Measurement of core flow distribution in a research reactor using plate-type fuel assembly

In the present study, the core flow distribution of research reactors that used a plate-type fuel was investigated by measuring the flow rates at all fuel assembly locations to determine the flow uniformity in the reactor core. A specially instrumented dummy fuel assembly called probe fuel was developed to measure the flow rate at each fuel assembly location. The probe fuel is exactly the same as the real one, except the pressure taps and the embedded pressure conduits for measuring the pressure drop. First, hydraulic experiments were conducted to find out the pressure drop dependency on the flow rate of the probe fuel in a single fuel assembly test loop. Three correlations between the pressure drop and flow rate, which considers the water temperature effect, were derived from the measurement data of the hydraulic experiments. Using the probe fuel, the flow rates of all fuel assembly locations in the research reactor core were obtained from the measured pressure drop of the probe fuel using the correlations. The investigation of the core flow distribution in the downward forced-cooled research reactor was performed under a nominal flow condition. The flow rate measurements at each fuel assembly location were conducted for two vertical control absorber rod (CAR) positions. The measurement results showed that the primary coolant flow in the reactor core was distributed evenly with a small deviation of −2.9%~+2.3%, even though the CAR position changed. However, the ratio of the core flow and the bypass flow in the reactor was changed slightly with the position of the CARs, which seemed to be due to the changes in the flow resistance depending on the CARs’ position. In addition, the total flow rate of the primary cooling system (PCS) also increased a little when the condition of the CARs was fully withdrawn.