Corrosion behaviors during the iron removal process for chemical cleaning of nuclear steam generators

Abstract

Corrosion behaviors have been tested to evaluate the corrosion of base metals during the iron removal process for chemical cleaning of the secondary side of nuclear steam generators. Before corrosion tests were performed, some sludge dissolution tests were conducted for two kinds of experimental conditions to remove iron species. The case using EDTA, N 2H 4 and NH 40H at 93°C shows more dissolving capacity of Fe 3O 4 sludge than the case using NTA, N 2H 4 and NH 4OH at 175°C. Inhibitor CCI 801 is effective on the corrosion control of carbon steel specimens in the wide tested range of concentration from 1.0 to 0.02% in the solution using EDTA. The corrosion rate for another carbon steel is reduced drasticallt by addition of CCI 801 while Fe ion concentration is not changed significantly with or without CCI 801 when Fe 3O 4 is loaded. As the temperature increases above 127°C, the corrosion rate increases rapidly for a carbon steel during the iron removal process. The corrosion rates for carbon steels during this process are quite high at 120°C in a solution containing 20% EDTA. Carbon steels show more corrosion with sludge during iron removal process, and sludge I containing Cu species shows a greater increase in corrosion than the Fe 3O 4 sludge. When the materials are tested with sludge I, the free surface of tested carbon steels above the sludge pile acquires a copper deposit which is somewhat protective and corrosion is reduced due to this copper deposition. However, Alloy 600 is not deposited by copper.