Relation Between the SHE and the Internal Ag∕AgCl Reference Electrode at High Temperatures

This article reviews the electropotential relation between the internal reference electrode used in nuclear light water reactor (LWR) applications and the standard hydrogen electrode (SHE). The focus is on the formation of complexes and how these might affect the potential of the electrode. In LWR applications the internal reference electrode is subjected to temperatures up to above , depending on reactor design. At temperatures of , the solubility products governing the concentration of complexes and thus the concentration of free in solution are different from what is known at room-temperature conditions. The potential of the electrode is in turn dependent on the concentration of free . Therefore, it is likely that also the potential of the reference electrode is altered, compared to the value derived by ignoring the formation of complexes. The review is based partially on data from literature and partially on thermodynamic calculations. Thermodynamical calculations based on the revised Helgeson–Kirkham–Flowers model were used to derive the equilibrium concentration of free . The revised electropotential relation between the internal reference electrode and the SHE assigns the electrode a higher potential compared to currently used models.