Investigation of natural circulation heat transfer in primary and secondary sides of pressurized water reactor steam generator

The Large Scale Test Facility (LSTF) of the Rig of Safety Assessment No. 4 (ROSA-IV) program is a volumetrically scaled (1/48) pressurized water reactor (PWR) system with an electrically heated core used for integral simulation of small break loss-of-coolant accidents (SBLOCAs) and operational transients. Two natural circulation experiments with 5% core power and one with 2% core power were performed at the LSTF to investigate hydraulic phenomena in the primary and secondary sides and primary-to-secondary heat transfer in the steam generators (SGs). The experimental conditions covered single- and two-phase natural circulation and the reflux condensation mode in the primary side and natural circulation in the secondary side. The effects of secondary water inventory on the primary-to-secondary heat transfer was also investigated. The effective overall heat transfer coefficient defined with the effective heat transfer area below the collapsed liquid level in the SG secondary side was estimated to be 1.2 to 2.0 kW/m/sup 2/K for single-phase natural circulation, 2.0 to 2.5 kW/m/sup 2/K for two-phase natural circulation and 2.2 to 3.4 kW/m/sup 2/K for the reflux condensation for 5% core power and 1.5 and 2.5 kW/m/sup 2/K for the reflux condensation for 2% core power. These values were analytically examined and confirmed to be applicable to a PWR SG