Vernon F. Nicolette

Coupling of Large Fire Phenomenon with Object Geometry and Object Thermal Response

The effect of an object in or near a large fire on the physical pro cesses which result in the heat flux from the fire is defined by the object geometry and temperature, and therefore the fire phenomena and the object physical states can be coupled. Two primary modes of coupling, radiative and convective, and their relative influence on heat flux, are investigated using observations from ex perimental data and numerical simulations. Radiative coupling occurs when a comparatively cold object reduces the incident heat flux (by up to 65%) due to radiative cooling of nearby media. Convective coupling includes: (1) changes in the geometry of the flame zone, and (2) object-induced turbulence which alters and often enhances the flow, mixing, and, hence, combustion processes within the fire. Increases in the heat flux approaching a factor of three have been observed due to these phenomena.

Estimates of the Extent and Character of the Oxygen-Starved Interior in Large Pool Fires

Based on data from large pool fire experiments and computational fire field model simulations, the size, shape, and character of the oxygen-starved interior in large pool fires is estimated. In the interior of the fire and near the pool surface, low average and low mean deviation temperatures were noted in experimental data for low wind conditions. These trends tend to indicate the presence of a non-combusting region. Using average and mean deviation temperature distributions (supplemented by heat flux measurements) from several data sets, the spatial extent of the vapor dome is estimated for a range of wind conditions. These estimates are compared with fire field model results of temperature and fuel/air concentration distributions. Predicted and measured temperature trends, supported by heat flux data, illustrate the importance of object placement within the fire during system fire survivability testing. The presence of this region also supplements conventional pool fire representations which are based on a continuous flame zone which extends to the pool surface.

A joint computational and experimental study to evaluate Inconel-sheathed thermocouple performance in flames.

A joint experimental and computational study was performed to evaluate the capability of the Sandia Fire Code VULCAN to predict thermocouple response temperature. Thermocouple temperatures recorded by an Inconel-sheathed thermocouple inserted into a near-adiabatic flat flame were predicted by companion VULCAN simulations. The predicted thermocouple temperatures were within 6% of the measured values, with the error primarily attributable to uncertainty in Inconel 600 emissivity and axial conduction losses along the length of the thermocouple assembly. Hence, it is recommended that future thermocouple models (for Inconel-sheathed designs) include a correction for axial conduction. Given the remarkable agreement between experiment and simulation, it is recommended that the analysis be repeated for thermocouples in flames with pollutants such as soot.

Fire models for assessment of nuclear power plant fires

Abstract This paper reviews the state-of-the-art in available fire models for the assessment of nuclear power plant fires. The advantages and disadvantages of three basic types of fire models (zone, field, and control volume) and Sandias experience with these models will be discussed. It is shown that the type of fire model selected to solve a particular problem should be based on the information that is required. Areas of concern which relate to all nuclear power plant fire models are identified.

Consequences of Surface Deposition of Molten Aluminum in High-Temperature Oxidizing Environments

In a potential accident scenario with a solid-propellant fire, aluminum present in the propellant and in surrounding structures is exposed to high-temperature environments. The enthalpy present in the aluminum particles is a substantial component of the heat release, both in terms of the particle sensible energy and its chemical energy. This paper examines the consequences of the deposition of aluminum particles present in the propellant in terms of heat transfer to surfaces. Also examined is the possibility that deposited aluminum will ignite in the high-temperature oxidizing environment. The examination is made using a computational fluid dynamics approach with some new models to describe the aluminum oxidation. In addition, these models provide a means to predict the aluminum ignition criteria that will be discussed.Copyright

A discussion of fire suppression induced equipment damage and systems impact through an examination of spurious fire suppression actuation incidents

Abstract This paper will discuss current work associated with the investigation of equipment damage induced by the application of fire suppressants. This discussion will be presented through an examination of several nuclear power plant incidents in which the spurious actuation of one or more fire suppression systems has occurred. The effects of these actuations on plant equipment, systems, and operation will be described. Also presented are the results of scoping calculations of the risk significance of spurious suppression system actuation. Finally, the paper will provide a description of efforts recommended to further investigate the impact of such incidents on plant operations and plant risk.