Preliminary study of annulus ECC flow oscillations. Research project 347-1, Interim report August 1978. [PWR

Abstract

The report documents an exploratory research effort under Research Project 347-1 that investigated timing and rate of delivery of simulated Emergency Core Coolant (ECC) to the lower plenum of a small-scale test section. The experimental model consisted of a broken and an intact loop connected to a simulated Pressurized Water Reactor (PWR) downcomer annulus. The transparent annulus section permitted observation of flow behavior, but design efforts to achieve visualization led to scaling distortions in the model. Core steam flow was simulated with the facility operating at atmospheric pressure. The exploratory test facility fabricated during this project was designed to provide flow visualization of potential annulus-flow instability mechanisms that may arise in future scale model tests. A preliminary examination of available data was the initial step followed by scoping tests to evaluate the possibility of periodic slug delivery to the lower plenum; slug delivery was present under certain conditions. The transparent model was then constructed to aid in the observation of such instability mechanisms; however, major distortions were necessary to study counter-current flow behavior as a separate effect. The experimental observations of the flow behavior are described for the two-loop model.