A potentiometric oxygen sensor for measuring an oxygen concentration of a liquid metal, which includes a metal tube forming at least one sensor body part, an electrochemical subassembly, and an insert made of a transition metal from group 4 of the Periodic Table or its alloy. The electrochemical subassembly contains 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 (HfO.sub.2), or of thoria (ThO.sub.2), which is optionally yttrium-doped or calcium-doped, or of yttrium-doped or calcium-doped zirconia (ZrO.sub.2). The reference electrode contains at least one metal and its oxide form at the operating temperature of the potentiometric oxygen sensor. The insert is arranged between the sensor body part and the electrolyte, and is attached to the sensor body part and brazed onto the electrolyte by a brazing joint.

In a sodium-cooled fast reactor, a breached fuel pin releases fission and activation products into the primary sodium coolant and into the cover gas. A portion of the primary sodium coolant is diverted to a distillation system where its constituents can be separated based on volatility. Condensing these constituents enables precise measurement of their concentration without delays caused by waiting for the decay of radioactive sodium background scatter, enhancing the detection and quantification of the dilute constituents. Additionally, the method continuously determines the initial concentration of constituents in the feed. Quantification is achieved using detectors, facilitating the continuous assessment of dilute constituent concentrations in the sodium coolant feed stream.

In a sodium-cooled fast reactor, a breached fuel pin releases fission and activation products into the primary sodium coolant and into the cover gas. A portion of the primary sodium coolant is diverted to a distillation system where its constituents can be separated based on volatility. Condensing these constituents enables precise measurement of their concentration without delays caused by waiting for the decay of radioactive sodium background scatter, enhancing the detection and quantification of the dilute constituents. Additionally, the method continuously determines the initial concentration of constituents in the feed. Quantification is achieved using detectors, facilitating the continuous assessment of dilute constituent concentrations in the sodium coolant feed stream.