Pages 159-160
As nuclear power plants are highly aging, readings of flowmeters for reactor feedwater systems drift due to the changes of flow profiles. The causes of those deviations are affected by the change of wall roughness of inner surface of pipings. To cope with those concems, time-of-flight ultrasonic flowmeters are being introduced to nuclear power plants in the United States. However, flow profile factors (PFs), which adjust measurand to real flow rates, also strongly depend on flow profiles. To determine profile factors for actual power plants, manufactures of flowmeters usually conduct factory calibration tests under ambient flow conditions. Indeed, flow measurements with high accuracy for reactor feedwater require them to conduct calibration tests under real conditions, such as liquid conditions and piping layouts. These make it inevitable in quite a few measuring errors for large pipings in power plants. Therefore, the measurement accuracy of flow rate by conventional time-of-flight ultrasonic flowmeters is questionable. This paper discussed sophisticated high-accuracy feedwater flowmeter which directly measures the flow profile of reactor feedwater.
