ELECTROCHEMICAL POTENTIAL MEASUREMENTS UNDER SIMULATED BWR WATER CHEMISTRY CONDITIONS

Electrochemical potentials (ECP) of stainless steel have been measured in a high-temperature test loop under various water chemistry conditions. Several types of reference electrodes were used in this study. Effects of chemical additives were systematically examined, and the shift of ECP was found to be relatively small (+/- 50 mV) by the addition of most common chemicals studied. However, the effects of Cu ions on the ECP of stainless steel and other materials are more significant. The effect of H2O2 was semi-quantitatively determined. The increase of ECP, compared with the dissolved O2 at similar levels, was found to range from approximately 200 mV to approximately-500 mV. The effect is attributed to the oxidizing radicals produced from the catalytic decomposition of H2O2 on the stainless steel surface. The effect of water flow rate was also studied for a type 304 SS sample. Without chemical additives, water flow rate (increased from 1 cm/sec to 80 cm/sec) appeared to have no effect on the ECP of 304 SS. However, the impurity and H2O2 effects on ECP were more significant at the higher water flow rate. The flow rate effect on ECP is discussed in terms of mass transfer process.