Walter W. Yuen

On the fundamental microinteractions that support the propagation of steam explosions

Abstract This paper makes available the first experimental data on the fragmentation kinetics of hot liquid drops in another liquid (coolant) under the influence of sustained pressure pulses. We observe the effect of “thermal” on “hydrodynamic” fragmentation and micromixing mechanisms, as deduced by the rates and morphology of the resulting particle “cloud”. We show how propagation can be quantified within the framework of a numerical model, and on this basis some interesting interpretations of an experimentally-observed triggered “detonation” in the KROTOS facility (in ISPRA) are offered.

Premixing-related behavior of steam explosions

Abstract Three recently published premixing experiments, the Magico, mixa , and Faro , are discussed comparatively, and two of them, the Magico and Faro , are analyzed with the help of the computer code Pm-alpha . The results of these analyses are shown to provide quantitative interpretations of the data, and to suggest conditions/measurements in further experiments to enhance the insights thus obtained. Also, a quantitative radiography technique is described and applied to Magico for the measurement of chordal-averaged void fractions in the mixing zone. The results are in excellent agreement with Pm-Alpha predictions, thus confirming the previously reported good comparisons with the local (point) measurements of Flute .

DEVELOPMENT OF A GENERALIZED ZONAL METHOD FOR ANALYSIS OF RADIATIVE TRANSFER IN ABSORBING AND ANISOTROPICALLY SCATTERING MEDIA

The generalized zonal method ( GZM) for the analysis of radiative heat transfer in absorbing, emitting, and anisutropically scattering media is developed and implemented. It is shown to be applicable both for media with arbitrary scattering phase function and general nondiffuse reflecting surfaces. Mathematically, the GZM is a generalization of the conventional zonal method ( CZM). In addition to the exchange factors utilized by the CZM, the GZM introduces scattering and reflecting exchange factors. These factors characterize the scattering properties of the medium and the reflectivities of the bounding surfaces. Expressions for the scattering and reflecting exchange factors are shown; their numerical and analytical properties are identified. To illustrate the implementation of the GZM, cubic enclosures in radiative equilibrium are analyzed. Based on numerical data, the effect of anisotropic scattering on three-dimensional radiative heat transfer is assessed.

The multiple absorption coefficient zonal method (MACZM), an efficient computational approach for the analysis of radiative heat transfer in multidimensional inhomogeneous nongray media

ABSTRACT The formulation of a multiple absorption coefficient zonal method (MACZM) is presented. The concept of generic exchange factors (GEF) is introduced. Utilizing the GEF concept, the MACZM is shown to be effective in simulating accurately the physics of radiative exchange in multidimensional, inhomogeneous, nongray media. The method can be applied directly to a fine-grid finite-difference or finite-element computation. It is thus suitable for direction implementation in an existing computational fluid dynamics (CFD) code for analysis of radiative heat transfer in practical engineering systems. The feasibility of the method is demonstrated by calculating the radiative exchange between a high-temperature (∼3,000 K) molten nuclear fuel (UO2) and water (with a large variation in absorption coefficient from the visible to the infrared) in a highly three-dimensional and inhomogeneous environment simulating the premixing phase of a steam explosion.

The probability of alpha-mode containment failure

Abstract Since the original quantification of the likelihood of α failure in NUREG/CR-5030, major experimental and analytical developments have taken place. By taking advantage of these developments, we believe it is possible to reduce the substantial conservatisms in the original quantification, and to thus conclude that even vessel failure by steam explosions may be regarded as physically unreasonable. We have illustrated how this can be done within the original framework, as well as in a complementary framework that takes advantage of current integral analysis capabilities. On this basis, the α-failure issue is now ripe for final resolution; what is needed is a complete set of calculations supporting a revised quantification of CR1 and CR3 and a final review step in the ROAAM process.

The prediction of 2D thermal detonations and resulting damage potential

Abstract The main purpose of this paper is to introduce a new concept for the processes responsible for the escalation and propagation of steam explosions. The concept recognizes that initially only a small quantity of coolant around each coarsely premixed melt mass “sees” the fragmenting debris coming off it, hence it is called the concept of “microinteractions”. We also derive the analytical basis for it, define the nature of the requisite constitutive laws and related experimental data, and demonstrate that this concept is essential for the prediction of steam explosion energetics in large-scale premixtures in 2D geometries. We also provide the first numerical illustrations of this concept, implemented in the computer code esprose .m. Further, we provide the first numerical results of steam explosions in large water pools, i.e. ex-vessel explosions. These results reveal two important mechanisms for explosion “venting” and thus for reducing the dynamic loads on adjacent structures. We conclude that, taken together, the “microinteractions” and “venting” make realistic predictions of steam explosion loads feasible and within reach in the near future.

Deposition of fuel droplets in horizontal intake manifolds and the behavior of fuel film flow on its walls

The behavior of liquid fuel droplets and the liquid fuel film within an intake manifold is studied. By considering the simultaneous processes of evaporation and acceleration of fuel droplets in an ongoing air stream, the deposition rate of the fuel droplets and their evaporation in an intake manifold is predicted. The fuel droplets deposited on the wall of an intake manifold become a liquid film flow. The behavior of the liquid flow is studied to determine the thickness and velocity of the film. A time constant describing the delay of fuel flow due to the liquid film is also determined.

Experimental simulation of microinteractions in large scale explosions

The fragmentation behavior of molten steel drops forced to explode in sustained pressure fields is investigated. The effect of pressure amplitude, melt superheat, and coolant velocity is considered. The data include external images from high-speed movies, internal structures from simultaneously obtained flash X-ray radiographs, and solidified debris size distributions and morphology from scanning electron micrographs. The results demonstrate the importance of all three parameters studied on both the rates and extent of the interaction/fragmentation.

The verification basis of the PM-ALPHA code

A set of instruments and method for use in knee replacement surgery, specifically to make the necessary femoral resections is described. The simplified set of instruments allows the necessary femoral resections to be performed with fewer instruments, and with fewer necessary steps for the surgeon to take. The set of instruments includes a three-dimensional jig which references the anterior and posterior femoral condyles to allow determinations as to alignment, placement, and prosthesis size before any bone cuts are made.

Multiphase transients in the premixing of steam explosions

Abstract This paper describes the first attempt to experimentally quantify the multiphase transient associated with the premixing of steam explosions — a hot particulated (heavy) phase falling, in film boiling, into a coolant pool, which is thus forced to rapid vaporization. The process is characterized by mixing-zone-averaged and local void-fraction transients, as well as mixing-front advancement histories, and the data are found to be in good agreement with predictions carried out with our PM-ALPHA code. In particular, these tests confirm the predicted water depletion phenomenon which is a crucial factor in limiting the energetics of large-scale steam explosions.