Study of the FIV exciting force on lower plenum structures of internal-pump-type BWRs

In internal-pump-type boiling water reactors (BWRs), core coolant flows from the reactor internal pumps to structures in the lower plenum. The discharged flow from the pump is fed to such structures as the control rod guide tubes (CRGTs) and the in-core monitor guide tubes (ICMGTs), which causes flow-induced vibration (FIV) of these structures. The exciting force for the FIV around the lower structures. The exciting force for the FIV around the lower plenum structures is examined. Many pumps are installed in the annulus region between the reactor pressure vessel (RPV) and the core shroud, and the discharged flow is fed to the common lower plenum region. The discharged flow, which induces flow vibration, is strongly affected by the pump exit configurations. Flow-induced vibration exciting forces for identical CRGTs, located at different interpump discharge configurations, are examined. Water flow tests, using a one-fifth (360-deg) scale model, were performed to evaluate the exciting force on the lower plenum structures. Models of the reactor internal pump, the CRGT, and the ICMGT were installed. The flow path configuration was similar to that of an actual internal-pump-type BWR