Kunihiko Kinugasa

Improvement of Jet Pump Inlet Mixer in Boiling Water Reactor for Mitigating Flow-Induced Vibration and Fouling

Jet pumps in Boiling Water Reactor (BWR) have risk of damages by Flow-Induced Vibration (FIV) for when increasing the core flow rate for power uprating. Especially, the vibration by leakage flow at the slip joint between an inlet mixer and a diffuser can cause serious damage on jet pumps. It is one of the obstructive factors for power uprating. Another problem is crud deposition on the inside surface of the inlet mixer and nozzle. Thus fouling causes performance degradation of jet pumps.To reduce the risk of an FIV problem, the gap flow passage of the slip joint was modified based on the leakage-flow-induced vibration theory. The effect and characteristic of vibration suppression for the improved design was confirmed by fundamental tests that simulated the slip joint configuration. To mitigate crud deposition, a sol-gel ceramic coating process using ZrTiO4, which generates electrostatic repulsion force to crud, was developed. The effect of the coating was confirmed by experiments using test pieces. These techniques for mitigating damage due to FIV and fouling were applied to inlet mixers of jet pumps for replacement in the actual BWR plant.Copyright

Flow-Induced Vibration Suppression of Jet Pump in Boiling Water Reactor by Slip Joint Extension

Jet pumps are key components to feed cooling water into reactor core in boiling water reactor. Inside condition of jet pumps is high flow condition. Therefore, jet pumps have risk of damages by flow-induced vibration, especially, the leakage-flow-induced vibration at the slip joint between the inlet mixer and the diffuser in extended power uprating condition with increasing core flow rate or particular operating condition such as single loop operation that increases differential pressure of the slip joint. To mitigate the risk of the leakage-flow-induced vibration, slip joint extension which can be installed on the top of diffuser was developed (See Figure 1). Self-excited vibration is treated as negative damping i.e. unstable state. It is well-known that the leakage flow through divergent gap flow passage causes the negative damping. However, the configuration of the gap flow passage of the slip joint with slip joint extension is complicated flow passage which consists of convergent, divergent and parallel flow passage region. To addition to this, the leakage flow direction in normal or power uprating condition is opposite to in abnormal operating condition such as single loop operating. Therefore, it is necessary to identify the optimum configuration of gap flow passage of the slip joint extension to suppress leakage-flow-induced vibration for various operating conditions. To achieve this goal, the gap flow passage of the slip joint extension was determined using transfer matrix method based on the leakage-flow-induced vibration theory. The effect and characteristic of vibration suppression for the slip joint extension was confirmed by fundamental tests that simulated the slip joint configuration.Copyright