2011 Volume 11 Issue Special_Issue Pages s127-s134
A nuclear fuel spacer is one of the components of a fuel rod bundle and its role is to maintain an appropriate rod-to-rod clearance. Since the fuel spacer influences liquid film flow on fuel rods in a fuel rod bundle of a Boiling Water Reactor(BWR)'s core, its specification has a strong effect on thermal hydraulics such as critical power and pressure drop. Though the spacers have been developed through empirical modifications, a large amount of test data has still been required for optimum design of the spacer. It is, therefore, an important subject to develop a model of the spacer based on the flow mechanism corresponding to shape changes in the spacer design of BWR fuel bundles. In the meantime it is considered that the droplet deposition on the fuel rod is enhanced downstream of the fuel spacer because a flow velocity distribution split by the spacer is recovered into a normal velocity distribution or profile. In the case, it is considered that droplets would be moved with the gas flow occurring in the process of a change from the higher velocity in the core to the lower velocity. In our previous work, a spacer model was proposed on the basis of two dimensional experimental data with a simple rectangular channel using air and water as working fluids with various thickness of test pieces and gap clearances. However, the channel configuration of an actual flow in the fuel bundle forms three dimensional shape.
In this study, the effect of spacer geometry on a gas velocity downstream of the spacer is investigated experimentally in the atmosphere with the use of an circular channel which has a similar hydraulic diameter to an actual fuel bundle. The model equation, which shows a lateral velocity profile based on rectangular channel data, is compared with circular channel data, and shows a good agreement with circular data by introducing a velocity reduction term as a three-dimensional effect.
