Numerical Simulation of Turbulent Mixing ...

Numerical simulation was carried out to study the turbulent mixing behaviour of two opposite flows inside a square chimney model of a pool type research reactor. This type of chimney structure is often used for open pool type reactors to prevent mixing of core outlet water directly into the pool. The chimney design facilitates guiding of the radioactive water from the reactor core towards the side outlet nozzles and simultaneously allows drawing water from the reactor pool through the chimney top opening. This helps to limit the radioactivity level at the pool top to a lower limit. The present work aims at studying the turbulent mixing inside a 2/9th scaled down model of chimney structure. The Reynolds numbers considered in the simulation are 1.36×106, 1.81×106, 2.26×106 and 2.72×106 which correspond to upward core flow of 12.5, 16.67, 20.83 and 25 kg/s respectively. The core bypass flow which is sucked in the downward direction varies to 0, 5, 10 and 15% of the core flow. The effects of flow ratio between the upward flow and downward flow on the mixing behaviour are analysed using PHOENICS code. Turbulence is modelled by using the Reynolds averaged Navier Stokes (RANS) equation. The results indicate that increase in downward flow causes the jet height to decrease. It is observed that the jet height mainly depends on the ratio of core bypass flow and core flow. The effect of change on core flow is insignificant.