PWR FLECHT SEASET unblocked bundle, forced and gravity reflood task. Data evaluation and analysis report. [PWR]

Abstract

This analysis of the unblocked bundle task data provides further understanding of reflood heat transfer mechanisms, which can be used for assessing prediction models. A new heat transfer correlation has been developed and shown to predict the FLECHT SEASET data as well as the older FLECHT data. The scaling logic of maintaining the same integrated power per unit flow area has been proved valid, and a method has been developed to calculate steam quality just above the quench front. Improved models for estimating effluence rate and preliminary exploration of the transition zone above the quench front are discussed. Droplet size and velocity data deduced from high-speed movies taken during the tests have led to better understanding of these parameters. A model has been proposed to predict the onset of droplet entrainment, and an analytical expression to predict critical void fraction developed. A network analysis of radiation heat exchange and calculation of convective heat transfer are among efforts expected to give better prediction for heat transfer and wall temperature transients. Recommendations evolving from the data analysis are also included.