Development of mutual inductance type sodium level detectors for PFBR

Highlights: • Designed longer level probe with change in pocket dimension for easy insertion. • Prototype fabricated and evaluated the performance for adequate sensitivity. • Simple, new temperature compensation technique with improved accuracy provided. • Developed Mutual Inductance type discrete level probes for PFBR. -- Abstract: The 500 MWe Prototype Fast Breeder Reactor (PFBR) is under advanced stage of construction at Kalpakkam, India. Continuous and discontinuous level sensors working on mutual inductance principle is used in PFBR for monitoring sodium level as well as for safety. The wide and high operating temperature, highly chemically active nature of sodium and its reaction with air make the sodium instrumentation special over conventional instrumentation. The traditional sodium level sensors such as Resistance Type Level Probe (RTLP) for discrete level measurements and MI type continuous level probe for continuous level measurement is used in Fast Breeder Test Reactor (FBTR). The challenges involved in making traditional continuous level sensors suitable for PFBR, include development of mechanically robust level sensors of longer length with better resistance to vibration, new method of temperature compensation to improve the accuracy over wide operating range from 150 to 550 °C and improved electronics circuit with better features. MI type discrete level probe has been developed as improvement over RTLP. This paper highlights construction of longer level probes with leak tight arrangement, performance evaluation of prototype level probes, recent development on temperature compensation technique, improvement in electronics and development of noncontact type discrete level probe for PFBR