ICONE11-36033 EXPERIMENTAL STUDY OF THERMAL-HYDRAULIC BEHAVIOR OF COOLANT OUT OF NEUTRON REFLECTOR FOR APWR DURING REFLOODING OF LARGE BREAK LOCA

Abstract

An experimental study was carried out to investigate the steam-water two-phase flow of coolant in the Neutron Reflector (N/R) during the reflooding of large break Loss OF Coolant Accident (LOCA). The experimental apparatus simulated the geometry of one hole of a typical N/R cooling-hole (including the corresponding thermal capacity), the lower and the upper plenum. The steam and water were used as the practical working fluids. The water flow rate at the inlet was kept constant at a fixed level through the injection pump. The boundary conditions including the LOCA phenomena, which were estimated by an analytical code, were supplied through the measurement of the system pressure and the entrance temperature of the water. The system pressure, temperature, and flow rate of steam and water were measured simultaneously to investigate the thermal-hydraulic behaviors at the end of the cooling-hole. Further, the behavior of liquid lumps and droplets flow during the simulated reflooding was observed at the outlet of the test section. The closed inspection revealed that the flow condition out of the test section were changing during the simulated reflooding and was classified into three stages. At the initial stage, the liquid lumps and the droplets flowed continuously like a fountain. At the medium stage, misty flow appeared, i. e. dispersed small droplets and/or liquid lumps flowed in steam flow. At the final stage, the liquid lumps flowed periodically with a little amount of steam flow. In this study, the effects of the reflooding velocity, the initial metal temperature, the reflooding water temperature and the upper plenum pressure were clarified. For the lower reflooding velocity, the ratio of steam flow rate increased. For the higher initial metal temperature, the integration of steam and water flow rate increased. The reflooding water temperature and the pressure of the upper plenum at the experimental conditions had little effects on the thermal hydraulic behavior of the coolant at the outlet of the test section.