Hideo Komita

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)

Pressure Drop of Annular Flow Channel Electromagnetic Pump Examined Using Divided Flow Channel Model

Abstract It has been reported that operating an annular flow channel electromagnetic pump (EMP) near the peak of the head pressure and flow rate curve sometimes suffers a drop of head pressure. This phenomenon was attributed to nonuniform distribution of inlet flow or magnetic field, but its mechanism has not been clarified. For fear of this undesired head pressure drop, current EMP design is sometimes too conservative in that the rated efficiency is set low compared with experimentally achieved values. Understanding this phenomenon clearly, therefore, will prospectively make possible more proper design. We modeled the annular channel with parallel divided channels to examine the response of the EMP for distributed inlet flow. For each of the divided channels, the equation of fluid motion is numerically solved including the pressure from the external flow loop. Since the time constant of the pressure from the external loop is slow compared with that of the divided channels, decreased flow in some divided channels can undergo reversed pressure and become unstable in certain cases. Transient behaviors, such as the total head pressure and the flow rate of the EMP, were examined, and conditions of this pressure drop occurrence were clarified, making possible more proper EMP design.