Oxygen potentiometric probe, for the measurement of the oxygen concentration of a liquid metal, application to the measurement of oxygen in liquid sodium of a nuclear reactor of type RNR-Na

A potentiometric oxygen sensor configured for measuring an oxygen concentration of a liquid metal, the sensor comprising:

• a metal tube forming at least one sensor body part;
• an electrochemical subassembly comprising an electrolyte, configured to be in contact with the liquid metal, and a reference electrode contained in the electrolyte, the electrolyte being made of yttrium-doped hafnia, calcium-doped hafnia, thoria optionally doped with yttrium or calcium, yttrium-doped zirconia, or calcium-doped zirconia, the reference electrode comprising a reference electrode metal and an oxide form of the reference electrode metal at an operating temperature of the potentiometric oxygen sensor;
• and
• an insert made of hafnium or hafnium alloy, arranged between the at least one sensor body part and the electrolyte, the insert being attached to the at least one sensor body part and brazed onto the electrolyte by a brazing joint,
• wherein the insert has a first coefficient of thermal expansion,
• wherein the at least one sensor body part has a second coefficient of thermal expansion, and
• wherein the first coefficient of thermal expansion is below the second coefficient of thermal expansion.