Electrochemical Measurements of Corrosion Processes in a Boiling Water Nuclear Reactor

The results of an electrochemical investigation of the corrosion behavior of reactor structural materials determined both in and out of reactor are presented. Electrochemical kinetic measurements in and out of reactor were fairly difficult to obtain because of the high purity (and associated poor conductivity) of the electrolyte. Three methods were used to account for the high values of overpotential cause by IR effects. All three methods gave similar results. The kinetic data showed large regions of linear behavior (500 mV overpotential cathodic and 200 mV overpotential anodic) on the materials studied. No correlation was found between electrochemically calculated corrosion rates and descaled weight loss measurements on identical material. It was concluded that electrochemical reactions involving dissolved O₂ and H₂ were playing a dominant role and obscuring the contribution from metal oxidation. Selected potential measurements were made with a specially designed 0.01N Ag/AgCl electrode which allowed determination of electrode potentials on the standard hydrogen scale at 266 and 288 C (510 and 550 F). A system designed to allow electrochemically controlled sustained load stress corrosion tests in high temperature electrolytes is described. The results from these tests agree with results from more conventional tests.