Thermohydraulics of fuel-element bundles with low water flow rates and steam-water counterflow

This paper examines the features of numerous types of natural circulation (core cooling) that occurs after large amounts of coolant has been lost from the primary loop. These types of flow included cascade flow, steam-condensate flow, interassembly natural circulation and descending circulation in the interassembly gap. The examination is based upon experiments done on natural circulation loop simulators of reactors and associated equipment. The experimental loops included electric mockups of fuel-element bundles for domestic water cooled reactors. The models considered were; (1) A VVER-1000 fuel element bundle, and (2) An AST-500 fuel element bundle. Under the conditions of the experiment, recommendations are made for calculating the steam content and the critical power for the fuel element bundle.