Significance of corrosion potential monitoring in a PWR primary system

Electrochemical measurements have been performed in the primary circuit of the Ringhals 4 pressurized water reactor. The major objective of this paper is to discuss our experience after three years of measurements and focus on possible future use of electrochemical monitoring in PWR primary systems. The results from the measurements at steady-state reactor operation show that the corrosion potentials of the materials exposed, including platinum, nickel base alloys, stainless steels and pressure vessel steel all coincide within a few mV with the potential of platinum, that is the hydrogen equilibrium potential. Measurements were also performed during start-ups and shut-downs of the reactor. The major changes from an electrochemical point of view occurred well below full reactor temperature. With the presently used water chemistry with high hydrogen contents electrochemical monitoring seems to be of limited practical value: the corrosion potentials coincide with the hydrogen equilibrium potential. If lower hydrogen contents will be used in the future corrosion potential monitoring will be helpful. (author)