Rewetting of Vertical Hot Surface in a Centrally Heated Annulus and a 6 x 6 Rod Bundle Geometry During Reflood Phase

A series of bottom reflood tests were carried out to investigate thermal-hydraulic characteristics during the reflood phase. This paper includes descriptions of three related groups of reflood tests categorized by the geometry of a flow channel and an electric power shape of heater rods. A centrally-heated annular geometry with an outer-visualizing tube was adopted for the first two groups of tests (group-A and -B), and a 6 x 6 rod bundle geometry for the other group of tests (group-C). The ranges of experimental parameters are 2∼8 cm/s of flooding velocity, 20∼80 deg. C of inlet subcooling temperature, and 500∼700 deg. C of initial wall temperature. In the single rod annular flow channel reflood test, quench front behavior can be easily observed through the visualizing window and a dominant flow regime near downstream of quench front is inverted annular film boiling regardless of the flooding velocity. For the case of the 6 x 6 rod bundle experiments, on the other hand, the dominant flow regime is dispersed flow film boiling (DFFB), and therefore the thermal hydraulic behavior becomes more complicated and chaotic due to the interaction between liquid phase such as droplet and liquid film and vapor phase generated from liquid-wall heat transfer. (authors)