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 for measuring the oxygen concentration of a liquid metal, comprising:

• a metal tube forming at least one sensor body part;
• an electrochemical subassembly comprising an electrolyte, intended to be in contact with the liquid metal, and a reference electrode contained in the electrolyte, the electrolyte being made of yttrium-doped or calcium-doped hafnia (HfO2), or of thoria (ThO2), which is optionally yttrium-doped or calcium-doped, or of yttrium-doped or calcium-doped zirconia (ZrO2), the reference electrode comprising at least one metal and its oxide form at the operating temperature of the sensor;
• and
• an insert made of a transition metal from group 4 of the Periodic Table or an alloy thereof, arranged between the sensor body part and the electrolyte, the insert being attached to the sensor body part and brazed onto the electrolyte by a brazing joint, the coefficient of thermal expansion of the insert being close to the coefficient of thermal expansion of the electrolyte and below the coefficient of thermal expansion of the sensor body part, the stiffness of the insert being higher than the stiffness of the sensor body part.