Construction of Prototype Fast Breeder Reactor (PFBR) a 500 MWe pool type sodium cooled breeder reactor with MOX fuel has started at Kalpakkam. Instrumentation & Control (I&C) of PFBR is designed for safe, reliable and economic operation of the plant. Special feature of breeder reactors is sodium instrumentation. Leaks in sodium systems have the possibility of being exceptionally hazardous due to the reaction of liquid sodium with oxygen and water vapour in the air. In addition, leakage from primary systems can cause radioactive contamination. Potential regions of leakage are near welds and high stress areas. Sodium also reacts with concrete releasing hydrogen and leading to damage and loss of strength of concrete structures. Leaking sodium catches fire depending on its temperature. Sodium temperature in the plant ranges from 423 K at filling condition to 820 K at reactor nominal power operating condition. Leak detectors are provided on pipelines, tanks and other capacities. Sodium leak detection systems are designed to meet requirements of ASME section XI- division 3 which specifies that sodium leak at the rate of 100 g/h are to be detected in 20 h for air filled vaults and 250 h for inert vaults. Diverse leak detection methods are employed for active and non-active sodium equipment and pipes. For detection of water leaks into Sodium in steam generators, Hydrogen in Sodium Detectors (HSD) are used. Hydrogen in Argon Detectors (HAD) are used for sodium temperatures below 623 K as HSD is not effective below this temperature due to non-dissolution of hydrogen formed. Choice and challenges posed in implementation of above leak detection requirements are discussed in this paper.

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