Study on the measurement accuracy of coolant flowrate in a nuclear fuel test rig

Abstract

To measure the heat generation rate of nuclear fuel rods during an irradiation test, the temperature deviation of the coolant that passes by the fuel rod and its flow velocity need to be measured. Although the temperature of the coolant can be measured by thermocouples instrumented in the nuclear fuel test rig, the flowrate of the coolant is difficult to measure owing to the narrow space of the test rig. Therefore, a noise analysis technique using fluctuation signals from thermocouples installed at both end parts of the fuel rod has been developed by several advanced groups. Although the noise analysis technique was also developed at the Korea Atomic Energy Research Institute, out of pile test results showed that the accuracy of the coolant flow measurement was more than 40%. In this study, the ground pattern of the control board and earth connection are enhanced to eliminate external noise. In addition, a heater unit is installed in the coolant flow simulator to obtain a strong fluctuation signal from the coolant. Thus, the coolant flow simulator is improved, and the accuracy of the coolant flow measurement shows an error of less than 5%.