The application of an externally-mounted leading edge flowmeter (LEFM) for the measurement of Sequoyah feedwater flow

Operating experience at PWRs worldwide shows that using secondary side calorimetry to determine reactor thermal power is susceptible to inaccuracies that exist in feedwater flow measurement. The principal source of the inaccuracies is the fouling with corrosion deposits that adhere preferentially to the venturi nozzle throats used in measuring flow. Prompted with evidence of venturi nozzle fouling at Sequoyah, TVA System Engineers contracted MPR Associates, Inc. and Caldon, Inc. to provide an alternate and diverse feedwater flow measurement system. The system provided was an externally-mounted ultrasonic system. This system was installed in February 1992. An accuracy assessment consistent with ASME guidelines is used to determine a 0.9% absolute accuracy for the ultrasonic meter installation and a 0.2% flow measurement repeatability. Included in this assessment is a calibration of the system at a NIST facility using a scaled hydraulic model. Comparisons between the measurements of the ultrasonic system and the venturi differential pressure system at Sequoyah confirm TVA fouling assessments. The ultrasonic system's measurement of feedwater temperature against RTD standards demonstrates an accuracy of about ±0.5 degree F. Flow measurement comparisons through the current operating cycle have shown repeatability and confirmed venturi fouling signatures