Detection of gas entrainment in sodium using ECFM

Liquid sodium coolant in the hot pool of the Prototype Fast Breeder Reactor (PFBR) are provided with argon cover gas to isolate the hot pool from outside environment. Various mechanism inside the hot pool viz. free level fluctuation, vortex formation etc may lead to argon entrainment in the core of the reactor. This entrainment of gas in the core is not desirable as it may lead to reactivity fluctuations, reduced heat transfer in IHX and may result in cavitation of pumps. Even though devices are developed and provided to mitigate gas entrainment during normal operation, it may happen due to various transient sources. Hence it is necessary to detect gas entrainment in sodium during reactor operation to relate the consequences arising due to it. Eddy Current type Flow Meter (ECFM) can be used as tool to detect the gas entrainment during reactor operation. Studies were carried out in sodium loop to verify the use of ECFM as gas entrainment detection method. This paper presents the details of the ECFM, experiments carried out, results and conclusion. (author)