Abstract
A nuclear power plant adopts the way of direct vessel injection to inject safety injection water directly into the downcomer of reactor pressure vessel after accident. In order to avoid the splash phenomenon when the high speed safety injection water coming through the direct vessel injection nozzle impacts the core barrel, a diversion structure installed on the barrel is introduced into the reactor pressure vessel to guide the direction of safety injection water from horizontal to downward. As the existence of the gap between the diversion structure and direct vessel injection nozzle, a significant proportion of leakage of safety injection water occurs and it will affect the effectiveness of safety injection. After the analysis of flow field around the gap, a optimization to the diversion structure is taken out to reduce the leakage flow rate by adding different shapes and dimensions of baffles, such as semicircular baffles and inverted U-shaped baffles. Computational fluid dynamics method is adopted to simulate the flow in downcomer of reactor pressure vessel with different diversion structures and the shape of downcomer is simplified into cuboid for the convenience of simulation. Results show that all the optimization schemes can reduce the leakage flow rate in different degrees. The diversion structure with semi-circular plates and rounded transition between top plate and back plate can reduce the leakage most. Current work shows the rationality of the research direction and provides guidance for similar research in the future.
