Investigation on Flow Field Characteristics of Rod Bundle Channel under Rolling Condition

The reactor is in an unsteady state under ocean conditions, which will cause tilt, swing, undulation and other motions of the reactor. These motions will introduce additional inertial force fields in the rod bundle channel, bringing additional influence on the flow field in the rod bundle channel. Therefore, it is necessary to study the rod bundle channel under rolling conditions. In this paper, based on the particle image velocimetry (PIV) technology, the research on the flow field distribution characteristics of the rod bundle channel with a pitch-to-diameter ratio of 1.326 under rolling condition is carried out. The difference of flow field distribution between steady state and transient state under the same flow rate is compared, and the flow field distribution characteristics at different positions in the rod bundle channel under the same acceleration are analyzed. The experimental results show that the rolling motion has a small effect on the middle of the rod bundle channel, and has a greater impact on both sides of the channel. The velocity field on both sides of the channel fluctuates periodically, with an anti-phase wave. In the case of low flow, reverse flow phenomenon will occur, but the spacer grid has no effect on the lateral speed upstream. Studies have shown that the flow field change caused by rolling motion is quite different from that caused by pulsating flow, in which the velocity field change caused by pulsating flow is uniform and pulsating, while the velocity field caused by rolling presents anti-phase fluctuation on both sides of the channel.