The isothermal-fluidic field of a secondary moderator jet in a ¼ scale CANDU-6 reactor model

The steady, isothermal-fluidic field of forced moderator streams in a ¼ scaled moderator circulation tank (MCT) of a CANDU-6 reactor is analysed. Particular focus is placed on characterizing a secondary jet formed by the collision of symmetric, counter flowing wall jets discharged upwards by nozzles installed at each side of the MCT’s horizontal axis. Two separate sets of experiments have been conducted employing water and air as the working fluids with different nozzle configurations (i.e., discrete dove-tail nozzles for water and two-dimensional slot jet nozzles for air). Then, cross validation of the fluidic data sets from these two different test facilities have been made where the fluidic similarity of the secondary jet generated by the inlet nozzles (particularly its rate of dissipation as it interacts with the calandria tubes (CTs)) has been established. Based on the established fluidic similarity, a series of numerical simulations have been performed according to the boundary conditions obtained extensively from the two-dimensional MCT experiments. Subsequently, the numerical results have been validated against the experimental data to assess the capability of a commercial code (ANSYS CFX V15.0) to resolve the moderator interaction with the CTs. It has been demonstrated that a monotonic decay of the secondary jet whose peak (having roughly 50% of the nozzle’s exit mean vertical velocity component) exists at the throat of the first row of the calandria tubes in the MCT takes place. After which, the momentum of the secondary jet is substantially reduced along its centreline. The rate of dissipation of the secondary jet is under-predicted by the default k-ω SST turbulence model, leading to a dramatic over-prediction of the penetration distance of the secondary jet into the core region. However, the accuracy of the numerical results can be substantially improved with turbulence model parameter tuning to achieve a closer fit with the reference experimental data.