Simulation and analysis of thermal-hydraulic phenomena in a PWR hot leg related to SBLOCA Original Research Article

Thermal-hydraulic phenomena in the hot leg of a pressurized water reactor during the small break loss-of-coolant accident (SBLOCA) are simulated and studied in this paper. They include the single-phase flow dynamics, the cocurrent stratified flow during the natural circulation conditions, and the countercurrent stratified flow during the reflux condensation conditions. Satisfactory results were obtained from the computations in comparison with the data from the German Upper Plenum Test Facility. It is revealed that the fluid flow exhibits strong multi-dimensional effects, i.e. an appreciable acceleration and deceleration along different regions of the hot leg, and a four-vortex secondary flow structure in the cross-section of the bend region. Cocurrent stratified flow under the natural circulation conditions is successfully simulated, presenting two different water transport mechanisms. Under the reflux condensation conditions, different countercurrent flow structures are found under the conditions away from and with the countercurrent flow limit.