To determine fuel assembly mechanical damping under PWR conditions during a postulated seismic event or LOCA, fuel assembly flowing water damping tests were needed. Since flowing water damping values are high, pluck tests were used in which the fuel assembly was deflected, pluck mechanism retracted, and fuel assembly vibration decay observed and measured. To allow for the pluck vibration to occur, an oversized flow housing was utilized, which allowed additional flow to bypass the fuel assembly in the gaps between the assembly and the flow housing walls that would otherwise flow through the bundle rodded region. Since a direct measurement of the average bundle flow velocity could not be made, a method was developed for determining the flowrate through the bundle using fuel assembly lift force measurements.
This paper will present the method for determining the actual flowrate that was used in recent testing. The use of custom load cells that were designed for this testing to measure the fuel assembly lift force will be described in this paper. Additionally, the paper will show how the correlation between total test flow and bundle flow was developed from a series of flow calibration tests at different hydraulic conditions. This correlation was then used to prescribe the loop flow setpoints necessary to achieve targeted bundle flow velocities during the pluck test series.
