Results of 0.5% Hot-Leg Break Loss-of-Coolant Accident Experiments at ROSA-IV/LSTF: The Effect of Break Orientation

Three 0.5% hot-leg small-break loss-of-coolant accident experiments are conducted at the ROSA-IV Large-Scale Test Facility (LSTF), a volumetrically scaled full-height model of a pressurized water reactor. Three experiments simulate breaks located at the side, bottom, and top of the horizontal hot-leg piping to investigate the effects of break orientation on system thermal-hydraulic responses. Although the overall system responses in the three experiments are qualitatively the same, the break flow rate is affected significantly by the break orientation for most of the time preceding the initiation of core uncovering: The break flow rate is largest for the bottom break and smallest for the top break. The RELAP5/MOD2 code fails to predict the differences in break flow rate observed in the experiments. However, several modifications, based on separate-effect experiments, made particularly to the break flow calculation models enable this code to simulate the experimental results well.