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.