Denting of steam generator tubes due to rapid corrosion of carbon steel support plates is a serious problem in many reactors on sea or brackish water locations. The objective of this program was to assess the effectiveness of sodium phosphate in minimizing corrosion and denting during leakage of seawater into a steam generator. Corrosion tests at 300°C were conducted on (a) electrically heated tubes of Alloy 800 equipped with crevice devices and exposed to dilute solutions of seawater and sodium phosphate, and (b) Alloys 800 and 600 tubes with carbon steel sleeves exposed to concentrated solutions of seawater and sodium phosphate + seawater. Exposure of heated tubes to seawater caused denting under carbon steel crevices. Addition of sodium phosphate to seawater prevented denting. Concentration factors within crevices were estimated by comparing the corrosion rates from heat transfer and isothermal tests; estimates ranged from 3700 to 6900, depending on the assumptions. Only shallow pitting was observed on the Alloys 800 and 600 tubes