effectively and efficiently accelerate the waste cleanup mission. The separator separates large particles from process streams across a broad range of particle sizes and has no moving parts or media to replace, regenerate, or clean. This separator design has an unusually large void volume, permitting operation at much higher flow rates (and lower pressures) than traditional filtration (e.g., dead-end filtration). Industrial-scale flow rates have been demonstrated. In performance testing, mesofluidic separators operate at might flow rates (>90 gpm (0.0006 m{sup 3}/s) in piping 3 inches (0.08 m) in diameter; Re>10{sup 5}), with modest pressure drop (∼25 psi (170 KPa) in testing). In complex, aggregating waste simulants, the separator loses <25% of flow projected over months without back pulsing or chemical cleaning. Mesofluidic separation presents infrastructure advantages, reduces risk, and provides mission impact. Infrastructure advantages include implementation within existing transfer systems, plug and play without facility modifications to safety systems, and operation at low pressures. The separator is flexible in location, may be positioned within or outside of waste tanks, and may replace or augment dead-end and cross-flow filters. Mesofluidic separation reduces risk by minimizing waste (no media to replace or regenerate and no cleaning chemicals to handle and dispose) and by minimizing filter change-out consistent with as low as reasonably achievable (ALARA) exposure to workers. The potential mission impact of these separators is substantial. The separator has potential to support, simplify, and accelerate in-farm transfers and waste feed delivery. Furthermore, the separator can free up settling and holding tanks in the Direct Feed Low-Activity Waste (DFLAW) mission by reducing or eliminating post-transfer settling and wait times with the potential to free up 1 Mgal (4000 m{sup 3}) of double-shell tank space. This paper quantitatively compares mesofluidic separation to dead-end filtration, discusses scale-up results, and considers the separator's potential to efficiently and effectively reduce the long-term environmental ability of particulate-rich nuclear wastes. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Contaminant Entrainment in a Liquid Fuel Fire with Multi-Component Evaporation Droplet Model

A number of fire scenarios can result in the release of hazardous chemical or radiological contaminants as sub-micron solid particulates, posing a significant danger of inhalation. These particulates may be entrained in the air around the fire through a variety of mechanisms including liquid droplet formation above the boiling surface of the contaminated fuel. The formation of both film drops from the rupture of a liquid film as a boiling bubble bursts and jet drops from the collapse of the cavity of a ruptured bubble may be involved. A 2015 study by Brown and Louie focused on such a fire scenario to investigate the physics of contaminant release. This paper extends that study by supplementing the existing physics models with a multicomponent evaporation mechanism, where liquid droplets formed near the boiling fuel surface experience evaporation of their various components at different rates based on distinct material properties (density, specific heat, heat of vaporization, etc.). As in the Brown and Louie study, the Sierra low-Mach module Fuego is used as the Lagrangian-Eulerian code for simulation of this scenario. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Development of Multiple Solid Components Capability in GOTHIC Droplet Fields

GOTHIC is a versatile and generally applicable software package that solves complex thermal hydraulics problems. GOTHIC solves the conservation equations for mass, momentum and energy for multicomponent, multi-phase flow in lumped parameter and/or multi-dimensional geometries. GOTHIC version 8.2 includes a new feature to model one or more solid components in each of the modeled droplet fields. A solid component is a material present in the water which has volume, density, and heat capacity. GOTHIC has supported modeling multiple droplet fields since version 8.0 - each field has its own mass, energy, and momentum equation. Recent work by Lane et. al. allowed multiple solid components to be tracked in the continuous liquid field. With the release of version 8.2 the droplet fields can now include one or more solid components within each droplet field. The addition of solid components to the droplet field allows faithful simulation of one or more solid components throughout the liquid and droplet fields. Preliminary expected applications are for scenarios such as GSI-191 and longer term desired applications are aerosol simulation. (authors)

42 ENGINEERING↗
DOE OSTI2024

Accelerating Thermochemical Equilibrium Calculations for Nuclear Reactor Applications

Thermochemical properties play a key role in modeling and simulation of several key phenomena in nuclear reactors. There has been an increasing interest in incorporating CALPHAD-based formulations in multiphysics simulations including for Molten Salt Reactors where knowledge of phase evolution of the salt and the chemical potentials of various elements are of utmost importance in source term analyses and redox control. However, the size of such simulations is often limited by the high computational cost of full thermodynamic equilibrium calculations. This work discusses the current efforts aimed at accelerating thermochemical equilibrium calculations for multiphysics simulations performed using the open-source finite element / finite volume code Multiphysics Object Oriented Simulation Environment (MOOSE) [1]. While several methods have been proposed for accelerating phase equilibrium calculations [2], most focus on relatively small systems and often rely on a- priori knowledge of the state-space of the system. Nuclear materials, however, are often multi-component systems owing to the evolution of composition under irradiation and an approach based on a-priori mapping of phase diagram is often not enough. This work is aimed at demonstrating an on-the-fly surrogate modeling framework that uses active learning to reduce the number of full equilibrium calculations that must be performed. By combining with efficient coupling approaches, the surrogate framework helps in reducing the computational cost of thermodynamic equilibrium informed multiphysics simulations of nuclear materials. The performance is benchmarked against full coupling with the thermochemistry library Thermochimica [3]. This work uses a machine learning based approach for constructing surrogate models to predict the stable phases in a multicomponent system. The surrogates were constructed using neural networks and Gaussian process classification. In this work, we compare the relative performance of the two methods. We also demonstrate the use of caching previous calculations by interpolating the values from nearest neighbors. References [1] Lindsay, A.D., et al. "2.0 – MOOSE: Enabling massively parallel multiphysics simulation", SoftwareX, 20 (2022): 101202. [2] Roos, W.A. and Zietsman J.H. "Accelerating complex chemical equilibrium calculations – A Review", Calphad, 77 (2022): 102380. [3] Piro, M.H.A., et al. "The thermochemistry library Thermochimica", Computational Materials Science, 67 (2013): 266-272.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Multiphysics Time-Integration for Turbulent Combustion at the Exascale

Turbulent reacting flow systems are often modeled with coupled time-dependent partial differential equations (PDEs). Solving such equations can easily tax the world's largest supercomputers. One pragmatic strategy for attacking such problems is to split the PDEs into components that can more easily be solved in isolation. This generic operator-splitting strategy leads to a set of ordinary differential equations (ODEs) that need to be solved as part of an "outer-loop" time-stepping approach. In many combustion applications, the ODEs to be solved can be very stiff, exhibiting timescales that span many orders of magnitude. The SUNDIALS library provides a plethora of robust time integration algorithms for solving these ODEs on exascale-capable computing hardware, yet for many complex applications (such multicomponent fuels or emissions predictions), the chemical models remain too complex to solve using reasonable resources. The Quasi-Steady State Approximation (QSSA) can be an effective tool for reducing the size and stiffness of the simulations. In this talk, I will discuss the use of the SUDIALS library of ODE solvers together with automatic code generation tools to solve complex turbulent reacting flow problems using QSSA models.

chemistry↗
DOE OSTI2025

Cluster Dynamics Modeling Needs for the Advanced Materials and Manufacturing Technologies Program

This milestone report aims to identify and assess the cluster dynamics (CD) modeling requirements within the Department of Energy's Office of Nuclear Energy (DOE-NE) Advanced Materials and Manufacturing Technologies (AMMT) program and to communicate these needs to the DOE-NE Nuclear Energy Advanced Modeling and Simulation (NEAMS) program. The goal is to ensure NEAMS is well-informed about the CD modeling requirements to support AMMT's mission of accelerating the development, qualification, demonstration, and deployment of advanced structural materials and manufacturing for nuclear energy applications. CD modeling is an essential tool for predicting the degradation of structural materials under irradiation, which is a key component of AMMT's accelerated qualification process. The AMMT program focuses on both additively manufactured and wrought structural alloys, such as laser powder-bed fusion 316H austenitic stainless steel, alloy 709, Haynes 244, and alloy 617. These materials require a generalized CD modeling framework to facilitate rapid model development and computational simulation. A flexible, generalized CD software, similar to the Multiphysics Object-Oriented Simulation Environment (MOOSE) finite element framework, would enable modeling of various cluster types, including defect clusters, defect-solute clusters, and multicomponent clusters, incorporating thermodynamics and kinetics parameters. Radiation effects, microstructural feature evolution, and multi-dimensional modeling are critical considerations for the CD model. The usability of the CD code should allow for easy modification and coupling with MOOSE-based simulations. Additionally, the software should adhere to Nuclear Quality Assurance-1 standards, include a testing suite for verification and validation, and be version-controlled within a national laboratory-managed Git repository. Benchmark problems are needed to assess code predictions and performance.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Self-Driving Microscopy for AI/ML-Enabled Physics Discovery and Materials Optimization

Materials are the bedrock of economy and foundation for all real-world technologies. The viability of space travel, grid energy storage, solar to fuels conversion, methane removal, and photovoltaic energy solutions hinge on the discovery and optimization of novel materials and rapid scaling toward manufacturing. The last 20 years have seen an exponential growth in the theoretical predictive capability for crystalline materials and small molecules. However, it is only in the last five years that we have seen the rapid expansion of high-throughput synthesis enabled by laboratory robotics and microfluidics, as well as a resurgence of combinatorial synthesis (Abolhasani and Kumacheva 2023; Epps and Abolhasani 2021; Jiang et al. 2022; Rajan 2008; Soldatov et al. 2021; Szymanski et al. 2023). Combinatorial synthesis, microfluidics, and ultimately dip-pen megalibraries have demonstrated the ability to “write” multicomponent nanomaterials at high throughput scale, generating millions of material examples in the 3D, 4D, and 5D composition spaces (Chen et al. 2016, 2019; Jibril et al. 2022).

36 MATERIALS SCIENCE↗
DOE OSTI2026

Non-Equilibrium Actinide Radiation Chemistry and the Nuclear Fuel Cycle

Actinides are inherently unstable elements that frequently coexist with other radioisotopes, generating intense ionizing radiation fields that drive the formation of non equilibrium oxidation states. These transient species exert a profound mechanistic influence on the radiation response of actinide containing systems due to their unique redox chemistry. Despite their importance, they remain poorly understood, yet such insight is essential for advancing actinide science and accurately predicting radiation driven behavior. Actinide separations—critical for nuclear energy technologies, strategic deterrence, space exploration, and nuclear medicine—depend on precise control of actinide oxidation states to recover targeted elements from complex matrices such as used nuclear fuel. However, during these processes, actinides, their coordination complexes, and the separation media are all exposed to intense, multicomponent (alpha, beta, gamma, etc.) radiation fields that can alter process efficiency, selectivity, and chemical stability. Understanding, controlling, and mitigating radiation induced reactions is therefore key to innovating and optimizing next generation separation technologies. This seminar will provide an overview of the nuclear fuel cycle and non equilibrium actinide radiation chemistry in the context of recovering actinides from used nuclear fuel, with a particular emphasis on direct dissolution–based reprocessing strategies. We will explore time resolved electron pulse radiolysis and alpha and gamma dose accumulation studies, integrated with multiscale computational modeling, to elucidate the molecular level roles of radiation driven, non equilibrium actinide species in process performance and in the radiolytic stability of organic ligands used for actinide recovery. These insights offer new pathways for designing advanced separation methods and next generation solvent systems, with broad implications for the future of the nuclear fuel cycle.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2026

Non-Equilibrium Actinide Radiation Chemistry and the Nuclear Fuel Cycle

Invited John and Naomi Fackler Lectureship in Chemistry and English seminar at Valparaiso University, IN, USA. Actinides are inherently unstable elements that frequently coexist with other radioisotopes, generating intense ionizing radiation fields that drive the formation of non-equilibrium oxidation states. These transient species exert a profound mechanistic influence on the radiation response of actinide-containing systems due to their unique redox chemistry. Despite their importance, they remain poorly understood, yet such insight is essential for advancing actinide science and accurately predicting radiation-driven behavior. Actinide separations—critical for nuclear energy technologies, strategic deterrence, space exploration, and nuclear medicine—depend on precise control of actinide oxidation states to recover targeted elements from complex matrices such as used nuclear fuel. However, during these processes, actinides, their coordination complexes, and the separation media are all exposed to intense, multicomponent (alpha, beta, gamma, etc.) radiation fields that can alter process efficiency, selectivity, and chemical stability. Understanding, controlling, and mitigating radiation-induced reactions is therefore key to innovating and optimizing next-generation separation technologies. This seminar will provide an overview of the nuclear fuel cycle and non-equilibrium actinide radiation chemistry in the context of recovering actinides from used nuclear fuel, with a particular emphasis on direct-dissolution–based reprocessing strategies. We will explore time-resolved electron pulse radiolysis and gamma dose accumulation studies to elucidate the molecular-level roles of radiation-driven, non-equilibrium actinide species in process performance and in the radiolytic stability of organic ligands used for actinide recovery. These insights offer new pathways for designing advanced separation methods and next-generation solvent systems, with broad implications for the future of the nuclear fuel cycle.

37 - INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL C↗
DOE OSTI2025

Grain Boundary Segregation Suppresses Local Short‐Range Ordering in Nanocrystalline High‐Entropy Alloys

Multi-principal-element alloys like high-entropy alloys (HEAs) have potential applications in many engineering fields due to their unique mechanical/functional properties. While HEAs are generally considered random solid solutions, recent studies revealed that they are prone to short-range-ordering (SRO) due to the complex multi-pair-wise interactions among the constituent elements. Meanwhile, SROs' evolution can sometimes be deleterious, and it is necessary to have control over their evolution. Examining the AlCoCrFe-Zr model alloy, long-range ordering occurs following the expectation of enthalpic predictions. Advanced characterization techniques—transmission electron microscopy, high-energy synchrotron X-ray diffraction/pair distribution function, and atom probe tomography, reveal that SRO is suppressed in as-milled and GB-decorated NC-(AlCoCrFe)100-xZrx (x = 0–1.5 atomic %). Warren-Cowley coefficient calculations are further used to validate the suppression of SRO. Besides the low segregation enthalpies of Cr, Fe, and Zr, and the high-mixing enthalpy of Cr and Fe, the short diffusion path to GBs due to high-GB density in the NC-HEAs and the higher energy state of the GBs than the matrix promotes GB-segregation that further alters the matrix chemistry and consequently disfavors SRO formation within the matrix. Despite the GB-segregation of Cr, Fe, and Zr, the matrices and GBs remain in a random solid solution.

36 MATERIALS SCIENCE↗