Abstract
Open pool type research reactors often use a chimney structure to prevent mixing of core outlet water directly into the pool in order to keep the radioactivity level at the pool top to a lower limit. This chimney structure facilitates guiding of the radioactive water from the reactor core towards the side outlet nozzles and simultaneously sucking water from the reactor pool through the chimney top. The present work aims at studying the turbulent mixing behaviour of water coolant inside a 1/6^<th> scaled down model of chimney structure. The range of dimensionless numbers considered in the simulation are 1.44×10^6 < Re < 2.88×10^6 and 0.002 < Ri < 0.008. The effects of flow ratio between upward flow & downward flow and their temperature difference on the mixing behaviour are analysed by means of commercial software. Turbulence is modelled by using the Reynolds averaged Navier Stokes (RANS) equation. The results indicate that the increase in downward (core bypass) flow, increases stagnation depth and try to keep the radio-activity well within the chimney region. On the contrary, the temperature difference between the hot upward fluid and cold downward fluid tries to reduce the stagnation depth. It is observed that if sufficient bypass flow is provided, no water from the core will reach the reactor pool through the chimney top opening.
