Effect of asymmetric airflow on liquid film behavior and emergency core coolant bypass in the downcomer geometry of a nuclear reactor pressure vessel

Abstract

In this study, experimental work was carried out using a 1/10 reduced-scale downcomer of a nuclear reactor pressure vessel to examine the liquid film behavior under emergency core coolant (ECC) bypass conditions. It is caused by the interaction between the transverse gas flow and the falling liquid film. The experiments were conducted considering the asymmetric gas velocity inside the downcomer. An air–water mixture was used as the working fluid in the experiment, forming a complex liquid film flow in the annular test section of the downcomer. To measure the local liquid film thickness, an electrical conductance sensor fabricated on a flexible printed circuit board was applied. The effect of the asymmetric airflow on the liquid film behavior was investigated using the liquid film thickness measurements. Results showed that the asymmetry influences the distribution of the liquid film; the larger the asymmetry, the closer is the liquid film is to the break with the same gas outlet velocity. It influences the trend of the ECC bypass fraction with respect to the gas velocity. The present study provides detailed understanding of the ECC bypass phenomenon under asymmetric airflow conditions; this enables determining how the liquid film behavior is changed by the gas flow and how it affects the ECC bypass.