Study into the Distribution of Mass Velocity and Enthalpy of Single-Phase and Two-Phase Flows in the Cross Section of a 19-Rod Bundle in an Electrically Heated Model of an RBMK-1000 Fuel Assembly

The results of experimental studies into the distribution of mass velocity and enthalpy of single-phase and two-phase flows over the cross section of a 19-rod bundle in an electrically heated model of an RBMK-1000 fuel assembly (FA) are presented. A description is given of the experimental section, which included a 19-rod electrically heated assembly of fuel-element simulators, a system for sampling a medium from cells, and a control system for moving samplers. A bunch of fuel rod simulators consisted of a central unheated rod and 18 electrically heated rods. The heated length of the rods bundle was 3500 mm. The sampling system from characteristic cells included sharp-edge samplers, a system for moving samplers from the starting position to the working position, and a cooling system and measuring sample parameters. Samplers corresponding in shape and geometrical dimensions to five characteristic cells were made of stainless steel. Single phase and two phase samples were taken from assembly characteristic cells under the condition of isokinetics. The condition for the isokinetics of the selection was that the parameters of the coolant flow that entered the sampler remained the same as they were before the sampler was introduced into the stream. In the experiments, the achievement of the isokinetic condition was determined on the basis of the measured difference in static pressures in the cells and on the wall of the assembly housing. The results of experiments performed under isothermal and nonisothermal coolant flows in a wide range of mass velocities and enthalpies are presented. It has been shown that the distribution of the reduced mass velocity and steam quality over the bundle cells depends on the flow regimes of the coolant flow that are formed in the cells.