Tsuyoshi Hagiwara

Evaluation of Flow-Induced Vibration for Fixed Type Guide Rods of Shroud Head and Steam Dryer in ABWR

For the purpose of shortening outage schedules, fixed type guide rods are expected to be used in the ABWR. Guide rods are the component for a shroud head and a steam dryer installation. However, guide rods are located near the main steam nozzle, therefore flow-induced vibration (FIV) is concern due to the high steam velocity. In the present study, tests of the 1/1.87-scale model and computational fluid dynamics (CFD) analysis for the 1/1.87-scale test and the actual ABWR model were conducted to prove the structural integrity of fixed type guide rods against FIV. As a result of CFD calculation, reduced damping was more than 5 and reduced velocity was approximately 1.44, so resonance did not occur fixed type guide rods. The maximum fluctuating stresses were conservatively evaluated as 8 MPa by the turbulence and 2 MPa by the Karman vortex shedding. Both values were below allowable limit. As noted above, the structural integrity against FIV was confirmed, so it is feasible to use the fixed type guide rods in the ABWR. (authors)

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 of a Control Valve in a Cavitating Flow

The vibration response of a typical globe valve was measured to determine the characteristics of flow-induced vibration in a cavitating flow, varying valve opening rate from 20% to 40%, and flow rate from 0.2 m3 /min to 1.4 m3 /min or maximum flow rate of the test facility. Strain gauges were mounted on the valve shaft for these measurements. The upstream and downstream pressures of the globe valve were also measured to calculate the cavitation number or cavitation coefficient. Moreover, fluctuating pressures on the valve seat were measured simultaneously with strain signals to examine the correlation between the fluctuating fluid force and the vibration response. Cavitation occurred when the cavitation coefficient reached within the range from 0.42 to 0.47. On the other hand, the amplitude of the valve shaft in the drag direction increased drastically when the cavitation coefficient exceeded 0.8. The correlation between the fluctuating fluid force and the strain was investigated considering the sum of the measured pressures on the valve seat as fluctuating fluid force. A strong correlation between the fluctuating fluid force and the strain was obtained. The phase difference between fluctuating fluid force and the strain was about 40°. It was therefore concluded that the physical phenomenon was self-excited vibration coupled with a cavitating flow. This oscillation system is therefore considered as a negative damping system excited by the fluid force with time lag.Copyright

Evaluation of Dynamic Loads due to Steam Condensation in Boiling Water Reactor ABWR Containment

The purpose of this study is to identify hydrodynamic loads due to steam condensation acting on the Suppression Pool (S/P) in Primary Containment Vessel (PCV) of Advanced-Boiling Water Reactor (ABWR) by using general-purpose analysis code, ANSYS™. The source load methodology has been used to evaluate the hydrodynamic loads, which are classified into condensation oscillation (CO) and chugging (CH). When setting the design source from the confirmation test, the calculation method due to the eigenfunction of the cylindrical coordinate system was used. Since, there were various limitations in the previous approaches, a new analysis approach has been expected. In this study, the pool of ABWR horizontal-vent confirmatory test facility is modeled with the ANSYS™ acoustic elements. The calculation results are in good agreement with the test pressure oscillations. It is confirmed that the proposed approach can create the design source enveloping the PSD of test results.Copyright

Critical Velocity for Bending Vibration of a Cantilever Cruciform Cylinder

Tip amplitudes of an isolated cantilever cruciform cylinder were measured, varying flow velocity approaching the cylinder and flow angles with 0° and 45° to a water test channel in order to investigate the vibration behavior and critical velocity for bending vibration. Flow velocity varied from about 0.4 m/s to 3.3 m/s, which corresponds to from 0.4 to 3.0 in reduced form using wing length of cruciform cylinder and from 1.6×104 to 1.4×105 in Reynolds number. The amplitudes were measured using strain gauges installed at the cylinder. In the case of 45°, it was observed that the amplitudes increased drastically in two regions. One region was from 0.65 to 1.0 in reduced velocity and oscillating direction is drag direction; the other was from 1.0 to 1.6 and oscillating direction is lift direction. On the other hand, such large amplitude vibration was not observed in the case of 0°. According to previous study on Strouhal number of vortex shedding from a cruciform cylinder, Strouhal numbers are 0.2 and 0.9. Therefore, this large amplitude vibration is not thought to be due to the resonance with the vortex shedding.Copyright