Application of particle image velocimetry on velocity distribution in 5 x 5 rod bundle channel under rolling motion

The Floating Nuclear Power Plant (FNPP) would be in rolling motion during operation. The rolling motion will introduce fluctuated inertial force periodically, resulting in periodic thermal and hydraulic parameters variation, and may threaten the reactor's safety. An experimental investigation was conducted to study the influence of rolling motion on flow characteristics to measure the flow field in 5 x 5 rod bundles by Particle Image Veloc-imetry (PIV) under rolling motion. Results show that the rolling motion can cause a strong secondary flow. The rolling motion has little effect on the central sub-channels but significantly influences the external sub-channels. When the Reynolds number is low, the external sub-channels will periodically backflow. This study shows that the flow field affected by rolling motion differs from the pulsating flow. The applicability of using pulsating flow to study the effects of rolling motion needs further evaluation, and the results can provide a reference for nu-merical simulations.