Fuel Assembly Oscillation-Induced Flow in Initially Stagnant Fluid

The effect of water on the dynamics response of fuel bundles in pressurized water reactors during external forcing is studied experimentally inside a large facility that houses a full-height bundle and is operated on an earthquake shake table. This configuration is directly relevant to earthquakes and loss-of-coolant accidents. Most data to date have been focused on structural response and some pointwise measurements of liquid velocity. Here, structure displacement coupled with velocity field are investigated with nonintrusive optical diagnostics in initially stagnant water. Data indicate that a flow develops as the structure oscillates: both a cross flow through the bundle and an axial pulsatile flow that was not anticipated. A physical mechanism is proposed as a source of this structure-induced flow that is driven by pressure gradients around the fuel bundle.