A Review of the Effects of Silica on Stress Corrosion Cracking of Steam Generator Tubes

This study evaluates the operating chemistry and outside diameter stress corrosion cracking (ODSCC) data from steam generators in several PWR plants to assess the effect of silica and boric acid on corrosion processes. The objective is to determine whether the combination of boric acid treatment of the secondary water and high silica concentrations can inhibit ODSCC. An extensive literature review was conducted to gather evidence, supplemented by laboratory tests, analysis of pulled tube examinations, and plant operating chemistry data. The results indicate that silica, when used alongside boric acid, demonstrates a significant inhibitory effect on ODSCC by acting as a buffer in various crevice environments. Despite these findings, the nuclear industry has not adequately recognized the potential benefits of silica as an inhibitor. Consequently, the study advocates for further consideration of silica in secondary water chemistry and recommends additional evaluations to explore its impact on heat transfer and to refine the existing chemistry guidelines. This comprehensive review underscores the necessity of a reevaluation of silica's role in corrosion inhibition to enhance the safety and efficiency of PWR steam generator operations.