Electrochemical Oxygen Sensors for Corrosion Control in Lead-Cooled Nuclear Reactors

Liquid metals have been used in various applications in nuclear systems. Lead-bismuth eutectic (LBE) is foreseen as a coolant and target for neutron generation in accelerator-driven systems (ADS), whereas pure lead will be used as coolant in Gen IV-type lead-cooled fast reactors (LFR). The advantage of heavy liquid metal alloys is their high thermal conductivity and their relative safety in case of an accident. A major problem in non-isothermal systems is the corrosion of their structural components, consisting mainly of ferritic/martensitic and austenitic stainless steels, since the solubility of dissolved elements depends strongly on temperature. The formation of oxide scales on structural components is considered a viable approach to limiting the corrosion rates. To maintain a specific oxygen content in lead or LBE, an oxygen control system (OCS) is crucial. This requires continuous measurement of the oxygen activity in the liquid metal by means of electrochemical sensors. It must be assured that no oxides of the liquid metal itself are formed; otherwise, the system can be blocked. Therefore, this paper addresses the development of oxygen sensors for corrosion control of martensitic and austenitic steels in a lead-bismuth eutectic system at Forschungszentrum Karlsruhe (FZK, Eggenstein-Leopoldshafen, Germany).