SIMULATION AND ANALYSIS OF THERMAL-HYDRAULIC PHENOMENA IN A PWR HOT LEG RELATED TO SBLOCA

Thermal-hydraulic phenomena in the hot leg of a pressurized water reac tor during the small break loss-of-coolant accident (SBLOCA) are simul ated and studied in this paper. They include the single-phase flow dyn amics, the cocurrent stratified flow during the natural circulation co nditions, and the countercurrent stratified flow during the reflux con densation conditions. Satisfactory results were obtained from the comp utations in comparison with the data from the German Upper Plenum Test Facility. It is revealed that the fluid flow exhibits strong multi-di mensional effects, i.e. an appreciable acceleration and deceleration a long different regions of the hot leg, and a four-vortex secondary flo w structure in the cross-section of the bend region. Cocurrent stratif ied flow under the natural circulation conditions is successfully simu lated, presenting two different water transport mechanisms. Under the reflux condensation conditions, different countercurrent flow structur es are found under the conditions away from and with the countercurren t flow limit.