Electrochemical corrosion tests for core materials utilized in BWR under conditions containing seawater

Electrochemical corrosion behavior under salt water in a type 304L stainless steel (SS) used to a part of BWR core materials was investigated to evaluate the possibility of crevice corrosion occurrence for the fuel assemblies which experienced seawater exposure in the Fukushima Daiichi Nuclear Power Plant (1F) accident. Especially, focusing on the upper end plug part having the 304L SS crevice structure, measurements of repassivation potential for crevice corrosion (E_R,CREV) were carried out using the crevice test pieces fabricated by 304L SS plates. The solution conditions were determined based on the long-term water quality environment change of the 1F spent fuel pools; chloride ion concentration and temperature were selected ranging from 10 to 10000 ppm and from room temperature to 80degC, respectively. As the results, E_R,CREV was lower than a spontaneous potential (E_SP) when the temperature was over 50degC and the chloride ion concentration was over 2500 ppm under the saturated concentration of dissolved oxygen. This indicates that there is a possibility that crevice corrosion will occur in the crevice structure composed of the 304L SS parts of the 1F fuel assemblies which experienced seawater exposure, even though the corrosion rate should be accurately estimated and the influence of the oxide film which is formed along the 304L SS surface during reactor operation as well as the effect of dissolved oxygen concentration on the crevice corrosion behavior should be evaluated. (author)