Eddy current flow sensor development and testing for LMFBR sodium pumps

500 MWe Prototype Fast Breeder Reactor (PFBR), under construction at Kalpakkam has two vertical centrifugal pumps in the primary system, operating in parallel. Eddy Current Flow Meter (ECFM) has been chosen to measure pump discharge flow. ECFM is an electromagnetic device in which the sensor consists of three coils wound on an iron former. Flow probe is replaceable and can be inserted vertically from the top in pump suction casing, at a point, upstream of the diffuser. The pump will have two probes; each with two flow sensors fitted one above the other. Flow is established through the sensor to the suction side. Theoretical and experimental hydraulic studies were conducted in water to assess flow through the sensor and the pressure drop characteristics. The sensor was calibrated in a sodium loop for velocities established from hydraulic experiments. The sensor was tested upto 773 K and with electronic temperature compensation circuits, the error limit was established. The sensor essentially gives the head developed by the pump. Correlation with respect to the actual pump flow, head developed at different pump speeds were established. This paper presents the details of the sensor and studies conducted. (author)