In the development of the Severe Accident Analysis Program for the Savannah River production reactors, it was recognized that certain accidents have -the potential for causing damaging steam explosions. Steam explosions can occur when metals, such as the aluminum-based fuel used at Savannah River, are melted and come into contact with water. This condition is unstable, and local turbulence can lead to the generation of great quantities of steam within a few milliseconds. This phenomenon has been observed in several reactor incidents and experiments (BORAX, SPERT-1, SL-1, probably Chernobyl) where it caused damage to the reactor and associated structures. The massive SRS reactor buildings are likely to withstand any imaginable steam explosion. However, reactor components and building structures including hatches, ventilation ducts, etc., could be at risk if such an explosion occurred. The goal for this study was to develop a computer code that could be used parametrically to predict the effects of various steam explosions on their surroundings. This would be able to predict whether a steam explosion of a given magnitude would be likely to fail a particular structure. This would require, of course, that the magnitude of the explosion be specified through some combination of judgment and calculation. The requested code, identified as the K-FIX(GT) code, was developed and delivered by the contractor, along with extensive documentation. The several individual reports that constitute the documentation are each being issued as a separate WSRC report. Documentation includes several model calculations, and. representation of these in graphic form. This report incorporates Report GTRSR-006, which gives an overview of the methods used in the development of K-FIX(GT), and the results of a comparison with experiments in the literature. The authors conclude that the results of the comparison calculation are in reasonable agreement with observations.

The two-fluid, three-dimensional, fluid dynamics code K-FIX has been modified to produce the K-FIX(GT) code, in order to simulate the expansion phase of steam explosions. For a given explosion, the interaction zone is represented by a high pressure bubble as an initial condition; subsequent calculations are made to determine pressure histories and impulse at the test vessel or confinement building walls and internal structures. Explosion energetics, i.e. the work and mechanical energy yield, are also calculated as a measure of the destructive potential of the explosion. The main modifications involved in developing the K-FIX(GT) code consist of adding new components representing a non-condensible gas, air, and debris particles to the two-phase water mixture, and introducing new exchange functions for mass, momentum, and energy which are particularly suited to this type of fast transient. This paper describes the theoretical models incorporated into the code. In addition, one of Sandia National Laboratories Fully Instrumented Test Series tests (FITS-2B) is simulated for the purpose of preliminary code and method validation. Comparison between experimental data and code predictions shows good agreement.

Accurately predicting the behaviour of multiphase flows is a problem of immense industrial and scientific interest. Modern computers can now study the dynamics in great detail and these simulations yield unprecedented insight. This book provides a comprehensive introduction to direct numerical simulations of multiphase flows for researchers and graduate students. After a brief overview of the context and history the authors review the governing equations. A particular emphasis is placed on the 'one-fluid' formulation where a single set of equations is used to describe the entire flow field and interface terms are included as singularity distributions. Several applications are discussed, showing how direct numerical simulations have helped researchers advance both our understanding and our ability to make predictions. The final chapter gives an overview of recent studies of flows with relatively complex physics, such as mass transfer and chemical reactions, solidification and boiling, and includes extensive references to current work.