Development of chemical sensors for Fast Breeder Reactor Technology

Fast breeder reactors use liquid sodium as heat transfer medium and generate high pressure steam at the steam generator to run the turbine. This high pressure steam is separated from sodium coolant by ferritic steel tubes of 4 to 5 mm wall thickness. Development of any material defect in these heat exchanger tubes during their service would result in the ingress of high pressure steam into the sodium circuit leading to sodium-water reactions. A high temperature electrochemical hydrogen sensor based on CaBr2-CaHBr solid electrolyte and capable of measuring ppb levels of dissolved hydrogen in sodium has been developed at the laboratory. A very sensitive system, using thermal conductivity detector and semiconducting oxide based sensor has also been developed for continuous monitoring of hydrogen levels in argon cover gas. An electrochemical carbon sensor using a molten carbonate electrolyte and an oxygen sensor based on yttria doped thoria oxide electrolyte are also under advanced stage of development for measuring carbon and oxygen levels in sodium. Materials chemistry issues involved in developing these sensors and their operational experience in sodium system are highlighted in this presentation