Simulation of the Coolant Hydrodynamics in the Outlet Section of the Fuel Assembly of the Cartridge Core of the RITM Type Reactor

The results of experimental studies into the hydrodynamics of the coolant at the outlet section of the cassette fuel assembly (FA) of the RITM-type reactor of a low-power ground-based nuclear power plant are presented. The purpose of the work is to analyze the distribution of the axial velocity and flow rate of the coolant at the exit from the fuel bundle, in the modernized head of the fuel assembly, near the coolant extraction pipe and the openings of the upper base plate as well as to determine those areas of the fuel bundle from which the coolant flow is most likely to enter the pipe selection to the resistance thermometer. To achieve this goal, experiments were carried out on a research stand with an air working medium on a model of the outlet section of a fuel cassette, which includes an outlet fragment of a fuel bundle with spacer grids, models of an upgraded fuel cassette head, an upper support plate, and a coolant extraction pipe. When studying the flow of the coolant flow in the outlet part of the fuel cassette, the pneumometric method and the method of injection of a contrasting impurity were used. An area covering the entire cross section of the model was chosen as the area under study. The picture of the coolant flow is represented by cartograms of the distribution of its axial velocity and flow rate as well as cartograms of the distribution of the contrasting impurity in the cross section of the experimental model. The results of the experiments can serve as a basis for making engineering decisions when designing new cores of RITM type reactors. The obtained database of experimental data can be used for validation of modern CFD programs and one-dimensional thermal-hydraulic codes used to justify the thermal reliability of cores.