High heat flux (>500 kW/m2) ignitions occur in scenarios involving metal fires, propellants, lightning strikes, above ground nuclear weapon use, etc. Data for material response in such environments is primarily limited to experimental programs in the 1950s and 1960s. We have recently obtained new data in this environment using concentrated solar energy. A portion of the experimental data were taken with the objective that the data be useful for model validation. To maximize the utility of the data for validation of predictive codes, additional focus is placed on repeatability of the data, reduction of uncertainties, and characterization of the environment. We illustrate here a portion of the data and methods used to assess environmental and response parameters. The data we present are novel in the flux range and materials tested, and these data constitute progress in the ability to characterize fires from high flux events.
Momentum, advection, diffusion, and turbulence are component physics relating to fire simulation tools like computational fluid dynamics (CFD). Magnetic Resonance Velocimetry and Magnetic Resonance Concentration MRV/MRC techniques can produce heretofore unrivaled detailed measurements of three-component velocity and concentration fields in turbulent flows. This study exhibits 3D flow comparisons between velocity and concentration fields obtained using MRC/MRV and SIERRA/Fuego for an urban geometry based on a section of downtown Oklahoma City. A 1:2500 scale water flow scenario provides 0.8 mm resolution data. Various techniques are employed to quantify the accuracy of the simulation results. The techniques all generally suggest a good comparison between the model and experiments throughout the compared volume. The selected metrics provide benchmark accuracy measures that can be used to indicate quantitative accuracy of the simulations, as well as for targets for future simulation improvements.
Irradiance from a nuclear weapon can be the source of heat on gas infrastructure. This exposure when sufficiently intense can result in failure. An estimation tool for this behavior is the object of this study. A lumped capacity technique is employed to estimate the system temperature rise. The temperature rise is related to three possible outcomes. Two of the outcomes are relatively certain failure and relatively certain lack of effect. A large range of exposures are assessed with the model, and a relatively small number of cases are in the uncertain range. This model is presented as a tool that can be used in conjunction with a structural assessment model to sensitivities to the overpressure and shock to screen potential outcomes from subject events .
Data from four TGA experiments conducted at Sandia National Laboratories was used for determination of a pyrolysis model using a commercial thermokinetics program developed by Netzsch Instruments (Kinetics NEO, version 2.1). The data measured at 1 K/min and the average of three measurements at 50 K/min were used as input into Kinetics NEO. The model was developed using data in the range 373 to 773 K. An initial estimate of the energy of activation (E) and pre-exponential constant (A) were determined from the model-free Friedman approach.
Melting and flowing of aluminum alloys is a challenging problem for computational codes. Unlike most common substances, the surface of an aluminum melt exhibits rapid oxidation and elemental migration, and like a bag filled with water can remain 2-dimensionally unruptured while the metal inside is flowing. Much of the historical work in this area focuses on friction welding and neglects the surface behavior due to the high stress of the application. We are concerned with low-stress melting applications, in which the bag behavior is more relevant. Adapting models and measurements from the literature, we have developed a formulation for the viscous behavior of the melt based on an abstraction of historical measurement, and a construct for the bag behavior. These models are implemented and demonstrated in a 3D level-set multi-phase solver package, SIERRA/Aria. A series of increasingly complex simulation scenarios are illustrated that help verify implementation of the models in conjunction with other required model components like convection, radiation, gravity, and surface interactions.
Airborne contaminants from fires containing nuclear waste represent significant health hazards and shape the design and operation of nuclear facilities. Much of the data used to formulate DOE-HDBK-3010-94, “Airborne Release Fractions/Rates and Respirable Fractions for Nonreactor Nuclear Facilities,” from the U.S. Department of Energy, were taken over 40 years ago. The objectives of this study were to reproduce experiments from Pacific Northwest Laboratories conducted in June 1973 employing current aerosol measurement methods and instrumentation, develop an enhanced understanding of particulate formation and transport from fires containing nuclear waste, and provide modeling and experimental capabilities for updating current standards and practices in nuclear facilities. A special chamber was designed to conduct small fires containing 25 mL of flammable waste containing lutetium nitrate, ytterbium nitrate, or depleted uranium nitrate. Carbon soot aerosols showed aggregates of primary particles ranging from 20 to 60 nm in diameter. In scanning electron microscopy, ~200-nm spheroidal particles were also observed dispersed among the fractal aggregates. The 200-nm spherical particles were composed of metal phosphates. Airborne release fractions (ARFs) were characterized by leaching filter deposits and quantifying metal concentrations with mass spectrometry. The average mass-based ARF for 238U experiments was 1.0 × 10−3 with a standard deviation of 7.5 × 10−4. For the original experiments, DOE-HDBK-3010-94 states, “Uranium ARFs range from 2 × 10−4 to 3 × 10−3, an uncertainty of approximately an order of magnitude.” Thus, current measurements were consistent with DOE-HDBK-3010-94 values. ARF values for lutetium and ytterbium were approximately one to two orders of magnitude lower than 238U. Metal nitrate solubility may have varied with elemental composition and temperature, thereby affecting ARF values for uranium surrogates (Yb and Lu). In addition to ARF data, solution boiling temperatures and evaporation rates can also be deduced from experimental data.
This interim report details model development, theory, and a literature review focusing on the evaporation induced entrainment (sub-boiling) of contaminated liquids. Entrainment from a variety of sources is the topic of DOE Handbook 3010, and this report deals more broadly with fire related airborne sources of contaminants in hazardous operations. Relatively few studies have examined sub-boiling behavior in the past, however, it can be a phenomenon that presents a fire related risk under hazardous operations. Molecular dynamics simulations are used to infer the gaseous evolution of coordinated complexes, and a model for a water/plutonium/nitrate system is deduced from the simulation results by evaluating the statistical trends of the results. Questions remain as to the chemical reactivity and longevity of entrained species. A generalized computer model capability and simple analytical model assumptions are developed for predicting the results of these and other (boiling and solid entrainment) scenarios. Verification related predictions using these models are illustrated.
The atmospheric dispersion of contaminants in the wake of a large urban structure is a challenging fluid mechanics problem of interest to the scientific and engineering communities. Magnetic Resonance Velocimetry (MRV) and Magnetic Resonance Concentration (MRC) are relatively new techniques that leverage diagnostic equipment used primarily by the medical field to make 3D engineering measurements of flow and contaminant dispersal. SIERRA/Fuego, a computational fluid dynamics (CFD) code at Sandia National Labs is employed to make detailed comparisons to the dataset to evaluate the quantitative and qualitative accuracy of the model. This work is the second in a series of scenarios. In the prior work, a single large building in an array of similar buildings was considered with the wind perpendicular to a building face. In this work, the geometry is rotated by 45 degrees and improved studies are performed for simulation credibility. The comparison exercise shows conditionally good comparisons between the model and experiment. Model uncertainties are assessed through parametric variations. Various methods of quantifying the accuracy between experiments and data are examined Three-dimensional analysis of accuracy is performed. The effort helped identify deficiencies in the techniques used to make these comparisons, and further methods development therefore becomes one of the main recommendations for follow-on work.