Investigation of the mixing of the coolant in the distribution collector systems of fast and BBÉR reactors

Abstract

Different ratios of the flow rate and temperature of the coolant flowing into the bottom (discharge) chamber from the circulation pumps of different loops, are possible during the operation of multiloop nuclear reactors. To estimate the operating temperature of the core, it is necessary to know the characteristics of the flow and mixing of the coolant from different loops in the distribution collector systems.Analysis of the results of experimental and computational investigations of the hydrodynamics and mixing processes of the coolant in the distribution collector systems with lateral feeding and central discharge of the flow [1][2][3][4] showed that the character of the flow rate of the coolant and the intensity of the mixing process in these systems depends on the construction of the flow through sections of the distribution collector system.An experimental investigation of the process of mixing of the coolant in the entrance collector of the core was performed for BN-800 ( Fig. 1) and BBER [5] reactors on an aerodynamic stand using the halide-tracer method. In this method an impurity is injected into the air flow and the impurity concentration is measured downstream with a calibrated halide leak detector.An experimental 1:5 scale model of the discharge chamber of a BN-800 reactor was built and met the conditions of geometric similarity with respect to one variant of the reactor design (Fig. 2). The model had two intake pipes for each of the three loops. A uniformly perforated shell was installed concentrically inside the cylindrical vessel of the model in the region of the intake pipes. The shell contained 115 simulators of the liners of the collectors in the core and the screen. A simulator of the liners of the screen and storage collectors were placed in the annular gap between the wails of the vessel and the shell. Openings were made at the bottom ends of the simulators to allow air to flow through and throttling devices were installed at the top ends.In the experiments, air from the loop of the aerodynamic bench, under a head of not more than 30 hPa, was fed through a flow meter and the distribution collector into the air ducts, which were equipped with flow regulators, flow meters, and devices for continuous injection of a tracer gas into the main flow. From the air ducts, the flow, separated in a T-joint into two parts, entered the bottom chamber through the intake pipes. Part of the flow moved in the gap between the vessel and the shell, while the other part entered the central part of the chamber through an opening in the shell. In both cases, the flow through the opening passed into the inner cavity of the liner and into the discharge chamber through the throttling inserts and removed from the model.To simulate the flow of the coolant at the higher temperature into the bottom chamber of the reactor through one of the intake pipes, a mixture of the tracer in the air flow was produced in one of the three air ducts.The liners, the outer wall, and the bottom of the model were equipped with devices for e...