Effect of Rod Bowing on Critical Power Based on Tight-Lattice 37-Rod Bundle Experiments

Abstract

The confirmation of thermal-hydraulic performance is one of the most important R&D requirements for the design of the Innovative Water Reactor for FLexible Fuel Cycle (FLWR). Since the effect of rod bowing on critical power has not been determined yet due to the lack of experimental data, a large-scale thermal-hydraulic experiment using a tight-lattice 37-rod bundle test section with a bowed rod was carried out with pressure ranging from 2-9 MPa and mass velocity at 200-1000 kg/(m 2 s). It was confirmed that boiling transition (BT) occurs downstream of the rod contact point, and that the wall temperature trace during the BT follows the typical BT pattern of BWR. The critical power with a bowed rod is about 10% lower than that without rod bowing. The critical power increases monotonically with the increase in mass velocity, with the decrease in inlet water temperature, and with the decrease in exit pressure, and these trends are similar to those of the basic bundle without rod bowing. Thus, there is a negligible effect of rod bowing on the dependence of critical power on the mass velocity, the inlet temperature, and the exit pressure.