Simulation of Blow-Down Through Two-Phase Flow Module and Orifice in HTHP Loop Using RELAP5/MOD 3.2

In nuclear reactors, leakages through small openings in the pressure boundary of primary heat transport (PHT) system can lead to loss of coolant accident (LOCA) termed as SBLOCA. The calculation of blow-down rates of single and two-phase water from the pipes, nozzles and orifices during LOCA is very essential for the safety analysis of water-cooled reactors. To study the two-phase blow-down characteristics of openings during LOCA conditions, experiments are planned using orifices of different sizes installed in the existing HTHP loop facility at Kalpakkam. The proposed setup has a homogenizer, two-phase flow measuring (TPFM) device and flow restricting orifice augmented in the HTHP loop. Before taking up the experimental studies, cases of blow-down of subcooled and near saturated water at different temperatures (300, 290 and 280 ℃) and pressures (120, 110 and 100 bar) with various sizes of flow restricting orifice (FRO) ranging from 3.0 to 10.0 mm (10 Numbers) are simulated using RELAP5/MOD 3.2 code. This paper summarizes the results of the simulations.