Effect of Heat Generation Difference among Fuel Bundles on Core Thermal-Hydraulics during 200% and 5% Loss-of-Coolant Accident Experiments at ROSA-III

摘要

The rig of safety assessment (ROSA)-III facility is a volumetrically scaled (1/424) boiling water reactor (BWR/6) system with an electrically heated core designed for integral loss-of-coolant accident (LOCA) and emergency core cooling system (ECCS) tests. Two 200% and two 5% recirculation pump suction line break LOCA experiments with and without heat generation difference among the bundles were conducted in order to investigate interaction of thermal-hydraulic phenomena in a multi-bundle core. The axial propagation of quenching tends to become more nonuniform in the same bundle as well as in the core in both large and small break experiments when the heat generation difference among the bundles exists. The small flow imbalance among the bundles which is caused by void fraction difference due to the heat generation difference among the bundles is estimated to make the flow condition nonuniform and more agitated and increase the radial scattering of the quenching propagation.