Publications

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In this work we have presented a particle resuspension model implemented in the SNL code SIERRA/Fuego, which can be used to model particle dispersal and resuspension from surfaces. The method demonstrated is applicable to a class of particles, but would require additional parametric fits or physics models for extension to other applications, such as wetted particles or walls. We have demonstrated the importance of turbulent variations in the wall shear stress when considering resuspension, and implemented both shear stress variation models and stochastic resuspension models (not shown in this work). These models can be used in simulations with of physically realistic scenarios to augment lab-scale DOE Handbook data for airborne release fractions and respirable fractions in order to provide confidences for safety analysts and facility designers to apply in their analyses at DOE sites. Future work on this topic will involve validation of the presented model against experimental data and extension of the empirical models to be applicable to different classes of particles and surfaces.

Abstract not provided.

In this work we have presented a particle resuspension model implemented in the SNL code SIERRA/Fuego, which can be used to model particle dispersal and resuspension from surfaces. The method demonstrated is applicable to a class of particles, but would require additional parametric fits or physics models for extension to other applications, such as wetted particles or walls. We have demonstrated the importance of turbulent variations in the wall shear stress when considering resuspension, and implemented both shear stress variation models and stochastic resuspension models (not shown in this work). These models can be used in simulations with of physically realistic scenarios to augment lab-scale DOE Handbook data for airborne release fractions and respirable fractions in order to provide confidences for safety analysts and facility designers to apply in their analyses at DOE sites. Future work on this topic will involve validation of the presented model against experimental data and extension of the empirical models to be applicable to different classes of particles and surfaces.

Safety basis analysts throughout the U.S. Department of Energy (DOE) complex rely heavily on the information provided in the DOE Hand book, DOE-HDBK-3010, Airborne Release Fractions/Rates and Resp irable Fractions for Nonreactor Nuclear Facilities , to determine source terms. In calcula ting source terms, analysts tend to use the DOE Handbook's bounding values on airbor ne release fractions (ARFs) and respirable fractions (RFs) for various cat egories of insults (representing potential accident release categories). This is typica lly due to both time constraints and the avoidance of regulatory critique. Unfort unately, these bounding ARFs/RFs represent extremely conservative values. Moreover, th ey were derived from very limited small- scale table-top and bench/labo ratory experiments and/or fr om engineered judgment. Thus the basis for the data may not be re presentative to the actual unique accident conditions and configura tions being evaluated. The goal of this res earch is to develop a more ac curate method to identify bounding values for the DOE Handbook using the st ate-of-art multi-physics-based high performance computer codes. This enable s us to better understand the fundamental physics and phenomena associated with the ty pes of accidents for the data described in it. This research has examined two of the DOE Handbook's liquid fire experiments to substantiate the airborne release frac tion data. We found th at additional physical phenomena (i.e., resuspension) need to be included to derive bounding values. For the specific cases of solid powder under pre ssurized condition and mechanical insult conditions the codes demonstrated that we can simulate the phenomena. This work thus provides a low-cost method to establis h physics-justified sa fety bounds by taking into account specific geometri es and conditions that may not have been previously measured and/or are too costly to do so.

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New aircraft are being designed with increasing quantities of composite materials used in their construction. Different from the more traditional metals, composites have a higher propensity to burn. This presents a challenge to transportation safety analyses, as the aircraft structure now represents an additional fuel source involved in the fire scenario. Most of the historical fire testing of composite materials is aimed at studying kinetics, flammability or yield strength under fire conditions. Most of this testing is small-scale. Heterogeneous reactions are often length-scale dependent, and this is thought to be particularly true for composites which exhibit significant microscopic dynamics that can affect macro-scale behavior. We have designed a series of tests to evaluate composite materials under various structural loading conditions with a consistent thermal condition. We have measured mass-loss, heat flux, and temperature throughout the experiments. Several types of panels have been tested, including simple composite panels, and sandwich panels. The main objective of the testing was to understand the importance of the structural loading on a composite to its behavior in response to fire-like conditions. During flaming combustion at early times, there are some features of the panel decomposition that are unique to the type of loading imposed on the panels. At load levels tested, fiber reaction rates at later times appear to be independent of the initial structural loading.

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Some fires may involve fuels that are contaminated with airborne particles such as hazardous chemicals or radioactive materials, and therefore pose a significant health risk by the potential inhalation of the contaminated material. In particular, consider a relatively inert solid material which is sub-micron in size that is suspended in a liquid solvent. Various mechanisms can lead to the solid becoming entrained in the air. First, as a liquid fuel is consumed it typically transitions through a boiling regime. As the vapor bubbles rupture at the liquid surface, the liquid response can result in the formation of film drops (collapsing bubble film) or jet drops (caused by liquid rapidly filling the vapor void). Surface wave action can also result in bubble formation and entrainment as the bubbles collapse. This mechanism is generally a function of wind speed and fluid properties. Also, mass may be entrained from a residual layer formed after consumption of the fuel. This paper reviews the existing literature on these entrainment mechanisms. Based on data from the review, the results from a Lagrangian/Eulerian coupled computational transport code are compared to some existing data on the entrainment of contaminants from liquid fuel fires. Since the multi-phase mechanistic prediction of the entrainment is not mature, the methods employ coupling of correlation data to the computational fluid dynamics (CFD) code.

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Aerosol release in the range of less than 10 μm is of concern in transportation accident situations, particularly those involving radioactive contaminants and fuel fires. An accurate approximation of the Airborne Release Fraction (ARF) is important to properly estimate the impact of the contaminant release to the environment and surrounding population. An experiment was selected which studied contaminant entrainment in a fire and contained enough data sufficiently well presented to simulate with existing computational fluid dynamics (CFD) tools. Work was enabled by utilizing source terms for similar physical systems as presented in other publications. It is possible to investigate physical sensitivities from this model, giving insight into the experimental behavior, and physical processes. The effort also helps prioritize model development in the interest in furthering this predictive capability. Four mechanisms were identified as contributing to contaminant entrainment. Two of these mechanisms, entrainment due to evaporation induction and boiling atomization, were the focus of this study. Parameters, including boiling regime duration, evaporation regime particle size and turbulence, were varied because of their numeric uncertainty, while others like particle injection location, simulation time, and fuel height were varied based on a presumed importance. Entrainment values, as collected downstream of a release, are dependent on the magnitude of the entrainment mechanism, in which boiling far exceeded evaporation in quantity of entrained mass.

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Thermal analysts address a wide variety of applications requiring the simulation of radiation heat transfer phenomena. There are gaps in the currently available modeling capabilities. Addressing these gaps would allow for the consideration of additional physics and increase confidence in simulation predictions. This document outlines a five year plan to address the current and future needs of the analyst community with regards to modeling radiation heat transfer processes. This plan represents a significant multi-year effort that must be supported on an ongoing basis.

This report consolidates technical information on several materials and material classes for a fire assessment. The materials include three polymeric materials, wood, and hydraulic oil. The polymers are polystyrene, polyurethane, and melamine- formaldehyde foams. Samples of two of the specific materials were tested for their behavior in a fire - like environment. Test data and the methods used to test the materials are presented. Much of the remaining data are taken from a literature survey. This report serves as a reference source of properties necessary to predict the behavior of these materials in a fire.

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