Development of hybrid feed water flow rate measurement system for light water reactors of nuclear power plants using pulse Ultrasound

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A new feed water flow rate measurement system for light water reactors of nuclear power plants using pulse Ultrasound has been developed for a new type of flow metering system. This new system is a hybrid of the time-of-flight (TOF) type ultrasonic flowmeter and the ultrasonic velocity profile type flowmeter with the advantages of these two types. Our final purpose is to apply the hybrid ultrasonic flow metering system to an accurate flow rate measurement of feed- water in nuclear power plants. The ultrasonic velocity profile type flowmeter called the UDM flowmeter is based on the pulse ultrasonic Doppler method (UDM) which has the capability to obtain instantaneous velocity profiles along an ultrasonic beam. The principle of the UDM flow metering system is based on the integration of an instantaneous velocity profile over a pipe diameter. The multi-beam system is expected to eliminate installation problems such as entry length, and also to follow transient flow rate precisely by incre … More asing the number of ultrasonic transducers. However, it needs reflectors for receiving ultrasonic Doppler signals. On the other hand, the TOF ultrasonic flow metering system does not need any reflector, but it needs profile factors (PFs) which depend on velocity profiles. PF is one of the important experimental coefficients for the accurate flow rate measurement. Therefore PFs must be corrected according to the changes in flow conditions. In the present study, we investigated to what degree the hybrid ultrasonic flow metering system can correct the profile factors of TOF ultrasonic flow meters by using the UDM.As results, the laboratory experiments appeared that for fully developed flow condition an accurate measurement of flow rate was achievable using only a single measuring line, and additionally, for non developed flow which is located just below the bend pipe the multi-lines method was successfully applied and the errors were less than 1%. The reflector of ultrasound was obtained very efficiently using ultrasonic cavitation bubbles. Even for the metallic wall pipe, it was appeared that cavitation bubbles were available to measure the instantaneous velocity profile and the flow rate accurately compared with using nylon powder. As mentioned above, it is indicated that the present multi-lines flow metering system by using ultrasonic Doppler method has very high accuracy under non-ideal flow conditions such as non-developed flow or non-axis-symmetric flow. And we constructed the basic system of a flow rate measurement in power plants using metallic pipes and cavitation bubbles as ultrasound reflectors. And according to the results of this experiment, deviation of PFs could be around 2-6% at maximum, which directly affects the estimation of flow rates. However by calibration with UDM measurement PFs could be better within ±1%. Less