Experimental studies on moderator circulation flow in the 1/4 scaled model of CANDU-6 calandria

Abstract

In this study the local velocity profile is measured by the Particle Image Velocimetry (PIV) measurement system to generate the experimental data necessary to validate the Computational Fluid Dynamics (CFD) code that will be used to predict the thermal-hydraulic behavior of moderator flow inside a 1/4 scale of calandria tank of a CANDU-6 reactor (pressurized heavy water reactor). The experimental results show that the flow inside the moderator tank of a CANDU-6 reactor during full power steady state operation is predicted to be operating in the mixed convection regime where competition between the upward buoyancy driven flows and the downward inlet jet driven inertial flows, results in the formation of asymmetric localized recirculation zones wherein the hottest spot may occur. Two inlet flows from the nozzles on the left and the right sides of the tank go through the upper boundary of the tank, impinge on each other, and form downward moving flows. Once the impingement point is located to one side by initial imbalance of two opposing jets, it cannot go to the other side. It is also shown that positional angle of the impingement point is affected by the dimensionless number, the ratio of buoyancy to inlet momentum.