The manufacture and properties of ceramic probes to measure oxygen content in liquid sodium

In sodium-cooled fast reactors (and elsewhere) it is important to be able to measure continuously the oxygen levels in the sodium circuits. For example, a sudden increase in the oxygen level in a secondary coolant circuit of a reactor might indicate a water leak from the heat exchanger. This paper outlines some aspects of the development of an electrochemical oxygen meter for use in sodium. A ceramic probe in the form of a closed-ended tube of thoria -7 1/2% yttria is immersed in the sodium and the EMF generated between the sodium and an internal standard reference electrode can be used to monitor the oxygen level in the sodium. The electrolyte tubes are manufactured by a procedure which gives a dense ceramic of high chemical purity and hence freedom from spurious EMFs caused by impurities. The properties of the probes and experience obtained with them in sodium are described. (author)