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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Multiphysics Simulation of Moisture-Graphite Oxidation in MHTGR

A small amount of moisture on the ppm level could present in the primary helium coolant under normal operations of High-Temperature Gas-cooled Reactors (HTGRs). One potential safety issue related to HTGRs is the chronic moisture-graphite oxidation, which could affect the integrity of the fuel blocks and reflectors in the reactor core, and the support columns in the hot plenum. However, it is infeasible to perform chronic moisture-graphite oxidation tests under the prototypic high-pressure, high-temperature conditions over a long period of time that is comparable to the full service time, i.e., 36 months for Modular High Temperature Gas-cooled Reactor (MHTGR). As an alternate, accelerated moisture-graphite oxidation tests at the atmospheric pressure and high moisture concentrations have been performed in the literature. Through these accelerated tests, global reaction rate equations have been proposed, which makes it possible to study the moisture-graphite oxidation numerically. This paper is aimed to establish a multiphysics model that can evaluate the moisture-graphite oxidation under MHTGR normal operation conditions. COMSOL Multiphysics was applied to couple the fluid flow, heat and mass transfer, chemical reaction and material structural changes. To reduce the calculation time, the prototypic three-dimensional (3-D) structures were simplified into a two-dimensional (2-D) simulation domain. The performance of four nuclear grades of graphite (IG-110, 2114, PCEA, and NBG-17) over a 36-month service period was then investigated under the most likely prototypic conditions of MHTGR. The simulation results indicate that most oxidation occurs in the three or four bottom fuel blocks due to their higher temperatures. In general, however, only a thin layer of 1 mm into the graphite will be considerably oxidized even for those three or four bottom fuel blocks.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

Multiphysics Simulations for LWR Analysis

Accurate prediction of the neutron and temperature distributions within an operating nuclear reactor requires the solution of multiple coupled physics equations. In a light water reactor (LWR), there is a very strong coupling between the power distribution (governed by the radiation transport equation) and the temperature and density distributions (governed by a thermal diusion equation in combination with a fluid flow model). This study aims to begin to quantify the impact of such feedback mechanisms as well as identify numerical diculties associated with such multiphysics problems. A description of the multiphysics model and current solution strategy within the Exnihilo code package will be presented, along with numerical results for a representative 3 3 PWR mini-assembly.

multi-physics↗
DOE OSTI2024

Increased accuracy of multiphysics simulations through flexible execution, transient algorithms, and modular physics

The MOOSE framework is a foundational capability used by the NEAMS program to create over 15 different simulation tools for advanced nuclear reactors. Due to MOOSE’s broad use, improvements to the framework in support of modeling and simulation goals are critical to the program. Such improvements can take many forms, including optimization, improved user experience, streamlined application programming interfaces (APIs), parallelism, and new capabilities. The work described in this report was conducted in direct support of the simulation tools and has already been deployed. The capabilities were implemented in the same order as they are covered in this report: multiple time integrators in the same input file, initial design of framework Components, an input file Application block, extension of NetGen to 3D geometries in MOOSE, and deployment of executors in the multi-system paradigm. These five additions are fundamental capabilities that will be leveraged by many NEAMS applications.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2024

3.0 - MOOSE: Enabling massively parallel multiphysics simulations

The development of MOOSE has kept accelerating since the last release, with over 2,100 pull requests merged over the last 30 months that involved nearly fifty contributors across close to a dozen institutions internationally. The growth in MOOSE's capabilities and downstream applications is reflected in the growth of the community. User support provided on the GitHub discussions forum has steadily increased to nearly 50 daily interactions. New simulation projects, notably to model advanced nuclear reactor and fusion devices, are driving a significant expansion of the capabilities. This paper reports on these developments, with several major released features, new physics modules, and key improvements to the user experience and simulation workflow.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

2.0 - MOOSE: Enabling massively parallel multiphysics simulation

The last 2 years have been a period of unprecedented growth for the MOOSE community and the software itself. The number of monthly visitors to the website has grown from just over 3,000 to now averaging 5,000. In addition, over 1,800 pull requests have been merged since the beginning of 2020, and the new discussions forum has averaged 600 unique visitors per month. The previous publication has been cited over 200 times since it was published 2 years ago. This paper serves as an update on some of the key additions and changes to the code and ecosystem over the last 2 years, as well as recognizing contributions from the community.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Multiphysics simulation of recent experiments on alkali‐silica reaction expansion in reinforced concrete members

Alkali‐silica reaction (ASR) is an important degradation process that causes volumetric expansion and damage in concrete, and is affected significantly by the local temperature, moisture and stress conditions that often vary across the regions of a structure. Numerical simulation is essential to predict the progression and effects of ASR on the performance of structures. Because of the interactions between thermal and moisture transport and mechanical deformation, it is important for numerical models to represent all these physical phenomena and the coupling between them. Simulations of ASR in reinforced concrete (RC) structures are further complicated by the need to capture interactions between concrete and embedded reinforcing bars. Here, this paper describes the implementation of a scalable, coupled‐physics ASR model for simulating RC structures and assesses the ability of that model to predict ASR‐induced expansion in recent laboratory tests on RC block and beam specimens. These laboratory tests and the simulation approach were selected because of their applicability to RC structural‐scale simulations. This validation study helps builds confidence the ability of this approach to model ASR expansion in large, complex RC structures, which is a current high‐priority need.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Multiphysics simulation of microscale copper printing by confined electrodeposition using a nozzle array

3D printing of metals at the microscale and nanoscale is crucial to produce high-density interconnects and intricate structures in electronic devices. Conventional melting and sintering processes are not suitable for these scales due to a reliance on individual metal particles in the size range of tens of micrometers. Confined electrodeposition (CED) is an established alternative to conventional metal 3D printing processes in which an electrolyte is used to selectively induce deposition of the metal on the printing surface. However, commercialization and efficiency of this process have been limited due to a reliance on sub-micrometer nozzles to achieve desirable deposition rates and single nozzle to achieve uniformity of printed structures. Here, we address these challenges by computationally analyzing an array of microscale nozzles. We tailor the convection within the electrolyte to alter both deposition rate and geometric uniformity of the printed structures. The results show that for large nozzles the evaporation alone is not sufficient to obtain high deposition rates, yet an external pressure can be used to increase deposition and alter uniformity (thickness) of printed structures. Our results can be used to design and analyze new experiments toward parallel multi-nozzle deposition using CED toward high-throughput metal printing.

3D printing↗
DOE OSTI2018

Microwave sintering of complex shapes: From multiphysics simulation to improvements of process scalability

The microwave sintering homogeneity of large and complex shape specimens is analyzed. A new approach enabling the fabrication of complex shapes ceramics via 3D printing and microwave sintering is presented. The use of a dental microwave cavity is shown to enable a substantial level of densification of complex shape components while restricting the grain growth. The homogeneity of the processed samples during microwave sintering is studied by an electromagnetic-thermal-mechanical simulation. The realistic densification behavior, that phenomenologically takes into account the microwave effect, is included in the modeling framework. We observe that the simulation indicates the sharp correlation between the microwave field distribution in the cavity, the temperature profile, and the specimen's shape distortion.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Multiphysics simulation of supercritical CO 2 gasification for hydrogen production

A bench-scale supercritical CO 2 gasifier is being considered by the U.S. Department of Energy’s National Energy Technology Laboratory (NETL). A reacting computational fluid dynamics (CFD) model was developed using ANSYS/Fluent in order to investigate the impact of various operating parameters on syngas composition. The model was validated using available data in the literature. Simulations were conducted over a range of coal-slurry loadings, reaction temperatures, system pressures, and oxygen mass flowrates with the goal of optimizing hydrogen production for the considered reactor. The results from the simulations identified a positive correlation between slurry loading and hydrogen production, while reactor temperature and pressure had a limited impact on H 2 production at the conditions of interest. Additionally, the simulations indicated that oxygen mass flowrate has less of an impact on hydrogen production at higher slurry loadings.

08 HYDROGEN↗