Impact of rapid condensations of large vapor spaces on natural circulation in integral systems

Abstract

In this study we demonstrated that the Interruption-Resumption flow mode (IRM) observed in the University of Maryland 2 × 4 loop is a unique and effective natural circulation cooling mode. The IRM flow mode consists of a series of large flow cycles which are initiated from a quiescent steady-state flow condition by periodic rapid condensation of large vapor spaces. The significance of this mass/energy transport mechanism is that it cannot be evaluated using the techniques developed for the commonly known density-driven natural circulation cooling mode. We also demonstrated that the rapid condensation mechanism essentially acts as a strong amplifier which will augment small perturbations and will activate several flow phenomena. The interplay of the phenomena involves a degree of randomness. This poses two important implications. First, the study of an isolated flow phenomenon is not sufficient for the understanding of the system-wide IRM fluid movement. Second, the duplication of reactor transients which involves randomness can be achieved only within certain bounds. The modeling of such transients by deterministic computer codes requires recognition of this physical reality.