PACTEL-ITE06, VVER-440 natural circulation stepwise coolant inventory reduction

1 - Description of test facility: PACTEL , out of pile model of VVER-440 reactor: - 144 fuel rod simulators with electrically heated and chopped cosine axial power distribution (maximum power 1 MW); - three double-capacity coolant loops to simulate VVER plant with six loops; - horizontally oriented secondary steam generators; - pressurizer, high and low pressure core cooling systems. Scaling Information: - 1/ 305 volume and power scaled model of Russian-designed PWR of the VVER-440 type; - maximum power 1 MW equivalent to 22 % of scaled full power; - full length fuel rod simulators; - elevation of main components including loop seals preserved; - diameter (overall height) of steam generators reduced. 2 - Description of test: The main goal was to study natural circulation in a VVER plant including several single- and two-phase natural circulation modes. The heat generated in the core is transported by the coolant to the steam generators. The steam generator secondary side conditions were held constant, eliminating disturbances caused by the secondary pressure variation. The primary coolant mass was reduced stepwise in the liquid form, and the amount of the drained water was given as a boundary condition. The draining period is very short compared to the stabilizing period, therefore the different natural circulation mechanisms are clearly identified. It was expected that the characteristics of natural circulation at constant pressure is mostly dependent on the primary coolant inventory and the core power level. During the whole experiment the steam generator level control was maintained. The secondary pressure was controlled by a PI controller