Experimental Study of the Core Cooling at the Reflooding Stage of a Large Break Loss-of-Coolant Accident

The paper presents a description of the experimental facility at OKB Gidropress designed to study thermohydraulic phenomena during the core reflooding caused by a large break loss of a coolant accident in a water-moderated water-cooled (VVER) power reactor. The performed studies yielded a statistically significant amount of experimental data on the time-dependence of the temperature of the fuel-rod simulator cladding at several sections of the fuel-assembly (FA) model that is necessary for the validation of computer codes. The experiments were carried out with two fuel-assembly models with uniform and nonuniform heat release distribution along the height. Each model included 120 heated fuel-rod simulators, 13 spacer grids, six guide channel simulators, and a fuel assembly’s upper nozzle. In the experiments, five options of cooling water supply—bottom, gravity-driven bottom, top, combined, combined gravity-driven—were implemented. To confirm the reproducibility of the experiments, most of them were repeated three to five times. The fuel-assembly models, fuel-rod simulators, used instrumentation items, and experimental procedure are described. Examples are presented of the cooling dynamics of the fuel-rod simulators for different methods of cooling water supply to the reactor model, and the features of each flooding pattern are outlined. The data on the flooding time of the fuel-assembly model are generalized in the form of linear dependencies of this parameter on the relative power of the fuel-rod simulators.