LEFM (Leading Edge Flow Meter) Ultrasonic Flowmeters have been installed in feedwater pipes in over 68 Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) nuclear plants worldwide since the late 1970s. The 8-path, crossed-plane configuration commonly installed in feedwater pipes has been demonstrated through extensive calibrations at nationally certified calibration laboratories to provide feedwater mass flow accuracy better than ±0.3%, regardless of upstream hydraulic conditions. The increased accuracy has been accepted by nuclear regulators in several countries as the basis for an increase in licensed thermal power of nuclear power plants.

LEFM technology provides the ability to methodically check all key contributors to flow measurement uncertainty, thereby providing continuous quality assurance of flow data provided by the system and assuring plant operators that the meters remain within their design basis.

This paper will describe how LEFM chordal ultrasonic flowmeter operation and data quality can be verified, thereby providing the basis for troubleshooting changing balance of plant indicators. The paper will discuss a methodology for estimating changes in moisture content of the steam produced by steam generators at a PWR and will present a recent case study showing how detailed analysis of on-line feedwater flow data has been used to reconcile readings of other plant instrumentation to identify changes in steam moisture of ±0.1%.

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